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Zadanie 2e

5 pktotwarteśrednie (szac.)Paper 2, maj 2024, TZ2

Wzorowane na: Chemistry HL Paper 2, May 2024, TZ2, pytanie 2(e). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.

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Polecenie

Atmospheric carbon dioxide and the pH of surface seawater were measured at a monitoring station over nineteen years. The graph shows the annual mean values.

graph of atmospheric carbon dioxide and surface seawater pH against year, with separate vertical axes

(i) Outline the relationship between the carbon dioxide mixing ratio and the pH of the seawater.

(ii) Comment, based on the graph, on the conclusion that increasing atmospheric carbon dioxide is the cause of the fall in pH.

(iii) The emission spectrum of lithium has a strong line at 671 nm. Determine the energy, in J, of one photon of this light. Use sections 1 and 2 of the data booklet.

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Odpowiedź z klucza

(i) a negative «inverse» correlation

OR

as the carbon dioxide mixing ratio rises, the pH falls ✔

(ii) any two of:

the data are consistent with the claim but cannot prove it

OR

a correlation does not show that one change causes the other ✔

a chemical link between the two must be given, e.g. CO2(g) + H2O(l) ⇌ H2CO3(aq) followed by ionization of H2CO3 to H+ ✔

other influences on the pH are possible, e.g. acid deposition, run-off, biological activity ✔

(iii) «f=cλ=3.00×108 m s−16.71×10−7 m=f = \dfrac{c}{\lambda} = \dfrac{3.00 \times 10^{8}\ \mathrm{m\,s^{-1}}}{6.71 \times 10^{-7}\ \mathrm{m}} =» 4.47 × 1014 «Hz» ✔

«E = hf = 6.63 × 10−34 J s × 4.47 × 1014 s−1 =» 2.96 × 10−19 «J» ✔

Schemat punktowania

(i) [1]: do not accept 'inversely proportional'. (ii) [2 max]: one mark per distinct point from the list. (iii) M1: frequency from c = fλ with the wavelength converted to metres; M2: E = hf. Award [2] for a correct final answer.

Komentarz

Photon energy needs the wavelength in metres; 671 nm entered as 671 gives a result 10^9 times too small.

Umiejętności w zadaniu