Experimental design
Section: Chemistry | Syllabus: Cambridge IGCSE Combined Science (0653)
Apparatus for Measurement
Different pieces of apparatus are used to measure time, temperature, mass and volume:
| Measurement | Apparatus |
|---|---|
| Time | Stop-watch |
| Temperature | Thermometer |
| Mass | Balance |
| Volume | Measuring cylinder - quick, approximate volume |
| Volumetric (bulb) pipette - one fixed, accurate volume | |
| Burette - a variable, accurately-delivered volume, used in titrations | |
| Gas syringe - measures the volume of a gas produced in a reaction |
Worked Example
- Question: name the apparatus you would use to measure out exactly 25 cm³ of a solution, and the apparatus you would use to measure the volume of a gas produced in a reaction. [2]
- Answer: a volumetric (bulb) pipette, for one fixed accurate volume [1]; a gas syringe, for the volume of gas produced [1]
Solute, Solvent and Solution
- Solute: a substance that is dissolved in a solvent
- Solvent: a substance that dissolves a solute
- Solution: a mixture of one or more solutes dissolved in a solvent
For example, in salt solution: sodium chloride is the solute, water is the solvent, and the mixture formed is the solution.
Worked Example
- Question: sugar is stirred into a cup of water until it disappears. Identify the solute, the solvent and the solution. [3]
- Answer: solute = sugar (the substance dissolved); solvent = water (the substance doing the dissolving); solution = sugar solution (the resulting mixture).
Saturated Solutions
A saturated solution is a solution containing the maximum concentration of a solute dissolved in the solvent at a specified temperature. No more solute will dissolve at that temperature - any extra solute added remains undissolved.
Residue and Filtrate
These terms describe the two products of filtration (and similar separation processes):
- Residue: a substance that remains after evaporation, distillation, filtration, or a similar process
- Filtrate: a liquid or solution that has passed through a filter
For example, when a mixture of sand and water is filtered: the sand left on the filter paper is the residue, and the water that passes through is the filtrate.
Common Mistakes
- ❌ Mixing up "residue" and "filtrate"
- ✓ the residue stays behind (on the filter paper, or after evaporation); the filtrate is the liquid that gets through - "filtrate" and "filters through" share the same root to help you remember which is which
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