GCSE CHEMISTRY
UNIT 1.10
SOLUBILITY
Pupil
Name
_______________________
Class
_______________________
Chemistry
Teacher
_______________________
1
1.10
SOLUBILITY
Water as a solvent
Water is a common solvent. Many substances dissolve in it.
Definitions
 A solvent is a liquid in which the solute dissolves.
 A solute is a solid which dissolves in the solvent.
 A solution is a mixture of the dissolved solute and solvent
 Soluble describes a substance that dissolves.
 Insoluble describes a substance that does not dissolve.
 A saturated solution is one where the maximum amount of solute has
dissolved in the solvent at a particular temperature.
Making a solution
The method used to make a solution is shown in figure 1 below.
Making a saturated solution
The method used to make a saturated solution is shown in figure 2 below.
2
NOTE: A glass rod should be used to stir. Do not stir with a spatula.
Spatulas used for stirring may contaminate other chemicals and sometimes a
metal spatula may react with a solution.
The excess solid remaining at the bottom can be removed by filtration.
GENERAL RULES FOR SOLUBILITY
 Ionic compounds are mostly soluble in water. The back of the Data Leaflet
gives information on which are soluble and insoluble. The general rules for
solubility of ionic compounds are:
- All nitrates are soluble in water.
- Most sulfates and chlorides are soluble in water but there are a few
exceptions.
- Most oxides, hydroxide and carbonates are insoluble in water but there are
a few exceptions.
- All sodium, potassium and ammonium compounds are soluble in water.
Covalent substances are mostly insoluble in water but there are exceptions such
as the gases ammonia, hydrogen chloride and sulfur dioxide as well as solid
substances like sugar. Giant covalent substances such as diamond and graphite
are insoluble in water.
HINT: You may be given information on the solubility of different substances in
water and be asked to determine the general rules for solubility between covalent
and ionic or among a range of ionic substances.
Look back at Section 1.2 - 1.4 to make sure you can decide on the structure of a
substance.
Making a solid dissolve more quickly
To make a solid dissolve more quickly several things can be done:
Stirring: a solid dissolves faster in a solvent if it is stirred.
Adding more solvent/water: a solid dissolves faster if there is more solvent.
Heating: a solid dissolves faster if the temperature of the solvent is increased.
Making the solid particles smaller: a solid dissolves faster if the solid is
crushed into a fine powder.
Figure 3
3
SOLUBILITY
Solubility is the maximum mass of a solute that can dissolve in 100 g
of water at a particular temperature. The units of solubility are g/100g
of water.
Another way of saying this is that the solubility is the mass of solute that will
saturate 100g of water (the solvent) at a particular temperature.
Typical Question
1.
What is meant by the term solubility?
[4]
Answer:
The maximum [1] mass [1] of solute which dissolves in 100 g of water [1] at a
particular temperature [1]
HINT: The most common mistake in this question is to miss the term ‘mass’ and
use ‘amount’ which is incorrect. This is a very common question and you should
learn the definition of solubility thoroughly.
Some solubility values
 Potassium chlorate(V), KClO3, has a solubility value of 14 g/100g water at 40
°C
NOTE: This means that 14 g of potassium chlorate(V) are required to saturate
100 g of water at 40 °C
 Potassium chloride, KCl, has a solubility value of 40 g /100g water at 40 °C
More on units of solubility
The units of solubility are important when you are working with graphs and for
understanding calculations.
 Mass is measured in g (grams)
Volume is measured in cm3 (cubic cm)
1 cm3 = 1 ml (millilitre) 1 litre is 1000 ml = 1000 cm3.
 Water has a density of 1 g/cm3
1 cm3 of water has a mass of 1 g
1 g of water has a volume of 1 cm3
100 g of water is the same as 100 cm3 of water
 The values for the solubility of most gases in water are low so the units are
usually mg/l (milligrams per litre).
1 mg is 1 010 0 th of a gram.
Preparing a Salt
Once a solution of a salt is prepared, it has to be crystallised.
This process involves heating to evaporate some water (usually until half the
volume of water is removed). The solution is left to cool and crystallise.
Crystallisation occurs because as the solution cools, the solubility of the salt
decreases.
