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225 Cards in this Set
- Front
- Back
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What are protons? |
Protons are much larger and heavier than electrons and have the opposite charge. Protons have a positive charge (+) and a relative mass of 1. |
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What are neutrons? |
Neutrons are large and have a similar mass to protons (1). However, neutrons have no electrical charge (0) |
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What are electrons? |
Electrons are extremely small particles that have a negative electrical charge (-). They exist outside the Centre (nucleus) of the atom. Electrons have a relative mass of 1/2000. |
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Using your own words, describe an atom: |
Atoms are tiny particles that consist of a nucleus of protons and neutrons with electrons surrounding this nucleus. |
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Name the three particles found inside atoms: |
Protons, neutrons and electrons |
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Which of the three particles is the smallest? |
Electrons |
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What two particles are found in the Centre of an atom? |
Protons and neutrons |
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What is the name given to the Centre of an atom? |
Nucleus |
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Complete the table |
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Getting To Know The Periodic Table |
If you look at the NCEA Periodic Table, you will notice that each element has a number associated with it. The number is called the atomic number and represents the number of protons found in the nucleus of a single atom of that element. Since the number of protons is equal to the number of electrons, the atomic number also tells you how many electrons there are in the energy levels around the nucleus. Another important number you will not find on the NCEA Periodic Table is called the mass number.This tells you the total number of particles, protons plus neutrons, found in the nucleus of an atom. So, if you know the mass number and the atomic number of an element, it is possible to work out the number of neutrons in the nucleus. By subtracting the number of protons from the mass number, you can calculate the total number of neutrons. |
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1. A lithium atom has a mass number of 7. State the number of protons, neutrons and electrons found in this atom. |
Number of protons or electrons = The atomic number. Therefore, the lithium atom has 3 protons and 3 electrons. Number of neutrons = Mass number - Atomic number. Therefore, the lithium atom has 7 - 3 = 4 neutrons |
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Patterns of the Periodic Table |
The elements of the Periodic Table are not just randomly placed on the table. They are placed in order according to their atomic number. For example, the 12th element on the Periodic Table is magnesium. Remember that the atomic number is a measure of the number of protons in an atom of that element, so the 12th element has 12 protons in the nuclei of its atoms.Elements are also arranged by group and by period. Groups are the vertical columns of elements whereas a period is a horizontal row. |
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What are groups |
Groups are the vertical columns of elements |
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What are periods |
a period is a horizontal row. |
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A Closer Look at Electrons |
Chemical reactions are occurring all around us. Metals are corroding, food is cooking, plants are photosynthesising, etc. But how can we tell if two chemicals are going to react? The answer depends on their electrons Electrons surround the nucleus of an atom in various energy levels (often referred to as ‘shells’ or ‘layers’). Each energy level can only contain a certain number of electrons. |
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How many electrons can the first shell of the atom hold? |
2 electrons |
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How many electrons can the second shell of the atom hold? |
8 electrons |
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How many electrons can the third shell of the atom hold? |
8 electrons |
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Electron Arrangement Shorthand |
Scientists don’t use drawings to show the arrangement of electrons. Instead they have devised a quicker method. To write the electron arrangement of a magnesium atom with 12 electrons you would write Mg 2,8,2. This means magnesium has 2 electrons in its innermost energy level, then 8 in the next level and 2 in its outermost level (or valence shell). |
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What is a valence shell |
The outermost shell of an atom |
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The Role of the Electron - Ion Formation |
During a chemical reaction, an atom wants to get a full valence (outer) shell of electrons. Once an atom has a full valence shell it is stable. Atoms get full valence shells by losing or gaining electrons, and in doing so will form an ion. |
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How does an atom become stable? |
Once an atom has a full valence shell it is stable. |
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How does an atom get a full valence shell? |
Atoms get full valence shells by losing or gaining electrons, and in doing so will form an ion. |
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Formation of the Sodium Ion |
A sodium atom has 1 electron in its valence shell. It can gain 7 electrons to get a full valence shell of 8, or it can lose 1 electron and have a ‘full’ second shell. It is easier for the atom to lose one electron than gain 7.Prior to a chemical reaction the atom has no electrical charge because: 11 Protons = +11 12 Neutrons = 0 11 Electrons = -11 Total charge = 0 During a reaction the sodium atom loses its valence shell electron and forms an ion. An ion is an atom with an electrical charge - either positive (+) or negative (-).After the reaction an ion with an electrical charge has formed because: 11 Protons = +11 12 Neutrons = 0 10 Electrons = -10 Total charge = +1 Sodium goes from an electron configuration of 2,8,1 with no charge, to an ion with an electron arrangement of 2,8 and a charge of +1. |
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Define the term ‘ion’: |
An atom that has lost or gained electrons |
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Why do atoms gain or lose electrons? |
In order to gain a full valence shell and therefore become 'stable'. |
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If an atom has 6 electrons on its valency shell, what is the easiest path for it to become stable? |
