3.1.2 Amount of substance

Question 1

How many particles are there in one mole of any substance?

Answer 1

6.02 × 10²³ particles

Question 2

How do you find the number of particles within the substance?

Answer 2

Number of particles = Number of moles × Avogadro’s constant

Question 3

What’s the mass of any 1 mole of substance?

Answer 3

1 mole of any substance has a mass that’s the same as its relative molecular mass in grams.

Question 4

How do you work out the amount of substance in moles?

Answer 4

Number of moles = Mass ÷ Molecular Mass

Question 5

What is concentration?

Answer 5

The concentration of a solution is how many moles are dissolved per 1 dm³ (1 litre) of solution. The units are mol/dm³.

Question 6

How do you find the concentration of a solution?

Answer 6

Concentration = Number of moles ÷ Volume

Question 7

What’s the formula of the ideal gas equation?

Answer 7

PV = nRT

P = pressure (Pa)
V = volume (m³)
n = number of moles (8.31 J K/mol)
R = ideal gas constant
T = temperature (K)

Question 8

What are ionic equations?

Answer 8

Ionic equations only show the reacting particles and the products they form.

Question 9

Define the term relative atomic mass.

[2 marks]

Answer 9

• The average mass of an atom…

- …relative to 1/12th mass of ¹²C atom.

Question 10

Explain why the relative atomic mass of any element is not a whole number.
[2 marks]

Answer 10

• Elements come in in mixtures of different isotopes in different abundances.
• The average mass of these isotopes isn’t a whole number.