Quantitative Chemistry: The Mole

Question 1

What is Avogadro’s constant?

Answer 1

The number of atoms, molecules or ions in 1 mole of a given substance

Question 2

What is the value of Avogadro’s constant?

Answer 2

6.02 x 10²³

Question 3

What is the formula linking mass, relative formula mass (Mr) and moles together?

Answer 3

mass = Mr x moles

Question 4

What is the mass of 20 moles of calcium carbonate, CaCO₃?

Answer 4

mass = Mr x moles
Mr = 100
100 x 20 =2,000g

Question 5

Calculate the amount of carbon dioxide in moles in 0.32g of carbon dioxide.

Answer 5

moles = mass/Mr
0.32/44 =0.00727

Question 6

Nitrogen and hydrogen form ammonia shown by the following equation:
N₂ + 3H₂ ⇄ 2NH₃.
Calculate the mass of nitrogen needed to form 6.8 tonnes of ammonia.

Answer 6

5.6 tonnes

Question 7

Hydrogen peroxide (H₂O₂) decomposes in water to form water and oxygen. How many grams of oxygen gas will be given off from 40.8g of hydrogen peroxide?

Answer 7

19.2g

Question 8

What’s are the two formulae linking concentration, mass and volume together?

Answer 8

Concentration (g per dm³) = mass (g)/volume(dm³)

Concentration (mol per dm³) = no. of moles /volume(dm³)

Question 9

31cm³ of potassium hydroxide solution neutralised 25cm³ of 2moldm^-3 nitric acid.

HNO₃ + KOH → KNO₃ + H₂O.
Calculate the concentration of the potassium hydroxide solution in moldm^-3.

Answer 9

1.61moldm^-3

Question 10

What is the molar volume of a gas at room temperature and pressure?

Answer 10

1 mole of a gas at room temperature and pressure occupies 24dm³