+2 electrons. |
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A ___________ion is formed when an ___________, or group of atoms, loses one or more __________. For example, when ________ loses its two valence _________ it forms Mg2+. |
A positive ion is formed when an atom, or group of atoms, loses one or more electrons. For example, when magnesium loses its two valence electrons it forms Mg2+. |
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A _______ ion is formed when an _______, or group of atoms, gains one or more ________. For example, when ________ gains two valence ________ it forms O2-. |
A negative ion is formed when an atom, or group of atoms, gains one or more electrons. For example, when oxygen gains two valence electrons it forms O2-. |
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Outline why atoms form ions? |
Atoms form ions to gain a full valence shell of electrons and become stable. |
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Describe why beryllium and calcium atoms both form ions with a charge of +2. |
Both elements have two valence electrons in valence shell (Be = 2,2 and Ca = 2,8,2). In a chemical reaction both will lose these two valence electrons and form the ions Be2- and Ca2-. The positive charge arises as they both have two more protons than electrons. |
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Neon has an atomic number of 10. It has 10 electrons arranged as 2,8. Suggest why neon is very unreactive. |
Neon needs neither to gain nor lose electrons to gain a full valence shell. It therefore remains chemically inert. |
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Explain why atoms are electrically neutral. In your answer, you should fully describe the atomic structure of lithium, beryllium and magnesium, including their electron configurations. |
All atoms contain the same number of protons as electrons. Protons have a charge of +1 and electrons a charge of -1. Because they occur in equal numbers, these charges cancel each other out and they are electrically neutral. The number of protons and electrons in an atom is equal to the atomic number of the element. For example lithium has an atomic number of 3, so lithium atoms have 3 protons and 3 electrons. The electron configuration of lithium is 2,1. Beryllium atoms have 4 protons and 4 electrons arranged 2,2 and magnesium atoms have 12 protons and 12 electrons arranged 2,8,2. |
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Explain why lithium and beryllium form ions with different charges. |
Ions form when atoms gain or lose electrons. Both lithium and beryllium atoms have a small number of electrons in their valence shell, so they will lose these electrons to form positively charged ions. From the electron configuration of lithium (2,1) we see that it will lose one valence electron and form the ion Li+. Beryllium has the electron configuration 2,2 so it will lose 2 valence electrons and form the ion Be2- |
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Explain why beryllium and magnesium form ions with the same charge. |
Both beryllium and magnesium are in Group 2 of the periodic table. Both have 2 valence electrons. Both will lose 2 electrons and form +2 ions. Beryllium has the electron configuration 2,2 and will form the ion Be2+. Magnesium has the electron configuration 2,8,2 and will form the ion Mg2+ |
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Naming Ions |
When naming ions, you must adhere to the following rules: • Positive ions (i.e. the metals and hydrogen) are usually named after the element they are formed from. For example, the ion formed when calcium loses two electrons is also called the calcium ion (Ca2+). • Negative monatomic ions (‘mono’ means one, so monatomic means ‘ions made of only one atom’) are usually named using the suffix - ide. For example, chlorine (Cl) forms the negative ion chloride (Cl-), and oxygen (O) forms the oxide ion (O2-) • Polyatomic ions (‘poly’ means many, so polyatomic means ‘ions made of many atoms’) are usually named using the suffix -ate. For example, SO42- is the sulfate ion and CO32- is called the carbonate ion. Exceptions to this rule include the hydroxide ion (OH-) and the ammonium ion ( NH4+). • Some ions can have more than one charge. For example, iron can be Fe2+ or Fe3+. Chemists use roman numerals to distinguish (tell the difference) between them. Therefore, Fe2+ is written as Iron(II) and Fe3+ is written as iron(III). |
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Chemists call positive ions, such as Mg2+, _____ |
Chemists call positive ions, such as Mg2+, cations. |
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Negative ions, such as O2-, are called _______ |
Negative ions, such as O2-, are called anions. |
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Ionic Coumpounds |
Chemists call positive ions, such as Mg2+, cations. Negative ions, such as O2-, are called anions. When a cation bonds to an anion, the resulting compound is called an ionic compound. The bond between a cation and an anion is called an ionic bond. This means that when a metal reacts with a non-metal, an ionic compound will form. The ions within an ionic compound are arranged in a three-dimensional lattice. This means each positive ion is surrounded by negative ions, and in turn, each negative ion is surrounded by positive ions. |
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What is a lattice? |
Atoms or ions arranged in a regular pattern. For example, sodium chloride forms an ionic lattice |
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What is an ionic compound |
A chemical compound in which ions are held together in a lattice structure by ionic bonds |
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What is an ionic bond |
A chemical bond in which one atom loses an electron to form a positive ion and the other atom gains an electron to form a negative ion |
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Identify which of the compounds below are ionic compounds |
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The Ionic Bond |
The term ‘ionic bond’ describes the force of attraction that holds ions together in an ionic substance. These bonds arise because of the strong electrostatic attractions between oppositely charged ions. |
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What is the ionic bond like in a cation? |
The cation, usually a metal atom that has lost one or more electrons, has a positive charge due to the excess number of protons in the nucleus, compared to the number of electrons remaining. |
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What is the ionic bond like in an anion? |
The anion, usually a non-metal atom, or group of atoms, has a negative charge due to having gained one or more electrons. There are more electrons on the ion than protons in the nucleus. |
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Describe the bonding in magnesium chloride. Your answer should include a description of the particles involved, and the forces holding the particles together. |
