3) Amount

Question 1

What is the definition of one mole?

Answer 1

The amount of substance that contains 6.02 × 10²³ particles (the Avogadro constant)

Question 2

What is the mass of one mole of atoms of an element?

Answer 2

It is equal to the relative atomic mass (Aᵣ) of that element in grams.

Question 3

What is the formula that links mass (m), amount in moles (n), and molar mass (M)?

Answer 3

n=m/M
​

Question 4

What is the molar mass of a compound?

Answer 4

The mass per mole of a substance. Its units are g mol⁻¹. It is calculated by adding the relative atomic masses of all the atoms in its formula.

Question 5

What is the difference between a molecular formula and an empirical formula?

Answer 5

Molecular formula: The actual number of atoms of each element in a molecule.

Empirical formula: The simplest whole-number ratio of atoms of each element in a compound.

Question 6

How do you calculate an empirical formula from mass data?

Answer 6

Find the moles of each element using
n=m/M
​

Divide each amount by the smallest number of moles.

Convert to the simplest whole-number ratio.

Question 7

What is water of crystallisation?

Answer 7

Water molecules that form an essential part of the crystalline structure of a compound (a hydrated salt).

Question 8

What is the formula of a hydrated salt?

Answer 8

It is written as e.g., CuSO₄*5H₂O, where the dot shows the water is associated with the ions.

Question 9

What formula links moles (n), concentration (c), and volume in dm³ (V)?

Answer 9

n=c×V (where V is in dm³)

Question 10

What is a standard solution?

Answer 10

A standard solution is a a solution of accurately known concentration prepared from a primary standard (a compound which is stable, of high purity, highly soluble in water and of a high molar mass to allow for accurate weighing) that is weighed accurately and made up to a fixed volume.

Question 11

What is the molar gas volume at room temperature and pressure (RTP)?

Answer 11

24.0 dm³ mol⁻¹

Question 12

What formula links moles of a gas (n) and its volume at RTP (V)?

Answer 12

n= 24/V

Question 13

What is the Ideal Gas Equation?

Answer 13

pV=nRT
Where:

p = pressure (Pa)

V = volume (m³)

n = moles

R = gas constant (8.314 J mol⁻¹ K⁻¹)

T = temperature (K)

Question 14

What is stoichiometry?

Answer 14

The molar ratio of reactants and products in a balanced chemical equation.

Question 15

What is the theoretical yield?

Answer 15

The maximum mass of product possible, calculated from the balanced equation and the amount of limiting reactant.

Question 16

What is the formula for percentage yield?

Answer 16

Percentage Yield = (Actual Yield / Theoretical Yield) × 100%

Question 17

What is the limiting reactant?

Answer 17

The reactant that is completely used up first in a chemical reaction. It determines the amount of product formed.

Question 18

What is atom economy and the equation to work it out?

Answer 18

A measure of the proportion of reactant atoms that become atoms in the desired product.

Atom Economy = (Molar Mass of Desired Product / Sum of Molar Masses of All Products) × 100%

Question 19

Why is a high atom economy important?

Answer 19

It makes processes more sustainable by reducing waste, preserving raw materials, and often reducing energy costs.