chem seperation techniques
whats an element
a pure substance made of only one type of atom
what is a compound
a substance formed when two or more elements are chemically bonded together
what is a mixture
contains two or more substances that are not chemically bonded, can be seperated using seperation techniques
describe the melting/boiling point of a pure substance
they have a sharp, fixed point
what will happen to the melting point if the substance is impure
it will be lower and the substance will melt over a broad range of temperatures
what will happen to a substance's melting point if it is pure
it will melt sharply at a specific temp
what will happen to the boiling point if a substance is impure
it will be higher than the pure substance
when do you use simple distillation and when does it work
when you want to get a pure liquid from a solution, two liquids when the substances have VERY different boiling points
describe the process of simple distillation
1. the liquid w the lowest boiling point evaporates first 2. the liquid turns into a gas and rises 3. the gas travels through a condenser, which is kept cool with cold water 4. the gas turns back into a liquid 5. the pure liquid drips out into a beaker
when would fractional distillation be used
to seperate two or more liquids with similar boiling points
describe the process of fractional distillation
1. the mixture is heated in a flask and the liquid w the lowest boiling point evaporates first 2. the vapour enters the fractioning column which is hot at the bottom and cool at the top 3. inside the column, vapours repeatedly condense and evaporate on the surfaces of beads/plates. liquids w higher boiling points condense and fall back down the coloumn 4. only the vapour with the lowest boiling point can reach the top of the column, because it can remain as a gas at the cooler temps higher up 5. the vapour is then passed into a condenser, where it is cooled and condensed back into a liquid 6. the liquid is collected as a pure fraction and the temp can be increased to collect the next liquid.
when would filtration be used
to seperate an insoluble solid from a liquid
describe the process of filtration
1. a piece of filter paper is placed over a funnel 2. the funnel is positioned over a conical flask 3. the mixture of solid and liquid is poured over the filter paper 4. the liquid passes through the filter paper and is called the filtrate 5. the insoluble solid is trapped and called the residue
when is crystallisation used
to obtain pure, solid crystals from a solution
describe the process of crystallisation
1. heat the solution gently to evaporate some solvent and make it more concertrated 2. stop heating when crystals form - this is called a saturated solution 3. as the solution cools, pure crystals form 4. collect the crystals/filter if necessary
when is chromotography used
to seperate/identify diff dyes/pigments in a mixture
describe the process of chromotography
1. draw a pencil line near the bottom of the paper 2. place a small spot of mixture on the line 3. put the paper into a solvent making sure it is not submerged 4. as the solvent moves upwards, it carries the diff dyes w it
when a substance is more soluble, does it move farther or not
farther
Rf value formula
distance moved by substance/distance moved by solvent