12 - Experimental Techniques & Chemical analysis Flashcards
Def. Physical Property
Characteristic of a substance that can be measured or observed without changing the substance
What are the main physical properties?
- Melting point
- Boiling point
- Colour
- Solubility in water
- Solubility in another solvent
- Rf value
- Density
- Hardness
- Malleability
- Thermal and electrical conductivity
Describe simple distillation
A process used to separate the solvent from a solute in a solution.
In the process of simple distillation, a solution is heated and when the water has enough energy to evaporate to steam, the steam passes through a condenser.
The steam is cooled and condenses. The distillate drips through the delivery tube to the beaker.
Generally, the solvent is distilated from the solute, but this is not always the case.
Compare the characteristics of water and ethanol
Ethanol
- Flammable
- Boils at 78 degrees celcius
- Density ~0.8gcm-3
Water
- Not flammable
- Boils at 100 degrees celcius
- Density ~1.0gcm-3
What are the chemical tests for water?
- Recognition that water boils at 100 degrees celcius
- Blue Cobalt Chloride Paper (CoCl2) that turns pink in the presence of water
- White anhydrous Copper Sulfate (CuSO4) that turns blue in the presence of water
Describe Fractional distillation
A process used to separate mixtures of liquids with different boiling points.
It is similar to simple distillation, but has a fractionating column allow only one liquid to evaporate and continue through the apparatus.
Each liquid is called a ‘fraction’.
Def. Pure Substance
A pure substance particles of the same formula.
It can be an element or a compound.
A formula can be written for the substance
The impure substance is called a mixture
What determines where a substance will appear on a piece of chromatography paper?
The solubility of the substance.
The more soluble, the higher up the chromatography paper it will go.
What 2 pure substances are you required to know and why is their purity important?
1) Food Additives - To not prokoke allergies
2) Drugs in medecine - To not produce side effects
Describe how chromatography works
1) Draw a pencil line at the bottom a a peice of chromatography paper
2) Put a spot of the dye/substance you want to test on the line
3) Place the bottom of the paper in water or another solution e.g. salt solution
4) Let the solution dissolve the substance as it rises, and wash the substances up the piece of chromatography paper
Why do dyes move up the chromatography paper in the process of chromatography?
Because the solution soaks the dyes up, dissolves them and carries them up the paper.
What is the result from chromatography called?
A Chromatogram
What do you use to detect colourless substances in chromatography?
Using a locating agent
What does Rf Value stand for in chromatography?
Retention Factor Value
Def. Rf Value
The ratio of the distance travelled by a spot (solute) over the distance travelled by the solvent.
What is the formula for the Rf Value?
Rf = Distance travelled by solute/Distance travelled by Solvent
Why do different metals, when burnt, emit different coloured flames?
Because of the different electron shells. As the metal is heated, the electrons move arounsd and emit light.
What is the colour of Copper when burnt?
Blue-Green
What is the colour of Potassium when burnt?
Lilac
What is the colour of Barium when burnt?
Light green
What is the colour of Sodium when burnt?
Yellow
What is the colour of Calcium when burnt?
Orange-red
What is the colour of Lithium when burnt?
Red
What is the test for Oxygen?
Test with glowing splint, positive if flame relights
