Experimental Techniques and Measurements

Mass	Volume	Time	Temperature
Kg	$c m^{3}$ or $d m^{3}$	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

$1 c m^{3} to 1000 c m^{3} or more$

Burette

For accurate measurements to $0.05 c m^{3}$

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

$H_{2}, O_{2}, C O_{2}$

Downward delivery

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

$C I_{2}$

Upward delivery

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

$N H_{3}, H_{2}$

Using a gas syringe

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

Methods of collecting dry gasses

Acidic

Concentrated sulfuric acid

$H_{2} S O_{4}$

Alkaline

Calcium Oxide

Neutral

Fused Calcium Chloride

Properties of common gasses

Gas	Formula	Color	Density (compared to air)	Solubility in water
Ammonia	$N H_{3}$	Colorless	Less dense	Extremely soluble
Carbon Dioxide	$C O_{2}$	Colorless	Denser	Slightly soluble
Chlorine	$C I_{2}$	Greenish-Yellow	Denser	Soluble
Hydrogen	$H_{2}$	Colorless	Less dense	Insoluble
Hydrogen Chloride	$H C I$	Colorless	Denser	Very soluble
Oxygen	$O_{2}$	Colorless	Slightly denser	Slightly soluble
Carbon Monoxide	$C O$	Colorless	Slightly denser	Slightly soluble
Nitrogen	$N_{2}$	Colorless	Slightly denser	Insoluble
Sulphur dioxide	$S O_{2}$	Brownish	Denser	Very soluble
Helium	$H e$	Colorless	Less dense	Insoluble

Testing for ammonia gas

Usually white fumes can be seen

Procedure:

Heat the test tube
Move test tube away from the flame
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
    - $N a C l$
  - Compound
    - White
      - Group I/II/???
        
        ${C O_{3}}^{2 -}$
        
        ${N O_{3}}^{-}$
        
        ${S O_{4}}^{2 -}$
      - Oxides/hydroxide
    - Colored
Solution
- Colored
- Colorless

Details

Calcium bicarbonate is soluble in lime water
Displacement reactions are exothermic

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