The bonding in magnesium chloride is ionic. Magnesium cations (Mg2-) are held to chloride anions (Cl-) by strong electrostatic forces of attraction between the oppositely charged ions. |
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Counting atoms pt.1 |
Chemical compounds and molecules are written in a very specific way according to some universal rules. Formulae are always written with the positive ion (cation) first. In this example, calcium is the cation. A subscript number applies to the atom in front of the number. In this example there are two chlorine atoms. Number of different atoms = 2 (calcium and chlorine). Total number of atoms = 3 (one calcium and two chlorine atoms). |
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Counting atoms pt.2 |
When you come across formulae with brackets around an ion, the subscript number applies to all the atoms within the brackets. Number of different atoms = 3 (iron, oxygen and hydrogen). Total number of atoms = 5 (one iron, two oxygens, two hydrogens). |
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When writing a chemical formula should the cation or the anion be written first? |
The cation is written first |
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Which ion in the formula Li2O does the subscript number apply to? |
The lithium ion |
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Writing Chemical Combinations |
A chemical formula is a combination of chemical symbols (such as Na, Cl, or Mg) and subscript numbers, that are used to show the composition of a compound. For example, the chemical formula for water is H2O. This shows that a water molecule is made up of two hydrogen atoms bonded to a single oxygen atom. Notice that if no number is given, as in the ‘O’ in H2O, then only one of that atom/ion is present. Ions with different charges combine during a chemical reaction to form compounds that have equal amounts of positive and negative charge. This means the resulting compound has no electrical charge. |
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Rules for Writing Simple Chemical Formulae |
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Table of Common Ions |
The table below shows the ions you may be required to use. You will get a table like this in your exam. However, it won’t have the names of the ions on it - you’ll need to learn them. |
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Complete the table |
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Dealing with Polyatomic Ions |
Ions that are made of more than one atom are called polyatomic ions (poly means ‘many’). This year you are expected to be able to deal with the following polyatomic ions: NH4+Ammonium OH–Hydroxide NO3–Nitrate HCO3–Hydrogen carbonate SO42–Sulfate CO32–Carbonate |
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What does the The small sub-script number associated with many polyatomic ions mean? |
The small sub-script number associated with many polyatomic ions, such as the ‘3’ in the NO3-, are a critical part of the ion and must never be altered. This means when you are constructing chemical formulae you will need to place brackets around the entire polyatomic ion to avoid confusion. |
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Construction of a compound using polyatomic ions |
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Understanding Chemical Formula |
Chemical compounds formed during a chemical reaction have no overall charge. The number of electrons released by the atom(s) forming the cation must equal the number of electrons accepted by the atom(s) forming the anion. Example 1: 2Ca(s) + O2(g) 2CaO(s) During the reaction between calcium and oxygen, calcium releases two electrons to form the calcium ion (Ca2+). Oxygen gains two electrons to form the oxide ion (O2-). Because the number of electrons released by calcium is equal to the number of electrons gained by oxygen, their charges are equal and opposite. Therefore, the formula of calcium oxide is CaO. |
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Use the format of the previous question to explain why the formula of calcium chloride is CaCl2 whereas the formula of potassium chloride is KCl. |
A calcium atom has the electron arangement 2,8,8,2. During a chemical reaction it will lose two valence shell electrons and form the calcium ion CA2-. A chlorine atom has the electron arrangement of 2, 8, 7. During a chemical reaction this atom will gain a single electron in order to have a full outer shell. Therefore the formula of calcium chloride is CaCl2. However a potassium atom has an electron arrangement of 2,8,8,1. It will only lose one electron during a chemical reaction and form the potassium ion, K+. This means only one potassium ion is required to balance the charge on the chloride ion. Therefore, the formula of potassium chloride is KCl |
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Aluminium is a reactive metal. It reacts readily with oxygen to form aluminium oxide. Determine the formula of aluminium oxide. In your answer you should: • Outline the electron arrangement of the atoms involved. • Describe the formation of their ions. • State the formula of aluminum oxide. • Discuss the formula in terms of electron transfer and the balanced overall charge on the compound. |
An aluminum atom has an electron arrangement of 2,8,3. During a chemical reaction this atom will lose three valence shell electrons and form the aluminum ion, Al3+. An oxygen atom has the electron arrangement of 2,6. During a chemical reaction this atom will gain two electrons in order to have a full outer shell. Therefore it will form the oxide ion, O2-. In order to balance the charges on the ions, two aluminum ions bond to three oxide ions to form aluminum oxide, Al2O3. Aluminum oxide has no overall charge as the number of electrons lost by the two aluminum atoms (6) is equal to the number of electrons gained by the three oxygen atoms (6). |
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Chemical Word Equations |
Chemical reactions (when a chemical change occurs) can be represented by chemical word equations. • The substances that are reacting together are called the reactants. • The substance or substances produced are called the products. • An arrow shows the direction of the reaction. Reactant + reactant → product(s) For example, if sodium reacts with chlorine to form sodium chloride, we would write the word equation as: Sodium + chlorine sodium → chloride |
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In the reaction above, what is the name of: (a) the product? (b) the reactants? |
(a) the product? Sodium chloride (b) the reactants? Sodium and chloride |
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What does the arrow represent in a word equation? |
It shows the direction in which the reaction progresses |
