16 (B410U10-1) Examiner only 13. A sample of witherite, an ore of barium, contains barium carbonate, BaCO3. A geologist investigated the ore to determine the percentage of barium carbonate present by adding a sample of ore to excess acid and then finding how much acid had been neutralised. He followed these instructions. Stage 1 Add a known mass of ore to about 100 cm3 of 0.500 mol dm–3 hydrochloric acid in a beaker. Stir until no further reaction occurs. The geologist used 19.15 g of ore. Stage 2 Filter and then add more acid to make the total volume of the solution up to exactly 250 cm3. Stage 3 Titrate 25.0 cm3 samples of this solution against 0.100 mol dm–3 sodium hydroxide using a suitable indicator. The geologist used a mean volume of 27.80 cm3 of the sodium hydroxide to neutralise the acid. (a) Explain why the geologist filtered the mixture in Stage 2 of the process. [1] (b) State which piece of apparatus the geologist would use to make exactly 250 cm3 of solution in Stage 2. [1] (c) State why an indicator is used in Stage 3. [1] (d) State how many titrations the geologist should carry out in Stage 3. Give a reason for your choice. [1] © WJEC CBAC Ltd. (B410U10-1) 17 Examiner only (e) Write the equation for the reaction of barium carbonate with hydrochloric acid. [1] (f) Calculate the total number of moles of hydrochloric acid added to the sample of ore. [1] Number of moles added = ........................................................ mol (g) Calculate the number of moles of hydrochloric acid neutralised in each titration and hence the number of moles neutralised by the original sample of ore. [3] Number of moles neutralised by ore = ........................................................ mol QUESTION 13 CONTINUES ON PAGE 18. © WJEC CBAC Ltd. Turn over. 18 (B410U10-1) Examiner only (h) State the number of moles of barium carbonate present in the original sample of ore and hence calculate the percentage by mass of barium in the ore. [3] Percentage barium in the ore = ........................................................ % (i) The true value for the percentage of barium present in the ore is higher than that calculated in part (h). Suggest a possible reason for this. [1] END OF PAPER © WJEC CBAC Ltd. 13 Examiner only (B410U10-1) 19 © WJEC CBAC Ltd. Additional page.
Get full Socratic AI guidance on this question — free in the Applaa desktop app
Appy Buddy guides you step-by-step toward the answer without giving it away. Type your attempt and get instant, mark-scheme-aware clues that teach you to think like an examiner.
Join Applaa Community
Create your own games, learn AI concepts, program interactive apps, and share with a kid-safe community approved by parents. Free forever on Windows and Mac.
Available for Windows and macOS · COPPA Compliant
Exam Specification Info
This question is part of the UK A-Level Chemistry syllabus. In the actual exam, structured questions typically require linking specific keywords to gain full marks. Applaa helps you drill these topics.
While Other Kids Get an AI Head Start, Is Yours Falling Behind?
Give your child the same AI app-building, exam prep and tutoring edge — free for the first month, no credit card needed.
Join 10,000+ students building their first AI-powered apps with Applaa