SOLUBILITY OF SOLIDS
Table 1 shows the change in solubility of potassium chloride (a typical solid) with
temperature. As the temperature increases, the solubility of potassium chloride
increases.
Temperature
(°C)
0
10
20
30
40
50
60
70
80
90
100
Solubility
(g/100g water)
28
31
34.5
37.5
40
43
45.5
48.5
51
54
56.5
4
SOLUBILITY OF GASES
 Oxygen, carbon dioxide and hydrogen are not very soluble in water. These
gases are collected over water
 Hydrogen chloride, sulphur dioxide and ammonia are very soluble in water.
These gases cannot be collected over water.
Thermal Pollution
Water is used as a coolant in many factories. As it cools the factory machinery,
the water becomes hot and runs out into rivers and lakes. The temperature of
the water in the lakes and rivers increases. The solubility of oxygen decreases at
a higher temperature. This leads to fish dying due to lack of oxygen.
Typical Question
Explain why many dead fish were found in a river into which a power station
released large amounts of hot water.
[3]
Answer:
solubility of oxygen [1] decreases as temperature increases [1]
so fish die from lack of oxygen [1]
HINT: Many answers to this type of questions miss the whole point which is to do
with the solubility of gases in water at different temperatures. Remember that
the solubility of a gas decreases as temperature is increases
Trends in solubility
SOLIDS:
As temperature increases, the solubility of a solid increases.
GASES:
As temperature increases, the solubility of a gas decreases.
Practical Method for determining solubility
You need to be able to plan an experiment which will allow you to determine a
solubility value. This is the most common practical procedure used.
The following steps are shown in the diagram below:
1. Wear safety glasses. Weigh a clean dry boiling tube
2. Add some solid and re-weigh the boiling tube.
3. Add 10 cm3 of deionised water from a pipette to the test tube
A pipette is an accurate method of measuring a volume of a liquid or solution.
Liquids are drawn up (sucked up) into the pipette using a pipette filler
4. Place a thermometer in the boiling tube
5. Heat the boiling tube in a water bath until all the crystals dissolve. Stir gently
using the thermometer.
6. Allow the solution to cool slowly (while still stirring) and record temperature
when crystals appear.
7. Repeat the experiment to ensure reliability of the results.
NOTE: Another variation of this experiment to determine solubility values uses a
fixed mass of solid and the volume of water is changed. The temperature at
which crystals are formed on cooling is again recorded. The solubility values can
be calculated in g/100g of water from the results of each experiment.
5
Figure 4
HEAT
Experiment procedures to determine solubility values
The data obtained from solubility experiments is usually the mass of solid, the
mass of water and the temperature.
These are the three pieces of information required to calculate a solubility value.
Example 1
1 g of sodium chloride was added to 10 g of water at 20 °C. The solution was
stirred. The solution was filtered and the residue dried. 0.64 g of residue
remained. Calculate the solubility of sodium chloride at 20 °C.
Mass of sodium chloride needed to saturate 10 g of water = 1 – 0.64 = 0.36 g
Solubility at 20 °C = 0.36 × 10 (as in 10 g of water) = 3.6 g/100g of water.
Example 2
3.1 g of potassium chlorate(V) were placed in 10 cm3 (10 g) of water in a boiling
tube and heated in a water bath until all the solid dissolved. The solution was
allowed to cool and crystals formed at 71 °C. Determine the solubility of
potassium chlorate(V) at 71 °C.
Mass of potassium chlorate(V) which saturates 10 g of water at 71 °C = 3.1 g
Solubility of potassium chlorate(V) at 71 °C = 31 g/100g water
NOTE: It is practically difficult to maintain a sample of water at a particular
temperature and also to determine the exact mass required to saturate the
water. Example 1 above is not a common method whereas example 2 is used
extensively. All methods give a mass of solid, a mass of water and a
temperature.
6
WATER OF CRYSTALLISATION
Water of Crystallisation is water which is chemically bonded into the crystal
structure.
Hydrated means that solid crystals contain water of crystallisation.
Dehydration means removal of water of crystallisation. This can be carried out
by heating or using a chemical dehydrating agent.
Anhydrous means without water of crystallisation.
