Zadanie 1a
Wzorowane na: Chemistry SL Paper 3, November 2023, TZ2, pytanie 1(a). 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-1d.
Grapefruit juice is a rich source of vitamin C (ascorbic acid). To destroy pathogenic bacteria, producers often heat-treat the juice by filling it into bottles at 85 °C. A food laboratory monitored the concentration of vitamin C in heat-treated juice and in untreated, cold-pressed juice. Both were stored in partly filled clear glass bottles at 10 °C for 56 days.
Polecenie
(i) Identify the dependent variable plotted on the graph.
(ii) Calculate the decrease in the concentration of vitamin C, in μg cm−3, caused by the heat treatment.
(iii) Calculate the average rate of decrease of the vitamin C concentration in the heat-treated juice over the 56 days, in μg cm−3 day−1.
(iv) Deduce, referring to the graph, whether heat treatment affects the rate at which the vitamin C concentration changes during storage.
(v) The absolute uncertainty in each concentration measurement was ±2 μg cm−3. Deduce, with a reason, which juice has the larger percentage uncertainty in its vitamin C concentration.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) concentration «of vitamin C» ✔
(ii) «372 − 196 =» 176 «μg cm−3» ✔
(iii) «average rate = (196 − 158) / 56 =» 0.68 «μg cm−3 day−1» ✔
(iv) no AND the two lines are parallel/have the same average gradient
OR
no AND both juices lose about 36–38 «μg cm−3» in 56 days ✔
(v) heat-treated «juice» AND the same absolute uncertainty is divided by a smaller concentration ✔
«e.g. 2/196 × 100 = 1.0 % compared with 2/372 × 100 = 0.54 %»
Schemat punktowania
One mark for each of (i)-(v). (i) The quantity measured is required: reject "vitamin C" on its own and "heat treatment". (ii) Any value from 170 to 185 is acceptable. (iii) Any value from 0.60 to 0.75 is acceptable; the sign is ignored. (iv) "Yes" is also acceptable if it is supported by the small difference in the loss or in the rate; "no AND same trend" is accepted. (v) A worked numerical comparison, or the reverse argument for the other juice, is accepted.
Komentarz
The dependent variable is the quantity that is measured, not the quantity that is deliberately changed (storage time) or the type of treatment.