Zadanie 1b
Wzorowane na: Chemistry HL Paper 2, May 2024, 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-1e.
An effervescent powder for a soft drink has the following composition by mass:
| Component | Percentage by mass |
|---|---|
| Sucrose, C12H22O11 | 20.0 |
| Tartaric acid, C4H6O6 | 33.0 |
| Sodium hydrogencarbonate, NaHCO3 | 47.0 |
When water is added, the tartaric acid reacts with the sodium hydrogencarbonate and the powder fizzes:
2 NaHCO3(s) + C4H6O6(aq) → Na2C4H4O6(aq) + 2 CO2(g) + 2 H2O(l)
Polecenie
The structure of a tartaric acid molecule is shown.
(i) State how many hydrogen atoms in a tartaric acid molecule are acidic.
(ii) Deduce the structural formula of the conjugate base of tartaric acid.
(iii) Predict, giving a reason, whether tartaric acid is a strong or a weak acid.
(iv) Explain, with reference to the tartrate ion, why a solution of disodium tartrate, Na2C4H4O6, has a pH above 7.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) two ✔
(ii) HOOC−CH(OH)−CH(OH)−COO− «one carboxyl group has lost its proton» ✔
(iii) weak AND carboxylic acid / has −COOH groups «so only partly dissociated» ✔
(iv) the tartrate ion is the conjugate base of a weak acid «so it accepts H+ from water»
C4H4O62− + H2O ⇌ HC4H4O6− + OH− ✔
OR
salt of a strong base and a weak acid ✔
Schemat punktowania
[1] for each part. (i) The hydroxyl hydrogens are not acidic. (ii) Accept the structure with either carboxyl group deprotonated. (iii) Accept "weak AND partially dissociated". (iv) A correct equation or a correct statement is enough.