DRAWING AND USING A SOLUBILITY GRAPH
Solubility values can be plotted against temperature and curve (or less often a
line) is drawn. The y axis is solubility (g/100 water). The x axis is temperature
(°C)
Example 1
Draw a solubility curve for potassium chlorate(V), KClO3, using the data shown in
the table.
Temperature
(°C)
0
10
20
30
40
50
60
70
80
90
100
Solubility of
KClO3
(g/100g water)
3
5
7.5
10.5
14
19
24
30
38
46
54
Plot the values shown in the table on a graph (Figure 5).
Figure 5
HINTS:
 You may be asked to plot a solubility curve using given data and then use you
graph to answer further questions or you may be given a curve and asked to
use it to carry out solubility calculations.
 Plot points using an × with the centre of the × at the exact coordinate
 The solubility at 0 °C is not 0 g/100 g water so do not plot (0,0) on a
solubility curve
 Draw the best-fit curve or line on the graph through the points. A curve is
usually more suitable than a line.
 The graph allows you to determine solubility values for temperatures in
between the given values
7
DETERMINING SOLUBILITY AT INTERMEDIATE VALUES
Example 2
From the solubility graph in Figure 5, what is the solubility of potassium
chlorate(V) at 25 °C?
On the graph, a vertical line is drawn from the required temperature up to the
solubility curve. A second line is drawn horizontally to the solubility axis to
determine the solubility at this temperature.
The solubility of potassium chlorate(V) at 25 °C is 9 g/100 g water
DETERMINING MASS OF CRYSTALS FORMED ON COOLING A SATURATED
SOLUTION
When a saturated solution cools down, the solubilty of the solid decreases as
the temperatue decreases. The mass of solid which can be dissolved in the
solution decreases as the temperature decreases.
The difference between the solubility values is the mass of solid formed on
cooling a saturated solution containing 100 g of water
Example 3
Using the solubility graph in Figure 5, determine the mass of solid formed on
cooling a saturated solution containing 100 g of water at 75 °C to 25 °C.
The solubility of potassium chlorate(V) at 75°C = 34 g/100 g water and its
solubility at 25°C = 9 g/100g water
When a saturated solution containing 100 g of water is cooled form 75 °C to 25
°C the mass of solid which crystallises is 34 – 9 = 25 g.
NOTE: Determining the mass of solid which crystallises when the mass of water is
not 100g in the saturated solution is a common question (See Example 4).
Example 4
If a saturated solution of potassium chorate(V) containing 50 g of water is
cooled from 75 °C to 25 °C what is the mass of solid crystals formed?
Solubility at 75°C = 34 g/100 g water
Solubility at 25°C = 9 g/100g water
When a saturated solution containing 100 g of water is cooled form 75 °C to 25
°C the mass of solid which crystallises is 34 – 9 = 25 g.
When a saturated solution containing 50 g of water is cooled from 75 °C to 25 °C
the mass of solid which crystalllises = 225 = 12.5 g
NOTE: If the mass of water is greater than 100 g, the difference in solubility
values will need to be multplied, for example with 500 g of water the difference in
solubility values will be multiplied by 5.
8
Typical Question
The solubility values of potassium nitrate are given in the table below.
Temperature (ºC)
0
10
20
30
40
50
60
Solubility of potassium
nitrate (g/100g water)
28
30.5
33
36
39
42
45
1.
Determine the mass of potassium nitrate which would be obtained on cooling
a saturated solution containing 1000 g of water from 60 °C to 20 °C. [4]
2.
A solution was prepared by mixing 15 g of potassium nitrate with 50 g of
water. Determine whether or not the solution is saturated.
[1]
Answers
1.
Solubility at 60 °C = 45 g/100g water
Solubility at 20 °C = 33 g/100g water
For a solution with 100g of water 45 – 33 [1] = 12 g [1]
For a solution with 1000g of water 12 × 10 [1] = 120 g [1]
HINT: The most common mistake in this type of question is to leave out the last
step where you convert to the mass of water given in the question. Always check
the question to make sure you have taken this into account. The marks are
usually for subtraction of the solubility values at the two temperatures and then
either division or multiplication depending on the mass of water present.
(Don’t subtract the temperature values.)
2.
Solubility of potassium nitrate at 30 °C = 36 g/100 g water.
Maximum mass of potassium nitrate which can dissolve in 50 g of water =
36
= 18 g.
