Reacting Volumes (AQA A Level Chemistry): Revision Note

Calculating volume from concentration

Calculate the volume of 1.0 mol dm^-3 hydrochloric acid required to completely react with 2.5 g of calcium carbonate.

Answer:

1. Write the balanced symbol equation

   • CaCO₃  +  2HCl  →  CaCl₂  +  H₂O  +  CO₂

2. Calculate the amount, in moles, of calcium carbonate:

   • n(CaCO₃) = $\frac{2.5\mathrm{g}}{100\mathrm{g}{\mathrm{mol}}^{-1}}$ = 0.025 mol

3. Calculate the moles of hydrochloric acid required using the reaction’s stoichiometry:

   • 1 mol of CaCO₃ requires 2 mol of HCl

   • So 0.025 mol of CaCO₃ requires 0.05 mol of HCl

4. Calculate the volume of HCl required:

   • Volume (HCl) = $\frac{\mathrm{amount}\left(\mathrm{mol}\right)}{\mathrm{concentration}\left(\mathrm{mol}{\mathrm{dm}}^{-3}\right)}$

   • Volume (HCl) = $\frac{0.05\mathrm{mol}}{1.0\mathrm{mol}{\mathrm{dm}}^{-3}}$ = 0.05 dm³

   • So, the volume of hydrochloric acid required is 0.05 dm³ 

Neutralisation calculation

25.0 cm³ of 0.050 mol dm^-3 sodium carbonate solution was completely neutralised by 20.0 cm³ of dilute hydrochloric acid.

Calculate the concentration, in mol dm^-3, of the hydrochloric acid.

Answer:

1. Write the balanced symbol equation:

   • Na₂CO₃  +  2HCl  →  Na₂Cl₂  +  H₂O  +  CO₂

2. Calculate the amount, in moles, of sodium carbonate reacted

   • n(Na₂CO₃) = 0.025 dm³ x 0.050 mol dm^-3

   • n(Na₂CO₃) = 0.00125 mol

3. Calculate the moles of hydrochloric acid required using the reaction’s stoichiometry:

   • 1 mol of Na₂CO₃ reacts with 2 mol of HCl, so the molar ratio is 1 : 2

   • Therefore, 0.00125 moles of Na₂CO₃ react with 0.00250 moles of HCl

4. Calculate the concentration, in mol dm^-3 of hydrochloric acid:

   • [HCl] = $\frac{\mathrm{amount}\left(\mathrm{mol}\right)}{\mathrm{volume}\left({\mathrm{dm}}^3\right)}$

   • [HCl] = $\frac{0.00250}{0.0200}$ = 0.125 mol dm^-3

Calculating the volume of gas

Complete the table to calculate the volume that the gases occupy:

Answers:

Calculating the number of moles of gas

Complete the table to calculate the number of moles of gas:

Answers: