The Wonder Of Water Module 4

Front 1

Suppose you want a precise measurement of rainfall in your area, so you set a rain gauge outside. After it rains, you measure the level of water in the gauge and record the result. You the empty the rain gauge and wait for the next rain. There are at least two sources of possible experimental error with this procedure. One will lead to a measurement that is too low and the other will lead to a measurement that is too high. What are these sources of error?

Back 1

There will be a length of time between when it stops raining and when you measure the amount of water in the gauge.

During that time, water will evaporate, causing your result to be too low.

The second source of error occurs when you dump the water out. Unless you dry the gauge thoroughly, there will be water droplets let in the gauge. If the next rain falls before these water droplets have a chance to evaporate, your next measurement will be too large. There could be more errors as well. These are just the two major errors that come to mind.

Front 2

The chemical formula for baking soda is NaHCO3 . How many atoms make up one molecule of baking soda?

Back 2

The Na is one atom since the second letter is lowercase. The other letters each represent an atom since they are all capitals. There are no subscripts after the Na, H, or C, so there is only one each of them.

There is a subscript of 3 after the O, indicating 3 oxygen atoms. This makes a total of 6 atoms.

Front 3

Vinegar’s active ingredient is acetic acid, C2H4O2. How many of each atom are present in a molecule of acetic acid?

Back 3

The C stands for carbon and there is a subscript of 2, indicating 2 carbon atoms.

The H is for hydrogen, and there is a subscript of 4 after the H, making 4 hydrogen atoms.

Finally, the O represents oxygen and there is a subscript of 2, indicating 2 oxygen atoms

Front 4

The sugar in green, leafy vegetables is called glucose. A molecule of glucose contains 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. What is the chemical formula for glucose?

Back 4

Carbon is represented by C, the symbol for hydrogen is H, and oxygen is represented by O. You put subscripts after each to indicate the number. Thus, the chemical formula is C6H12O6

Front 5

Suppose you had a positively charged object to hold next to the stream of water in Experiment 4.2. Would the stream bend the same way as it did with the comb, or would it bend the opposite way? Why?

Back 5

The stream will bend the same way it did before: toward the comb.

If you thought it should bend the other way because of the opposite charge, think about it for a moment. The water molecules are originally all jumbled around, pointing in all directions.

The reason the steam bends is that in the presence of a charged object, the water molecules reorient themselves so that the opposite charge is facing the object.

Thus, the water stream will always be attracted to the charged object, because the water molecules can point whichever way they want. They will always point so that the small charge on the molecule opposite the charge on the object is pointed toward the object.

Front 6

Hydrochloric acid, HCI, is a powerful acid often used in cleaning. While “H” stands for hydrogen, “CI” stands for chlorine. Chlorine atoms can pull on electrons much more strongly than can hydrogen atoms. Is HCI polar?

Back 6

If so, where is the small negative charge: on the chlorine atom or the hydrogen atom?
HCI is polar. The chlorine will have the small negative charge. After all, if the chlorine can pull on the electrons with more strength, it will ‘win the battle’ and get the electrons

Front 7

Chlorine gas, CI2, is a molecule composed of 2 chlorine atoms bonded together with a chemical bond. Is this molecule polar? Why or why not?

Back 7

Chlorine gas is not polar, because the only two atoms in the molecule are the same. Thus, they pull on electrons with equal strength. Since they pull with equal strength, neither one of them will win more than its fair share of electrons.

Front 8

4.8 Water does not dissolve gasoline. Is gasoline most likely made up of ionic, polar, or nonpolar molecules?

Back 8

Gasoline is made up of nonpolar molecules. If water cannot dissolve a substance, it is likely that the substance is nonpolar.

Front 9

4.9 Suppose you did Experiment 4.3 with gasoline instead of water. (Don’t actually do it; the fumes are dangerous!) Would table salt dissolve in gasoline? What about canola oil?

