separating substances

Question 1

what is it called when a substance goes straight from a solid to a gas

Answer 1

sublimation

Question 2

what is it called when a substance goes straight from a gas to a solid

Answer 2

deposition

Question 3

what is a physical change

Answer 3

physical changes can be reversed as the particles do not change but the arrangement and movement and amount of stored energy does, the chemical properties stay the same

Question 4

what is lost when a solid is heated

Answer 4

attractive forces

Question 5

how do tell apart the melting point of an impure substance and a pure substance

Answer 5

pure has a sharp clear melting point, a mixture doesn’t

Question 6

solution =

Answer 6

solute + solvent

Question 7

what is a mixture

Answer 7

contains elements/compounds that aren’t chemically bonded, doesn’t have a fixed composition and can be separated through physical processes

Question 8

why will a pure substance have a sharp melting point

Answer 8

because it has the same composition in every part of the substance, its physical properties are the same all throughout it

Question 9

how do filters separate mixtures

Answer 9

they let smaller pieces of liquids through but trap insoluble substances

Question 10

what are some examples of filters

Answer 10

coffee maker, cars, vacuum cleaners, air conditioning

Question 11

what is a saturated solution

Answer 11

contains the maximum amount of solute that can be dissolved by the solvent at that temperature

Question 12

how do salt crystals form from a saturated solution

Answer 12

if more water evaporates or the solution cools

Question 13

what is a filtrate and residue

Answer 13

filtrate = the solvent and solute that pass through the filter's fine holes
residue = bits of insoluble substances that cannot fit through the tiny holes in the filter paper

Question 14

what are some bad things that could come from overheating the filtrate during crytalisation

Answer 14

hot crystals may spit out

crystals may change chemically

Question 15

what’s the difference between a risk and a hazard

Answer 15

hazard = something that could cause harm
risk = chance of a hazard causing harm

Question 16

why does the temperature stay the same at the melting and boiling point?

Answer 16

the substance is still being heated but the added energy is making the particles break away from their fixed arrangement

Question 17

in paper chromatography, what ink would be carried further up the paper

Answer 17

the more soluble ink molecules

Question 18

why does paper chromatography work

Answer 18

because the different inks in a mixture all dissolve to different extents in the solvent, the more attracted the ink is to the paper the less high it will travel up the paper leading the different inks to spread out (separate)

Question 19

what is the mobile phase and the stationary phase in paper chromatography

Answer 19

paper = stationary phase
solvent = mobile phase

Question 20

what number is Rf value always below

Answer 20

1

Question 21

how do you calculate Rf value

Answer 21

distance travelled by spot / distance travelled by solvent

Question 22

what can paper chromatography be used for

Answer 22

identifying substances at crime scenes

distinguishing between pure and impure substances

Question 23

what does distillation do

Answer 23

makes a substance pure

Question 24

how do simple distillation and fractional distillation differ

Answer 24

simple separates a liquid from minerals and dissolved or solid substances
fractional separates two liquids that have different boiling points

Question 25

what do anti-bumping granules do

Answer 25

make the liquid boil smoothly, reduce the risk of boiling over, small bubbles of the vapour form on the corners of the granules

Question 26

what is a distillate

Answer 26

the pure substance that is the result of distillation

Question 27

what is the temperature gradient in a fractionating column

Answer 27

hotter at the bottom and gets cooler at the top

Question 28

why do fractions with a lower boiling point reach the top of the fractionating column first

Answer 28

it is cooler at the top of the column, when the column is still warming up, fractions with high boiling points would condense back to liquid when they reach the cooler top of the column whereas a lower boiling point means it could stay as a gas even at the cool top

Question 29

why is the starting line draw in pencil on a chromatogram

Answer 29

because pencil is insoluble so it won’t travel up the paper

Question 30

where abouts on the ink dot do you measure from in paper chromatography

Answer 30

the middle of the dot

Question 31

what is producing pure water from sea water called

Answer 31

desalination

Question 32

what is the order of treating fresh water to make it drinking safe

Answer 32

screening with a sieve
sedimentation for small particles to settle
filtration in a filtration tower, beds of sand and gravel
chlorination to kill bacteria

Question 33

what does the amount of energy needed for a substance to change state depend on

Answer 33

the strength of the forces between particles

Question 34

why is there a thermometer in simple distillation

Answer 34

to make sure the highest boiling point is not exceeded as then both liquids would boil and they wouldn’t get separated