Zadanie 1b
Wzorowane na: Chemistry HL Paper 3, November 2023, TZ1, 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.
A food chemistry group investigated how the processing and storage of fruit juice affects its vitamin C (ascorbic acid) content.
Polecenie
Ultraviolet (UV) light is being investigated as a way of killing micro-organisms in juice without heating it, so that less vitamin C is lost. The absorption spectrum of a dilute aqueous solution of sorbic acid, a preservative that is added to some bottled juices, was recorded.
(i) Deduce the region of the electromagnetic spectrum that is absorbed by sorbic acid. Use section 5 of the data booklet.
(ii) Deduce the colour of the dilute solution of sorbic acid and give a reason.
(iii) Suggest why UV treatment is much less effective at killing micro-organisms in a cloudy, pulpy juice than in clear water.
(iv) Identify two ways of slowing down the oxidation of vitamin C in a bottle of juice during storage.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) UV/ultraviolet ✔
(ii) colourless/white «OR no colour» AND no absorption in the visible region/between 400 and 700 nm ✔
(iii) «UV does not reach the micro-organisms because it is» absorbed by other substances in the juice «sugars, vitamins, pigments, aromatic compounds» OR scattered/blocked by suspended particles/pulp ✔
(iv) Any two of:
store at a lower temperature/in a refrigerator ✔
exclude oxygen/air «seal the bottle completely, fill it to the top, pack under nitrogen or vacuum» ✔
add an antioxidant/reducing agent ✔
store in the dark/in an opaque bottle/limit exposure to light ✔
Schemat punktowania
(i) 1 mark: UV. (ii) 1 mark: colourless or white AND a reason that refers to the absence of absorption between 400 and 700 nm; a reason alone or a colour alone earns nothing. (iii) 1 mark: UV is absorbed or scattered before it reaches the micro-organisms; do not accept 'UV waves are too small' or arguments about other wavelengths. (iv) 1 mark each for any two different ways; do not accept 'add additives' alone; accept the correct name of an antioxidant.
Komentarz
The wavelength of a UV photon is irrelevant to the answer to (iii); what matters is that it is removed from the beam before it reaches the cells.