Chemistry · Oct / Nov 2025 · Paper 42 · Question 3
0620
As printed in the paper
The question as text
A student prepares a sample of the insoluble salt barium sulfate, BaSO4. The student adds aqueous sodium sulfate, Na2SO4(aq), to aqueous barium chloride, BaC! 2(aq). The student carries out the following steps. step 1 Dissolve 0.100 moles of solid BaC! 2 in 100 cm3 of distilled water in a beaker to form BaC! 2(aq). step 2 Add an aqueous solution which contains 0.100 moles of Na2SO4(aq) to the beaker containing the BaC! 2(aq) from step 1. step 3 Stir the mixture and then filter it. step 4 Dry the solid left in the filter paper.
Read automatically from the paper; the printed page above is exact.
Show the answer and mark scheme
3(a)[2]
→ BaSO4(s) + 2NaCl(aq)
M1 2NaCl (only)
M2 (s) and (aq)
3(b)[2]
M1 Mr BaCl2 = 208
M2 208 × 0.1 = 20.8
3(c)[1]
0.100 ‣ 1.25 (× 1000) = 80 (cm3)
3(d)[1]
white
3(e)[1]
residue
3(f)[2]
M1 rinsing the residue (with water)
M2 (mass was greater) because (dry) residue contains solid sodium chloride / NaCl adds to the mass (of residue)
3(g)[1]
precipitation
3(h)[3]
M1 named soluble barium salt other than barium chloride e.g. (barium) nitrate
M2 named soluble sulfate salt other than sodium sulphate e.g. potassium (sulfate) / ammonium (sulfate)
M3 named insoluble barium salt other than barium sulfate e.g. (barium) carbonate
Make a free account to save your answers and see your weak topics and ask the AI why a wrong answer is wrong.