Elements, compounds and mixtures (checklist)

Question 1

all substances are classified into one of three types :

Answer 1

compounds
mixtures
elements

Question 2

what is an element

Answer 2

A substance made of only one type of atom cannot be split into anything simpler

Question 3

what is a compound

Answer 3

A pure substance made up of two or more elements chemically combined

Question 4

what is a mixture

Answer 4

A combination of two or more substances (elements and/or compounds) that are not chemically combined

Question 5

can mixtures be separated by physical methods

Answer 5

yes, by filtration and evaporation

Question 6

can compounds be separated by physical methods

Answer 6

no

Question 7

example of element

Answer 7

gold, silver, sodium

Question 8

example of a compound

Answer 8

carbon dioxide, sodium chloride

Question 9

example of a mixture

Answer 9

the atmosphere

Question 10

if you have a pure substance, when the melting/boiling point is reached, what happens

Answer 10

the entire substance will melt or boil at the same time

Question 11

a pure substance has a ___ melting/boiling point

Answer 11

fixed

Question 12

when you melt a mixture,

Answer 12

each part gets melted separately

Question 13

a mixture does/doesn’t have a fixed melting / boiling point

Answer 13

doesn’t

Question 14

mixtures melt and boil over a ____ of temperatures

Answer 14

range

Question 15

simple distillation separates

Answer 15

two liquids with different boiling points

Question 16

fractional distillation separates

Answer 16

more than two liquids with different boiling points

Question 17

filtration separates

Answer 17

an insoluble solid and a liquid

Question 18

crystallisation separates

Answer 18

a soluble solid and a liquid

Question 19

paper chromatography separates

Answer 19

more than one soluble liquid

Question 20

how is simple distillation done

Answer 20

• solution is heated ( in between the boiling points of both liquids, so that only one evaporates)
• the vapour will travel through a tube which has a condenser around it, which will be pouring cold water win, and cold water out. This causes the vapour to cool so condense back into a liquid

when it gets back to the other side of the tube, it is back into liquid form and has been separated

Question 21

how is fractional distillation done

Answer 21

the same as simple distillation, just that because there are more than 2 liquids, you need to switch the beaker after you have separated the first one from the others.

Question 22

how is filtration done

Answer 22

get a funnel with filter paper

pour the mixture into that

the liquid will fall through and into the beaker

the insoluble solid will remain stuck because of the filter paper and so you will have separated them

Question 23

how is crystallisation done

Answer 23

• you need a bunsen burner, a tripod, a beaker dull of water and a cruscible on an evaporating dish

put the solution in the cruscible and heat it until it reduces by about half the amount

leave it to dry naturally

the crystals of the dissolved solid will form as the solvent evaporates

Question 24

how is paper chromatography done

Answer 24

• a pencil line is drawn of the paper and spots of the sample are drawn on it
• paper is lowered into solvent container and the pencil line must be right above the level of solvent so the samples don’r wash into the solvent container
• the solvent will then travel up the paper, taking some of the coloured susbtance with it
• Different substances have different solubilities so will travel at different rates

This causes the substances to separate

Those substances with higher solubility will travel further than the others

This will show the different components of the ink / dye

Question 25

in paper chromatography, what does it mean if some of the dies have travelled the same distance for each sample

Answer 25

it means they contain some of the same die

Question 26

original line drawn in pencil at the bottom in chromatography paper is called the

Answer 26

base line

Question 27

the line at the top of chromatography paper is called ___ and it shows

Answer 27

the solvent front
where the water has moved up to

Question 28

how do you calculate the Rf value for chromatography

Answer 28

distance spot has moved / distance solvent front moved

Question 29

Rf values range from

Answer 29

0 to 1

Question 30

if the Rf values of a dye are different that means that

Answer 30

they are not the same dye

Question 31

PRACTICAL PAPER CHROMATOGRAPHY

Answer 31

• you need some chromatography paper, a bowl or beaker, water and food colouring or felt tipped pens
• draw a line ( in pencil) along the bottom of the paper
• insert the paper into the beaker so that the water reaches just below the pencil line
• draw a few dots of felt tip pen on the pencil line
• allow water to be sucked up into the chromatography paper ( keep paper in water but need something to hold it up)

Question 32

what separation technique would you use for mud mixed with water

Answer 32

filtration

Question 33

a solution of salt and sugar

Answer 33

paper chromatography

Question 34

what separation technique would you use for ethanol mixed with water

Answer 34

simple distillation

Question 35

what separation technique would you use for copper sulfate dissolved in water

Answer 35

crystallisation

Question 36

what separation technique would you use for crude oil

Answer 36

fractional distillation