Back 9

Table salt would not dissolve, but canola oil would. After all, nonpolar substances dissolve other nonpolar substances. Since table salt is ionic, it will not dissolve in a nonpolar substance. Since canola oil is nonpolar, it will dissolve in a nonpolar substance.

Front 10

Water has a very high boiling point (the temperature at which it boils) compared to most other substances that are liquid at room temperature. Use hydrogen bonding to explain why this is the case.

Back 10

Water has a high boiling point because the hydrogen bonds hold the molecules together. In order to turn into a gas, the water molecules need to get far apart form one another. When you heat something, you are giving it energy. Because the hydrogen bonds hold the molecules together, it takes a lot of energy (thus a high boiling temperature to pull them apart.

Front 11

4.11 Butane is a gas at room temperature, but it is stored under pressure as a liquid in a butane lighter. The chemical formula is C4H10. Isopropyl alcohol (commonly called rubbing alcohol) is another liquid you might have around the house. Its chemical formula is C3H8O. One of these liquids participates in hydrogen bonding. Which one?

Back 11

Isopropyl alcohol participates in hydrogen bonding. Remember, hydrogen bonding in water takes place between the hydrogen and oxygen atoms. There are plenty of hydrogen atoms in butane, but no oxygen atoms. The other way you can tell is that butan is a gas at room temperature, indicating that its molecules are held more tightly together. Between the two, then, the alcohol is the more likely one to have hydrogen bonds.

Front 12

Calcium and magnesium ions are both the result of atoms that lose electrons. Thus, they are positively charged ions. Suppose you actually could remove calcium and magnesium ions from water without replacing them with other positive ions. If you slowly started removing only calcium and magnesium ions from the water, you would find that as time went on, removal of the ions would become more and more difficult. Eventually, it would be nearly impossible to remove any more calcium or magnesium ions in the water, even though there might still be many ions left. Why?

Back 12

Think about this one. Calcium and magnesium ions are positive. A sample of tap water, however, has no net electrical charge. Why? Well, for every positive ion in the tap water, there is a negative ion somewhere to cancel it out. If you removed only the positive ions, the negative ions that balance them out would still be there. As a result, as time went on, the tap water itself would become more and more negatively charged. Negative charges attract positive charges. Thus, with each positive ion you removed, the tap water would become more negative, and that would more strongly attract the remaining positive ions. At some point, the negative charge of the tap wate would be so great that it would attract the remaining positive ions so strongly that it would take enormous amounts of energy to pull the positive ions away. This is why you cannot simply remove the calcium and magnesium ions from hard water. The water itself would quickly become negatively charged. Thus, rather than removing the calcium and magnesium ions, water softeners replace them with other positive ions. That keeps the tap water neutral overall.

Front 13

Define the following term:

Electrolysis

Back 13

The use of electricity to break a molecule down into smaller units.

Front 14

Define the following term:

Polar molecule

Back 14

A molecule that has slight positive and negative charges due to an imbalance in the way electrons are shared

Front 15

Define the following term:

Polar molecule

Back 15

A molecule that has slight positive and negative charges due to an imbalance in the way electrons are shared

Front 16

Define the following term:

Solvent

Back 16

A liquid substance capable of dissolving other substances

Front 17

Define the following term:

Solute

Back 17

A substance that is dissolved in a solvent

Front 18

Define the following term:

Cohesion

Back 18

The phenomenon that occurs when individual molecules are so strongly attracted to each other that they tend to stay together, even when exposed to tension.

Front 19

Define the following term:

Hard water

Back 19

Water that has certain dissolved ions in it – predominately calcium and magnesium ions.

Front 20

Suppose you did an electrolysis experiment like experiment 4.1 on hydrogen peroxide, which has a chemical formula of H2O2. If it worked properly, which of the following results would you expect:
a) same as with water
b) equal amounts of hydrogen and oxygen
c) twice as much oxygen as hydrogen

Back 20

The result would be equal amounts of oxygen and hydrogen (option b). The chemical formula says that there are 2 hydrogens and 2 oxygens in each molecule of hydrogen peroxide. Thus, there are equal amounts of each atom, resulting in equal amounts of each gas.

Front 21

Suppose you performed Experiment 4.1 with a test tube that had a crack in it. Gas could slowly leak out that crack, but not nearly as quickly as it was being made in the experiment. Suppose further that the crack was in the test tube that held hydrogen gas. Which chemical formula might result from such a botched experiment: HO or H4O.

Back 21

The chemical formula HO would be the more likely erroneous result.

If the test tube that held hydrogen had a slow leak, it would look like less hydrogen was collected than what should have been collected. Thus, the experiment would indicate a chemical formula with less hydrogen atoms in it. H4O is an erroneous result that indicates there were more hydrogens, HO is the one that indicates less hydrogens.

Front 22

Epsom salts, which you used in experiment 4.1, has the chemical formula MgSO4. If Mg is the symbol for magnesium, S stands for sulphur, and O represents oxygen, how many of each atom exists in a molecule of Epsom salts?

Back 22

There are no subscripts after the Mg or the S, indicating one magnesium atom and one sulphur atom. There is a subscript of 4 after O, indicating four oxygen atoms.

Front 23

Calcium carbonate is an ionic substance commonly called ‘chalk’. If this molecule has one calcium atom (Ca), one carbon atom (C), and three oxygen atoms (O), what is its chemical formula?

Back 23

You put the subscripts after each symbol to indicate the number of atoms. If the number is one, there is no subscript. This leads to an answer of CaCO3.

Front 24

One of the most common household cleaners is ammonia, which has a chemical formula of NH3. How many atoms are in a molecule of ammonia?

Back 24

There is no subscript after the N, indicating one atom there. The next letter is capital, so it must represent another atom. There is a subscript of 3 after it, indicating three of those. Thus, there are a total of four atoms

Front 25

A certain molecule is composed of atoms that all pull on electrons with the same strength. Will this molecule be polar?

Back 25

No, the molecule will not be polar. If the atoms all pull on electrons with the same strength, none will be able to get more than its fair share.

Front 26

Baking soda dissolves in water. Will it dissolve in vegetable oil, which is a nonpolar substance?

Back 26

Baking soda will not dissolve in vegetable oil. Since baking soda dissolves in water, it is either ionic or polar. (It is ionic). Either way, it will not dissolve in a nonpolar substance because only other nonpolar substances will dissolve in nonpolar substances.

Front 27

Carbon tetrachloride will not dissolve in water . Is it most likely made of ionic molecules, polar molecules, or nonpolar molecules?

Back 27

Carbon tetrachloride is probably made of nonpolar molecules, otherwise it probably would have dissolved in water.

Front 28

Suppose you were able to count the molecules in a substance. Which would have more molecules, a litre of liquid water or 1 litre of ice?

Back 28

The liquid would have more molecules, because the molecules in solid water are farther apart than they are in liquid water. For the same volume, then, there would be more molecules in the liquid.

Front 29

If the substance in question #10 were virtually any other substance, what would the answer be?

Back 29

For nearly any other substance, the answer would be that the solid would have more molecules. For almost all other substances, molecules are closer together in the solid state, so there would be more molecules in an equal volume as compared to the liquid.

Front 30

What is responsible for water being a liquid at room temperature as well as for water’s cohesion?

Back 30

Hydrogen bonding is responsible. Hydrogen bonding brings the molecules close together and makes them want to stay close together.

Front 31

What causes surface tension?

Back 31

Cohesion causes surface tension.

You could say hydrogen bonding here if you are talking about water. However, other substances exhibit surface tension, even if they do not hydrogen bond. Hydrogen bonding just makes water’s surface tension larger than that of many other substances.

Front 32

Why is water harder in certain regions of the world than in others?

Back 32

Water is harder in some regions of the world because there is a higher amount of metal-containing substances in some regions than others. It is the dissolved metal ions that cause hard water.

Front 33

We can live for as many as two weeks without food, but if we were to go even a few days without _____, we would surely die. Indeed, without water, _______as we know it simply cannot exist.

