Download Unit 4: Mixtures and Separation Techniques 1. Look at this candle

Unit 4: Mixtures and Separation Techniques
4.8
1.
CW Exercises
Look at this candle burning. Which label (A or B) shows a
A
chemical change and which shows a physical change?
2.
A
__chemical change_________
B
__physical change__________
B
Give two general differences between physical and chemical changes.
Physical change
3.
Chemical change
However no new substances are made
new substances are formed
Reversible
Irreversible
Using the word bank below, fill in the table with the appropriate word to match the definition.
Solution
Compound
Solute
Compound
Solution
Immiscible
Distillate
Immiscible
Miscible
Filtrate
Insoluble
Distillate
Solute
Element
Suspension
A solid that will dissolve in a liquid
Contain 2 or more types of atoms which are chemically bonded
A mixture of a solute and a solvent
Liquids that do not mix
A liquid that drips from the end of a condenser during distillation
Filtrate
A liquid or solution that drips through a filter paper
Miscible
Liquids that mix
Suspension
A cloudy mixture of a solid and a liquid
Insoluble
A solid that does not dissolve in a liquid
Solvent
A liquid that is used to dissolve another chemical
Element
Contains only one type of atom
Stella Maris College
Solvent
1
Unit 4: Mixtures and Separation Techniques
4.
Using the definitions of elements, compounds and mixtures, complete the table by putting a
tick in the correct column. The first one has been done for you.
Substance
Element
Mixture
Compound

Copper

Air

Distilled water

Brine (salty water)

Sodium

Cupro-nickel
Sodium chloride

Copper (II) sulphate

Sulphur

Oxygen

Bronze

Petrol

Blue ink

Steel


Steam

Milk
5. Look at the boxes below:
A
B
C
D
Which box contains;
a. one element.
___B_______
b. a mixture of elements.
___D_______
c. a pure compound.
___A_______
d. a mixture of elements and compounds.
___C_______
e. an example of molecules made from just two elements.
___A_______
Stella Maris College
2
Unit 4:separating
Mixtures and Separation Techniques
funnel
6.
When two liquids do not mix they are called
immiscible.
The liquids can be separated in a separating funnel.
a) Draw and label the separating funnel containing
oil and water.
oil
water
b) How do you separate the two liquids?
A mixture of oil and water were poured into a separating funnel. The funnel was shaken with
vigour and clamped over a conical flask. The liquids were allowed to separate to form two
distinct layers. The tap was opened and water was allowed to run into the concial flask.
The tap was closed just before the boundary between the two liquids. The boundary was run into
a beaker closing the tap just above what was the dividing line. Oil remains in the separating
funnel.
7.
A mixture of salt and sugar has to be separated, using the solvent ethanol.
a)
Which of the two substances is soluble in ethanol? ___sugar_
b) How would you obtain:
i)
salt from the mixture
ii) sugar crystals from the sugar solution?
Add 50cm3 of ethanol to the salt and sugar mixture and stir. The sugar dissolves in ethanol but salt
does not. Pour the mixture over a filter funnel placed in a conical flask. The salt is the residue and
the filtrate is a solution of sugar dissolved in ethanol.
Pour the sugar solution into an evaporating dish and heat gently over a water bath.
When most of the ethanol is evaporated from the solution, dip the stirring rod in solution. If
crystals form on the rod, allow the solution to cool at room temperature and crystallise.
c) On a foolscap, draw a labelled diagram to show which apparatus you are going to use in this
experiment.
Sugar solution
filter
paper
filter
funnel
water
salt
(residue)
heat
Sugar
solution
(filtrate)
Stella Maris College
Heating on a water bath
3
Unit 4: Mixtures and Separation Techniques
8.
a)
Describe how you could separate and collect the first substance (in bold and italics) from each
mixture:
salt and sand
Add distilled water to the mixture of salt and sand. The sand is insoluble in water
and is removed by filtration. The salt dissolved in water and is collected as a
filtrate. The solution is evaporated to obtain salt crystals
b)
iron filings and sugar
Use a magnet and the iron fillings are all attracted by means of the magnet
c)
water and salt
The salty water is placed in a distillation apparatus and it is heated. The water
evaporates and condenses in the condenser which is collected as a distillate
d)
iodine and sand
The mixture is heated in a beaker. Iodine sublimes but sand does not. An
evaporating basin filled with cold water is placed on the beaker. The iodine will
solidify on the cold surface.
e)
blue dye and red dye
A drop of the mixture of dyes is placed on the chromatography paper. The paper
is placed in a beaker filled with water (solvent) which is absorbed by the filter
paper and the colours separate.
f)
ethanol (alcohol) and water.
The mixture is placed in a round bottom flask and fractionally distilled. The
ethanol distils off first because it has a lower boiling point and it collected in a
flask. Water will evaporate but it will drip in the fractionating column.
Stella Maris College
4
Unit 4: Mixtures and Separation Techniques
4.9
HW Exercises
Name: _____________________________
1.
Class: _____________
Look at the boxes below:
1
2
3
4
5
Which box contains:
a) mixtures of gases
_3__
b) a solid
_5__
c) a gaseous compound __2_
d) oxygen (O2)
_1__
e) a gas made up of single atoms _4_
(5 marks)
2.
From the list below, indicate which substances are elements or compounds.
Name and Chemical symbol
Element
Compound

Water (H2O)
Sulfur (S)
Sodium hydroxide (NaOH)


