Experimental Techniques and Measurements

Mass	Volume	Time	Temperature
Kg	\(cm^3\) or \(dm^3\)	Hours/minutes/seconds	Celsius or Kelvin
Beam/electronic balance	Measuring cylinder or burette	Stopwatch	Thermometer

Measuring apparatus

Electronic balance

Accuracy: 2 d.p.

Tip

Why is there a mini glass enclosure around the balance?

To prevent wind from affecting measurement

Measuring cylinder

For approximate measurements

\(1cm^3 \textrm{ to } 1000cm^3 \textrm{ or more }\)

Burette

For accurate measurements to \(0.05cm^3\)

Pipette

• Very accurate
• Measure fixed volumes

Volumetric flask

• Very accurate
• Measure fixed volumes
• Used to prepare standard solutions of exact concentration

Syringe

• (small syringe) small volume of liquids
• (large syringe) large volume of gasses

Warning

Read at bottom of meniscus

Common questions

Why do we need to collect gasses?

Allow us to determine the rate and progress of a reaction

Why do we need to add distilled water/filter?

To separate soluble and insoluble compounds

Methods of collecting gasses

Considerations to be made

• Density (compared to air)
• Solubility (in water)

Displacement of water

For gasses which are insoluble in water

• \(H_2, O_2, CO_2\)

Displacement of water

Downward delivery

For gasses which are denser than air (and soluble in water)

• \(CI_2\)

Downward delivery

Upward delivery

For gasses which are less dense than air (and soluble in water)

• \(NH_3, H_2\)

Upward delivery

Using a gas syringe

When there is a need to monitor the rate of evolution of a gas

Gas syringe

Methods of collecting dry gasses

Acidic

Concentrated sulfuric acid

• \(H_2SO_4\)

Acidic

Alkaline

Calcium Oxide

Alkaline

Neutral

Fused Calcium Chloride

Fused calcium chloride

Properties of common gasses

Gas	Formula	Color	Density (compared to air)	Solubility in water
Ammonia	\(NH_3\)	Colorless	Less dense	Extremely soluble
Carbon Dioxide	\(CO_2\)	Colorless	Denser	Slightly soluble
Chlorine	\(CI_2\)	Greenish-Yellow	Denser	Soluble
Hydrogen	\(H_2\)	Colorless	Less dense	Insoluble
Hydrogen Chloride	\(HCI\)	Colorless	Denser	Very soluble
Oxygen	\(O_2\)	Colorless	Slightly denser	Slightly soluble
Carbon Monoxide	\(CO\)	Colorless	Slightly denser	Slightly soluble
Nitrogen	\(N_2\)	Colorless	Slightly denser	Insoluble
Sulphur dioxide	\(SO_2\)	Brownish	Denser	Very soluble
Helium	\(He\)	Colorless	Less dense	Insoluble

Testing for ammonia gas

Usually white fumes can be seen

Procedure:

1. Heat the test tube
2. Move test tube away from the flame
3. Place damp litmus paper over mouth of test tube

Boiling tubes

• To collect filtrate
• For strong heating of solutes
  • Thermal decomposition

Identify colors of compounds

• Solid
  • Shiny
    • Metal
      • Gray
        • Group I
      • Colored
        • Transition metals
  • Powder
    • Non metallic elements
      • \(NaCl\)
    • Compound
      • White
        • Group I/II/???
          • \({CO_3}^{2-}\)
          • \({NO_3}^-\)
          • \({SO_4}^{2-}\)
        • Oxides/hydroxide
      • Colored
• Solution
  • Colored
  • Colorless

Details

• Calcium bicarbonate is soluble in lime water
• Displacement reactions are exothermic

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Last update: June 11, 2023
Created: June 11, 2023