CAIE Chemistry (9701)

A student plans an experiment to find a value for the molar volume, V , of hydrogen gas at room conditions.

The student is provided with the following materials: graduations for the collection of gas measuring cylinder The student plans the following procedure. Step 1 Prepare the piece of magnesium ribbon for use in the experiment. Step 3 Attach the conical flask to a collection system for the hydrogen gas. Step 4 Place the magnesium ribbon in the conical flask. Step 5 Stopper the flask. Step 6 Wait until the final volume of gas collected is constant. Step 7 Wait for an additional 2 minutes, then measure and record the final volume of gas collected.

Complete Fig. 1.1 to show how the apparatus should be assembled for the collection and measurement of gas. Label your diagram.

The surface of the magnesium ribbon has an oxide layer.

State how the student should prepare the piece of magnesium ribbon before it is used in this experiment.

State what additional information about the magnesium is required before the experiment is performed.

The student waits for 2 minutes before taking a reading of the volume. Suggest why the student waits for 2 minutes before measuring the volume of gas in step 7. of hydrogen gas during the experiment.

Calculate the percentage error in collecting the hydrogen gas. Show your working. percentage error =

Calculate the molar volume of hydrogen gas using the student's results from this experiment. molar volume = cm

The student's experimental value for the molar volume of hydrogen is lower than the value quoted in the table of important values, constants and standards on page 11. Suggest one experimental weakness that might have led to this outcome. Explain how the method could be improved to overcome the weakness you have noted. experimental weakness improvement [2] [Total: 12]

In a neutral solution, aqueous potassium iodide acts as a catalyst for the decomposition of aqueous hydrogen peroxide. O(l) + O

A student plans to carry out an investigation to find how temperature affects the initial rate of the decomposition of aqueous hydrogen peroxide, H

, in the presence of aqueous potassium iodide, K I(aq). The student knows that the initial rate of the reaction can be measured by timing the production of the oxygen. The student carries out a series of experiments. In experiment 1 the student notes the temperature of the H

and KI(aq) under room conditions. The solutions are mixed in apparatus designed to collect the oxygen produced. A stop-watch is started at the beginning of the reaction. The volume of oxygen is noted at regular time intervals. In experiments 2-8 the solutions are heated to different temperatures before mixing and measurement of the oxygen produced. The data collected is used to determine a value for the activation energy of the decomposition of

in the presence of K I(aq).

State the independent variable.

State two variables that need to be controlled. 1 2

required for preparation of the solution. Give the name and capacity of any key apparatus which should be used. Write your answer as a series of numbered steps.

Hydrogen peroxide causes eye and skin irritation. State what precaution should be taken when preparing the solution in (c)(i) other than wearing goggles.

(i) The student performs experiments 1-8 using a range of temperatures. The results are shown in Table 2.1. Complete the table and record the values of to three significant figures and the values of log initial rate to three significant figures. Table 2.1 experiment number temperature temperature -1 initial rate -1 log initial rate 1 20 293 5.75 × 10 2 25 298 7.94 × 10 3 30 303 1.17 × 10 4 35 308 1.45 × 10 5 39 312 2.19 × 10 6 46 319 3.72 × 10 7 52 325 5.25 × 10 8 55 328 6.31 × 10

Plot a graph on the grid to show the relationship between log initial rate and Use a cross (×) to plot each data point. Draw a line of best fit.

Circle the point on the graph you consider to be most anomalous. Suggest one reason why this anomaly may have occurred during this experimental procedure. 0.003050.00310 0.00320/ Klog initial rate 0.00330 0.00340 -4.2 -4.3 -4.4 -4.5 -4.6 -4.7 -4.8 -4.9 -5.0 -5.1 -5.2 -5.3 0.00350

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. coordinates 1 coordinates 2 gradient = K

The relationship between log initial rate and is given by the expression: log initial rate = constant - Use the gradient calculated in (d)(iv) to calculate a value for the activation energy, E not the correct value.)

It is not possible to repeat the investigation. State whether the data from the investigation is reliable. Justify your answer. [Total: 18] Important values, constants and standards Faraday constant F = 9.65 u 10 Avogadro constant L = 6.022 u 10 electronic charge e = ?1.60 u 10?19 molar volume of gas V at room conditions ionic product of water K = 1.00 u 10?14 To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. Group The Periodic Table of Elements hydrogen 1.0 He helium 4.0 12131415161718 34567891011123Li lithium 6.9 beryllium 9.0 atomic number atomic symbolKey name relative atomic mass sodium 23.0 magnesium 24.3 potassium 39.1 calcium 40.1 rubidium 85.5 strontiu m 87.6 caesium 132. 9 barium 137.3 francium Ra radium boron10.8 13 Al aluminium 27.0 31 Ga gallium 69.7 49 In indium 114.8 thallium 204.4 carbon 12.0 14 Si silicon 28.1 32 Ge germanium 72.6 50 Sntin 118.7 82 Pb lead 207.2 titanium 47.9 40 Zr zirconium 91.2 72 Hf hafnium178. 5 rutherfordium vanadium 50.9 41 Nb niobium 92.9 73 Ta tantalum 180.9 105 Db dubnium chromium 52.0 42 Mo molybdenum 95.9 74 W tungste n 183.8 106 Sg seaborgium manganese 54.9 43 Tc technetium rhenium 186. 2 107 Bh bohrium iron 55.8 44 Ru ruthenium 101.1 76 Os osmium 190.2 108 Hs hassium Co cobalt 58.9 45 Rh rhodium 102.9 iridium192.2 109 Mt meitnerium nicke l58.7 46 Pd palladium 106. 4 platinum 195. 1 110 Ds darmstadtium copper 63.5 47 Ag silver 107. 9 79 Au gold 197. 0 111 Rg roentgenium zinc 65.4 48 Cd cadmium 112.4 80 Hg mercury 200. 6 112 Cn copernicium flerovium livermorium nitrogen 14.0 phosphorus 31.0 33 As arsenic 74.9 51 Sb antimony 121.8 bismuth 209.0 oxygen 16.0 sulfur 32.1 34 Se selenium 79.0 52 Te tellurium 127.6 84 Po polonium fluorine 19.0 17 Cl chlorine 35.5 35 Br bromine 79.9 iodine 126.9 Ne neon 20.2 18 Ar argo n39.9 krypto n 83.8 54 Xe xenon131. 3 86 Rn radon nihonium moscovium tennessine oganesson scandium 45.0 yttriu m 88.9 57?71 lanthanoids 89?103 actinoids 57La lanthanum 138.9 89 Ac lanthanoids actinoids actinium Ce cerium 140.1 90 Th thoriu m232.0 praseodymium 140.9 91 Pa protactinium 231.0 neodymium 144.4 uranium 238.0 promethium neptunium samarium 150.4 94 Pu plutonium europium 152.0 95 Am americium gadolinium 157.3 96 Cm curium terbiu m158.9 97 Bk berkelium dysprosium 162. 5 californium holmium 164. 9 99 Es einsteinium erbium 167. 3 100 Fm fermium Tm thulium168. 9 101 Md mendelevium ytterbiu m 173. 1 102 No nobelium lutetium 175.0 lawrencium