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What happens to the sodium and the chlorine? Where do they go? |
They have become ions and have formed an ionic substance |
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Balancing Chemical Equations pt.1 |
Nearly 2 500 years ago, Greek philosophers (early scientists) came up with the theory that “nothing comes from nothing”. Over time many scientists have further refined this theory to suggest that “matter can not be created or destroyed” - a statement that scientists refer to as the “Law of Conservation of Mass”. In simple terms, this means if you weighed the ingredients of a cake, then baked it in a closed system, the mass of the cake at the end would equal the mass of the ingredients. The same is true for chemical reactions. The number of atoms in the reactants will always equal the number of atoms in the products. Scientists show this by writing balanced equations. For example, consider hydrogen gas reacting with oxygen gas to create water. The equation is unbalanced. There are 4 atoms in total on the left-hand side of the equation and only 3 atoms on the right hand side - an oxygen atom is missing! In order to balance an equation there are a couple of rules you must stick to: • You can never add small numbers to a compound (e.g. H2O cannot become H2O2) • You can only add numbers to the front of a compound. This number multiplies all the atoms in that compound. |
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Balancing Chemical Equations pt.2 |
To fix the example above we need to add a 2 in front of the hydrogen and another 2 in front of the water, so... |
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Balance the following equations: |
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Define the term ‘ion’. |
An ion is an atom, or group of atoms, that have lost or gained electrons and developed an electrical charge. |
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Outline how atoms gain full valence shells of electrons. |
Atoms gain a full valence shell by gaining or losing electrons |
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An atom of sodium has a mass of 23 whereas an atom of magnesium has a mass of 24. (a) Explain why atoms are electrically neutral. In your answer, you should fully describe the atomic structure of sodium and magnesium, and state their electron configurations. |
An atom consists of a nucleus containing neutrons and protons, and one or more electron around the nucleus. Protons have a mass of 1 and an electrical charge of +1. Neutrons have a mass of 1 and no electrical charge. Electrons have virtually no mass (1/2000) and an electrical charge of -1. Because the number of protons in an atom is equal to the number of electrons, atoms have no net electrical charge. Magnesium has 12 protons, 12 neutrons and 12 electrons. Its electron configuration is 2,8,2. The 12 protons in a magnesium atoms nucleus have a charge of +12. The 12 electrons around the nucleus have a charge of -12. This means a magnesium atom has no overall net charge. Sodium has 11 protons, 12 neutrons and 11 electrons. Its electron configuration is 2,8,1. The 11 protons in a sodium atoms nucleus have a charge of +11. The 11 electrons around the nucleus have a charge of -11. This means a sodium atom has no overall net charge. |
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Explain why the ions in sodium hydroxide combine to give the formula NaOH but the ions in magnesium hydroxide combine to give the formula Mg(OH)2. In your answer, you should: • Compare the charges on the individual ions found in the compounds sodium hydroxide and magnesium hydroxide. • Explain why the ions combine in the ratios the way they do to form the compounds NaOH and Mg(OH)2 |
Sodium atoms have the configuration 2,8,1 and will lose one valence electron to form the Na+ ion. Magnesium atoms have the electrons configuration 2,8,2 and will lose two valence electrons to form the Mg2- ion. The hydroxide ion (OH-) has a single negative charge. Ionic substances have no overall charge because the number of cations and anions is such that the positive and negative charges cancel. In NaOH one sodium cation is matched with one hydroxide anion so that their charges cancel. In mg(OH)2 two negatively charged hydroxide ions are needed to balance the positive charge on Mg2+. |
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What is particle theory? |
All matter is made up of tiny particles (atoms, ions or molecules) and these particles are in constant motion. Temperature affects the speed of the particles (i.e. when the temperature increases the speed of the particles also increas |
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What is collision theory? |
In order for a chemical reaction to occur, two or more reactant particles must collide with sufficient force (energy) and at the correct orientation. The minimum amount of energy required for a chemical reaction to proceed is called the activation energy. |
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Visualizing the Collision Theory |
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Reactant particles will only ________ together if they _______ with sufficient ________, and at the correct _________to break bonds. This is called the _________ theory. |
Reactant particles will only react together if they collide with sufficient force, and at the correct orientation to break bonds. This is called the collision theory. |
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How does temperature affect rate of a reaction? |
The rate of a chemical reaction can be increased by raising the temperature of the reaction. Raising the temperature causes the reactant particles to move more quickly. This means they have more energy (specifically kinetic energy). Particles that are moving more quickly, with more energy, have a higher chance of colliding successfully and will collide more often. |
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How does concentration affect the rate of a reaction? |
The rate of a chemical reaction can be increased by increasing the concentration of one or all of the reactants. Increasing the concentration means particles are more numerous and closer together, so there is an increased chance of collisions. |
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How does surface area affect the rate of a reaction? |
Increasing the surface area of a reactant leads to an increase in reaction rate. If a solid reactant is broken into small pieces, or ground into a powder, then its surface area has increased. This means more particles are exposed, meaning more particles are able to collide. |
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How do catalysts affect the rate of a reaction? |
Catalysts are special chemicals that speed up the rate of reaction but are not used up in that reaction. Some catalysts provide a specific site for collisions to occur, while others lower the amount of energy required to start the reaction (known as the activation energy). |
