Elements Compounds And Mixtures Flashcards
What is an element
A substance that consists of one type of atom only
It cannot be broken down into any other substance
What is a compound
A substance that is made up of two or more different elements which are chemically bonded together
Ie carbon dioxide
What is a mixture
A substance that is made of two or more different substances which have no chemical bond between its different parts - it can be separated out easily
Pure substance
Definition
Completely made up of a single element or compound
Pure substance
Quality / property
- each pure susbstance has a SPECIFIC MELTING POINT and BOILING POINT
Is a mixture pure
No
It will melt or boil gradually over a range of temperatures
Give (5) techniques for separating mixtures
Simple distillation Fractional distillation Filtration Crystallisation Paper chromatography
Describe simple distillation
Used for
Method
Problem
Used for:
Separating out a liquid from a solution
Method:
- solution is heated.
- part of solution with lowest boiling point evaporates
- vapour is cooled, condenses and is collected
- rest of solution is left behind in flask
Problem:
Only use it to separate substances with different boiling points
Condenses meaning
Turns back into liquid
Describe fractional distillation
Used
Method
Used:
When there is a mixture of liquids with similar boiling points that need to be separated
Method:
- put mixture in flask and put a fractionating column on top
- heat it
- different liquids will evaporate at different temperatures
- liquid with lowest boiling point evaporated first.
- when the temperature on the thermometer matches the boiling point of this liquid it will reach top of column
- liquids with higher boiling points might also start to evaporate
- but column is cooler towards the top so they will only get part of the way up before condensing and running back down the flask
- when the first liquid has been collected you raise the temperature until the next reaches the top
Describe filtration
Used
Method
Used:
Separate insoluble solid from a liquid
Method:
- put some filter paper into a funnel and put onto beaker
- pour mixture into filtered funnel
- liquid part of mixture runs through paper, leaving behind solid residue
Describe crystallisation
Used for
Method
Used for:
Separating a soluble solid from a solution
Method:
- pour solution into an evaporating dish and gently heat the solution
- some of the water will evaporate and the solution will get more concentrated
- once some of the water has evaporated or when you see crystals start to form remove dish from heat and leave solution to cool
- the salt should start to form crystals as it becomes insoluble in the cold highly concentrated solution
- filter the crystals out of solution and leave in a warm place to dry
Describe Chromatography
Used for:
Separating out dyes
Method:
- draw line near bottom of a sheet of filter paper (baseline) using pencil
- add spots of different inks to the baseline at regular intervals
- put bottom edge (just below baseline) in a beaker of solvent ie water
- place a lid on the container to stop solvent evaporating
- solvent seeps up paper carrying the inks with it
- each different dye in the inks will move up paper at a different rate and form a spot in different place
- when solvent has nearly reached top of paper take paper out of beaker and leave to dry
- end result is called chromatogram
How does a chromatogram provide information about composition of a mixture
- works because different dyes will move up the paper at different rates
- some will stick to the paper and others will dissolve more readily in the solvent and travel more quickly
- the distance the dyes travel up the paper depends on the solvent and the paper you use
How to calculate Rf value for each component of the mixture
Formula
Formula:
distance travelled by solute Rf = —————————————
distance travelled by solvent
