C12 Flashcards
What is a pure substance
A pure substance is a substance that is not mixed with any other substance ( it can be an element or a compound)
What are the differences between the melting and boiling points of pure and impure substances
- Pure substances have a specific fixed melting and bioling point
- Impure substances melt and boil over a range of temperatures
How can you tell wether a substance is pure or impure
You can tell wether a substance is pure or impure by loooking at its melting and boiling point
- It it melts and boils at specific temperatures it is a pure substance
- If it melts and boils over a range of temperatures it is a impure substance
What is a formulation
- A formulation is a complex mixture that has been designed as a useful product
- In a formulation the quantity of each component is carefully measured out so the product has the properties we need
- Formulations include fuels , medicine , food
How do you conduct a chromatography experiment
- Take a sample of unkown food colouring that is a mixture of colourings , label it U for unknown
- Take 4 smaples of known food colourings it could contain
- Use a ruler to draw a horizontal PENCIL line at the bottom of the chromatography paper (2cm from the bottom)
- Mark 5 pencil spots on the line (1cm between each one)
- Use a capillary tube to put a small spot of each known food colouring and the unkown food colouring(each colouring must have only spot) on the pencil spots. ~keep the spots small as this prevents the colours spreading into each other
- pour solvent into beaker at a depth of 1cm from the bottom
- Attach the chromatography paper to a glass rod using tape and lower the paper into the beaker . NOTE:the bottom of the paper should dip into the solvent but the pencil line with the spots must be above the water as the solvent will wash the ink off if not
- The sides of the paper must not touch the sides of the beaker as this will interfere with the way the solvent moves. Also put a lid on the beaker to prevent the solvent evaporating
- The solvent will move up the paper and the colours will be carried up
- Remove the chromatography paper when the solvent has travelled 3/4 of the way up the paper. Mark where the water has gone up to
- Hang the chromatography paper up to dry
How can you find out what food colourings where in the unknown one
-Compare the spots the unkown colour has seperated into with the other spots of the known food colourings to determien which colurorings the unknown one is a mixture of
How can you test the chemicals in a substance
To work out the chemicals in a substance (e.g food colouring) in paper chromatography you have to work out the Rf value
What is the equation to work out Rf value
To work out Rf value you have to do - Distance travelled by substance/ Distance travelled by solvent
Rf value has no units
- The distance travelled by the substance is the distance between the pencil line at the bottom of the chromatogram and the centre of the spot of substance
- The distance travveled by the solvent is the distance the solvent has moved from the pencil line
How do you then work out what chemical it is from the Rf value
- Look up the Rf value on a database to tell you the identity of the chemical
- There may be multiple chemicals with the same Rf value , if this is the case you will have to conduct the experiment again with a differnt solvent to find out the chemical
- If there are no chemicals matching the rf value then further analysis will have to be done
What can you do to test for hydrogen
- To test for hydrogen insert a burning splint into a test tube possibly containing hydrogen gas
- If it is hydrogen gas it will produce a pop sound as hydrogen burns rapidly
How can you test for oxygen
- To test for oxygen gas insert a glowing splint into a test tube possibly containing oxygen
- If the gas is oxygen the splint will relight as there is a plentiful supply of oxygen in the test tube
How can you test for carbon dioxide
To test for carbon dioxide you need limewater. Limewater is an aqueous solution of calcium hydroxide
-Draw some of the gas in the test tube (that is possibly carbon dioxide) into a pippete. Bubble the gas through the limewater in the other test tube . If the gas is carbon dioxide the limewater should turn cloudy /murky
How do you test for chlorine gas
To test for chlorine insert a peice of damp litmus paper into the mouth of a test tube possibly containing chlorine gas
-If chlorine gas is present then it will bleach the limtus paper so the litmus paper will turn colourless. This will happen because chlorine is a bleach
How do you calculate Rf value
Rf = distance travelled by spot of substance / distance travelled by solvent
Why does the limewater turn murky when carbon dioxide is bubbled through it
The limewater turns murky as the carbon dioxide and the limewater react to form chalk which turns it cloudy
