Zadanie 3b
Wzorowane na: Chemistry HL Paper 1B, May 2026, TZ3, pytanie 3(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 3a-3c.
A student estimated the acid dissociation constant, Ka, of propanoic acid, CH3CH2COOH, by measuring the pH of a 0.0200 mol dm−3 standard solution of the acid with a pH probe that had been calibrated beforehand. Three trials gave the pH values below.
| Trial | pH (± 0.1) |
|---|---|
| 1 | 3.4 |
| 2 | 3.2 |
| 3 | 3.3 |
Polecenie
Ka was also calculated for Trials 2 and 3, and the experimental error was found for each, as shown in the table. Determine the experimental error for Trial 1, using a literature value of Ka = 1.35 × 10−5 for propanoic acid. If you have no value from part 3a, use 7.0 × 10−6, which is not the correct answer.
| Trial | pH (± 0.1) | Ka | Experimental error (%) |
|---|---|---|---|
| 1 | 3.4 | ||
| 2 | 3.2 | 2.1 × 10−5 | 56 |
| 3 | 3.3 | 1.3 × 10−5 | 4 |
Sprawdź rozwiązanieUkryj rozwiązanieKlucz CKE i punktacja
Odpowiedź z klucza
«experimental error = =» 40 «%» ✔
Schemat punktowania
[1] for 40 % (accept 38 to 42 %). Award the mark for 48 % if 7.0 × 10−6 was used. Do not penalize failure to copy the Ka result into the table.