Methods Of Separating And Purifying Substances Flashcards
What is a pure substance?
A substance made up of only one element or compound
What is a mixture?
A substance with more than one compound or different elements mixed together
What does every pure substance have?
A specific melting and boiling point
How can you test purity?
Record he boiling points of the substance. If it is always the same it is pure
What is distillation used for?
Separating mixtures that contain liquids
How do you do simple distillation?
Pour the mixture into the distillation flask.
Connect the bottom of the condenser to a cold tap and run cold water through it.
Gradually heat the distillation flask, the part of the mixture that has the lowest boiling point will evaporate.
The gas created passes through the condenser and turns back to a liquid into the beaker to be collected.
How do you do fractional distillation?
Pour your mixture in a flask and attach the fractionating column above the flask.
Gradually heat the flask, the different liquids will have different boiling points so they will evaporate at different temperatures.
The liquid with the lowest boiling point will evaporate first. When the temperature on the thermometer matches the boiling point of this liquid it will reach the top.
The liquids with higher boiling points may also start to evaporate but the top of the column is cooler so it will condense back into the flask.
When the first liquid has been collected, raise the temperature until the next one reaches the top.
What is filtration used for?
Separating an insoluble solid from a liquid
How do you do filtration?
Put some filter paper in a funnel and pour the mixture through. The solid will stay on the paper and the liquid will run through
What is crystallisation used for?
Separating a soluble solid from a solution
How do you do crystallisation?
Pour the solution into an evaporating dish and heat gently.
Once some of the water has evaporated or you start to see crystals remove the dish from the heat and let it cool.
The salt should start to form crystals.
Filter the crystals out of the solution and leave in a warm place to dry.
What is chromatography used for?
Separating a mixture of soluble substances and identifying them
What are the two phases in chromatography?
A mobile phase - where the molecules can move. This is always an liquid or a gas.
A stationary phase - where the molecules can’t move. This can be a solid or a really thick liquid.
What happens in chromatography?
The components in the mixture separate out as the mobile phase moves over the stationary phase. They all end up is different places in the stationary phase.
This happens because each of the chemicals in a mixture will spend different amounts of time dissolved in the mobile phase and stuck to the stationary phase.
How do you do paper chromatography?
Draw a line near the bottom of the paper using a pencil and pencil marks are insoluble, this is the baseline.
Put a spot of the mixture on the baseline.
Put some solvent in the beaker and dip the paper in but not the spot.
Put a watch glass on top of the beaker to stop any solvent from evaporating away.
The solvent will start to move up the paper. When the chemicals in the mixture dissolve they will start to moe up the paper as well.
You will see the different chemicals in the sample separate out forming spots at different places on the paper.
Remove the paper from the beaker before the solvent reaches the top.
Mark the distance the solvent has moved in pencil, this is the solvent front.
