Copy of MGS Chemistry P3 (Answers)

1 METHODIST GIRLS’ SCHOOL CHEMISTRY PRELIMS 2024 Paper 3 Question Skill Indicative Material Mark Total 1(a) MMO PDO MMO Conducting the titration experiments Results Table: Record all burette readings for full set of experiments in the table to nearest 0.05 cm 3 Calculate the volume of Q used in each set of experiment correctly Results: A full set of data is recorded showing 2 sets of consistent titration readings of 22.00 cm3 within 0.20 cm3 of each other. Volumes of R within 0.20 cm 3 of Supervisor’s results (Note for teachers: solutions to be standardised to obtain 22.00 cm3 of Q from titration) 1 1 1 1 1 [5] 1(b) ACE Calculate the average volume of Q used correctly based on 2 consistent readings. 1 [1] 1(c) ACE Calculate the number of moles of KIO3 using concentration in mol/dm3 and 25.0 cm3 of solution used in titration. Calculate the number of moles of I2 correctly using mole ratio of KIO3 : I2 = 1:3 1 1 [2] 1(d) ACE Calculate the number of moles of R correctly using mole ratio of I2 : R = 1 : 1 1 [1] 1(e) ACE Calculate the mol/dm3 of R from (d) and volume of titre Calculate the relative molecular mass of R correctly using g/dm3 and mol/dm3. 1 1 [2] Total : [11]

2 2(a) PDO Vertical axis – independent variable Horizontal axis - dependent variable Axis labels + units appropriate scale, more than 50% of graph Points correctly plotted (allow only 1 error), include point of origin Straight line of best fit 1 1 1 1 [4] 2(b) ACE Change in temperature/ decrease in temperature increases with number of moles of C. 1 [1] 2(c) ACE Value (with unit) from the graph with unit and marking shown on both x and y axes. 1 [1] 2(d) PDO Show calculation for number of moles of C Show recording of initial temperature, final temperature temperature change with correct unit. 1 1 [2] 2(e) ACE Graph shows a trend based on 5 temperature readings (data points) 1 [1] 2(f) P Variables to be controlled : volume of solvent, temperature, speed of stirring , dry beaker Independent variable : type of solvent Dependent variable : maximum mass of the organic acid that has dissolved Add a known mass of solid organic C + stir to dissolve completely Continue adding until no more of the solid organic acid dissolves 1 1 1 1 1 [5] 3(a) Test 1 NMO White solid turned yellow / orange when hot white solid when cold 1 1 [2] Test 2 NMO Bubbles of gas formed Gas formed white ppt in lime water. Carbon dioxide evolved. 1 [1] Test 3 NMO White ppt Ppt dissolves in excess to form colourless solution 1 [1]

3 Test 4 NMO White ppt Ppt dissolves in excess to form colourless solution 1 [1] Test 5 NMO Dirty green ppt, ppt insoluble in excess, Upon standing, reddish brown/orange ppt