Zadanie 5c
Wzorowane na: Chemistry HL Paper 2, May 2024, TZ1, pytanie 5(c). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Polecenie
In a titration, 25.0 cm3 of 0.100 mol dm−3 ethanoic acid, CH3COOH, was placed in a flask and 0.100 mol dm−3 sodium hydroxide solution was added from a burette. The pH curve is shown.
(i) Using section 18 of the data booklet, identify the most suitable indicator for this titration.
(ii) Sketch on the graph the curve expected if 25.0 cm3 of 0.100 mol dm−3 hydrochloric acid were titrated with the same sodium hydroxide solution.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) phenolphthalein ✔ «the equivalence point at pH 8.7 lies within its range 8.3-10.0»
(ii) the new curve starts at pH 1 and rises slowly, with a vertical section at the same equivalence volume, 25.0 cm3, running from about pH 3 to about pH 11 ✔
after the equivalence point the curve levels off towards pH 12-13, close to the original curve ✔
Schemat punktowania
(i) [1]; do not accept phenol red or the other indicators in the table, whose ranges lie below the equivalence point. (ii) M1: starts at about pH 1 and the vertical section is at 25.0 cm3 and extends to a lower pH than the original curve (about pH 3 to 11); M2: levels off at pH 12-13. The equivalence volume must be the same for M1.