Topic 3 - Quantitative Chemistry

Question 1

What is the definition of relative atomic mass?

Answer 1

The average mass of all the isotopes of that element

Question 2

What is the symbol for relative atomic mass?

Answer 2

Ar

Question 3

What is the symbol for relative formula mass?

Answer 3

Mr

Question 4

What is the formula that links mass, moles, and Mr?

Answer 4

mass = moles x Mr

Question 5

What does the law of conservation of mass state?

Answer 5

No atoms are lost or made during a chemical reaction

Question 6

What is a chemical change?

Answer 6

A rearrangement of the atoms in the reactants, to form the products

Question 7

What does it mean for a reactant to be a ‘limiting reactant’?

Answer 7

It all reacts and limits how much product can be formed

Question 8

What does it mean for a reactant to be ‘in excess’?

Answer 8

It does not all react, and has no affect on the amount of product formed

Question 9

What is the formula for finding concentration from mass and volume?

Answer 9

concentration = mass / volume

Question 10

What do you do to convert cm3 to dm3?

Answer 10

Divide by 1000.

Question 11

What’s the equation that links the volume of a gas, to the number of moles of that gas.

Answer 11

volume (dm3) = moles x 24

Question 12

What is the atom economy of a reaction?

Answer 12

A measure of the proportion of starting materials that end up as useful products

Question 13

What’s the formula for atom economy?

Answer 13

Atom economy = Mr of desired products / Mr of all products X 100

Question 14

What are the problems with low atom economy?

Answer 14

• It will be less sustainable as it will use more resources
• There will be more waste products which will have to be disposed of

Question 15

Identify other factors, besides atom economy, that should be considered when choosing between two different methods of producing a useful product.

Answer 15

1. Percentage yield
2. Cost of raw materials
3. Position of equilibrium
4. Rate of reaction
5. Cost of maintaining the right conditions
6. Environmental impact of waste products

Question 16

What is the percentage yield of a reaction?

Answer 16

The actual yield of a reaction compared to the maximum theoretical yield

Question 17

Suggest 3 reasons why the percentage yield of a chemical reaction may be less than 100%.

Answer 17

1. The reactants may not all react (e.g. because the reaction is very slow or reaches equilibrium)
2. There may be side reactions, meaning that other products are produced instead
3. Some of the products may be lost (e.g. gases may float off, or some solids may be left on the filter paper)