2023 SOTA Yr 6 Chem HL Prelim Exam MS3

2023 Prelim Chemistry HL Paper 3 Mark Scheme Section A 1a Ag+(aq) + I-(aq) à AgI(s) Correct products and balancing ✔ Correct state symbols ✔ bi Oxidising agent ; ✔ ii To provide an acidic medium /H+ ions needed for the redox reaction ; ✔ Do not accept catalyst ci (5.20 + 5.30) / 2 = 5.25 cm3 ✔ Reject other values ii % uncertainty = 0.10 / 5.25 x 100% = 1.9% ; ✔ ECF from c(i) iii Dilute/lower the concentration of sodium thiosulfate solution OR Increase the mass of fish OR Increase volume of iodine solution used OR more repeats ✔ Reject: “bigger” or “larger” sample 2a P ¡water = 3.2 kPa ✔ Accept any answer from 3.1 kPa to 3.3 kPa. b The vapour pressure will increase with temperature. ✔ c 7 kPa ✔ Accept any answer from 6.8 kPa to 7.2 kPa. d Pure ethanol has a higher vapour pressure than water. ✔ e(i) Award [2 max] for the following: There is strong intermolecular forces of attraction/hydrogen bonding between the ethanol molecules. ✔ The ethanol molecules has a significant size and occupies space. ✔ The collisions between ethanol molecules are not elastic. ✔

e(ii) Award [2 max] for each of the following: Starting point at origin (P = 0 kPa) Ending point at P = 8.0 kPa A straight line from these two points.

Section B 3a TD50 is the amount / dose that negatively affects / produce toxic effects in 50% of the population. ü LD50 is the amount / dose that kills 50% of the population. ü Award 1 mark max: TD50 is used in human studies but LD50 is used in animal studies. b The risk of overdose is high because of the low therapeutic index. ü Accept: The drug must be used with caution. c intravenous / IV <<injection>> OR injection into the bloodstream ü d Any one of: • «negative» side-effects of medication on patient / volunteers ü • effects on environment «from all materials used and produced» ü • potential for abuse ü • drugs may be developed that are contrary to some religious doctrines ü • animal testing ü • risk to benefit ratio ü • appropriate consent of patient volunteers ü

4a ethanoic anhydride / (CH3CO)2O OR ethanoyl chloride / CH3COCl ü Accept: ethanoic acid / CH3COOH b It has a <<large>> benzene ring / arene ring which is non-polar / hydrophobic / cannot form hydrogen bonds with water. ü It has carboxyl / COOH / hydroxyl / OH <<and ester group>> which is polar / hydrophilic / can form hydrogen bonds with water. ü c OR C6H4(COOCH3)COOH + NaOH → C6H4(COOCH3)COONa + H2O ü Accept: ionic equation, any other strong base Charges (O– and Na+) are not necessary to score the mark. d Similarities: Award 2 marks max • Both have <<strong>> absorption from 1700-1750 cm-1 for C=O <<in carboxylic acid>>. ü • Both have <<strong and very broad>> absorption from 2500-3000 cm-1 for O–H <<in carboxylic acid>>. ü • Both have <<strong>> absorption from 1050-1410 cm-1 for C–O <<in alcohol/phenol>>. ü • Both have <<<<strong>> absorption from 2850-3090 cm-1 for C–H. ü Difference: Award 1 mark max • Salicylic acid has a <<strong and broad>>