Zadanie 1a
Wzorowane na: Chemistry HL Paper 3, November 2024, 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-1c.
Tributyltin (TBT) compounds were once used in antifouling paints for ships. In harbour water, TBT is present as tributyltin ions, (C4H9)3Sn+, which are absorbed by marine animals, then slowly metabolized and excreted.
Polecenie
Young mussels were placed in a contaminated harbour. Samples were taken at regular intervals and the tin content of the soft tissue was determined.
(i) The tin content follows a linear trend during the first six weeks. Deduce the equation for this part of the graph, using tin content in μg Sn g−1 and time in weeks.
(ii) Suggest why the tin content changed very little after 10 weeks.
(iii) State why (C4H9)3Sn+ ions are more likely to be absorbed by mussels than Sn2+ ions.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) gradient «= 0.60 / 6 =» 0.10 «μg Sn g−1 week−1» ✔
tin content = 0.10 × t «with t in weeks; the line passes through the origin» ✔
(ii) the rate of uptake equals the rate of metabolism and excretion
OR
all the binding sites in the tissue are occupied / the tissue is saturated
OR
the tissue is in equilibrium with the tin in the water ✔
(iii) the butyl groups are non-polar so the ion is lipid-soluble «and passes through cell membranes more easily» ✔
Schemat punktowania
(i) M1: gradient from the graph. M2: equation with the gradient and no intercept. Accept a gradient in the range 0.095-0.105 for M1; accept y = 0.10x for M2. (ii) Any one of the three ideas. Accept 'the mussels have stopped growing, so the maximum concentration is reached'. (iii) Accept 'less polar', 'more hydrophobic' or 'more soluble in fat'. Do not accept 'ionic' or 'polar' alone, and do not accept 'smaller ion'.