IGCSE
Experimental Techniques
Grade (10)
IGCSE
Grade (10)
IGCSE
Grade (10)
“Measurements”
1. Volume:
a) Gas →is measured using gas syringe (cm3), or measuring cylinder.
b) Liquid:
* Accurate →burette, volumetric pipette or graduated pipette (cm3)
* Rough → measuring cylinder (cm3)
c) Solid →measuring cylinder [VSolid = V2 – V1]
2. Time:
➢ Stop clock → seconds or minutes which is usually accurate to one or two decimal
places
3. Mass:
➢ Top pan balance (digital balance) 🡆 which normally give readings to two decimal
places. These must be tarred (set to zero) before use gram
4. Temperature:
➢ Thermometer→ can normally give readings to the nearest degree Celsius ºC
“Apparatus in the Lab.”
• Test tube: used for any chemical reaction.
• Filter funnel: to filter solution.
• Burette : is the most accurate way of measuring a variable volume of liquid between
0 cm3 and 50 cm3 (e.g. in a titration)
• Volumetric pipette , usually 10 cm3 or 25 cm3( multiple of 5)
• Measuring cylinder: used to measure approximate volumes where accuracy isn´t an
important factor. These are graduated (have a scale so can be used to measure) and
are available in 25 cm3, 50 cm3, 100 cm3 and 250 cm3
• Beaker: used for dissolving.
• Bunsen burner, Tripod and Gauze: strong heating system.
• Watch glass: for covering and reduces evaporation.
• Glass rod: For stirring and does not involve in the reaction.
IGCSE
Grade (10)
Diagram of the set-up for an experiment involving gas collection
IGCSE
Grade (10)
IGCSE
Grade (10)
“Matter”
Mixture
Pure
Made of two or more substances mixed together
Made of one type of
(not bonded) in any ratio
particles
Element
Made of only one
type of atoms
Compound
Made of two or more
elements chemicallybonded together in
fixed ratio
Monoatomic
Diatomic
Ex. Inert gases
Ex. Cl2, H2, O2
 N.B.
➢ Impurity is the unwanted substance, mixed with the substance you need.
➢ Medical drugs, water and food flavoring must not contain any impurities that could
harm people (must be safe).
➢ To make sure of the purity of a certain substance, measure its m.p & b.p.
➢ Pure substance has a definite, sharp m.p & b.p.
➢ When the substance has impurities its melting point falls and its b.p rises and both
will be over a range.
➢ The more impurity there is, the bigger the change in m.p and b.p, and the wider the
range over which melting and boiling occur.
IGCSE
Grade (10)
Differences between mixtures and compounds:
Mixture
1- It contains two or more different
substances in any ratio.
2- No chemical change takes place
Compound
1- It is a single substance made of
two or more different elements
chemically bonded in a definite
ratio.
2- Involves a chemical change.
3- The components can be separated
by physical means
3- The components can be separated
by chemical means.
4- Keeps the properties of their
components.
4- Its properties are different from
those of its components.
5- No change in energy when the
mixture is formed.
5- Energy is given out or absorbed
6- Ex. Fe / S
6- Ex. FeS
“Types of Mixtures”
(1) Solid / Liquid Mixture.
(2) Liquid / Liquid Mixture.
(3) Gas / Gas Mixture.
(4) Solid / Solid Mixture.
 How to separate the components of a mixture?
(1)
Solid / Liquid Mixture
Soluble
1) Evaporation.
2) Simple distillation.
3) Crystallization
Insoluble
1) Decantation:
- Pouring the liquid off the insoluble substance
[big particles]
2) Filtration:
- Sand & Water [small particles]
3) Centrifugation:
- The sample is spun round very fast and the solid is
flung to the bottom of the tube [tiny particles (blood)]
IGCSE
Grade (10)
Solution (salty water) = Solute (table salt) + Solvent (water)
• Solution: is a mixture of solute and solvent.
• Solute: is the substance that dissolves in solvent to form solution.
• Solvent: is the substance that used to dissolve the solute [Ex. water , ethanol]
Solutions can be either:
• Diluted solution: Small amount of solute / 1 dm3 solution.
• Concentrated solution: Large amount of solute / 1 dm3 solution.
• Saturated solution: Formed when no more solute can dissolve in the solution
at a certain temperature.
• Solubility: is the maximum amount of solute in gram which dissolves in 100 g of
solvent at a given temperature.
Solubility curve:
These are curves that show how the solubility of a solid changes with temperature
At 20 oC the solubility of KNO3 is 32 g / 100 g water.
