Separating mixtures

Separating mixtures

1. Dissolving (This section in purple)

   • A common way mixtures are made
   • When you add a solid (solute) to a liquid (solvent)...
     • The bonds holding the solute Particles together sometimes break...
       • The solute Particles then mix with the particles in the liquid forming a solution
         • Solution
           • A mixture of a solute and a solvent that does not separate out.
           • Saturated
             • A solution that won't dissolve any more solute at that temperature
     • Solute
       • The solid being dissolved
       • Solubility
         • A measure of how much solute will dissolve
       • At higher temperatures...
         • more solute will dissolve in the solvent as particles move faster.
           • Some solute won't dissolve in certain solvents.
     • Solvent
       • The liquid its dissolving into
       • If you evaporated off the solvent, you would see the solute again
   • Soluble
     • it will dissolve
   • Insoluble
     • It will not dissolve
   • When salt dissolves...
     • It hasn't vanished, its still there, no mass is lost
   • Solubility
     • Increases with temperature

2. Mixtures (This section in back)

   • Substances not chemically joined up
   • Pure substance
     • Made up of only one type of element or compound. It can't be separated into anything simpler without a chemical reaction
     • example
       • pure water is made up of H2O molecules only. These molecules can't be separated without a chemical reaction.
   • contains two or more different substances. These substances aren't chemically joined up so you can separate them using physical methods.
   • example
     • sea water and air contain several different substances which aren't chemically combined
   • properties
     • Its constituent parts (the parts its made from)

3. The four separation techniques (This section in orange)

   • All four make use of the different properties of the constituent parts to separate them out.
   • Evaporation Distillation Filteration Chromatography
     • Evaporation and Filteration
       • Rock Salt
         • A mixture of salt and sand
           • Salt and sand
             • Both compounds but salt dissolves in water, sand doesn't. This vital difference in the physical properties gives us a great way to separate them
               • Method
                 • 1. Grind the rock salt
                   • 2. Dissolve in a beaker and stir
                     • 3. Filter through filter paper in a funnel
                       • 4. Evaporate in an evaporating dish
                         • You get really big crystals by boiling off half the water then leaving the dish in a warm place to evaporate slowly
             • Sand
               • doesn't dissolve its insoluble so it stays as big grains and these won't fit through the tiny holes in the filter paper so it collects on the filter paper
             • Salt
               • Dissolves in solution so it does go through and when the water's evaporated, the salt forms as crystals in the evaporating dish. This is called crystallisation

4. Chromatography (This section in blue)

   • Ideal for separating dyes in inks
     • Different dyes in ink wash through at different rates
       • Some will stick to the paper and others will dissolve in the solvent and travel through it quickly
   • Method 1
     • 1. Dots of ink are put onto filter paper
       • 2. A wick is cut from part of the paper
         • 3. The solvent washes the dyes through the paper
     • Method 2
       • 1. Put spots of ink onto a pencil baseline on chromatography paper
         • 2. Roll the sheet up and put it in a beaker
           • 3. The solvent seeps up the paper carrying the dyes with it
             • 4. Each different dye will form a spot in a different place
               • 5. You can compare a forged ink to a known ink to see which it is

5. Distillation (This section in green)

   • Simple Distillation
     • Can be used for separating out a mixture of the liquid and a solid. The liquid is heated and boils off
       • Its then cooled, condensed and collected leaving the solid behind.
     • Great for getting pure water from sea water or suspected tap water
   • Fractional Distillation
     • Used for separating a mixture of liquids like crude oil
     • Different liquids will boil off at different temperature around their boiling point
       • Fractionating column
         • Ensures that the wrong liquids condense back down and only the liquid properly boiling at the temperature on the thermometer will make it to the top
           • When each liquid has boiled off, the temperature reading rises until the next fraction starts to boil off
       • A pure chemical substance has fixed melting and boiling points
         • E.g pure water boils at 100C and pure ice melts at 0C
           • These figures are known for a huge range of substances. This helps us to identify unknown substances
             • E.g if a liquid boils at exactly 100C its likely to be pure water
         • Impunities change melting and boiling points.
           • E.g impunities in water cause it to boil above 100C.
             • This means you can test the purity of a substance you've separated from a mixture
     • Examples
       • Distilling whisky
       • Separating crude oil into petrol, diesel and other fuels