CIE Nov 2013 v1 Paper 5 Q2

Answers available below

Examiners For Use The solubility of hydrated sodium sulfate, Na2SO4.10H2O, in water increases with temperature. At a temperature between 25 C and 70 C there is a transition and the solubility becomes that of Na2SO4. The units of solubility are grams per one hundred grams of water, g / 100 g water. An experiment was carried out to investigate this solubility and determine the transition temperature between the two forms of sodium sulfate.An empty boiling tube was weighed and the mass recorded. Some distilled water was added to the boiling tube and the new mass recorded. A small sample of hydrated sodium sulfate was added and this new mass recorded. The boiling tube was carefully heated with stirring until all the solid had dissolved. The apparatus was cooled slowly while constantly stirring and the temperature recorded when therst crystals appeared in the tube. (a) The results of several of these experiments are recorded below. Process the results in the table to calculate the solubility, in g / 100 g water, of the sodium sulfate for each of the temperatures listed. Record these values to two decimal places in the additional columns of the table. You may use some or all of the columns. Label the columns you use. For each column you use include units where appropriate and an expression to show how your values are calculated. Use the column headings A to H for these expressions (e.g. AB). experiment number mass of boiling tube mass of boiling tube water / g 35.20 30.35 35.10 29.20 32.95 34.90 30.70 30.45 35.05 40.10 / g 10.20 10.35 10.10 9.80 9.95 9.90 9.70 10.45 10.05 10.10 10 mass of boiling tube crystallising temperature + water + solid / g 36.45 31.60 40.10 36.96 44.06 46.65 40.32 39.55 46.30 53.45 C 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0UCLES 2013 9701/51/O/N/13 [3]<br /> (b) Plot a graph to show the variation of solubility (y-axis) with temperature (x-axis). Draw two curves of bestt and extrapolate to locate their intersection at the transition temperature.UCLES 2013 9701/51/O/N/13 [4] [Turn over<br /> Examiners For Use (c) From your graph, state the transition temperature and the solubility at which it occurs. [2] (d) (i) In an attempt to repeat the 4th experiment using the same masses of water and solid, the temperature was mistakenly read and recorded before crystals appeared. Place a cross on your graph to represent the point that would have been obtained. (ii) If this was a valid point, what effect would this have on your transition temperature? Explain your answer.[2] (e) It was found that all the mass recordings in columns C and D had been made with a balance that had been zeroed incorrectly and they should all have been 0.3 g smaller. The masses recorded in column B can be considered to be accurate. Using the corrected masses from experiment 6 calculate the new value of the solubility. By comparing this with the original solubility value for experiment 6 calculate the percentage error difference. [2]UCLES 2013 9701/51/O/N/13<br /> Examiners For Use (f) From the pattern of solubility demonstrated by your graph, predict and explain whether the dissolving of the two forms of sodium sulfate in water are exothermic or endothermic reactions. prediction for Na2SO4.10H2Oexplanationprediction for Na2SO4explanation[2] [Total: 15]UCLES 2013 9701/51/O/N/13 [Turn over<br />

Show answer