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Measuring Reaction Rates |
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Outline why Reactions start out at a relatively fast rate: |
This is when the concentration of reactants is the highest. There is the highest frequency of collisions |
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Outline why Reactions slow down after a period of time: |
Reactant concentration falls so collisions become less frequent |
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Outline why reactions eventually stop |
Eventually all the reactant particles have reacted and no further reactant collisions can occur |
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Define the term ‘catalyst’: |
A catalyst is a substance that changes the rate of a chemical reaction but is not used up in that reaction |
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In terms of rates of reaction, outline why food lasts longer if it is stored in the freezer. |
The temperature in the freezer is low. The chemical reactions that spoilage organisms use to live, reproduce and degrade food stop or happen very slowly. |
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In terms of rates of reaction, outline why wood burns easier if it is split into kindling |
Kindling has a greater surface area exposed to the fire which means there are more wood particles exposed, resulting in a greater chance of successful collisions. |
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Write an aim for this investigation |
To investigate the effect of changing surface area on the reaction between CaCO3 and HCl. |
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Outline which variables would need to be controlled (kept the same) during this investigation. |
Volume of acid, concentration of acid, temperature of acid, mass of calcium carbonate |
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Which line on the graph represents the powdered calcium carbonate? |
1 |
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Justify your answer to the previous question |
Line 1 is the powdered calcium carbonate because it shows the fastest initial reaction rate |
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Explain why the final volume of CO2 produced was the same for all three experiments. |
The final volume of gas produced was the same because the mass of the reactants used was the same for all three experiments. |
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Which line, A, B or C, shows the results of the experiment in which the acid had the highest temperature? |
Experiment A In order for a chemical reaction to occur, two or more particles must collide with sufficient energy and at the correct orientation/angle. Increasing temperature gives the particles more kinetic energy meaning they move faster and collide more frequently. Also more collisions will be at or above the activation energy so the reaction rate will be faster. |
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In experiment B, how did the rate of reaction change after one minute compared with the rate of reaction after two minute |
The rate at which CO2 was produced was faster for the first minute than for the second minute. For example, between 0 and 1 minute, 38mL of CO2 was produced. Between minutes 1 and 2, only 8mL of CO2 was produced. |
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Explain why the reaction rate changes during experiment B. |
At the beginning of the reaction the concentration of reactant particles is the highest so there is a greater chance of successful collisions and a fast reaction rate. Over time the concentrations fall and there are less collisions between reactants and a slower reaction rate. |
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What are acids? |
Acids are substances composed of one or more hydrogen atoms chemically bonded to one, or a group of, non-metal atoms. For example, sulfuric acid (H2SO4) is composed of two hydrogen atoms (H) bonded to a sulfate group (SO42-). |
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What happens when an acid molecule is added to water? |
When an acid molecule is added to water, it will dissociate (break apart) into its ions. For example, hydrochloric acid is a solution of hydrogen chloride (HCl) in water. The HCl molecule dissociates into hydrogen ions (H+) and chloride ions (Cl-). |
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What do strong acids do when they come into contact with water |
Strong acids completely dissociate, releasing all of their hydrogen ions when they come into contact with water. The common laboratory acids (hydrochloric, sulfuric and nitric acids) are all strong acids. Weak acids, on the other hand, do not completely dissociate and only release some of their hydrogen ions when they come into contact with water. Organic acids (acetic, citric and other carboxylic acids) are weak acids. |
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Define the term ‘dissociate' |
When an ionic or molecular substance separates into ions when placed in water or some other solvent |
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Name the three common laboratory acids |
Hydrochloric acid, Sulfuric acid and Nitric acid. |
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Name the ion common to all acids |
The hydrogen ion |
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Compare and contrast the terms strong acid and weak acid. |
Strong acids fully dissociate when added to water. Every acid particle will dissociate into ions. Weak acids only partially dissociate when added to water. Only a small percentage of the acid dissociate separate into ions. |
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What are bases |
Bases can be described as ‘acid opposites’. They will remove hydrogen ions from a solution. They are usually metal oxides, metal hydroxides, metal carbonates or metal hydrogen carbonates. Many bases are insoluble - they do not dissolve in water. If a base does dissolve in water we call it an alkali. For example, copper oxide is a base because it will react with acids, but it is not an alkali because it does not dissolve in water. However, sodium hydroxide is a base because it will react with acids and it is also an alkali because it dissolves in water. |
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What do alkalis do when placed into water? |
Alkalis dissociate when placed into water and create hydroxide (OH-) ions. |
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What do strong alkalis do in water? |
Strong alkalis completely dissociate when they come into contact with water. Hydroxides of any of the group 1 metals (Li, Na, K, etc.) are strong alkalis. Weak alkalis, on the other hand, do not completely dissociate and only release a small number of hydroxide ions. |
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Describe the difference between a base and an alkali. |
