Fig. 1 shows a food scientist using a burette to measure lactic acid in yoghurt. A 10.0 cm3 yoghurt extract requires 18.60 cm3 of 0.100 mol/dm3 sodium hydro...
Question 1 Report
Fig. 1 shows a food scientist using a burette to measure lactic acid in yoghurt. A 10.0 cm3 yoghurt extract requires 18.60 cm3 of 0.100 mol/dm3 sodium hydroxide solution. The reaction between lactic acid and sodium hydroxide is 1:1.
(a) Give the number of moles of sodium hydroxide used. [2]
(b) What is the number of moles of lactic acid in the extract? [1]
(c) Use the sample volume to calculate the concentration of lactic acid. [2]
(d) Name the piece of apparatus used to deliver the sodium hydroxide accurately. [1]
Answer Details
Titration concentration: Use \[n=cV\] with volume in dm3. Since lactic acid and sodium hydroxide react in a 1:1 ratio, they have equal amounts in moles at the end-point.
- (a) \[18.60\ \mathrm{cm^3}=0.01860\ \mathrm{dm^3}\] \[n=0.100\times0.01860=0.00186\ \mathrm{mol}\] [2]
- (b) The amount of lactic acid is 0.00186 mol. [1]
- (c) \[10.0\ \mathrm{cm^3}=0.0100\ \mathrm{dm^3}\] \[c=\frac{0.00186}{0.0100}=0.186\ \mathrm{mol\ dm^{-3}}\] [2]
- (d) The sodium hydroxide is delivered accurately using a burette. [1]
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