Most candidates completed all questions in the time available; very few blanks.
Planning Q4: do not list apparatus/aims/safety at the start. Credit for apparatus only when its use is stated.
(a) Apparatus correctly identified as a beaker (trough/ice-bath also acceptable). Easy
(b) Heat arrow placed correctly; a few heated the ice bath. Easy
(c) Challenging: steam cooled by ice bath then condensed to water; some thought lead/lead(II) oxide or methane collected. Difficult
(d) Increased surface area ? faster reaction. Easy
(e) Methane is a flammable gas; many incorrectly wrote “toxic”. Moderate
(a) Completed table with five times & temperatures; keep one decimal place (e.g. 27.0 °C); record time in seconds only. Moderate
(b) Choose sensible scale; plot five points; draw a single thin best-fit line (does not need to pass through points). Moderate
(c) Identify Experiment 5 as fastest rate (not just “highest temperature”). Easy
(d) Show working on graph: horizontal from 55 s to line then down to x-axis; many omitted this. Moderate
(e) Cotton wool acts as insulator ? steadier temperature; not a more accurate thermometer. Some confused with CaCO3/acid gas loss. Moderate
(f)(i) Burette more accurate than measuring cylinder. Easy
(f)(ii) Pipette issue here: slow run-out delays start relative to thiosulfate addition; “pipettes measure fixed volume” is irrelevant. Moderate
(g) Reaction is occurring while mixture is heated. Easy
(h) Asked how results change: shallower depth in larger beaker makes text visible quicker (dependent variable is time). Many discussed rate/temperature instead. Difficult
(a) Many unfamiliar with flame test; about half mentioned nichrome/platinum wire or (wet) splint; few introduced sample into hot/blue flame. Difficult
(b) Gas correctly identified as ammonia. Easy
(c) Cation identified as ammonium by most, but fewer stated the ion by name. Moderate
(d) About half noted white precipitate; others wrote fizzing/no change. Moderate
(e) Correct observations: effervescence and limewater turns milky; “gas given off” alone not an observation; some omitted the limewater result. Moderate
(f) Formation of an insoluble green precipitate reported by most. Easy
Quantitative task using data provided. Typical successful method: wash with water to remove ethanoic acid/propanol, then use dilute nitric acid to react with Fe(III) oxide; isolate SiO2 residue and determine % by mass.
Good plan steps: add known mass of metal polish to dilute HNO3 in beaker/conical flask & heat; filter to collect unreacted SiO2; wash & dry residue; find mass; % by mass = (mass of residue ÷ mass of polish)×100.
Common issues: unsuitable container (e.g., measuring cylinder); omitting washing/drying; mixing up residue/filtrate; investigating components instead of a polish sample; listing aims/apparatus without uses.
Write a public review