2
So a solution containing 15 g of potassium nitrate in 50 g of water is not
saturated.
(3 g more of potassium nitrate could be dissolved to make the solution
saturated.)
9
QUESTIONS
1.
Water is the most common solvent and is used to dissolve a variety of
solutes and gases forming coloured and colourless solutions.
(a)
What is meant by the following terms?
(i)
solvent
________________________________________________
________________________________________________________ [2]
(ii)
solute
________________________________________________
________________________________________________________ [2]
(iii)
solution
________________________________________________
________________________________________________________ [2]
(iv)
solubility
________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
________________________________________________________ [4]
(b)
Some substances are soluble and some are insoluble. Complete the table
by placing a tick () in the appropriate column to indicate whether the
substances are soluble or insoluble. You may find a Data Leaflet useful in
answering this question
Substance
Soluble
Insoluble
copper(II) oxide
silver(I) chloride
sodium carbonate
zinc hydroxide
lead nitrate
magnesium chloride
barium sulfate
[7]
10
2.
A large sample of potassium chloride is added to a beaker of water. Some
potassium chloride remains at the bottom of the beaker.
potassium chloride
spatula
beaker
water
potassium chloride remaining at bottom of beaker
(a)
(b)
Suggest two ways in which more potassium chloride could be made to
dissolve.
1.
_____________________________________________________
2.
__________________________________________________ [3]
What name is give to a solution in which no more solid can be dissolved?
________________________________________________________ [1]
(c)
Explain how you would remove the solid potassium chloride which does
not dissolve.
________________________________________________________ [1]
3.
As well as solids, some gases dissolve in water.
(a)
Describe how the solubility of a gas changes with temperature.
___________________________________________________________
________________________________________________________ [2]
(b)
How does thermal pollution from factories kill fish in rivers and lakes?
___________________________________________________________
________________________________________________________ [2]
11
4.
The table below gives some solubility values for potassium chloride.
(a)
Temperature (°C)
20
40
60
80
100
Solubility (g/100
g water)
34.5
40.0
45.5
51.0
56.5
On the graph below plot a solubility curve for potassium chloride.
[4]
60
50
Solubility g/100g water
40
30
20
10
0
0
20
40
60
Temperature /°C
12
80
100
(b)
Using the graph, determine the solubility of potassium chloride at the
following temperatures:
0 °C
__________________________________________________ [1]
50 °C __________________________________________________ [1]
90 °C __________________________________________________ [1]
(c)
(d)
Using the graph, determine the temperature at which the solubility of
potassium chloride is:
30 g/100g water
_______________________________________ [1]
50 g/100 g water
_______________________________________ [1]
Calculate the mass of potassium chloride which is required to saturate 50
g of water at 20 °C.
Mass of potassium chloride ______________ g [1]
(d)
Using your graph, calculate the mass of solid which would crystallise when
a saturated solution of potassium chloride is cooled from 70 °C to 25 °C.
Mass of potassium chloride ______________ g [4]
(e)
9 g of potassium chloride were placed in 20 g of water at 40 °C. The
solution formed was described as saturated.
(i)
In terms of the mass of solid added, explain why the solution is saturated.
___________________________________________________________
________________________________________________________ [1]
(ii)
Calculate the mass of potassium chloride which remained at the bottom.
________________________________________________________ [1]
13
5.
Hydrated iron(III) sulfate can also be called iron(III) sulfate-9-water. Its
solubility in water at 20 °C is 440 g/100g water.
(a)
Write a chemical formula for iron(III) sulfate-9-water.
________________________________________________________ [2]
(b)
What is meant by hydrated?
___________________________________________________________
________________________________________________________ [2]
(c)
Calculate the mass of water required to completely dissolve 88 g of
hydrated iron(III) sulfate at 20 °C.
Mass of water =
14
_____________ g
[2]
6.
The graph below shows the solubility curves for potassium chlorate and
potassium nitrate
potassium chlorate
potassium nitrate
(a)
At what temperature is the solubility of the two compounds the same?
________________________________________________________ [1]
(b)
State the trend in solubility for potassium nitrate.
___________________________________________________________
________________________________________________________ [2]
15
(c)
Using the graph, determine the mass of potassium nitrate required to
saturate 25 g of water at 20 °C.