A base is any substance that will remove hydrogen ions from a solution. An alkali is a base that is soluble in water |
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Describe the difference between a strong alkali and a weak alkali. |
A strong alkali is a base that full dissociates into ions when placed in water. A weak alkali only partially dissociates into ions when placed in water. |
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Name three strong alkalis found in the laboratory |
Sodium hydroxide, Potassium hydroxide, Lithium hydroxide |
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Name the ion common to all solutions of alkalis. |
Hydroxide ions |
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Name a product that would be formed if an alkaline solution containing hydroxide ions (OH-) was added to a solution containing hydrogen ions (H+) ions. |
Water |
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Suggest why the following household items are usually alkaline a) Oven Cleaner b) Indigestion tablets |
a) To convert fats and oils to soluble soaps. To break down proteins. b) To neutralize stomach acids |
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Concentrated and Dilute |
The strength of an acid or an alkali does not change depending on concentration. Concentration is a measure of how many acid/alkali particles there are per unit volume of water. Students often confuse the terms concentrated with strong and dilute with weak when discussing acids and alkalis. The terms ‘concentrated’ and ‘dilute’ refer to how much of an acid or an alkali has been added to water. |
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How is The reactivity of an acid/alkali determined? |
The reactivity of an acid/alkali is determined by the concentration of ions in the solution. Therefore, concentrated acids/alkalis solutions are more reactive than dilute acids/alkalis of the same type. |
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Is it possible to have a dilute solution of a strong acid? Explain your answer. |
Yes. A small amount of a strong acid added to a large amount of water would make a dilute solution of a strong acid. |
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What is the pH scale? |
The pH scale is used to represent the concentration of acids and bases. pH values have no units and generally range from 0 to 14. A pH of 7 is given to neutral solutions. Solutions with a pH lessthan 7 are acids, whereas solutions with a pH greater than 7 are alkaline. |
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What is the pH a measure of? |
pH is a measure of the concentration of hydrogen ions in a solution. The more hydrogen ions present, the more acidic is the solution. |
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What is the pH scale like? |
The pH scale is logarithmic. Each unit on the pH scale represents a tenfold change in acidity. For example, a solution with a pH of 4 is ten times more acidic than a solution with a pH of 5, and 100 times more acidic than a solution with a pH of 6. |
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The _____ scale is used to _______ how acidic or basic a solution is. A very strong acid can have a pH of ________ and a strong base will have a pH of _______. Solutions such as pure water have a pH of 7, meaning they are _________. |
The pH scale is used to show how acidic or basic a solution is. A very strong acid can have a pH of zero and a strong base will have a pH of 14. Solutions such as pure water have a pH of 7, meaning they are neutral. |
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What are indicators? |
Chemists use indicators to show visually whether a solution is acidic, neutral or alkali. A number of natural dyes change colour, depending on whether they are placed in an acid or base. |
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What is a litmus indicator? |
Litmus Indicator - Litmus indicator solution turns red in acidic solutions and blue in alkaline solutions. Litmus also comes in a paper form. Blue litmus paper will turn red in an acidic solution and remain blue when added to an alkali solution. Litmus does not tell you how strong the acid or alkali is. |
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What is a universal indicator? |
Universal Indicator - Universal indicator shows us how strongly acidic or alkaline a solution is. This is measured using the pH scale. Universal indicator has many different colour changes, from red for strong acids to dark purple for strong bases. In the middle, neutral is indicated by green. |
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Outline the purpose of an indicator |
To show visually whether a solution is acidic, basic or neutral |
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What is neutralization? |
A chemical reaction occurs when you mix together an acid and a base. The base cancels out the effects of the acid. The reaction is called a ‘neutralization’ reaction because a neutral (pH 7)solution is made if you add just the right amount of acid and base together. As previous discussed, when an alkali dissociates in water it releases hydroxide (OH-) ions and when an acid dissociates it produces hydrogen (H+) ions. When hydroxide ions collide with hydrogen ions, water is produced. |
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A chemical reaction occurs when you mix together... |
A chemical reaction occurs when you mix together an acid and a base |
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What does the base do when combined with an acid? |
The base cancels out the effects of the acid. The reaction is called a ‘neutralisation’ reaction because a neutral (pH 7)solution is made if you add just the right amount of acid and base together. |
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What happens when an alkali disassociates in water |
As previous discussed, when an alkali dissociates in water it releases hydroxide (OH-) ions and when an acid dissociates it produces hydrogen (H+) ions. When hydroxide ions collide with hydrogen ions, water is produced. |
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You enter the laboratory to find a large puddle of an unknown liquid on your workbench. You suspect it is an acid spill. Describe how you could test to determine if it is an acid and outline how it could be made safe before wiping it up. |
Place a few drops of universal indicator into some of the spill. If it turns red it is an acid. A solution of sodium carbonate could be mixed with the spilt acid to neutralize it. |
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What are salts? |
Salts are formed when acids reacts with metals, bases or carbonates. Salts are ionic substances composed of a positively charged metal ion and a negatively charged non-metal ion. Salts have relatively high melting points and many are soluble in water. One of the most common salts is sodium chloride (NaCl), otherwise known as “table salt”. A salt is always made when an acid is neutralized by a base. The general equation for most neutralization reactions is: |
