A laboratory checks the concentration of hydrochloric acid in an acidic cleaning solution.
A student dilutes 10.0 cm310.0\,\mathrm{cm^{3}}10.0cm3 of the cleaning solution with distilled water to make 250 cm3250\,\mathrm{cm^{3}}250cm3 of diluted solution. The student transfers 25.0 cm325.0\,\mathrm{cm^{3}}25.0cm3 portions of the diluted solution into a conical flask and titrates them with 0.100 mol/dm30.100\,\mathrm{mol/dm^{3}}0.100mol/dm3 sodium hydroxide solution.
HCl+NaOH→NaCl+H2O \mathrm{HCl + NaOH \rightarrow NaCl + H_{2}O} HCl+NaOH→NaCl+H2OThe student's burette readings are shown in the table.
| Titration | Initial burette reading in cm3\mathrm{cm^{3}}cm3 | Final burette reading in cm3\mathrm{cm^{3}}cm3 |
|---|---|---|
| Rough | 0.20 | 10.50 |
| 1 | 10.50 | 20.50 |
| 2 | 20.50 | 30.55 |
| 3 | 30.55 | 40.65 |
Calculate the mean titre from the burette readings.
Calculate the concentration of hydrochloric acid in the original cleaning solution.
The student rinses the burette with distilled water instead of sodium hydroxide solution before repeating the experiment.
Explain how this would affect the calculated concentration of hydrochloric acid in the original cleaning solution.
152 exam-style questions on OCR GCSE Chemistry 5.1 Monitoring chemical reactions, covering 5.1.1 The technique of titration, 5.1.2 Theoretical mass, percentage yield and atom economy, 5.1.3 Concentration of a solution in mol/dm3, 5.1.4 Concentration calculations and titration results, 5.1.5 Molar gas volume and volumes of gases in reactions, and 5.1.6 Choosing a reaction pathway. Each one has a worked solution and a mark scheme showing where the marks go.