Back 33

water

life

Front 34

What is the chemical formula for water?

Back 34

H2O

Front 35

Some metals tend to absorb oxygen but not hydrogen. Suppose such a metal was covering the battery in an electrolysis experiment like Experiment 4.1. Which is the more likely erroneous result the experiment would yield for the chemical formula of water: HO2 or H4O?

Back 35

H4O would be the more likely erroneous result.

If the oxygen was being absorbed by the metal covering on the battery, there would be less collected in the tube. This would make it look water molecules had a lot less oxygen. HO2 would be a chemical formula that indicates more oxygen.

Front 36

Why is water a liquid at room temperature when all other chemically similar substances are gases at room temperature?

Back 36

Hydrogen bonding keeps the water molecules close together.

Front 37

Carbon dioxide (CO2) is one of the gases that we exhale when we breathe. Carbon monoxide (CO2) is a poisonous gas associated with burning things under conditions of low oxygen. How many atoms are in one molecule of CO2? How many atoms are in one molecule of CO?

Back 37

There are 3 atoms in a carbon dioxide molecule and two atoms in a carbon monoxide molecule. Remember, each capital letter signifies an atom, and if there is no subscript, that means there is only one atom.

Front 38

An important component of gasoline is octane, which is composed of molecules that have 8 carbon atoms (C) and 18 hydrogen atoms (H). What is the chemical formula of octane?

Back 38

The chemical formula is C8H18.

Front 39

Why are water molecules polar?

Back 39

Water molecules are polar because both the oxygen atoms and the hydrogen atoms are fighting over the electrons they are supposed to be sharing. Oxygen can pull on those electrons harder, so it gets more than its fair share of electrons, making it slightly negative. Since the hydrogen atoms get less than their fair share of electrons, they end up slightly positive.

Front 40

If a substance does not dissolve in water, is it most likely ionic, polar or nonpolar?

Back 40

It is most likely nonpolar because water dissolves both polar and ionic substances.

Front 41

If a substance dissolves in water, will it dissolve in vegetable oil, a nonpolar substance?

Back 41

It will not dissolve in vegetable oil because if it dissolves in water, it is either ionic or polar. Either way, such a substance will not dissolve in a nonpolar liquid like vegetable oil.

Front 42

Is hard water the result of a city's water treatment process?

Back 42

No. Hard water is the result of the calcium-containing compounds in the region from which the water is taken.

Front 43

The use of electricity to break a molecule down into smaller units is called________. When you use this procedure on water, you produce _______and________. If you measure the volumes of each, you will find twice as much _______as________.

Back 43

electrolysis
hydrogen
oxygen

hydrogen
oxygen

Front 44

Often, experiments produce incorrect results due to________________. A good scientist tries to _____the amount of it in an experiment and does not ______experiments that have a lot of it. When a scientist performs an experiment that seems to lead to a new, interesting conclusion, other ______in the field look closely at the experiment in an effort to spot ________________that the original scientist did not recognize. This process is called________. An example of the importance of this process is seen in Drs. Martin Fleischmann and Stanley Pons, who claimed to have discovered cold_______, a potential source of cheap, unlimited power. They did not submit their experiments to ____________before publicizing their results. As a result, they were embarrassed because other scientists had to publicly announce the ______________in their experiments.

Back 44

experimental error
reduce
trust
scientists
experimental errors
peer review
fusion
peer review
experimental errors

Front 45

The chemical symbol of an atom contains either ____or ____letter. If there are _____letters, only the _____is capitalized. The letter soften come form either the _____or _____name of the atom. A ______________tells you the composition of a molecule because the ___________in the chemical formula tell you how many of each atom is present. If there is no subscript next to an atom’s symbol, there is ___of those atoms in the molecule. Thus, the molecule CaCO3 has ____calcium (Ca) atom, ____carbon (C) atom, and _____oxygen (O) atoms.

