Chapter 3: Quantitative Chemistry

Question 1

What is an isotope?

Answer 1

A version of an atom with a different number of neutrons

Question 2

What is relative atomic mass?

Answer 2

The ratio of the average mass of all of the isotopes of an element to one twelfth of the mass of an atom of carbon-12. So, the relative atomic mass of oxygen would be 16

Question 3

What is relative formula mass?

Answer 3

The total of the relative atomic masses of each element in a formula. For example, H2O is (2x1) + (1x16) = 18

Question 4

What is the law of conservation of mass?

Answer 4

Mass is never lost or gained in any chemical reaction

Question 5

Why can it sometimes seem as though mass has been lost?

Answer 5

Because some of the reactants could become gasses

Question 6

What is Avogadro’s constant

Answer 6

6.02 x 10^23, the amount of particles in a mole of anything

Question 7

How much would 1 mole of carbon atoms weigh?

Answer 7

12 grams (the atomic weight)

Question 8

What is a mole?

Answer 8

The relative formula mass of a substance, given in grams, is 1 mole of a substance. 12g of carbon is a mole

Question 9

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

Answer 9

mass (g) = Mr x moles

Question 10

What is a balanced chemical equation?

Answer 10

An equation where the number of atoms of each element on each side of the equation is the same

Question 11

Why is the mass of the product greater than that of the reactants when metals react with oxygen?

Answer 11

The extra mass comes from the oxygen in the air

Question 12

What is a thermal decomposition reaction?

Answer 12

A reaction where heat causes a substance to break down into simpler substances. Some gas may escape into the air

Question 13

What do metal carbonates decompose into when heated?

Answer 13

Metal oxide and carbon dioxide

Question 14

How do you do reacting mass calculations?

Answer 14

Remember, the balancing number means that many moles of the substance. Work out the relative formula masses of both elements in the question. Calculate the moles of the substance whose mass is given. You can then use molar ratios to work out the rest, before converting back into mass

Question 15

What can these ratios be used for?

Answer 15

To calculate how many moles would react and be produced in reactions

Question 16

How do you deduce the balancing numbers from the masses?

Answer 16

Calculate the moles of each substance, then find the simplest whole number ratio by dividing by the smallest mole value

Question 17

What is an excess?

Answer 17

When the amount of a reactant is greater than the amount that can react

Question 18

What is a limiting reactant?

Answer 18

The reactant we don’t have an unlimited supply of, which determines the amount of products formed

Question 19

Why are excesses used?

Answer 19

To ensure that all the reactant is used up, especially when it’s expensive

Question 20

What is percentage yield?

Answer 20

The mass of the product formed compared to the mass of the reactants (the largest theoretical mass)

Question 21

List 3 reasons a reaction’s yield might not be 100%

Answer 21

Some reactions do not finish completely, Some may be left on the apparatus when it’s removed, The reactants might also take part in other reactions

Question 22

What is the atom economy?

Answer 22

A way of measuring what percentage of the mass of the reactants ends up in the desired product

Question 23

How do you calculate the atom economy?

Answer 23

100 x (sum of relative formula mass of desired product) / (sum of relative formula mass of all reactants)

Question 24

How does the volume of a gas vary with the temperature?

Answer 24

Higher temperature = Greater volume. If the temperature and pressure are the same, equale numbers of moles of gases will have the same volume

Question 25

What is the volume of 1 mole of a gas at room temperature?

Answer 25

24 dm^3

Question 26

What equation links the volume of a gas to the number of moles?

Answer 26

volume (dm^3) = 24 x moles

Question 27

What equation links mass, concentration, and volume?

Answer 27

mass (g) = concentration (g/dm^3) x volume (dm^3)

Question 28

How many cm^3 are in 1dm^3?

Answer 28

1000

Question 29

How do you measure how concentrated a solution is in mol/dm^3?

Answer 29

moles = concentration (mol/dm^3) x volume (dm^3)

Question 30

How do you convert mol/dm^3 to g/dm^3?

Answer 30

mol/dm^3 x relative formula mass

Question 31

What are titrations?

Answer 31

Techniques that can be used to find the concentration of a reaction by reacting it with a solution of known concentration

Question 32

Describe the 6 steps of titration

Answer 32

1. A known volume of solution of an acid is measured out with a pipette and placed in a conical flask
2. A few drops of indicator (phenolphthalein) are added
3. The other solution is added from the burette until the indicator changes colour
4. The volume added from the burette is recorded, and the experiment optionally repeated

Question 33

How can the concentration of a solution be found using the results of a titration?

Answer 33

1. Work out the moles of the solution with the known concentration
2. Use the molar ratios of the balanced equation to work out the moles of the unknown solution
3. Use c=m/v to work out the concentration