At 60 oC the solubility of KNO3 is 110 g / 100 g water.
Dissolving increases by:
1. Heating
2. Stirring
3. Crushing the solute [large surface area]
N.B. Solubility of gases in liquids decreases by heating
IGCSE
Grade (10)
1) Evaporation:
The solution is boiled till dryness to evaporate the solvent, the powder solid is left
behind.
2) Simple distillation:
- A way to obtain the solvent from a solution.
- The solution is heated till it boils, turns to vapour, and rises into the condenser.
- The solvent is condensed back to a pure liquid and collected, the salt is left behind.
3) Crystallization:
Heat till point of crystallization. Leave to cool, filter and dry between two filter paper.
IGCSE
Grade (10)
 N.B.
➢ Saturated solution must be left at room temperature to cool down ,to get large
crystals
➢ Do not:
1. stir
2. put in refrigerator
1) Decantation: [big particles]
- Pouring the liquid off the insoluble solid.
2) Filtration:
[smaller particles]
• Residue is a substance that remains after filtration,
evaporation or distillation.
• Filtrate is a liquid r solution that has passed
through a filter
• Filter off the insoluble solid. Rinse with distilled water
to remove the soluble substance.
3) Centrifugation:
[very small particles]
- The sample is spun round very fast and the solid is flung to the bottom of the tube.
IGCSE
Grade (10)
(2)
Liquid / Liquid Mixture
Immiscible liquids
Miscible liquids
- They do not mix easily.
- They are uniformally mixed.
- They are separated using separating
- Their
separation
depends
on
funnel according to the difference in
difference in boiling point. (Ex. water
their densities. (Ex. oil & water)
& ethanol)
[by fractional distillation]
Fractional Distillation
- Used to separate liquids with different b.p.
- The liquid with the least b.p distills first.
Uses of frictional distillation:
1. To separate liquids from each other.
2. To separate fractions of crude oil.
3. To separate gases such as nitrogen from liquid air, the gases boil off one by one.
IGCSE
Grade (10)
(3)
Gas / Gas Mixture
• Air is a mixture of gases; its components can be separated by fractional distillation of
liquid air.
• Air is liquefied by applying high pressure and low temperature, then allowed to warm
up :
Nitrogen boils first at -196 o C.
Argon boils second at -186 o C.
Oxygen boils third at – 183o C.
• Diffusion as a less dens gas diffuses faster, ex. H2 and CO2
(4) Solid / Solid Mixture
• By magnet [magnetic property]:
Ex. (Fe , Co , Ni)
- Iron /sulfur mixture can be separated by magnet.
• Solvent extraction [solubility]:
Ex. (sand / table salt)
Steps:
* crush the mixture
* add water
* stir with gentle heating
* filter
((Filter))
Filtrate
Residue (sand)
- Heat the filtrate till crystallization point, leave to cool to get crystals or
- Evaporate the filtrate till dryness to get powder
- Mixture of salt and sugar can be separated by dissolving in ethanol (water dissolves
both). Sugar dissolves in ethanol but not salt. Ethanol is flammable, so should be
evaporated on water bath.
IGCSE
Grade (10)
Chromatography:
- Used to separate a mixture of substances [in small amount].
 N.B.
1. Draw the base line in pencil which does not produce spots (ink is not used as it
leaves spots).
2. Apply the spot on the base line, and put the paper in the solvent such that its level is 2
cm below the base line
3. Leave till the solvent reaches near the end of the paper, remove it and dry
4. If the spot is from one substance, it will leave one spot.
The use of chromatography :
1. Testing for the purity of substances.
2. Discover the substances present.
3. In medical labs.
The separation by chromatography is due to:
1. Different solubility of the components in the solvent.
2. Different degree of diffusion through the chromatogram paper (capillarity).
IGCSE
Grade (10)
• Number of spots = Number of components
• Proteins separate to amino acids and carbohydrates separate to glucose sugar, both
are colourless, so we spray the spots with locating agent to make them visible.
• To identify the spots ,we refer to control or calculate the flow rate Rf (retention
factor)
Y
X
Distance moved by the substance
Rf =
<1
Distance moved by the solvent
Rf
X
= ---Y
IGCSE
Grade (10)
Using Rf values to identify components of a mixture
N. B. To get a chromatogram of chlorophyll follow the following steps:
1. Crush small pieces of green leaves with sand to increase friction and get more extract
2. Add ethanol to dissolve chlorophyll then filter
3. Concentrate the solution over water bath as ethanol is flammable
4. Run chromatography you will get two spots