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CIE Jun 2014 v3 Paper 3 Q2
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![You will determine the enthalpy change, H, for the reaction between magnesium and dilute sulfuric acid. The equation for the reaction is given below. PMT Mg(s) + H2SO4(aq)MgSO4(aq) + H2(g) FA 3 is 1.00 mol dm3 sulfuric acid, H2SO4. two different coiled lengths of magnesium ribbon, Mg. (a) Method Read through the method before starting any practical work and prepare a table for your results in the space below.Weigh the shorter piece of magnesium ribbon and record its mass. Support the plastic cup in the 250 cm3 beaker. Use the measuring cylinder to transfer 50 cm3 of FA 3 into the plastic cup. Place the thermometer in the FA 3 in the plastic cup and record the initial temperature. Add the shorter piece of magnesium ribbon into the plastic cup. Ensure that all of the magnesium is in contact with the acid. (Care: acid spray may occur.) Stir the mixture and record the maximum temperature. Empty and rinse the plastic cup. Shake out any excess water. Repeat the experiment using the longer piece of magnesium ribbon and record all your data. Results [4] (b) Calculations Show your working and appropriate signi cantgures in thenal answer to each step of your calculations. (i) Show by calculation that the sulfuric acid, FA 3, was used in excess in both experiments. (Ar: Mg, 24.3)UCLES 2014 9701/33/M/J/14<br />
PMT (ii) State an observation which con rms that the sulfuric acid, FA 3, was in excess.(iii) Calculate the heat energy produced when the shorter piece of magnesium was added to FA 3. (Assume that 4.3 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 C.) (iv) Calculate the enthalpy change, in kJ mol1, for the reaction between the shorter piece of magnesium and the sulfuric acid. heat energy produced =J enthalpy change =kJ mol1 (sign) (value) (v) Calculate the heat energy produced when the longer piece of magnesium was added to FA 3. (Assume that 4.3 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 C.) (vi) Calculate the enthalpy change, in kJ mol1, for the reaction between the longer piece of magnesium and the sulfuric acid. heat energy produced =J enthalpy change =kJ mol1 (sign) (value) [5] (c) (i) What is the maximum error in a reading of the thermometer used in this experiment? (ii) Which of your temperature changes has the higher percentage error?(iii) Calculate this maximum percentage error. maximum error =C. maximum percentage error in the temperature change =% [1]UCLES 2014 9701/33/M/J/14 [Turn over<br />
PMT (d) Apart from errors due to heat loss and thermometer readings, suggest another signi cant source of error in this experiment. State what improvement could be made to the procedure to reduce this error.[2] [Total: 12]UCLES 2014 9701/33/M/J/14<br />](https://learnah.org/wp-content/uploads/2018/08/June_2014_v3_QP_-_Paper_3_CIE_Chemistry_A-level_2-0.jpg)
![Page 4 Mark Scheme GCE AS/A LEVELMay/June 2014 Syllabus 9701 Paper 33 Question Sections Indicative material Mark Total (a) PDO Recording Four thermometer readings and two masses tabulated with correct headings and units. (mass/g or (g) or in g; temperature/temp/T/C, etc.) If units are omitted from the headings then they must appear next to each entry in the table. Display Consistent dp for balance readings and (minimum 3) thermometer readings to .0/.5. Correct temperatures to nearest 0.5 C. Examiner calculates T for longer piece of magnesium for Supervisor and candidate. (a) MMO Quality Award one mark if the difference between candidate and Supervisor is2.0 C. Award second mark if the difference between candidate and Supervisor is1.0 C. (b) ACE Interpretation mass longer Mg 24.3 50 1.00 1000 in (i) MMO Collection II No solid/metal left/all Mg disappeared/dissolved in (ii) ACE Interpretation III Expression 504.3T or correct answers in (iii) and (v) PDO Display IV Uses in (iv) answer (iii) to mass shorter Mg/24.3 (v) answer to and mass longer Mg/24.3 Allow ecf from (i) in (vi) ACE Interpretation V Correct answers given to 24 sf in kJ and minus signs in (iv) and (vi) (c) (d) ACE Interpretation ACE Interpretation Improvements (20.5/smaller T)100 for shorter piece of Mg in (iii) Mass of/weighing Mg (ribbon) or volume of H2SO4 used or corrosion on Mg Use greater mass/balance to more dp or use burette/pipette (to measure volume) or use sand paper or emery paper or use lid or taller beaker or taller cup to prevent acid spray 1 1 1 1 [4] [5] [1] [2] Qn 2 Total [12]Cambridge International Examinations 2014<br />](https://learnah.org/wp-content/uploads/2018/08/June_2014_v3_MS_-_Paper_3_CIE_Chemistry_A-level_2.jpg)