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 formula K₂CO₃.

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

Solid lead nitrate can be obtained from lead nitrate solution by evaporating the water, which leaves behind the solid crystals.

The balanced equation for the reaction is:

$\text{PbO} + 2 \text{HNO}_3 \rightarrow \text{Pb(NO}_3\text{)}_2 + \text{H}_2\text{O}$

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

To calculate the empirical formula:

1. Convert the masses to moles:

   • Moles of lead (Pb): $\frac{6.21}{207} \approx 0.03$
   • Moles of oxygen (O): $\frac{0.72}{16} \approx 0.045$

2. Find the simplest ratio:

   • Ratio for Pb = 0.03 / 0.03 = 1
   • Ratio for O = 0.045 / 0.03 = 1.5
   • Multiply by 2 to get whole numbers:
   • Empirical formula = Pb₂O₃.