1) States of Matter and Mixtures

Question 1

whats it called when you change a solid to a liquid?

Answer 1

melting

Question 2

whats it called when you change a liquid to a solid?

Answer 2

freezing

Question 3

whats it called when you change a liquid to a gas?

Answer 3

evaporating

Question 4

whats it called when you change a gas to a liquid?

Answer 4

condensing

Question 5

whats it called when you change a solid to a gas?

Answer 5

subliming

Question 6

why are chemical changes different to physical changes?

Answer 6

• bonds break

- substances change to form different products

Question 7

what is a pure substance?

Answer 7

substance completely made up of a single element

Question 8

what are mixtures?

Answer 8

substance with different elements like air

Question 9

how can you use melting points test for purity?

Answer 9

• pure substances have specific melting points

- if a mixture it ill all melt at different points

Question 10

how does simple distillation work?

Answer 10

1. poor sample into sibilation flask
2. heat
3. lowest boiling point will evaporate first into condenser
4. and collect in beaker
5. good fo separating seawater

Question 11

how does fractional distillation work?

Answer 11

1. mixture in flask
2. attach fractionating column
3. heat
4. different substances will boil at different points
5. collect in testtubes

Question 12

how does filtration work?

Answer 12

1. place filter paper in funnel
2. let run though
3. leaving solid residue

Question 13

how crystalisastion work?

Answer 13

1. put solution in evaporating dish
2. heat, water will evaporate
3. once crystals start to form, remove from heat
4. cool, more crystals will form
5. filter crystals out of solution

Question 14

how does paper chromatography work?

Answer 14

1. draw line at bottom of paper and add drop of mixture
2. put solvent into beaker, add paper but spot not touching solvent
3. allow solvent to move up and separate out different chemicals

Question 15

what will happen to pure substances in paper chromatography?

Answer 15

-wont sepoate, stay together

Question 16

what is the Rf value?

Answer 16

ratio between the distance travelled by the dissolved substance

Question 17

how do you calculate the Rf value?

Answer 17

distance travelled by solute / distance travelled by solvent

Question 18

how would you investigate the composition of inks using simple distillation and paper chromatography?

Answer 18

1. ink is different dyes in a solvent
2. use simple distillate to evaporate the solvent
3. carry out paper chromatography on remaining in to separate dyes
4. compare Rf values

Question 19

how can waste and ground water be made portable?

Answer 19

• filtrate
• sedimentation- iro sulphate added to make small particles clump together and sink
• chlorination- chlorine gas toil bacteria

Question 20

how can sea water be made portable?

Answer 20

• distilling

- used in poorer countries

Question 21

why in chemistry must water be deionised?

Answer 21

• take out ions like calcium

- small quantities, but still give experiments false results