Mass of potassium nitrate = ______________ g [2]
(d)
Using the graph determine the mass of potassium chlorate which would
crystallise when a saturated solution at 80 °C is cooled to 20 °C.
Mass of potassium chlorate = _____________ g [2]
(e)
(i)
Four different mixtures, A, B, C and D were prepared as detailed below.
Mixture
Solid
Mass of solid
(g)
Mass of
water (g)
Temperature
(°C)
A
potassium
chlorate
20
100
60
B
potassium
nitrate
20
100
60
C
potassium
chlorate
4
10
70
D
potassium
nitrate
5
25
80
Which of the solutions formed will be saturated?
________________________________________________________ [2]
(ii)
Which of the solutions formed will not be saturated?
________________________________________________________ [2]
16
7.
In determining the solubility of a solid in water, the following procedure
was used.
4.0 g of potassium chlorate were placed in 10.0 g of water in a boiling
tube at 20 °C.
The mixture was heated in a water bath, while stirring with a
thermometer, until all of the solid dissolved.
The solution was allowed to cool, with continuous stirring, until crystals
started to form and the temperature was recorded. (temperature = 82 °C)
The solution was heated again until the solid dissolved and again allowed
the cool and the temperature at which crystals started to form was
recorded. (temperature = 82 °C)
(a)
Calculate the average temperature at which crystals started to form.
________________________________________________________ [1]
(b)
Suggest why the experiment was repeated.
___________________________________________________________
___________________________________________________________
________________________________________________________ [1]
(c)
Calculate the solubility at 82 °C.
Solubility =
(d)
_______________ g/100g water
[1]
State two possible sources of error in this experiment and one way in
which you could minimise one of these sources of error.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
________________________________________________________ [3]
17
(e)
Draw a labelled diagram of the assembled apparatus which is used to heat
the solution.
[4]
(f)
Suggest how the experiment could be changed to determine the solubility
value at a different temperature.
___________________________________________________________
___________________________________________________________
________________________________________________________ [1]
(g)
Explain practically how you would measure 10.0 g of water.
___________________________________________________________
___________________________________________________________
________________________________________________________ [2]
18
8.
In an experiment to determine the solubility of potassium nitrate in water
at different temperatures a student carried out the following procedure.
10.0 g of potassium nitrate were weighed out and placed in a clean dry
boiling tube.
8.0 cm3 of deionised water were added and the mixture heated in a water
bath with stirring until all the solid had dissolved.
The solution was allowed to cool and the temperature at which crystals
appeared was recorded.
An additional 2.0 cm3 of deionised water was added to the boiling tube and
the mixture was again heated with stirring until all the solid has dissolved.
It was then allowed to cool and the temperature at which crystals started
to form was recorded.
This was repeated until the volume of water was 20.0 cm3.
The results are shown in the table below.
Mass of
potassium
nitrate (g)
Mass of
water (g)
Temperature
(°C)
10.0
8.0
81
10.0
10.0
58
10.0
12.0
43
10.0
14.0
34
10.0
16.0
31
10.0
18.0
28
10.0
20.0
23
Solubility
(g/100g water)
1.
Complete the table to calculate the solubility values at each temperature
using the mass of solid potassium nitrate and the mass of water.
[3]
2.
Suggest how you would improve the experiment to attain more accurate
results.
___________________________________________________________
________________________________________________________ [1]
3.
State one possible source of error in this experiment and one way in which
you would change the experiment to minimise the error.
___________________________________________________________
___________________________________________________________
___________________________________________________________
________________________________________________________ [2]
19
4.
Plot a graph of solubility of potassium nitrate against temperature on the
axes below.
130
120
110
100
Solubility g/100g water
90
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
Temperature /°C
20
70
80
90
100
5.
Answer the following questions using the graph you have drawn.
(a)
Determine the solubility of potassium nitrate at 40 °C.
________________________________________________________ [1]
(b)
Determine the temperature at which the solubility of potassium nitrate is
90 g /100g water.
________________________________________________________ [1]
(c)
Calculate the mass of potassium nitrate required to saturate 10 g of water
at 30 °C.
