seperation technique

• Describe what happens in paper chromotography ?

  This technique can be used to seperate different dyes in ink

  
  

  1) draw a line near the bottom of a sheet of filter paper

  (use a pencil to do this-pencil marks are insoluble and won't dissolve ina solvent)

  2) add a spot of ink to the line and place the sheet in a beaker of solvent eg) water

  3) the solvent used depends on what's being tested. Some compounds dissolve in water, but sometimes other solvent like ethanol are needed

  4) make sure the ink isn't touching the solvent - you don't want it to dissolve into it

  5) place a lid on top of the container to stop the solvent from evaporating

  6) the solvent seeps up the paper, carrying the ink with it

  7) each different dye in the ink will move up the paper at a different rate so the dyes will seperate out.

  8) if any dyes in the ink are insoluble (won't dissolve) in the solvent you've used, they'll stay on the baseline

  9) when the solvent has nearly reached the top of the paper take the paper out of thed beaker and leave it to dry

  10) the end result is a pattern of spots called chromatogram
• Describe what happens in filtration ?

  filtration seperates insoluble solids from liquids

  filter paper is folded into a cone shape- the solid is left in the filter paper
• Which two ways can you seperate soluble solids from solutions?

  evaporation

  crystalisation
• How would u perform evaporation? (seperation technique)

  1) pour the solution into an evaporating dish

  2)slowly heat the solution. The solvent will evaporate and the solution will get more concentrated. Eventually crysals will start to form

  3) Keep heating the evaporating dish until all you have left are dry crystals
• When would u use crystallisation?

  you can only use evaporation if the salt doesn't decompose when it's heated. otherwise you will need to use crystallisation
• how do u perfom cytallisation?

  1) pour the solution into an evaporating dish and gently heat the solution. Some solvent will evaporate and the solution will get more concentrated

  2) once some of the solevent has evaporated or when you see crystals start to form, remove the dish from the heat and leave the solution to cool

  3) the salt should start to form crystals as it becomes insolube in the cold, higly concentrated solution

  4) filter the crystals and leave them in a warm place to dry. you could leave them in a dry oven
• how would u seperate rock salt?

  rock salt is a mixture of salt and sand

  salt and sand are both compounds- but salt dissloves in water and sand doesn't

  vital difference in there physical properties give a great way to seperate them

  1) grind the mixture to make sure the salt crystals are small, so will dissolve easily

  2)put the mixture in water and stir. The salt will dissolve and the sand won't

  3) filter the mixture. The grains of sand won't fit through the tiny holes in the filter paper, so they collect on the paper instead. The salt passes through the filter paper as it's part of the solution

  4) Evaporate the water from the salt so that it forms dry crystals - you could also use crystalistation if you wanted to make nice, big crystals
• when would u perform simple distilation?

  simple distillation is ued for seperating out a liquid from a solution
• How would u perform simple distillation?

  1) the solution is heated. The part of the solution that has the lowest boiling point evaporates first

  2) the vapour is cooled, condenses ( turns back into a liquid) and is collected

  3) the rest of the solution is left behind in the flask

  4) you can use simple distillation to get pure water from seawater. the water evaporates and is condensed and collected. eventually you'll end up with just salt left in the flask
• What is the problem with simple distillation ?

  You can only use it to separate things with very different boiling points - if the temperature goes higher than the boiling point of the substance with the highest boiling point, they will mix again
• how would u perform fractional distillation?

  1) you put your mixture in a flask and stick a fractioning column on top. Then you heat it.

  2) the different liquids will all have different boiling points- so they will evaporate at different temperatures

  3) the liquid with the lowest boiling point evaporates first. When the temperature on the thermometer matches the boiling point of this liquid, it will reach the top of the column

  4) liquids with higher boiling points might also start to evaporate, but the column is cooler towards the top so they will only get half way before condensing and running back towards the flask

  5) when the first liquid has been collected, you raise the temp until the next oned reaches the top