The label on a bottle of a probiotic yogurt drink lists the mass of lactic acid, C3H6O3\text{C}_3\text{H}_6\text{O}_3C3H6O3, in mg, in a typical serving of 100 cm3100\text{ cm}^3100 cm3.
A student carries out an investigation to check the lactic acid content in the yogurt drink.
Lactic acid is neutralised by sodium hydroxide according to the following equation:
C3H6O3(aq)+NaOH(aq)→C3H5O3Na(aq)+H2O(l) \text{C}_3\text{H}_6\text{O}_3(\text{aq}) + \text{NaOH}(\text{aq}) \rightarrow \text{C}_3\text{H}_5\text{O}_3\text{Na}(\text{aq}) + \text{H}_2\text{O}(\text{l}) C3H6O3(aq)+NaOH(aq)→C3H5O3Na(aq)+H2O(l)The student dilutes a 100 cm3100\text{ cm}^3100 cm3 serving of the yogurt drink with distilled water to 200.0 cm3200.0\text{ cm}^3200.0 cm3 in a volumetric flask.
The student then titrates a 20.0 cm320.0\text{ cm}^320.0 cm3 volume of this diluted solution with a 4.50×10−3 mol dm−34.50 \times 10^{-3}\text{ mol dm}^{-3}4.50×10−3 mol dm−3 sodium hydroxide solution, NaOH(aq)\text{NaOH}(\text{aq})NaOH(aq).
The mean titre of NaOH(aq)\text{NaOH}(\text{aq})NaOH(aq) is 18.50 cm318.50\text{ cm}^318.50 cm3.
Determine the mass, in mg, of lactic acid in the 100 cm3100\text{ cm}^3100 cm3 serving of the yogurt drink. Give your answer to 3 significant figures.
199 exam-style questions on OCR A A Level Chemistry Atoms and reactions, covering Atomic structure and isotopes, Compounds, formulae and equations, Amount of substance, Acids, and Redox. Each one has a worked solution and a mark scheme showing where the marks go.