Apparatus for Measurements (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

Time

• Time can be measured using a stopwatch or stopclock which are usually accurate to one or two decimal places
• The units of time normally used are seconds or minutes
  • Other units may be used for extremely slow reactions (e.g. rusting)
• Remember: 1 minute = 60 seconds

Temperature

• Temperature is measured with a thermometer or digital temperature probe

• Laboratory thermometers usually have a precision of a half or one degree
  • Digital temperature probes are available which are more precise than traditional thermometers and can often read to 0.1 ^oC
• Traditional thermometers rely upon the uniform expansion and contraction of a liquid substance with temperature
  • Digital temperature probes can be just as, if not, more accurate than traditional thermometers
• The units of temperature are degrees Celsius (ºC)

Mass

• Mass is measured using a digital balance which normally gives readings to two decimal places
  • Balances should be tared (set to zero) before use
  • Balances should also be allowed time to settle on a final measurement / reading before it is recorded

• The standard unit of mass in kilograms (kg)
  • However, in chemistry grams (g) are most often used
• Remember: 1 kilogram = 1000 grams

Volumes of liquid

• The volume of a liquid can be determined using different pieces of apparatus
  • The choice of apparatus depends on the level of accuracy needed
• Three common pieces of apparatus for measuring the volume of a liquid are:
  • Burettes
  • Volumetric pipettes
  • Measuring cylinders

• Burettes are the most accurate way of measuring a variable volume of liquid between 0 cm³ and 50 cm³
  • They are most commonly used in titrations
  • Careful: Read the burette scale from top to bottom as 0.00 cm³ is at the top of the column
• Volumetric pipettes are the most accurate way of measuring a fixed volume of liquid,
  • They have a scratch mark on the neck which is matched to the bottom of the meniscus to make the measurement
  • A pipette filler is used to draw the liquid into the volumetric pipette
  • The most common volumes for volumetric pipettes are 10 cm³ and 25 cm³
• Measuring cylinders are used when approximate volumes are required (accuracy is not an important factor)
  • These are graduated (have a scale so can be used to measure)
  • Measuring cylinders typically range from 10 cm³ to 1 litre (1 dm³)
• Whichever apparatus you use, you may see markings in millilitres, ml, which are the same as a cm³

Volumes of gas

• For some experiments, the volume of a gas produced needs to be measured
• This is typically done by using one of the following methods:
  • Using a gas syringe 
  • By downward displacement of water
• A gas syringe is more precise and accurate than downward displacement of water

Diagram of the set-up for an experiment involving a gas syringe

• Downward displacement of water is where a measuring cylinder is inverted in water to collect the gas produced
  • This method does not work if the gas is soluble in water

Diagram of the set-up for an experiment collecting gas by downward displacement of water

• • If the gas happens to be heavier than air and is coloured, the cylinder does not need to be inverted