1.b Elements, compounds and mixtures

Question 1

definition of element

Answer 1

consist of one type of atom only
.oxygen, copper
(anything on periodic table )

Question 2

definition of compound

Answer 2

substance that is made up of 2 or more different elements which are chemically bonded together

eg. carbon dioxide

Question 3

definition of mixture

Answer 3

made up of substances which at not chemically bonded together

eg. iron powder and sulphur powder

Question 4

definition of chromatography

Answer 4

method used to separate mixtures

Question 5

what can paper chromatography be used to separate

Answer 5

dyes

eg. inks, paints, food colourings

Question 6

definition of chromatogram

Answer 6

pattern of spots ( end of result of chromatography )

Question 7

what info does a chromatogram provide

Answer 7

info about the composition of a mixture

Question 8

describe how to carry out paper chromatography

Answer 8

1. draw a line near the bottom of sheet of filter paper in pencil ( pencil= insoluble= wont dissolve in solvent)
2. add spots of different inks to line at regular intervals
3. loosely role up sheet and put in a beaker of solvent eg. water ( solvent depend on what being tested - sometimes solvents like ethanol are better)
4. make sure level of solvent is below the baseline (pencil line ) - ( don’t want inks dissolving into solvent)
5. ( place lid on container to stop solvent evaporating)
6. solvent seeps of pare carrying inks with it
7. each different dye in the inks will move up the pare at different rates + form a spot in a different place
8. when solvent has nearly reached the top of the paper take the paper out of beaker and leave it to dry.
9. end result= pattern of spots = chromatogram

Question 9

explain how chromatography separates mixtures

Answer 9

1. different dyes will move up the paper at different rates
2. some will stick to the paper and others will dissolve more readily in the solvent and travel more quickly

Question 10

what does the distance the dyes travel up the paper ( in chromatography) depend on

Answer 10

on the solvent and the paper you use

Question 11

definition of Rf value

Answer 11

the ratio between the distance travelled by the dissolved substance ( the solute) and the distance travelled by the solvent

Question 12

what is the formula for the Rf value

Answer 12

Rf = distance travelled by solute ( ink) / distance travelled by solvent ( water)

Question 13

how do you find the distance travelled by the solute ( in chromatography)

Answer 13

measure from the baseline to the centre of the (ink) spot

Question 14

how to measure distance travelled by solvent

Answer 14

measure from baseline to solvent line ( where solvent has risen to)

Question 15

definition of solvent

Answer 15

liquid that dissolves substances

Question 16

definition of solute

Answer 16

substance that dissolves

Question 17

definition of insoluble

Answer 17

substance that cant dissolve in a particular solvent

Question 18

definition of solution

Answer 18

mixture formed by a solvent and a solute

Question 19

describe a pure substances melting/boiling point

Answer 19

has fixed melting/ boiling point

Question 20

describe a mixtures melting/boiling point

Answer 20

may melt or boil over a range of temperatures

Question 21

definition of simple distillation

give example

Answer 21

used to separate out solutions
(used to separate out a liquid from a solution)

eg. used to get pure water from salt water

Question 22

describe simple distillation

Answer 22

1. solution heated = part of solution with lowest boiling point evaporates
2. vapour cooled= condenses + collected
3. rest of solution left behind in the flask

Question 23

what is the problem with simple distillation

Answer 23

can only be used to separate things with very different boiling points

Question 24

definition of fractional distillation

give example

Answer 24

used to separate a mixture of liquids

eg different compounds in crude oil

Question 25

describe fractional distillation

Answer 25

1. mixture in flask + stick fractionating column on top + heat it
2. different liquids have different boiling point = evaporate at different temperatures
3. liquid with lowest boiling point evaporates first ( when temp on thermometer matches this boiling point ) = goes to top of the column
4. column is cooler toward top = liquids with high boiling points only evaporate half way up = condense and run back down towards flask
5. when 1st liquid collected= raise temp until next liquid reaches the top.

Question 26

definition of filtration

Answer 26

used to separate an insoluble solid from a liquid

Question 27

describe filtration

Answer 27

1. put filter paper into funnel
2. pour mixture into it
3. liquid part of mixture runs through paper= leaves behind a solid residue

Question 28

definition of crystallisation

Answer 28

used to separate soluble solid from a solution

Question 29

describe crystallisation

Answer 29

1. pour solution into evaporating dish + gently heat= some water evaporate= solution more concentrated
2. once some water evaporated or when crystals start to form ( point of crystallisation ) = remove dish from heat + leave solution to cool
3. salt should start to form crystals as it becomes insoluble in the cold, highly
   concentrated solution
4. filter crystals out of solution + leave in warm place to dry ( could also use a drying oven or a desiccator)

Question 30

definition of desiccator

Answer 30

contains chemicals that remove water from surroundings