Zadanie 1f
Wzorowane na: Chemistry SL Paper 1B, May 2026, TZ2, pytanie 1(f). 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-1h.
A student investigated how temperature affects the intensity and the duration of the light given out when alkaline luminol solution reacts with hydrogen peroxide in the presence of a catalyst, hexacyanoferrate(III) ions.
Four beakers, each holding 50.0 cm3 of the same alkaline luminol solution, were placed one at a time in a water bath inside a darkened box, the bath being at a different temperature for each run. In every run, 10.0 cm3 of hydrogen peroxide solution and one small crystal of the catalyst were added and the mixture was stirred once. A light sensor beside the beaker recorded the light intensity every 30 seconds for 60 minutes.
The results are shown on the graph. Each curve is labelled with the temperature of the water bath.
Polecenie
Explain how the rate at which the light intensity was falling after 15 minutes in the 44.8 °C run could be determined from the graph.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz CKE i punktacja
Odpowiedź z klucza
draw a tangent to the 44.8 °C curve at 15 minutes ✔
calculate the gradient of the tangent «change in light intensity ÷ change in time»; the magnitude of the negative gradient is the rate of decrease ✔
OR
fit a function to the curve and differentiate it, then substitute t = 15 min «award [2]» ✔
Schemat punktowania
M1: tangent drawn at the stated time on the correct curve. M2: gradient of the tangent found from two points on it. Award [2] for a clear description of differentiating the curve. A calculation of the average rate between two data points scores 0 for M1.
Komentarz
The graph is curved, so the gradient changes from point to point; only a tangent gives the rate at one moment.