Zadanie 27
Wzorowane na: Chemistry HL Paper 1, May 2023, TZ2, pytanie 27. Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Polecenie
The ionic product constant of water, Kw, has the value 2 × 10−15 at 5 °C and 1 × 10−13 at 60 °C. One solution at 5 °C and another solution at 60 °C each have a pH of 6.50. Which statement compares the concentrations of hydrogen and hydroxide ions in the two solutions correctly?
A. [H+] = [OH−] at both temperatures
B. [H+] > [OH−] at 5 °C and [H+] = [OH−] at 60 °C
C. [H+] = [OH−] at 5 °C and [H+] < [OH−] at 60 °C
D. [H+] < [OH−] at 5 °C and [H+] > [OH−] at 60 °C
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
B ✔
«[H+] = 10−6.50 = 3.2 × 10−7 mol dm−3 at both temperatures. At 5 °C [OH−] = 2 × 10−15/3.2 × 10−7 = 6.3 × 10−9, so [H+] > [OH−]. At 60 °C [OH−] = 1 × 10−13/3.2 × 10−7 = 3.2 × 10−7, so the concentrations are equal and the solution is neutral»
Schemat punktowania
One mark for the correct option.