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Summary Study / Revision notes - Topic 2 Experimental tecniques - Chemistry CIE IGCSE (A* student)
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LUCÍA ROMERO2. EXPERIMENTAL TECHNIQUES
DEFINITIONS
1. Element: a substance that cannot be decomposed into anything simpler by chemical means, a substance made up of atoms all of which
have the same atomic number (same number of protons).
2. Compound: a substance which contains 2 or more elements chemically combined and fixed proportions by mass.
3. Mixture: contains 2 or more substances (elements or compounds) that are not chemically combined. Mixtures do not have a chemical
formula.
4. Solution: a liquid which contains a substance or substances dissolved in it
5. Solvent: a pure liquid in which a substance is dissolved
6. Solute: a dissolved substance in a solution.
2.1 MEASURMENT
Time
Units → seconds / minutes
Measured using... a stopclock or a stopwatch
Temperature
Units → degrees Celsius
Measured using... a thermometer (digital for a more precise measurement) (traditional for a more accurate measurement)
Mass
Units → grams / kilograms (1kg = 1000g)
Measured using... a weighing balance or top pan balance or digital balance
Volume
Units → cm3/dm3/ml/l
( 1cm3 = 1ml 1dm3 = 1l 1000cm3 = 1dm3 = 1l )
LIQUIDS
• For approximate volumes where accuracy is not an important factor → measuring cylinders are used
- to measure volume quickly
- These are graduated (have a scale so can be used to measure) and are available in 25 cm 3, 50 cm3, 100 cm3 and 250 cm3
• Volumetric pipettes → the most accurate way of measuring a fixed volume of liquid, usually 10 cm 3 or 25 cm3
- also, to TRANSFER and deliver a liquid
• Burettes → the most accurate way of measuring a variable volume of liquid up to 50 cm3 (e.g. in a titration) - only used to DELIVER
liquids
GASES
• A gas syringe is usually the apparatus used
2.2 PURITY
What are pure substances?
Substances that...
1. Have no particles of another substance mixed with them
2. Melt and boil to temperatures unique to them
3. Melt sharply at their melting point
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