SACE Year 11 Chemistry practice exams with worked answers

A material is chosen for a job because measurable properties suit the conditions. Electrical conductivity matters for a wire, thermal conductivity for a saucepan base, and low thermal conductivity for its handle. A useful solid must remain below its melting temperature during use; a liquid coolant must not boil unexpectedly. Solubility describes how much solute dissolves in a specified solvent under specified conditions. A water-resistant coating should have low water solubility. Nanomaterials contain particles with dimensions approximately 1–100 nm.

Their large surface area relative to volume can alter reactivity and useful behaviour; bulk-material results cannot automatically establish nanoparticle safety.

Mixture separation exploits physical differences. Filtration retains an insoluble solid while liquid and dissolved substances pass through. Evaporation removes volatile solvent to recover a non-volatile solute, but usually loses the solvent. Distillation vaporises and then condenses a component, allowing solvent recovery. Draw a distillation diagram with heated flask, vapour path, water-cooled condenser and receiving vessel; cooling water enters the lower condenser port. Never heat sealed apparatus. Dissolved salt does not become removable by ordinary filter paper.

To investigate how temperature affects dissolving time, ask a testable question with a defined endpoint. Temperature is independent, time is dependent; control solute mass, grain size, solvent volume, vessel and stirring. Room drafts and observer reaction time may be imperfectly controlled and should be recorded. Use a thermometer, balance, measuring cylinder and timer, with at least three trials at each of several temperatures. Use safe warm water, eye protection and teacher-approved substances; avoid nanopowders.

Share roles fairly, rotate measuring and timing, record your own observations as well as the group table, and never invent missing data. A labelled apparatus sketch supplies visual primary evidence. A cited reference solubility table supplies secondary evidence.

Tabulate temperature in K and time in s with instrument resolution recorded. Plot the independent variable horizontally and mean time vertically; use an appropriate smooth trend rather than forcing a straight line. Interpolation within measured temperatures is more defensible than extrapolation far outside them. Repeats reveal random scatter and improve reliability; they do not remove a miscalibrated thermometer's systematic offset. A timer resolving 0.01 s does not eliminate human reaction uncertainty.

Accuracy concerns closeness to a reference, precision concerns agreement, and validity concerns whether the method answers the intended question. Dissolving time measures rate under these conditions, not equilibrium solubility.