Chemistry: Chapter 2 - Measurement and Experimental Techniques

2.1 Measuring Time
S.I. unit: second (s)
Other units: minute (min), hour (h)
Apparatus used: stopwatch 

2.2 Measuring Temperature
S.I. unit: Kelvin (K)
Other units: degree Celsius (°C)
Apparatus used: Mercury thermomenter, data logger

2.3 Measuring Mass
S.I. unit: kilogram (kg)
Other units: gram (g)
Apparatus used: Electronic balance, beam balance

2.4 Measuring Volume
S.I. unit: cubic metre (m³)
Other units: cubic centimetre (cm³), litre (ℓ), millilitre (ml)
Apparatus used: beaker, measuring cylinder, burette, pipette
Accuracy:

1. beaker -  used to estimate the volume of a liquid e.g. approximately 100cm³
2. measuring cylinder - more accurate than a beaker; measures up to the nearest cm³
   
3. burette - accurately measures out the volume of a liquid to the nearest ± 0.1cm³
   
4. pipette - accurately measures out fixed bolumes of liquids e.g. 20.0cm³

2.5 Collecting Gases and Measuring Volumes of Gases

To collect a gas, we have to take note of the

• Solubility - how soluble the gas is in water
• Density - how dense the gas is compared to air

Methods to collect gas:

• Displacement of water - suitable for gas which are insoluble or slightly soluble in water
• Downward delivery - suitable for gas that are soluble in water and denser than air
• Upward delivery - suitable for gas that are soluble in water but less dense that air

Measuring of gas

Using a gas syringe can measure the volume of a gas.

2.6 Determining if a Substance is Pure
A pure substance is made up of only one substances.

a) Solids
A pure solid will melt completely at one temperature.
Impurities affect the melting point of a substance in two ways.

• The > the amount of inpurities, the lower the melting point.
• They cause melting to take place over a range of temperatures.

b) Liquids
A pure liquid has an exact and constant boiling point.
Impurities affect the boiling point.

• Boiling point will increase and will boil over a range of temperatures.

Pressure will affect the boiling point.

• If pressure ↑, boiling point is raised. 
• If pressure ↓, boiling point is lowered. 

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Common gases arranged in terms of Solubility:

Ammonia (Extremely soluble) -> Hydrogen Chloride, Sulphur Dioxide (Very soluble) -> Oxygen (Very slightly soluble) -> Chlorine (Soluble) -> Carbon Dioxide (Slightly soluble) -> Hydrogen (Not soluble)

Common gases arranged in terms of Density

Sulphur Dioxide, Hydrogen Chloride, Chlorine, Carbon Dioxide (Denser) -> Oxygen (Slightly denser) -> Ammonia, Hydrogen (Less dense)