Unit 1 (Chemistry)

• Measurement


  The act of determining the size, amount, or degree of something, especially by comparison with a standard
• Experimental Techniques


  Methods and procedures used in scientific experiments
• In competitive sports like swimming, the difference in timing between two swimmers could be a tenth or hundredth of a second
• The metric system is used in Singapore
• S.I. Units


  The modern metric system used to measure quantities of different things
• Scientists use S.I. units as a common standard for their measurements
• Mass


  The S.I. unit is the kilogram (kg), smaller masses are measured in grams (g), and the tonne (t) is used to measure heavy objects
• Apparatus for measuring mass

  • Beam balance
  • Electronic balance
• Time


  The S.I. unit is the second (s), other units like minute (min) and hour (h) are used for longer intervals
• Apparatus for measuring time

  • Analogue stopwatch
  • Digital stopwatch
• In Chemistry experiments, time is usually recorded to the nearest second
• Temperature


  The S.I. unit is the kelvin (K), the degree Celsius (°C) is also commonly used
• Apparatus for measuring temperature

  • Mercury thermometer
  • Alcohol thermometer
  • Temperature sensor connected to data logger
• Volume


  The S.I. unit is the cubic metre (m³), the cubic centimetre (cm³) and the cubic decimetre (dm³) are also used
• Apparatus for measuring volumes of liquids

  • Measuring cylinder
  • Burette
  • Pipette
• Bottled drinks are commonly sold in litres (l) and millilitres (ml), 1 litre is equal to 1 dm³
• Meniscus


  The curved surface formed when water or a solution is placed in a container
• Apparatus for measuring volumes of gases

  • Gas syringe
• Gas syringe


  • Measures a maximum volume of 100 cm³
  • Plunger is pushed in fully at the start to expel any gas
  • As gas enters, it pushes the plunger outwards
• As a general guide, a gas is less dense than air if its molecular mass is less than 30
• Methods for collecting gases

  • Displacement of water
  • Displacement of air - downward delivery
  • Displacement of air - upward delivery
• The collection of poisonous gases should be carried out in a fume cupboard
• Solubilities, densities and methods of collection of some gases

  • Refer to Table 2.2
• Methods of collecting gases

  • Displacement of water - for gases insoluble or slightly soluble in water
  • Downward delivery - for gases soluble in water and denser than air
  • Upward delivery - for gases soluble in water and less dense than air
• Drying a gas


  1. Pass gas through drying agent (concentrated sulfuric acid, quicklime, fused calcium chloride)

  2. Removes moisture from gas
• Gas syringe


  Used to collect and measure volume of gas
• Solubility and density of some gases

  • Hydrogen - not soluble, less dense than air
  • Oxygen - very slightly soluble, slightly denser than air
  • Carbon dioxide - slightly soluble, slightly denser than air
  • Chlorine - soluble, denser than air
  • Hydrogen chloride - very soluble, denser than air
  • Sulfur dioxide - very soluble, denser than air
  • Ammonia - extremely soluble, less dense than air
• Ammonia, chlorine and hydrogen chloride cannot be collected by displacement of water
• Collecting dry methane gas


  Displace air upwards
• Concentrated sulfuric acid cannot be used to dry ammonia gas as it reacts with ammonia
• Quicklime (calcium oxide) is used to dry ammonia gas
• Methane is insoluble in water and less dense than air