Chemistry SL Paper 1B, May 2025, TZ1

Determine the mass of sodium thiosulfate pentahydrate, $\ce{Na2S2O3 * 5H2O}$, needed to prepare 250.0 $\mathrm{cm^3}$ of a 0.2000 $\mathrm{mol\,dm^{-3}}$ solution.

Explain how the 0.2000 $\mathrm{mol\,dm^{-3}}$ solution is prepared in a volumetric flask from the weighed solid.

Suggest how to prepare 100.0 $\mathrm{cm^3}$ of a 0.05000 $\mathrm{mol\,dm^{-3}}$ sodium thiosulfate solution from the 0.2000 $\mathrm{mol\,dm^{-3}}$ solution.

The student's results are shown below. Each time was measured to ± 0.1 s. Concentration of $\ce{Na2S2O3}$ / $\mathrm{mol\,dm^{-3}}$ Time, trial 1 / s Time, trial 2 / s Time, trial 3 / s Time, trial 4 / s Time, trial 5 / s Average time / s 0.2000 ± 0.08 % 17.2…

State one safety concern arising from a product of this reaction, and a precaution that should be taken because of it.

Suggest a sequence of experimental steps that would give a pure sample of each of the three components.

The student recorded the following masses. Sample Mass / g (± 0.01 g) Percentage by mass Mixture before separation 6.35 not applicable Iron after separation 2.58 Calcium carbonate after separation 1.71 Potassium chloride after separation 2.31 36.4 % Calculate…

The three percentages in 2b add up to more than 100 %. Suggest an error that would explain this result and how it could be reduced or eliminated.

The results did not support the student's hypothesis. Suggest what the student overlooked when forming the hypothesis.

Draw a line of best fit on the graph, extrapolating it beyond the range of the data.

State, in mathematical terms, how the absorbance of these solutions depends on their concentration.

Deduce the equation that relates absorbance to concentration for these solutions, including the numerical value of the constant.

Estimate the absorbance of a 0.400 $\mathrm{mol\,dm^{-3}}$ solution of nickel(II) sulfate.