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How are salts formed? |
Salts are formed when acids reacts with metals, bases or carbonates. |
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What type of substances are salts? |
Salts are ionic substances composed of a positively charged metal ion and a negatively charged non-metal ion. |
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How do salts behave? |
Salts have relatively high melting points and many are soluble in water. |
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What is one of the most common salts? |
One of the most common salts is sodium chloride (NaCl), otherwise known as “table salt” |
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How is a salt made? |
A salt is always made when an acid is neutralized by a base. The general equation for most neutralization reactions is Acid + Base = Salt + Water The exact salt made depends upon which acid and base were used. For example, sodium chloride (NaCl) is produced during the neutralisation reaction between hydrochloric acid and sodium hydroxide |
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There are three common laboratory acids, so figuring out the second part of any salt produced by these acids is easier if you learn the following table. |
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Copper oxide + sulfiric acid (arrow) _______ + ________ |
Copper oxide + sulfiric acid (arrow) copper sulfate + water |
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Making a Salt using Soluble Bases or Soluble Carbonates |
If the base or carbonate being used to prepare a salt is soluble, you cannot tell if the acid has been used up because excess solids will dissolve even after the acid has been neutralised. Or if a colourless liquid base or carbonate is used, it will just form a colourless solution with the acid. Therefore, an indicator must be used to determine when neutralisation has been achieved and just the right amount of base or carbonate has been added. |
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Explain how litmus paper could be used during the process shown above to show the salt solution being produced is neutral. |
Use blue litmus paper. A drop of the solution in the beaker will turn the paper red while the solution is still acidic. Stop adding potassium hydroxide when the solution no longer changes the color of the litmus paper |
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Complete the general equation for the reaction between an acid and a metal hydroxide. Acid + Metal Hydroxide (Arrow) |
Acid + Metal Hydroxide (Arrow) Metal salt + Water |
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Complete the general equation for the reaction between an acid and a metal oxide Acid + Metal Oxide (Arrow) |
Acid + Metal Oxide (Arrow) Metal Salt + Water |
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A student decided to make potassium chloride using powdered potassium oxide as a reactant. Name the other reactant the student should use |
Hydrochloric Acid |
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Write a word and balanced symbol equation for this reaction. |
Hydrochloric Acid + Potassium oxide (Arrow) Potassium chloride + water 2HCl + K2O (Arrow) 2KCl + H2O |
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Explain how litmus paper could be used during the process described to show the salt solution being produced is neutral. |
Use blue litmus paper. If the acid has not been neutralized, samples of it will turn the blue litmus paper red. If the blue litmus paper remains blue, test the solution with red litmus. If it turns blue then the solution has been made basic. When the solution is neutral testing with red and blue litmus will show no change to the color of either |
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There are two main types of carbonates: |
Metal carbonates are made of a metal ion and a carbonate ion (CO32-). Common examples include sodium carbonate (Na2CO3), calcium carbonate (CaCO3) and magnesium carbonate (MgCO3). Metal hydrogen carbonates are made of a metal ion and a hydrogen carbonate ion (HCO3-). A common example is sodium hydrogen carbonate (NaHCO3), more commonly known as baking soda. |
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What happens when a carbonate reacts with acid? |
When a carbonate reacts with acid it will form a salt, carbon dioxide and water. Carbon dioxide is a gas and can be seen as bubbles as the reaction proceeds. |
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Write balanced chemical equations for the following actions: |
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Write balanced chemical equations for the reaction between the following compounds: |
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Acid Rain: |
When fossil fuels such as coal, oil and natural gas are burned, carbon dioxide, nitrogen oxides and sulfur dioxide escape into the air. These molecules dissolve in the water in clouds and make rainwater more acidic than normal. When this happens it is called acid rain. Oamaru Stone is one of New Zealand’s most important building materials and is a very pure limestone (calcium carbonate). It is soft enough to be readily sawn and worked. Unfortunately, it is very susceptible to the effects of acid rain. |
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Rainwater is naturally a weak acid with a pH of between 5-6. If you added universal indicator to rainwater what color would you expect it to turn? |
Yellow |
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Would you expect the pH of acid rain to be higher or lower than the pH of normal rain? |
Lower - Acids have a pH lower than 7 |
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What is the chemical formula of limestone? |
CaCO3 |
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One of the acids that contributes to acid rain is nitric acid. What is the formula of nitric acid? |
NHO3 |
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Write a word equation for the reaction between limestone and nitric acid. |
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Write a balanced chemical equation for the reaction between limestone and nitric acid. |
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A student carried out an experiment in the lab using the following method: Write a scientific aim for this experiment: |
To make the neutral salt, sodium chloride, using a neutralization reaction between hydrochloric acid and sodium hydroxide. |
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Write a word equation and balanced symbol equation for this reaction |
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Explain the purpose of each step in the method and how the equipment and chemicals used achieve that purpose. |
