Chapter 3: Amount of substance (3.1-3.4)

Question 1

Water of crystallisation

Answer 1

water molecules that are bounded into a crystalline structure of a compound

Question 2

Moles =

Answer 2

mass / Mr

Question 3

Explain what the difference is between a hydrated and an anhydrous salt

Answer 3

Hydrated salts have water within their crystals when the crystals are formed from water; an anhydrous salt is where the crystal has had the water driven out. Water of crystallisation occurs for two reasons

Question 4

What is the difference between one mole go H and one mole of H2?

Answer 4

One mole of H is one mole of hydrogen atoms and one mole of H2 is one mole of hydrogen molecules.

Question 5

Why do blue crystals of hydrated copper (ii) sulphate turn white when heated?

Answer 5

Bonds holding the water within the crystal are broken and the water is driven off.

Question 6

How do you work out the water of crystallisation?

Answer 6

1) Calculate the amount, in mol, of the anhydrous salt formed
2) Calculate the mass and amount , in mol, of water
3) Divide by the smallest number of moles: simplest whole number ratio
4) Write down the value of X and write in the formula of the salt