White vinegar is a colourless solution containing ethanoic acid. You are provided with two samples of white vinegar labelled A and B. You are going to investigate the reaction between these samples and 0.400mol/dm³ aqueous sodium hydroxide. Read all the instructions carefully before starting the experiments. Instructions You are going to do four titration experiments. Rinse and fill a burette with A.

1. (a)Experiment 1 • Use a volumetric pipette to add 25.0cm³ of 0.400mol/dm³ aqueous sodium hydroxide to a conical flask. • Add five drops of thymolphthalein indicator to the conical flask. • Record the initial burette reading in Table 1.1. • Add A from the burette while swirling the flask, adding drop by drop near the end-point, until the solution just changes colour. • Record the final burette reading in Table 1.1. Experiment 2 • Empty the conical flask and rinse it with distilled water. • Refill the burette if necessary. • Repeat Experiment 1. Complete Table 1.1 with the volume used in each experiment.[4]
2. (b)Experiments 3 and 4 • Pour away any A remaining in the burette. • Rinse and fill the burette with B. • Empty the conical flask and rinse it with distilled water. • Repeat Experiments 1 and 2 using B. • Record the initial and final burette readings for Experiments 3 and 4 in Table 1.2. • Complete Table 1.2 with the volumes used in Experiments 3 and 4.[2]
3. (c)State the colour change observed in the flask in each experiment. from ........................................................................ to ........................................................................[1]
4. (d)Calculate the mean volume of A and B needed to neutralise 25.0cm³ of 0.400mol/dm³ aqueous sodium hydroxide. mean volume of A ............................................................ cm³ mean volume of B ............................................................ cm³[1]
5. (e)Suggest why the titrations using A and B are repeated.[1]
6. (f)The equation for the reaction between ethanoic acid and sodium hydroxide is shown. CH₃COOH + NaOH → CH₃COONa + H₂O The answer to (d) shows the mean volume of B used to neutralise 25.0 cm³ of 0.400mol/dm³ aqueous sodium hydroxide. Calculate the concentration of ethanoic acid in B. Give your answer to an appropriate number of significant figures. concentration ............................................................ mol/dm³[2]
7. (g)Use your answer to (f) to calculate the mass of ethanoic acid in 500cm³ of B. [Mᵣ: ethanoic acid, 60] mass ............................................................ g[2]
8. (h)Use your answers to (d) and (g) to calculate the mass of ethanoic acid in 500 cm³ of A. mass ............................................................ g[1]
9. (i)Suggest why the conical flask should be rinsed with distilled water and not 0.400mol/dm³ aqueous sodium hydroxide between titrations.[2]
10. (j)Some vinegars are brown rather than colourless. Suggest why this titration method would not be suitable for finding the concentration of ethanoic acid in brown vinegar.[1]