Fig. 1 shows a student measuring a sulphuric acid solution with a pipette before adding it to a flask containing sodium hydroxide. The student uses a suitab...
Question 1 Report
Fig. 1 shows a student measuring a sulphuric acid solution with a pipette before adding it to a flask containing sodium hydroxide. The student uses a suitable indicator and then records three titres from the burette. The sodium hydroxide volume is 20.0 cm3 and its concentration is 0.150 mol dm-3.
| titre number | volume of H2SO4 / cm3 |
|---|---|
| 1 | 14.9 |
| 2 | 15.1 |
| 3 | 15.0 |
H2SO4 + 2NaOH → Na2SO4 + 2H2O
(a) Record the mean titre. [1]
(b) Use the sodium hydroxide data to calculate its amount in the flask. [2]
(c) Use the equation and mean titre to calculate the concentration of sulphuric acid. [3]
Answer Details
(a) The titres are 14.9 cm3, 15.1 cm3 and 15.0 cm3, so their mean is:
\[\frac{14.9+15.1+15.0}{3}=15.0\text{ cm}^3\]
The mean titre is 15.0 cm3. [1 mark]
(b) Convert the sodium hydroxide volume:
\[20.0\text{ cm}^3=0.0200\text{ dm}^3\]
Use \(n=cV\):
\[n=0.150\times0.0200=0.00300\text{ mol}\]
The amount of sodium hydroxide is 0.00300 mol. [2 marks]
(c) The equation shows that 1 mole of sulfuric acid reacts with 2 moles of sodium hydroxide:
\[n(\mathrm{H_2SO_4})=\frac{0.00300}{2}=0.00150\text{ mol}\]
\[15.0\text{ cm}^3=0.0150\text{ dm}^3\]
\[c=\frac{n}{V}=\frac{0.00150}{0.0150}=0.100\text{ mol dm}^{-3}\]
The sulfuric acid concentration is 0.100 mol dm-3. [3 marks]
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