Quantitative Chemistry

Question 1

What is relative formula mass (M_r)?

Answer 1

Masses of all atoms in molecular formula added together

Question 2

One mole contains how many atoms/molecules i.e. what’s “the Avogadro constant”?

Answer 2

6.02 x 10²³

Question 3

How do you work out 1 mole of substance?

Answer 3

Work out its relative formula mass

Question 4

In a chemical reaction, mass is ___ ______

Answer 4

Always Conserved

Question 5

During a chemical reaction, are atoms are destroyed and created?

Answer 5

NO

Question 6

How do we know mass is conserved during a reaction?

Answer 6

Same no. + types of atoms on each side of reaction equation (& total of M_r of all reactants = total M_r of products)

Question 7

When may you observe a change of mass?

Answer 7

When the reaction takes place in an unsealed reaction vessel

Question 8

If mass increases in a reaction, what’s likely to have happened?

Answer 8

1. Reactant = gas - not contained in reaction vessel = can’t account for its mass
2. Gas reacts to form part of product = becomes contained inside reaction vessel

Question 9

If mass decreases in a reaction, what’s likely to have happened?

Answer 9

1. Product = gas - before reaction, all reactants contained in reaction vessel
2. Vessel isn’t enclosed = gas escapes from reaction vessel as it’s formed ∴ can’t account for its mass

Question 10

What is the volume of one mole of any gas at room temperature and pressure?

Answer 10

24 dm³

Question 11

When does a reaction stop?

Answer 11

When all of one reactants is used up

Question 12

E.g. Reaction with 2 reactants: Why might one reactant be added in excess?

Answer 12

To make sure other reactant is used up

Question 13

What is a limiting reactant?

Answer 13

Reactant that’s used up in a reaction

Question 14

Amount of ____ _____ is ____ ______ to amount of limiting reactant

Answer 14

product formed is directly proportional

Question 15

Why is the amount of product formed directly proportional to amount of limiting reactant?

Answer 15

Because if you add more reactant there will be more reactant particles to take part in the reaction = more product particles

Question 16

What is concentration?

Answer 16

Amount of substance (e.g. mass or the number of moles) in a certain volume of a solution

Question 17

How increase the concentration of solution, in given a volume?

Answer 17

Increase amount of solute

Question 18

1ml = ….

Answer 18

1cm³

Question 19

Why are yields are always less than 100%?

Answer 19

1. Reversible reactions may not go to completion (i.e. Not ALL the reactants react to make a PRODUCT)
2. Some reactants may react in an expected way (i.e. there may be SIDE REACTIONS)
3. Some product may be lost when you SEPARATE IT from the reaction mixture

Question 20

Why should industrial processes have as high percentage yield as possible?

Answer 20

To reduce waste and costs

Question 21

State how to get from:

m³ → dm³ → cm³

Answer 21

m³ (x1000)→ dm³ (x1000)→ cm³

Question 22

State how to get from:

cm³ → dm³ → m³

Answer 22

cm³ (÷1000)→ dm³ (÷1000)→ m³

Question 23

Name the formula for working out concentration (mass) and state the units

Answer 23

Concentration = Mass of Solute ÷ Voume of Solvent

c = m/v

c = g/dm³

m = g

v = dm³

Question 24

Name the formula for working out concentration (moles) and state the units

Answer 24

Concentration = No. of Moles of Solute ÷ Voume of Solvent

c = /v

c = mol/dm³ or mol/dm^-3

n = mol

v = dm³

Question 25

How do you calculate percentage yield?

Answer 25

(Actual yield ÷ Predicted yield) x 100

Question 26

What’s the formula for working out the concentrations - titrations?

Answer 26

C_b x V_b = C_a x V_a

Question 27

What’s the formula for working out the volume of a gas?

Answer 27

v = 24 x n

Question 28

What do you multiply the empirical formula by to find the molecular formula?

Answer 28

Molar mass of molecular formula

Molar mass of empirical formula