(3 marks)
Stella Maris College
5
Unit 4: Mixtures and Separation Techniques
3.
The differences between a mixture and a compound can be determined by carrying out the
same tests on a mixture of iron and sulfur, and on the compound of iron (II) sulfide. Complete
the table below to give the missing results of the tests.
Test
Iron/Sulfur mixture
Iron:
Colour
Action of a magnet
Dark grey powder
Sulphur: Yellow powder
Iron (II) Sulphide: Black
Iron: attracted to the magnet
Iron (II) Sulphide:
Sulphur: Not attracted by magnet
Not attracted by magnet
Iron: Very little reaction when
Effect of Hydrochloric
acid
Iron (II) Sulfide
cold. When warm gas is
produced.
Iron (II) Sulphide: A foul smelling
gas is produced with some
Sulphur: No reaction with HCl
effervescence
(7 marks)
4.
A student carried out the following simple experiments:
Experiment 1:
Experiment 2:
a.
A small piece of sodium metal was added to some water in a beaker and a
violent reaction occurred.
Some common salt (sodium chloride) was added to water in a beaker and
stirred.
State, giving reasons, whether a physical or chemical change took place in each experiment.
Experiment 1: Chemical change as a new substance was produced.
Experiment 2: physical change as no new substance was produced, the crystals only
dissolved
(4)
b.
Give two general differences between physical and chemical changes.
A chemical change produces a new substance and is not reversible.
A physical change produces no new substance and is reversible.
(2)
(6 marks)
Stella Maris College
6
Unit 4: Mixtures and Separation Techniques
5.
Eight coloured substances were spotted onto a filter paper, which has then stood in a covered
glass tank containing a solvent called propanone. Three of the substances were the basic
colours red, blue and yellow and the other dyes labelled A, B, C, D, E. The resulting
chromatogram is shown below:
a) Which dye contains only one basic colour?
________B_____________
b) Which dye contains all three basic colours?
________A_____________
c) Which basic colour is most soluble in propanone? ________Red____________
d) What is this technique called?
___chromatography________
(4)
e) The experiment was then repeated using water as a solvent this time, but the experiment did
not work. Explain why the experiment worked with propanone but not with water.
The dyes are soluble in propanone but not in water hence they did not separate.
(1)
(5 marks)
Stella Maris College
7
Unit 4: Mixtures and Separation Techniques
6.
The separation technique below was used to separate water from potassium permanganate
crystals.
C
Water out
D
B
Water in
A
E
heat
Distillate
a) What is the name of this technique?
__simple distillation________
(1)
b) Write the names of the parts of the apparatus labelled A to E.
A
B
C
D
E
__tripod____________
__round bottom flask__
__thermometer_______
__condenser__________
__conical flask________
(5)
c) What is the purpose of apparatus labelled D?
it will condense the vapour into a liquid due to the surrounding jacket of water
(1)
d) To separate water from potassium permanganate solution, a number of instructions for setting
up and carrying out the experiment need to be followed. Give a reason why each of these
practical steps is important.
i.
Some pieces of glass are added to the mixture before heating as anti-bumping granules.
These prevent vigorous boiling
ii. The bulb of the thermometer should be placed as shown in the diagram, not in the mixture.
To measure the temperature of the vapour not the mixture.
(2)
(9 marks)
Stella Maris College
8
Unit 4: Mixtures and Separation Techniques
7.
You have found a glass bottle in the Chemistry laboratory containing a mixture of blue and
black powder. Your teacher has informed you that this mixture contains two chemicals that
have been accidentally mixed together. You were told that these two chemicals are copper
(II) sulfate and copper (II) oxide. You are given the task to separate these two chemicals. This
is the information you have available:
Copper (II) sulfate
Copper (II) oxide
Blue crystals
Black solid
Soluble in water forming a blue solution
Insoluble in water
a) Describe how you can obtain dry black powder copper (II) oxide and dry blue crystals of
copper (II) sulfate separately.
Add 50cm3 of distilled water to the mixture and stir. Heat the mixture gently to help
the crystals to dissolve. filter the mixture and the black copper (II) oxide which is
insoluble will be obtained as a residue.
Wash it with distilled water to remove
impurities and leave it to dry.
Pour the filtrate (blue solution) into an evaporating dish and heat gently. When most of
the water is evaporated from the solution, dip the stirring rod in solution. If crystals
form on the rod, allow the solution to cool at room temperature and crystallise.
(5)
b)
Draw a fully labelled diagram of the apparatus you would use to obtain dry black powder
copper (II) oxide and dry blue crystals of copper (II) sulfate separately in the space provided
below.
mixture
CuSO4 (aq)
CuO
CuSO4
solution
CuSO4 (aq)
CuO
(3)
(8 marks)
salt solution
Stella Maris College
9
Unit 4: Mixtures and Separation Techniques
8.
The figure below shows laboratory apparatus, which can be used to produce almost pure
ethanol from a mixture of ethanol and water. Boiling point of ethanol is 780C and that of
water is 1000C.
thermometer
water out
fractionating column
cold
water in
flask
heat
a) Name the process being used.
Fractional disillation
(1)
b) What is the purpose of the fractionating column?
Since the two liquids have close boiling points both will evaporate. However water
has a lower boiling point and it will condense on the glass beads. Ethanol will
evaporate and keep on passing through the fractionating column.
(2)
c) List three precautions taken during the experiment.
add anti-bumping granules to prevent vigorous boiling
water in the condenser is filled from the bottom to flow upwards and pushes out
all the air.
the thermometer is placed to measure the temperature of the vapour.
(3)
d) What will be left in the flask at the end of the process? __water___________
(1)
(7 marks)
(Total: 50 marks)
Stella Maris College
10