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The page below was taken from a student’s lab manual. Complete the write-up of their investigation. |
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What is the pH scale used to measure? |
The pH scale is used to show how acidic or basic a solution is |
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The statements below are all incorrect. Rewrite each statement, changing a single word or number to make the statement correct. All acids have a pH number greater than 7 |
All acids have a pH LOWER than 7. |
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The statements below are all incorrect. Rewrite each statement, changing a single word or number to make the statement correct. Strong alkalis have a low pH. |
Strong alkalis have a HIGH pH |
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The statements below are all incorrect. Rewrite each statement, changing a single word or number to make the statement correct. Acids turn blue litmus paper blue |
Acids turn blue litmus paper RED |
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The statements below are all incorrect. Rewrite each statement, changing a single word or number to make the statement correct. A solution with a pH of 5 is neutral. |
A solution with a pH of 7 is neutral |
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The statements below are all incorrect. Rewrite each statement, changing a single word or number to make the statement correct. A concentrated acid contains a large number of hydroxide ions. |
A concentrated acid contains a large number of HYDROGEN ions. |
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Two beakers are shown below. Beaker one contains sulfuric acid solution and 5 drops of universal indicator. Beaker two contains pure water and 5 drops of universal indicator. Sodium hydroxide solution was added to both beakers until no more changes were observed. Write a word equation AND a balanced symbol equation for the reaction between sulfuric acid and sodium hydroxide. |
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What is the color of universal indicator in each solution at the start? |
Beaker 1 (Acid): Red Beaker 2 (Water): Green |
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Describe the colour changes as sodium hydroxide solution is added to each beaker, AND explain what this tells you about the changing pH of each solution. |
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A student wanted to make a dry sample of neutral salt, copper(II) sulfate (CuSO4). (a) Explain how to make copper sulfate by mixing copper carbonate and sulfuric acid solutions using school laboratory equipment (your explanation may use notes and diagrams). |
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Explain how litmus paper could be used during the process described to show the salt being produced is neutral. |
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Write a word equation AND a balanced symbol equation for the reaction between copper carbonate and sulfuric acid. |
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Sodium atoms form an ion with a charge of +1, whereas chlorine atoms form an ion with a charge of -1. Explain why sodium and chlorine atoms form ions with different charges. In your answer, you should: • Define an ion. • Explain why atoms form ions. • Identify the group on the Periodic Table where each atom is found. • Explain why sodium forms ions with a charge of +1 and chlorine forms ions with a charge of -1. |
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A scientist claimed to have discovered a new element which he named silverbackium (Sv). He stated that silverbackium belongs in Group 1 of the Periodic Table. You have been asked to predict other properties of Silverbackium. In your answer you should: • Predict how many outer shell electrons an atom of silverbackium has. • Predict the charge on the silverbackium ion and explain why it has this charge. • Write the formula of silverbackium hydroxide and silverbackium carbonate. |
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Silverbackium sulfate is a green salt and can be prepared in the laboratory using silverbackium oxide and an acid.
Name the acid you would use to prepare silverbackium sulfate. Justify your choice. |
Sulfiric acid. The salts formed by metal carbonates and sulfiric acid are metal sulfates. |
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A student is investigating the reaction between sulfuric acid and sodium hydroxide. She puts 10 mL of dilute sulfuric acid into a beaker and then adds 5 drops of universal indicator solution to the acid. She then takes a solution of sodium hydroxide (at the same concentration as the acid) and, drop by drop, adds it to the acid. She keeps adding the sodium hydroxide until the solution in the beaker stops changing colour. |
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A student is investigating the reaction between sulfuric acid and sodium hydroxide. She puts 10 mL of dilute sulfuric acid into a beaker and then adds 5 drops of universal indicator solution to the acid. She then takes a solution of sodium hydroxide (at the same concentration as the acid) and, drop by drop, adds it to the acid. She keeps adding the sodium hydroxide until the solution in the beaker stops changing colour. |
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A student is investigating the reaction between sulfuric acid and sodium hydroxide. She puts 10 mL of dilute sulfuric acid into a beaker and then adds 5 drops of universal indicator solution to the acid. She then takes a solution of sodium hydroxide (at the same concentration as the acid) and, drop by drop, adds it to the acid. She keeps adding the sodium hydroxide until the solution in the beaker stops changing colour. |
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Zinc carbonate chips are added to dilute hydrochloric acid in a conical flask. The flask is connected to a gas syringe. The volume of gas produced is measured over a few minutes, and the results used to sketch a graph. The slope of the graph is steep at the beginning and then levels off over time. Explain what is happening, in terms of particles and collisions, during this reaction |
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Zinc carbonate chips are added to dilute hydrochloric acid in a conical flask. The flask is connected to a gas syringe. The volume of gas produced is measured over a few minutes, and the results used to sketch a graph. Discuss the effect on the reaction rate of using powdered zinc carbonate with hydrochloric acid compared with using zinc carbonate chips. You should: • Compare the rates of reaction. • Explain the differences in the reaction rate by discussing how crushing the zinc carbonate affects the number of successful particle collisions. • Include a word equation and a balanced chemical equation for the reaction. |
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