Question Constellation Sign up for free AQA · GCSE · Combined Science · Higher
Reacting mass calculation
Gold reacts with the elements in Group 7 of the periodic table.
0.175 g of gold reacts with chlorine.
The equation for the reaction is:
2 Au + 3 Cl2 → 2 AuCl3
Calculate the mass of chlorine needed to react with 0.175 g of gold.
Give your answer in mg
Relative atomic masses (Ar): Cl = 35.5 Au = 197
Mass of chlorine = mg
Write your answer first. You can study the marking guidance whenever you need it.
Study the marking See what earns credit and compare it with a full-mark answer.
Marking points
- 1 Calculate moles of gold: 0.175 / 197 = 0.000888.
- 2 Use the 2:3 ratio to calculate moles of chlorine: 0.000888 x 3/2 = 0.00133.
- 3 Calculate mass of chlorine: 0.00133 x 71 = 0.0946 g.
- 4 Convert grams to milligrams: 94.6 mg.
Full-mark answer
Moles of Au = 0.175 / 197 = 0.000888. From 2 Au : 3 Cl2, moles of Cl2 = 0.000888 x 3/2 = 0.00133. Mass of Cl2 = 0.00133 x 71 = 0.0946 g = 94.6 mg.