This question is about compounds - AQA - GCSE Chemistry - Question 5 - 2015 - Paper 2

A soluble compound that contains carbonate ions is potassium carbonate, represented by the chemical formula K₂CO₃, or sodium carbonate, Na₂CO₃.

A metal oxide is classified as a base, which can react with acids to produce salts.

Solid lead nitrate can be obtained from lead nitrate solution by evaporating the solution or by crystallization.

The balanced equation for the reaction is:

In the formula Pb(NO₃)₂, there are a total of 9 atoms: 1 lead atom, 2 nitrogen atoms, and 6 oxygen atoms.

To calculate the empirical formula, first find the number of moles of lead and oxygen:

• Moles of Pb: rac{6.21 ext{ g}}{207 ext{ g/mol}} = 0.03 ext{ moles}
• Moles of O: rac{0.72 ext{ g}}{16 ext{ g/mol}} = 0.045 ext{ moles}

Next, divide both by the smallest number of moles:

• For Pb: rac{0.03}{0.03} = 1
• For O: rac{0.045}{0.03} = 1.5

Multiplying both by 2 gives the ratio of Pb to O as 2:3, resulting in the empirical formula Pb₂O₃.