Zadanie 2d
Wzorowane na: Chemistry HL Paper 1B, May 2026, TZ2, pytanie 2(d). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Informacja do zadań 2a-2f.
Specific energy is the heat energy released per unit mass of fuel burnt. A student determined the specific energy of ethanol by burning it in a spirit burner under a copper can containing 120.0 g of water. The diagram shows the apparatus used.
The burner was weighed before and after each of five trials, and the temperature of the water was measured before and after heating. Fresh water was used for every trial.
| Spirit burner with ethanol | Trial 1 | Trial 2 | Trial 3 | Trial 4 | Trial 5 |
|---|---|---|---|---|---|
| Initial mass / g (± 0.001 g) | 148.236 | 147.801 | 148.115 | 147.652 | 148.021 |
| Final mass / g (± 0.001 g) | 147.374 | 146.870 | 147.370 | 146.774 | 147.121 |
| Water in copper can | Trial 1 | Trial 2 | Trial 3 | Trial 4 | Trial 5 |
|---|---|---|---|---|---|
| Initial temperature / °C (± 0.05 °C) | 20.4 | 19.8 | 22.0 | 21.2 | 21.3 |
| Final temperature / °C (± 0.05 °C) | 34.0 | 35.3 | 29.0 | 34.7 | 35.8 |
Polecenie
Determine the mean specific energy of ethanol from the five trials, explaining your method.
If you did not obtain an answer to (c), use 8000 J g−1 for trial 5; this is not the correct value.
| Trial 1 | Trial 2 | Trial 3 | Trial 4 | Trial 5 | |
|---|---|---|---|---|---|
| Specific energy / J g−1 | 7914 | 8351 | 4713 | 7713 |
Sprawdź rozwiązanieUkryj rozwiązanieKlucz CKE i punktacja
Odpowiedź z klucza
ignore trial 3 «because it is much lower than the other values, an anomaly/outlier» ✔
«(7914 + 8351 + 7713 + 8081)/4 =» 8015/8.01 × 103 «J g−1» ✔
Schemat punktowania
M1: trial 3 identified as anomalous and left out. M2: mean of the remaining four values. Accept 7994 or 7995 if 8000 is used for trial 5. Award [1 max] for 7354 «not ignoring the outlier».
Komentarz
Trial 3 gave only about half the temperature rise of the other trials although the mass of ethanol burnt was similar, which points to a procedural fault such as a draught or a flame that went out.