Charles' law states that for a fixed mass of gas at constant pressure, its volume is proportional to its absolute temperature. Most gases are non-ideal and do not obey this law, but at lower pressures and high temperatures some gases are close to ideal behaviour. One gas that behaves like this is oxygen. Oxygen can be prepared by decomposing hydrogen peroxide with the catalyst manganese(IV) oxide, MnO2. The equation for the decomposition of hydrogen peroxide is shown. 2H2O2(aq) → 2H2O(l) + O2(g) Safety hazard: hydrogen peroxide is corrosive to skin and can cause serious eye damage. gas syringe oxygen heat thermometer beaker water [Figure 2.1] Once the apparatus is assembled the volume of oxygen in the gas syringe is 2cm³. There are 80 cm³ of oxygen remaining in the flask. The total volume of oxygen is 82 cm³. Charles' law is investigated by the following method. step 1 Once assembled allow the apparatus to reach room temperature. step 2 Record this temperature and the total volume of oxygen reading on the syringe. step 3 Gently heat the apparatus until the temperature reaches 30 °C and record the total volume of oxygen. step 4 Repeat at intervals of 5°C until the temperature reaches 70°C. The student carried out the experiment and obtained the following results: Table 2.1 temperature /°C absolute temperature/K total volume of oxygen gas/cm³ 24 297 82 30 303 84 35 308 88 40 313 88 45 318 89 50 323 91 55 328 93 60 333 95 65 338 97 70 343 98

1. (a)Other than the wearing of safety goggles, give a safety precaution that the student must take during the preparation of oxygen.[1]
2. (b)(i)Complete the following diagram to show how the student can obtain oxygen by gas collection over water for use in the experiment shown in Fig. 2.1. H2O2(aq) MnO2 catalyst[2]
3. (b)(ii)Suggest how the student could ensure they collect pure oxygen gas in the conical flask.[1]
4. (c)(i)Plot a graph on the grid to show the relationship between volume of oxygen and absolute temperature. Use a cross (×) to plot each data point. Draw a line of best fit.[2]
5. (c)(ii)Determine the gradient of your line of best fit. State the coordinates of both points you used in your calculation. These must be selected from your line of best fit. Give the gradient to three significant figures.[2]
6. (d)(i)On the graph, circle the point which you believe to be the most anomalous.[1]
7. (d)(ii)Suggest a possible explanation for this anomaly.[1]
8. (e)(i)Identify the independent variable.[1]
9. (e)(ii)Suggest how the experiment could be made to be more reliable.[1]
10. (f)The ideal gas equation is shown. pV = nRT p = the pressure of the gas in Pa; V = the volume of gas in m³; n = the number of moles of gas; R = the universal gas constant 8.31 Jmol-1K-¹ and T = absolute temperature in K Using this equation, describe how the gradient of the graph you have plotted would be affected by using a smaller volume of oxygen at the start of the experiment. Explain your answer.[1]

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