Chapter 3

Question 1

Amount of moles

Answer 1

N = m/Mr

Question 2

What is the empirical formula

Answer 2

The simplest ratio of elements

Question 3

Calculating relative formula mass

Answer 3

Add together the relative mass of each element present in a formula

Question 4

What are hydrated crystals

Answer 4

Crystals with water particles as part of their crystalline structure

Question 5

What do crystals become after the water is removed from them

Answer 5

Anhydrous

Question 6

How could you determine the water of crystallisation in hydrated crystals in an experiment

Answer 6

Step 1: weigh a crucible

Step 2: add the hydrated salt to the weighed crucible and weigh the crucible with the salt inside

Step 3: support the crucible on a tripod with a pipe-clay triangle, heat the crucible gently for one minute then strongly for three more minutes

Step 4: leave the crucible to cool then weigh the crucible and anhydrous salt

Question 7

Calculating the formula of anhydrous salt

Answer 7

Step 1: calculate the amount of water in crystals

Step 2: calculate the mass and amount in mol of water

Step 3: find the smallest whole-number ratio

Step 4: write down the amount of mols of water in the formula

Question 8

What assumptions must be made to make the amount of water in a hydrated salt accurate

Answer 8

Assumption 1: all the water has been lost

Assumption 2: the salt cannot decompose any further