AQA AS Jun 2016 Paper 2 Q2 (with explained solutions) |

Skip to content

AQA AS Jun 2016 Paper 2 Q2

Answers available below

2 Alcohols such as methanol (CH3OH), ethanol (CH3CH2OH) and propan-1-ol (CH3CH2CH2OH) are good fuels. 0 2 . 1 A student carried out an experiment to determine the enthalpy of combustion of methanol.Methanol was placed in a spirit burner and the mass of the spirit burner measured. The student placed 100 g of water in a copper calorimeter and clamped it above the spirit burner. The burner was lit and allowed to burn for a few minutes. The flame was then extinguished and the new mass of the spirit burner found. The measured temperature rise was 38.0 C. The specific heat capacity of water is 4.18 J K1 g1. Figure 1, a diagram of the apparatus, is shown alongside Table 1 which shows the measurements the student recorded. Figure 1 Table 1 Mass of burner containing methanol before experiment Mass of burner containing methanol after experiment 214.02 g 212.37 g Use the students data to calculate an experimental value for the enthalpy of combustion of methanol in kJ mol1. [4 marks] *04* M/JUN16/7404/2<br />
. 2 Suggest one reason, other than incomplete combustion or heat transfer to the atmosphere, why the students value for the enthalpy of combustion of methanol is different from that in a Data Book. [1 mark] . 3 The uncertainty in each of the temperature readings from the thermometer in this experiment was 0.25 C. This gave an overall uncertainty in the temperature rise of 0.5 C. Calculate the percentage uncertainty for the use of the thermometer in this experiment. [1 mark] . 4 The student said correctly that using a thermometer with an overall uncertainty for the rise in temperature of 0.5 C was adequate for this experiment. Explain why this thermometer was adequate for this experiment. [1 mark] . 5 The enthalpy of combustion of ethanol is 1371 kJ mol1. The density of ethanol is 0.789 g cm3. Calculate the heat energy released in kJ when 0.500 dm3 of ethanol is burned. Give your answer to an appropriate number of significant figures. [3 marks] 0 2 0 2 0 2 0 2 *05* Turn overM/JUN16/7404/2<br />

Show answer

Question Marking Guidance 02.1 = 15 884 / 15 880 / 15 900 / 16 000 (J) (OR 15.884 / 15.88 / 15.9 / 16 (kJ)) M1 (q = mcT = 100 x 4.18 x 38(.0)) M2 Moles (methanol = 1.65 / 32.0) = 0.0516 or 0.052 M3 Heat change per moles = M1/M2 M4 Answer = 308 (kJ mol1) (allow 305 to 310) (15 884 / 0.0516 / 1000 = 308 (kJ mol1) (allow 305 to 310) 02.2 Heating up copper / calorimeter / container / thermometer / heat capacity of copper / calorimeter / thermometer not taken into account OR Evaporation of alcohol/methanol OR Experiment not done under standard conditions 02.3 (100 x 0.5 / 38 =) 1.3 or 1.32 or 1.316% (minimum 2 sf) 02.4 Idea that heat loss is more significant issue OR Idea that temperature change/rise is (significantly / much) bigger than uncertainty MARK SCHEMEAS-LEVEL CHEMISTRY 7404/2JUNE 2016 Mark Comments 1 1 1 Award full marks for correct answer M1 mark is for value not expression (at least 2sf); penalise incorrect units here only if M1 is the only potential scoring point in M1-M3 M2 at least 2sf M3 at least 2sf; answer must be in kJ mol-1 M4 this mark is forsign (mark independently) Not human errors (e.g. misreading scales) Not impure methanol Allow evaporation of water Allow correct answer to at least 2sf; Allow 1.31 or 1.315% One of these two ideas only and each one must involve a comparison 10 of 24<br />
02.5 M1 Mass of ethanol = 500 x 0.789 (= 394.5 or 395 (g)) M2 Moles of ethanol = M1 / 46.0 (= 8.576 or 8.58) M3 Heat released = M2 x 1371 = 11800 (kJ) must be 3 sf MARK SCHEMEAS-LEVEL CHEMISTRY 7404/2JUNE 2016 Correct answer to 3sf scores 3; correct value to 2sf or more than 3sf scores 2 Answers that are a factor of 10x out score 2 if given to 3sf or 1 if given to a different number of sf M3 ignore units, but penalise incorrect units M3 ignore sign M2 and M3allow consequential marking 11 of 24<br />

Question 1 2 3 4 5 6 7 8 9

About us | Need Help? | Feedback

Proudly powered by WordPress | Theme: Sydney by aThemes.