Stop-watch, thermometer, balance
Three of the four quantities in this topic have one standard instrument each. Stop-watch measures time -- how long a precipitate takes to form, or a fixed collection interval. Thermometer measures temperature -- the rise or fall during a reaction, or a water bath. Balance measures mass -- a solid reactant before a reaction, or the mass lost as a gas escapes. Name each one precisely: "timer" or "clock" is weaker than stop-watch, and "scales" is weaker than balance.
Volume -- four apparatus, four jobs
Volume is the only quantity here with four named apparatus, because each does a different job. Burette -- a variable volume of liquid, read precisely from its scale (added drop by drop to a colour change). Volumetric pipette -- one single fixed, very accurate volume; a pipette delivers exactly that. Measuring cylinder -- an approximate volume, where accuracy is not critical. Gas syringe -- the volume of a gas, read off its scale.
Solvent, solute, solution, saturated
Solvent dissolves a solute; solute is dissolved in a solvent; solution is a mixture of one or more solutes dissolved in a solvent. Saturated solution -- contains the maximum concentration of solute at a specified temperature; both halves are needed -- the same solvent dissolves more solute when warmer. Residue -- the solid left after evaporation, distillation or filtration. Filtrate -- the liquid or solution that has passed through a filter.
Drawn from real examiner reports.
Residue is solid, filtrate is liquid
They are the two separated halves of one filtration. Residue is the SOLID that stays behind -- caught on the filter paper, or left in the dish after evaporating. Filtrate is the LIQUID or solution that has passed THROUGH the filter. Candidates routinely write one word for the other, calling the sand caught on the paper "the filtrate".
Burette is not just "a pipette"
Examiners want the specific instrument, not a family name. Writing "a pipette" where a burette is needed is not credited: a burette dispenses a variable volume read precisely, while a volumetric pipette delivers only ONE fixed volume. Reaching for a measuring cylinder where burette accuracy is required is the same failure -- match apparatus to the precision needed.
Flagged Jun 2022 P11 Q14; Nov 2022 P31 Q2bi
Solute is dissolved, solvent dissolves
The solvent does the dissolving; the solute is the substance dissolved. Candidates reverse them -- often calling water the solute because there is more of it -- or define solute as "the thing that dissolves", which actually describes the solvent. Say "is dissolved in a solvent" for solute, and "dissolves a solute" for solvent.
Gas syringe: subtract the start reading
A gas syringe often does not start at zero. If it reads 4 cm3 before the reaction and 61 cm3 at the end, the gas collected is the DIFFERENCE, 57 cm3 -- not the final reading of 61 cm3. The same weighing-by-difference logic applies to a balance: subtract the empty-container mass from the full one.
Saturation scales by mass, not by moles
Saturated-solution questions in 0654 Core are solved by scaling mass ratios -- the mole concept is Extended (Supplement) only and is no part of this sub-topic. If 40 g of solute saturates 100 g of water at a fixed temperature, then 250 g of water needs 40 x 2.5 = 100 g. Reach for direct proportion, never for a mole or molar-concentration formula.
Evaporation never yields a pure liquid
Heating a solution drives the solvent off as vapour and leaves the dissolved solute behind as a solid residue -- it does not produce a pure liquid. To collect pure water from a salt solution you need distillation, which condenses and collects the escaping vapour separately; simple evaporation loses that vapour to the air.
Flagged Jun 2022 P21 Q14
Convert units before the arithmetic
Convert every reading to one consistent unit BEFORE any arithmetic, not after. A stop-watch showing 2 minutes 18 seconds is not "2 + 18" -- the 2 minutes is 120 s first. Never mix grams and kilograms in one calculation (). Then finish by writing the unit next to the final number; a correct value with no unit still drops the mark.
The two-step apparatus routine
Identify the quantity first: time -> stop-watch, temperature -> thermometer, mass -> balance. Only volume needs a second step -- variable and precisely read -> burette; one fixed accurate volume -> volumetric pipette; approximate -> measuring cylinder; a gas -> gas syringe.
Convert first, unit last
For any calculation from an apparatus reading, convert all values to the same unit before substituting, then attach the unit to the final answer. Do not quote a formula built out of units, and do not mix a word, a symbol and a unit in one expression.
Answer the command word, hit the tariff
"Name the apparatus" wants the instrument only; "explain why" wants a reason, not a restatement of the question; "describe" is not "explain". Then match the number of separate points you make to the mark tariff -- a 3-mark answer needs three.
Give both halves of the definition
The definitions here are two-element. Saturated solution needs BOTH "maximum concentration" AND "at a specified temperature"; solute needs BOTH "is dissolved" AND "in a solvent". A one-element answer is under-credited even when nothing in it is actually wrong.
Cambridge 0654 spec reference: Section C12 "Experimental techniques and chemical analysis", sub-topic C12.1 "Experimental design" (Core only, no Supplement statement in this leaf). This leaf covers: naming apparatus for measuring time, temperature, mass and volume; and the set-book definitions of solvent, solute, solution, saturated solution, residue and filtrate.
Apparatus for measuring time, temperature and mass:
| Apparatus | Measures | Typical use |
|---|---|---|
| Stop-watch | Time | Timing how long a reaction takes, or a fixed interval during an experiment |
| Thermometer | Temperature | Monitoring the temperature of a reaction mixture or water bath |
| Balance | Mass | Weighing a solid reactant, product, or a container before/after a reaction |
Apparatus for measuring volume (there are four -- each suited to a different purpose):
| Apparatus | Measures | Precision / purpose |
|---|---|---|
| Burette | A variable volume of liquid, dispensed and read precisely | Precisely measured, variable volumes -- e.g. adding a solution drop by drop |
| Volumetric pipette | One single, fixed volume of liquid | Very high accuracy for ONE specific, fixed volume (e.g. "a pipette") |
| Measuring cylinder | An approximate volume of liquid | Adequate where high accuracy is not required |
| Gas syringe | The volume of a gas | The only apparatus of the four suited to measuring a GAS, not a liquid |
Definitions (two-element, mark-scheme-precise):
| Term | Mark-scheme-precise meaning |
|---|---|
| Solvent | A substance that dissolves a solute |
| Solute | A substance that is dissolved in a solvent |
| Solution | A mixture of one or more solutes dissolved in a solvent |
| Saturated solution | A solution containing the maximum concentration of a solute dissolved in the solvent at a specified temperature |
| Residue | A solid substance that remains after evaporation, distillation, filtration, or a similar process |
| Filtrate | A liquid or solution that has passed through a filter |
Define solvent.
Sugar is added to water and stirred until it disappears. Define the terms solvent, solute and solution as they apply to this mixture, and identify which substance is which. (3 marks)