Back 45

One
Two
Two
First
English
Latin
chemical formula
subscripts
one
one
one
three

Front 46

Magnesium hydroxide is a chemical often used in antacid tablets. It has one Magnesium (Mg)atom, two oxygen (O) atoms, and two hydrogen (H) atoms. Thus, its chemical formula is______. The chemical formula of sodium nitrate is NaNO3. This molecule has a total of ___ atoms: ___sodium (Na) atom, ___nitrogen (N) atom, and __ oxygen (O) atoms.

Back 46

MgO2H2
5
1
1
3

Front 47

Atoms in molecules are linked together with____________, which are made up of ______electrons. If the atoms in a molecule do not _____electrons equally, small _____result within the molecule, and it is called a ____molecule. In Experiment 4.2, the small _____charges on the _____atoms of the water molecules were attracted to the ______charge on the comb. That’s what made the stream of water bend ____the comb.

Back 47

chemical bonds
shared
share
charges
polar
positive
hydrogen
negative
towards

Front 48

When you dissolve a substance in a liquid, we say you have made a_____. When making a solution, you use a ____to dissolve a_____. When you dissolve sugar in water, for example, water is the___, sugar is the_____, and sugar water is the_____.

Back 48

Solution
Solvent
Solute
Solvent
Solute
solution

Front 49

In general, a polar or ionic solute can only dissolve in a ______solvent. A nonpolar solute can only dissolve in a ___________solvent. A solute dissolves in a solvent because the molecules of the solvent are _________to the molecules (or ions) of the solute.

Back 49

Polar
Nonpolar
attracted

Front 50

In a water molecule, the positive charge on one molecule is attracted to any other ______charge. In a sample of water, there are many other molecules, so they will tend to align themselves so that the positive charge on the _______of one molecule will be as close as possible to the negative charge on the _______of another molecule. This results in____________, which causes water molecules to be very close to one another. In fact, most molecules that are chemically similar to water are gases at room temperature. Water, however, is a _____at room temperature. Water, however, is a liquid at room temperature because of______________.

Back 50

Negative
Hydrogens
Oxygen
hydrogen bonding
liquid
hydrogen bonding

Front 51

While the solid phase of most substances _____the liquid phase of that same substance, solid water (ice) _____in liquid water. This is because the molecules of liquid water are ________than the molecules in solid water. This convenient fact allows lakes to _____from the top down. As a result, a reasonably deep body of water will never _______freeze, because the _____at the surface insulates the water below. This allows fish (and other aquatic animals) to ______the winter.

Back 51

Sinks
floats
closer together
freeze
completely
ice
survive

Front 52

Because of hydrogen bonding, individual water molecules are so strongly ____to one another that they tend to stay together, even when subjected to an outside force. This gives water its _____which, in turn, causes_________, the phenomenon that caused the needle to float in Experiment 4.5. This same phenomenon is exploited by water striders, allowing them to ____on water. The _______of water is also what makes it possible for water to travel up through the xylem of a tall plant.

Back 52

attracted
cohesion
surface tension
walk
cohesion

Front 53

Although water’s _____is strong, it can be overcome. In Experiment 4.6 for example, water ‘beaded up’ on the _____surface of the glass, because water molecules are attracted to _______more ______than they are to the molecules that make up wax. However, the water did not ‘bead up’ on the unwaxed glass, because water molecules are attracted to _____________________________

Back 53

more strongly than they are to each other.
Cohesion
Waxed
each other
strongly
the molecules that make up glass

Front 54

When water has ions like calcium and magnesium dissolved in it, we call it ____water.
It is ____the result of treatment done to make the water safe to drink.
Instead, it is the result of the ____from which the water is taken.
In a______, calcium and magnesium ions are ‘exchanged’ with either _____or ______ions so that the calcium and magnesium ions are not in the water we drink and use. People who are on strict _____diets should either not soften their water or use more expensive, sodium-free water-softener salts, like_________.

Back 54

hard
not
source
water softener
sodium
potassium
low-sodium
potassium chloride