Topic 2 Flashcards
(31 cards)
Are the interconversions between the three states of matter a physical change or a chemical change?
A physical
Name the interconversion from solid to liquid and from liquid to solid?
solid to liquid = melting
liquid to solid = freezing
Name the interconversion between liquid to gas and gas to liquid?
Liquid to gas = evaporating
Gas to liquid = condensing
Name the interconversion between solid to gas?
Subliming
What does pure mean in everyday life?
It’s when something is ‘clean’ or ‘natural’
What does pure mean in chemistry?
when a substance is completely made up of a single element or compound
What is it called if a substance contains more than one compound, or different elements that arent part of a single compound?
A mixture
How could you distinguish between a pure substance and a mixture?
Pure substances have sharp melting/boiling points whilst mixtures melt gradually over a range of temperatures
Descrbe how to separate out seawater using simple distillation
1- Pour sample of seawater into distillation flask
2- Connect bottom end of condenser to a cold tap using rubber tubing. Run cold water through condenser
3- Gradually heat flask. The part of the solution that has the lowest boiling point will evaporate e.g. water
4- Water vapour passes into condenser where it cools and turns back into water. It can be collected by a beaker so you’re left with the salt and pure water in separate flasks
Descrbe how to separate out solutions using fractional distillation
1) Put your mixture in a flask. Attach fractionating column and condenser above the flask
2) Gradually heat flask. Different liquids will evaporate at different temps
3) liquid with lowest bp will reach top of column when the temperature on the thermometer matches the boiling point of the liquid
4) other liquids with a higher boiling point might then start to evaporate but column is cooler at the top so they will only get part of the way there before condensing and returning to flask
5) When first liquid has been collected, raise temp until next one reaches the top
When is filtration used?
When you want to separate an insoluble solid from a liquid
When is crystallisation used?
When you want to separate a soluble solid from a solution
Describe how to carry out crystallisation?
1) pour the solution into an evaporating dish and gently heat solution. Some water will evaporate and solution will get more concentrated
2) Once some water has been evaporated, or when you see crystals, remove dish from heat and leave solution to cool
3) filter crystals and leave them in a warm place to dry. Or you could use a drying oven/desiccator to dry them
When is chomotography used?
When you want to separate a mixture of soluble substances
What is the stationary phase in paper chromotography?
The piece of paper
What is the mobile phase in paper chromotography
The solvent
Describe how to carry out paper chromotography?
1- Draw a line near the bottom of the paper IN PENCIL AS PENCIL IS INSOLUBLE)
2- Put some of the solvent (water) into a beaker. Dip the bottom of the paper into the solvent.(NOT THE SPOT)
3- Put a watch glass on the top of the beaker to stop any solvent from evaporating away.
What would you observe in paper chromotography?
1) The solvent and the chemicals that dissolve will move up paper (if on is insoluble it won’t move from baseline).
2) You will see the different chemicals separate out and form spots on the paper
Define RF value
The ratio between the distance travelled by the solute and the distance travelled by the solvent
What is the formula to work out Rf?
Rf = distance travelled by solute/distance travelled by solvent
How would you know if a substance is pure or not, in chromotography?
Pure substances wont be separated by chromotography. (one blob only)
How would you identify a substance by comparing it with a known substance in paper chromotography?
Run a pure sample of a substance that you think might be in your mixture. If the sample has the same Rf value as one of the spots, they’re likely to be the same substance
How can you use distillation and paper chromotography to analyse the composition of ink?
1- use distillation to work out what the solvent in the ink is. You can work out what the solvent is by looking at its boiling point
2- use paper chromotography to separate the different dyes of the ink (and compare different dyes Rf values)
What is surface water?
Water from lakes, rivers and reservoirs
