Wzorowane na: Chemistry HL Paper 1B, May 2026, pytanie 2(d). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Informacja do zadań 2a-2e.
In a student experiment, the apparatus shown was used to prepare propanoic acid,
1.80 g of propan-1-ol, excess oxidizing agent (acidified ) and a few anti-bumping granules were placed in the round-bottom flask.
(d) The student used distillation to obtain pure propanoic acid from the reaction mixture.
(i) State two impurities, apart from unreacted propan-1-ol, that were present in the propanoic acid before distillation.
(ii) The approximate experimental yield of propanoic acid was calculated from the mass of propanoic acid collected in the distillation. The student's hypothesis was that impurities collected together with the propanoic acid during the distillation lowered this calculated yield.
Evaluate this statement.
(i) Any two of:
sulfuric acid, «unreacted/excess» ✔
OR
chromium(III) ions/salts «, from the reduced oxidizing agent» or unreacted ✔
OR
water ✔
(ii) the statement is false: any carried over into the distillate would also react with the
(i) [1] for any two of the accepted impurities; unreacted propan-1-ol is explicitly excluded by the question and must not be credited again. (ii) [1] for correctly judging the statement false, with the reasoning correctly reversed (an acidic impurity increases, rather than decreases, the titre and hence the calculated yield); ‘false’ alone, with no reason, earns nothing.
Klucz własny: oficjalny markscheme IB dla maja 2026 nie był jeszcze dostępny przy imporcie; do uzgodnienia po jego publikacji. Distillation removes the non-volatile impurities (the sulfuric acid and the chromium salts), which is exactly why the titration on the distillate in 2e gives a trustworthy yield, unlike the titration on the crude mixture in 2c.
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