Chapter+6

Separating Mixtures Mixtures can be separated into their constituents by using **physical methods** (i.e. no chemical reaction involved). Separation techniques are physical methods. Which technique to use depends on the different properties of the constituents. That is, different states, solubility, boiling and melting points. Below lists some of the most common separation techniques:

**// Some of the example mixtures that can be separated using the above mentioned techniques:
 * **// Chromatography - To separate different coloured dyes. The dyes travel up the chromatography paper at different distances before they cannot remain in solution. The more soluble dyes move further up than the less soluble ones, hence separating from each other. //**
 * **// Distillation - to separate and collect a liquid from a solution of a soluble solid. The solution is heated in a flask until the liquid boils. The vapour produced passes into the condenser where it is cooled and condenses to a liquid. The pure liquid (distillate) is collected in a beaker. //**
 * **// Evaporation - This method is suitable to separate a soluble solid from a liquid. If the solution is heated, the liquid evaporates leaving the solid behind. //**
 * **// Fractional Distillation - This is a special type of distillation used to separate a mixture of liquids. Different liquids boil at different temperatures. When heated, they boil off and condense at different times. The apparatus features a fractionating column, which ensures that only the liquid boils at its boiling point will pass into the condenser. //**
 * **// Filtration - To separate an insoluble solid from a liquid. The solid remains in the filter paper and the liquid goes through the paper into the beaker. //**

(1) separating dyes in inks, or chlorophyll in plants (ethanol as solvent) - chromatography;

(2) separating sand from water - filtration;

(3) separating ethanol and water - fractional distillation;

(4) separating water from ink - simple distillation;

(5) separating salt from water - evaporation //** Click here for the powerpoint:


 * Separating Mixtures **

Imagine you have a box of plastic counters. Some of them are green, some blue, some red and some yellow. If each counter represented a different substance we would say we had a **mixture .**
 * 1) [|**Using a sieve**]
 * 2) **[|Using a magnet]**
 * 3) **[|Filtration]**
 * 4) **[|Evaporation]**

We have a mixture when there is more than one substance in our container.
 * Example**: muddy water would be a mixture  .  It countains  ** mud ** **  __and__   water  **

How can I separate my mixture? Well, if we had counters it would be easy. We would tip them all out of the box and arrange them into four piles: green counters, blue counters, red counters and yellow counters With real substances it is more difficult to separate them.

We can make water water clean by pouring it through a **filter**. The particles of mud get stuck in the holes and clear water drips through. Four ways to separating a mixture
 * Example:**

1. Using a sieve A sieve is used to separate small solid particles from larger ones.
 * [[image:http://www.mikecurtis.org.uk/images/sieve.gif width="300" height="200"]] || Example: using a sieve to sparate gravel (small pebbles) from sand

A sieve is a shallow tray with holes in. The mixture is placed in the sieve which is then shaken from side to side. The sand particles are much smaller than the gravel so fall though the holes in the sieve. || Using a sieve to separate sand from pebbles. **2. Using a magnet** Separates **magnetic** substances (eg substances containing **iron**) from non-magnetic substances. Using a magnet to separate iron filings from sand **3. Filtering** Filtering is used to separate small solid particles from a liquid
 * [[image:http://www.mikecurtis.org.uk/images/magnet.gif width="324" height="187"]] || **Example: separating iron filings from sand**
 * Picture 1**: we have a mixture of iron filings and sand on a piece of paper
 * Picture 2**: When a magnet is slowly pulled away from the mixture the iron sticks to the magnet leaving the sand behind ||
 * [[image:http://www.mikecurtis.org.uk/images/filter1.gif width="320" height="291"]] || Example: Separating dirt from water by filtering

The dirty water is poured through a piece of filter paper. Water particles pass through the tiny holes in the filter paper. The particles of dirt, which are larger than the particles of water, get stuck in the holes and do not get through. When the process is finished the dirt is trapped in the filter paper and the clear water has dripped through into the beaker below. Any liquid that has been filtered is known as a filtrate || Using filter paper to remove dirt from water . **4. Evaporation** Evaporation is used when we want to get back a substance that has been dissolved The salty water is put into an evaporating basin (or any shallow dish such as a saucer). It is left in a warm place and the water evaporates leaving behind the salt crystals. We see the salt crystals starting to form at the edge of the salty water but eventually all the water would go, leaving behind just the salt. || Evaporating water from salty water to get the salt Pure Substance When we have only one substance, for example just blue counters, we say that it is pure. Perfectly clean water is pure because it contains **only** water Salty water is a mixture because it contains salt **and** water.
 * [[image:http://www.mikecurtis.org.uk/images/evaporation.gif width="259" height="154"]] || Example: Getting salt out of salty water

** FRACTIONAL DISTILLATION THEORY ** :

Imagine green liquid is a mixture of a blue liquid (boiling point 80oC) and a yellow liquid (boiling point 100oC), so we have a coloured diagram simulation of a colourless alcohol and water mixture! As the vapour from the boiling mixture enters the fractionating column it begins to cool and condense. The highest boiling or least volatile liquid tends to condense more i.e. the yellow liquid (water). The lower boiling more volatile blue liquid gets further up the column. Gradually up the column the blue and yellow separate from each other so that yellow condenses back into the flask and pure blue distils over to be collected. The 1st liquid, the lowest boiling point, is called the 1st fraction and each liquid distils over when the top of the column reaches its particular boiling point to give the 2nd, 3rd fraction etc. In the **distillation of crude oil** the different fractions are condensed out at different points in a huge fractionating column. At the top are the very low boiling fuel gases like butane and at the bottom are the high boiling big molecules of waxes and tar.
 * To increase the separation efficiency of the tall fractionating column **, it is usually packed with glass beads, short glass tubes or glass rings etc. which greatly increase the surface area for evaporation and condensation.

(1) The liquid or solution mixture is **boiled to vaporise** the most volatile component in the mixture (**liquid** ==> **gas**). The ant-bumping granules give a smoother boiling action. (2) The vapour passes up through a **fractionating column**, where the separation takes place (theory at the end). This column is not used in the simple distillation described above. (3) The vapour is cooled by cold water in the condenser to **condense** (**gas** ==> **liquid**) it back to a liquid (the distillate) which is collected. This can be used **to separate alcohol from a fermented sugar solution**. It is used on a large scale **to separate the components of crude oil**, because the different hydrocarbons have different boiling and condensation points
 * Fractional distillation** involves 2 main stages and both are physical state changes. **It can only work with liquids with different boiling points**. However, this method only works if all the liquids in the mixture are miscible (e.g. alcohol/water, crude oil etc.) and do NOT separate out into layers like oil/water.

Click here for a video on a distillation tower: []