Chemical analysis and the dilute hydrochloric acid group
Answers are for parents and teachers.
1
A 8.0 g sample of rock salt contains 6.8 g of NaCl. Find its percentage purity.
6.8 ÷ 8.0 × 100 = 85 %.
2
Find the mass percentage of chlorine in potassium chloride, KCl (K = 39, Cl = 35.5).
M = 74.5 g/mol; 35.5 ÷ 74.5 × 100 = 47.7 %.
3
Complete and balance the test for lithium carbonate: Li₂CO₃ + HCl → ?
Li₂CO₃ + 2HCl → 2LiCl + H₂O + CO₂.
4
Complete and balance: FeS + HCl → ? Name the gas and the paper that shows it.
FeS + 2HCl → FeCl₂ + H₂S; the gas is H₂S and it blackens lead acetate paper.
5
Give two reasons why the lime water test alone cannot prove that a salt is a carbonate.
A hydrogencarbonate also gives CO₂, and a sulphite gives SO₂, which also turns lime water milky.