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27 Cards in this Set
- Front
- Back
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What is relative atomic mass (Aᵣ) used for? |
It's a way of saying how heavy different atoms are compared with the mass of an atom of carbon-12. |
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What does the atomic number (the lower number) measure? |
The number of protons (and therefore, the number of electrons). |
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What does the mass number measure? |
The number of protons AND neutrons that the element has. If you take the atomic number from the mass number, you'll end up with the number of neutrons. |
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Why do some elements have a mass number that isn't an integer? (The mass number has .5 - it's not a whole number.) |
When an element has more than one stable isotope, the relative atomic mass is an average value of all the different isotopes (taking into account how much there is of each isotope). |
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What is the relative formula mass (Mᵣ)? |
All of the relative atomic masses added together. |
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What is "one mole" of a substance equal to? |
Its Aᵣ/Mᵣ (relative atomic mass/relative formula mass) in grams. |
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State the formula used to convert between moles and grams. |
No. of moles = Mass in g (of element/compound) ---------------------------------------------- Mᵣ/Aᵣ (of element/compound) |
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State the formula to calculate the % mass of an element in a compound. |
Aᵣ x No. of atoms (of that element) --------------------------------------------------- x 100 Mᵣ (of whole compound)
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What does 'Aᵣ' mean? |
Relative atomic mass |
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What does 'Mᵣ' mean? |
Relative formula mass |
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What is the empirical formula? |
A molecular formula reduced to the lowest common denominator. |
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What is the empirical formula used for? |
To show the ratio of atoms in an element. |
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How do we work out the empirical formula of a compound? |
1) List all the elements in the compound. 2) Underneath them, write their experimental masses or percentages. 3) Divide each mass or percentage by the Aᵣ for that particular element. 4) Turn these numbers into a ratio by multiplying or dividing. 5) Get the ratio in its simplest form - this tells you what the empirical formula of the compound is. |
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What are the three important steps for calculating masses of reactants and products in a reaction? |
1) Write out the balanced equation. 2) Work out Mᵣ for the substances that you want. 3) Apply the rule: divide to get one, then multiply to get all. |
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What is the amount of product you get from a reaction known as? |
The yield. |
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Complete this sentence: The more reactants you start with... |
...the higher the yield will be. |
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What is the percentage yield? |
The ratio of actual mass of products obtained compared with the maximum theoretical mass. |
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What is the formula used to calculate percentage yield? |
actual yield (grams) --------------------------------- x 100 predicted yield (grams) |
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What is the predicted yield calculated from? |
The balanced reaction equation. |
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What does a 100% percentage yield mean? |
That you got all the product that you expected to get. |
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What does a 0% percentage yield mean? |
No reactants were converted into product (no product was made). |
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Even though no atoms are gained or lost in a chemical reaction, it is not always possible to obtain the calculated amount of the product. Why? |
1) The reaction may not go to completion because it is reversible. 2) Some of the product may be lost when it is separated from the reaction mixture. 3) Some of the reactants may react in ways different from the expected reaction. |
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What is a reversible reaction? |
Where the products of a reaction can themselves react to produce to original reactants. |
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What is the symbol used to represent a reversible reaction? |
The equilibrium symbol |
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Why won't you get a 100% percentage yield if the reaction is reversible? |
Some of the products are always reacting together to change back to the original reactants. |
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Why is thinking about product yield important for sustainable development? |
Using as little energy as possible to create the highest product yield possible means that resources are saved. A low yield means wasted chemicals - not very sustainable. |
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How is a reversible equation represented? |
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