Zadanie 1b
Wzorowane na: Chemistry HL Paper 2, May 2023, TZ1, pytanie 1(b). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Informacja do zadań 1a-1b.
Solutions of hydrobromic acid, HBr(aq), and methanoic acid, HCOOH(aq), of the same concentration were compared in a school laboratory.
Polecenie
Outline one chemical test, other than the use of an indicator, that can distinguish between the two acids, and state the expected result.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
Test: add magnesium ribbon «or any reactive metal, or a carbonate / hydrogencarbonate» to a sample of each acid
AND
Expected result: faster / more vigorous effervescence «or greater temperature rise» with HBr(aq) ✔
OR
Test: add silver nitrate solution, AgNO3(aq), to a sample of each acid
AND
Expected result: cream / pale yellow precipitate with HBr(aq) and no precipitate with methanoic acid ✔
OR
Test: add a base / a metal oxide «with temperature measurement»
AND
Expected result: higher temperature rise with HBr(aq) ✔
Schemat punktowania
[1] for a valid test together with the expected result for the two acids. Do not accept 'a metal' without 'reactive' or a named metal. A test without the expected result scores zero.
Komentarz
The precipitate of silver bromide is cream or pale yellow, not white; a white precipitate would be silver chloride.