Chem - Seperation of mixtures

Seperation of mixtures

1, Separating mixtures is a scientific process in which two or more substances are separated, which were once together. 2. To remove undesirable components
3. To obtain useful components
4. To obtain pure substances from mixtures

Filtration

Undissolved solid from a solid-liquid solution. eg. pure salt from rock salt eg. sand and water
1. Filter paper is placed in a filter funnel above another beaker
2. The mixture is poured into the filter funnel
3. Filter paper only allow small liquid particles to pass through; filtrate
4. Solid particles are too large to pass through the filter paper so will stay behind as a residue

Crystallisation

dissolved solid from a solution, when the solid is more soluble in hot solvent than in cold. eg. copper sulphate from a solution of copper sulphate in water)
1. The solution is heated, allowing the solvent to evaporate and leaving a saturated solution behind. test by dipping a clean dry cold glass rob into the solution
2. If the solution is saturated, crystals will form on the glass rod when it is removed and cooled
3. After cooling, solids will come out of the solution as solubility decreases and crystals will grow.
4. Crystals are collected by filtering, washed with distilled water, allowed to dry

Simple Distillation

Used to separate the liquid from soluble solid in a solution (e.g., water from a solution of sodium chloride or products of fermentation like alcohol and water) or a pure liquid from a mixture of liquids
1. Solution is heated, pure water evaporates producing vapour which rises thru the neck of the round-bottomed flask
2. Vapour passes through condenser surrounded by a water jacket, where it cools and condenses into pure water and collected in a beaker.
3. After all water evaporated, only solid solute will be left behind

Fractional Distillation

Used to separate two or more liquids that are miscible with one another (e.g. ethanol and water from a mixture of the two)
1. Solution is heated to the temperature of the substance with lowest boiling point
2. This substance will rise and evaporate first, pass through the fractionating column then to condenser and condense, turning into a liquid that is collected in a beaker
3. All of the substance is evaporated and collected, leaving behind other components of the mixture.
4. If other components somehow get evaporated, it will condense back due to the cool top of fractionating column and higher boiling point.

Paper chromatography

Used to separate substances that have different solubilities in a given solvent (e.g. different coloured inks that have been mixed to make black ink) The pattern you get is called a chromatogram
1.Draw a line 1 cm above bottom of paper with pencil
2. Use teat pipette or capillary tube to put a spot of the mixture of dyes on the pencil line allow it to dry
3. Suspend the chromatography paper in a beaker that contains solvent below the pencil line
4. Put a lid on the beaker to stop evaporation of solvent
5. When solvent moved until 1cm from the top remove paper and draw a line for highest level of solvent distance; solvent front
6. Leave the paper to dry so all solvent evaporates

Factors affecting distance moved by dyes

1. If it has a high affinity for the paper (how well they stick to the paper)
2. How soluble they are in the solvent.
eg. if a spot doesn’t move, it has high affinity for paper and isn’t soluble in solvent.

Locating agents

Substances which react with the sample to produce a colored product that is visible. Chromatogram is treated with the agent after chromatography.

Retention Factors (Rf values)

Retentian factor = Distance travelled by substance/Distance travelled by Solvent
1. Used to identify components of mixtures.
2. Rf value of a particular compound is always the same
3. Allows chemists to identify unknown substances cuz can be compared with other known Rf values