OCR A Jun 2017 Paper 1 Q24

Answers available below

24 Ethanoic acid, CH3COOH, is the main dissolved acid in vinegar. (a) Ethanoic acid is a weak acid. 20 What is meant by acid and weak acid?[1] (b) Aluminium is reacted with ethanoic acid. (i) The unbalanced equation for the reaction is shown below. Balance the equation. . Al (s) + . CH3COOH(aq). (CH3COO)3Al (aq) +H2(g) [1] (ii) This reaction is a redox reaction. Deduce which element has been oxidised and which element has been reduced, and state the changes in oxidation number. Element oxidised:oxidation number change: fromtoElement reduced:oxidation number change: fromto[2]<br /> 21 (c) A student plans to determine the concentration, in mol dm3, of CH3COOH in a bottle of vinegar. The student will carry out a titration with aqueous barium hydroxide, Ba(OH)2(aq). The students method is outlined below.Dilute 10.0 cm3 of vinegar from the bottle with distilled water and make the solution up to 250.0 cm3. Add the diluted vinegar to the burette. Titrate 25.0 cm3 volumes of 0.0450 mol dm3 Ba(OH)2 with the diluted vinegar.The mean titre of the diluted vinegar is 25.45 cm3. The reaction in the students titration is shown below. 2CH3COOH(aq) + Ba(OH)2(aq)(CH3COO)2Ba(aq) + 2H2O(l) (i) Calculate the concentration, in mol dm3, of CH3COOH in the original bottle of vinegar. Show your working. concentration of CH3COOH =mol dm3 [4] (ii) Suggest one assumption that the student has made that might mean that their calculated concentration of ethanoic acid in the vinegar is invalid. Predict, with a reason, how the experimental result would differ from the actual concentration of CH3COOH if the assumption were not correct.[2]<br />

Show answer