Experimental techniques and chemical analysis

• A physical quantity is one which has a magnitude and a unit
• Examples of physical quantity:

  • Mass
  • Temperature
  • Volume- liquid and gas
  • Colour intensity
• MASS:

  symbol: m

  Unit: gram

  SI unit : g

  Apparatus: Electronic balance
• TIME:

  Symbol: t

  Unit: second

  SI unit: s

  Apparatus: Stopwatch
• TEMPERATURE:

  Symbol: T

  Unit: degree celcius

  Symbol of unit: °C

  Apparatus: thermometer
• VOLUME GAS:

  Symbol: V

  Unit: centimeter cube

  Symbol of unit: cm3

  Apparatus: gas syringe
• VOLUME LIQUID:

  Symbol: V

  Unit: centimetre cube

  Symbol of unit : cm3

  Apparatus:

  • Burette
  • Pipette
  • Volumetric flask
  • Measuring cylinder
  • Beaker
  • Conical flask
  • Test tube
  • Boiling tube
• Burette: 1 division= 0.50 cm3

  measure up to 50cm3 of solution accurately to the nearest 0.50cm3
• Pipette: 10cm3 pipette or 25cm3 pipette

  • Measure accurately a fixed volume of liquid.
  • A safety bulb or pipette filler is used to suck the sol. and not the mouth to prevent swallowing of toxic sol.
• Volumetric flask: 100, 250, 500, 1000, 2000 cm3. Measure a fixed volume accurately
• Measuring cylinder: Measure varying volumes approximately
• Beaker: Plastic or glass

  Measure fixed varying volumes approximately.

  
  

  25, 50, 75, 100, 150, 200, 250, 500, 750, 1000cm3
• Conical flask ( glass only):

  Measure fixed varying volumes approximately

  250 & 150cm3
• Test tube & Boiling tube ( glass):

  • Measures volume very approx. using depth of sol.
  • Mainly used for holding liquids
• Crucible ( made of porcelaine): Used to heat a solid
• Gas syringe: 50, 100, 250, 500, 1000cm3
• COLLECTION OF GAS:

  • Displacement of air
  • Displacement of water
• DISPLACEMENT OF AIR

  1. Upward collection
  2. downward collection
• Upward collection: Used to collect gases less dense than air

  EXAMPLE:

  • Hydrogen
  • Ammonia
  • Helium
  • Methane
• DOWNWARD COLLECTION: Used to collect gases denser than air

  EXAMPLE :

  • Chlorine
  • sulfur dioxide
  • Carbon dioxide
• DISPLACEMENT OF WATER: Used to collect gases insoluble in water

  EXAMPLE:

  • All noble gases: Helium, neon, argon etc...
  • nitrogen
  • methane
  • hydrogen
• DRYING OF A GAS: When a gas icollected by displacement it is mixed with water vapour . It must be passed through a drying agent or dehydrating agent
• DRYING AGENT: Is an anhydrous solid (contains no water) which absorbs water to become hydrated (contains water)
• Examples of drying agents:

  • Anhydrous magnesium sulfate, MgSO4
  • Anhydrous calcium chloride, CaCl2
• • Powder: NO WATER
  • Crystals: CONTAINS WATER
• Dehydrating agent: A substance which removes water from another substance.

  • Mainly a concentrated acid therefore found in liquid state
  • Example: Concentrated sulfuric acid, H2SO4
  • When it absorbs water it becomes dilute