Zadanie 1b
Wzorowane na: Chemistry HL Paper 3, November 2023, TZ2, pytanie 1(b). 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
UV-C irradiation is an alternative to heat treatment that causes less loss of nutrients. The absorption spectrum of a solution of vitamin C is shown.
(i) Deduce the type of electromagnetic radiation absorbed by vitamin C. Use section 5 of the data booklet.
(ii) Deduce, giving a reason, the colour of vitamin C in solution.
(iii) Suggest why UV-C light is not effective for the elimination of pathogenic bacteria in grapefruit juice.
(iv) Identify two ways to decrease the rate at which vitamin C is lost by oxidation during storage of the juice.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) UV/ultraviolet ✔
(ii) colourless «solution»/white «solid» AND does not absorb in the visible region/between 400 and 700 nm ✔
(iii) UV-C is absorbed by other substances in the juice «sugars, other vitamins, aromatic compounds, suspended particles» so it does not reach the bacteria
OR
juice is cloudy/not transparent «pulp and oils» so UV-C does not penetrate it ✔
(iv) Any two of:
lower the storage temperature ✔
exclude air/oxygen «seal the bottle, fill it completely, store under nitrogen» ✔
add an antioxidant/reducing agent ✔
store in the dark/in brown bottles/limit exposure to light ✔
Schemat punktowania
One mark for each of (i)-(iii) and two marks for (iv). (iii) Reject answers saying only that UV is too weak or too small to affect bacteria, and answers that argue about a different wavelength. (iv) Do not accept "add additives" alone; accept a named antioxidant. Accept "heat-treat the juice" only if the answer to 1(a)(iv) was "yes".