___________________________________________________________
________________________________________________________ [2]
(d)
Calculate the mass of potassium nitrate which could crystallise from
solution if a saturated solution is cooled from 75 °C to 35 °C.
Mass of potassium nitrate = _______________ g [4]
21
PRACTICAL 1
To determine the solubility of sodium chloride at 20 °C
Equipment
Safety Glasses
Evaporating basin
Bunsen burner
Tripod
Heatproof mat
Gauze
Electronic balance
Chemicals
Saturated solution of sodium chloride (at 20 °C)
Risk Assessment

There is the potential for burns from the hot apparatus, boiling liquid and
Bunsen flame – be careful when working with the apparatus and keep it away
from the edge of the desk; keep the Bunsen burner on a safety flame or turn
it off when it is not being used; do not touch the hot apparatus; use tongs to
move the evaporating basing to the electronic balance.

There is also the potential for burns from salt spitting as the solution
evaporates – keep the apparatus away from the edge of the desk

If a burn occurs inform your teacher and flood the affected area with cold
water for 10 minutes.

There is the potential for cuts if any glassware is broken – inform your
teacher of any breakages and make sure broken glass is disposed of in the
broken glass bin.

Sodium chloride is a slight irritant to skin and eyes so wear safety glasses at
all times and wash any of the solution off your skin if there is a spill with
plenty of cold water.
Method
1. Weigh a clean, dry evaporating basin and record its mass.
2. Place approximately 50 cm3 of saturated sodium chloride solution in the
evaporating basin and accurately record the mass.
3. Heat the solution to evaporate the water, strongly at first and then more
gently to avoid spitting as the volume reduces.
4. Allow to cool and then reweigh.
5. Heat for a further 5 minutes, cool and reweigh.
6. Continue heating, cooling and reweighing until the mass remains constant to
ensure that all the water has been removed.
Labelled Diagram of Assembled Apparatus
22
Results
Mass of evaporating basin
_______ g
Mass of evaporating basin + salt solution
_______ g
Mass of evaporating basin + salt
_______ g
Mass of salt
_______ g
Mass of water
_______ g
Calculation
Calculate the solubility of sodium chloride at 20 °C using the expression given
below:
solubility=
mass of salt
 100
mass of water
units are g/100g water
Solubility of sodium chloride at 20 °C =
_______________ g/100 g water
Additional Question
A saturated solution of potassium chloride was made at 20 °C. A sample of the
solution was evaporated to dryness and the following data was recorded.
Mass of evaporating basin
Mass of evaporating basin + solution
Mass of evaporating basin + dry salt
=
=
=
56.31g
105.93g
68.90g
Calculate the solubility of potassium chloride at 20 °C.
Solubility of potassium chloride at 20 °C =
23
__________ g/100 g water [2]
PRACTICAL 2
Determining the relationship between temperature and the solubility of potassium
chlorate(V), KClO3, in water.
Potassium chlorate(V) is oxidising and an irritant.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Wear safety glasses.
Set up a water bath by placing approximately 150 cm3 of tap water in a
250 cm3 beaker.
Place a tripod on a heatproof mat with a gauze on top of the tripod. The
beaker should be placed on the gauze with a Bunsen burner below the
centre of the gauze.
Weigh out between 1 and 5 g of solid potassium chlorate(V) in a weighing
boat.
Place the solid in a clean dry boiling tube and add 10.0 cm 3 of deionised
water from a burette. 10.0 cm3 is the same as 10.0 g of water as the
density of water is 1.0 g/cm3.
Clamp the boiling tube in place in the water bath and put a thermometer
into the boiling tube.
Heat until all the solid has dissolved, stirring with the thermometer. DO
NOT BOIL THE WATER.
Remove the boiling tube from the water bath and allow to cool, continually
stirring. OBSERVE THE BOILING TUBE CAREFULLY AND RECORD THE
TEMPERATURE WHEN CRYSTALS START TO FORM.
Repeat the experiment with the same boiling tube and record a second
temperature when crystals start to form.
Using a different mass of potassium chlorate(V), repeat the experiment.
Gather 4 sets of repeated results for 4 different masses of potassium
chlorate(V) from your class mates.
Record the results in the table below.
Mass of
potassium
chlorate(V)
(g)
Mass of
water (g)
Temperature
1
(°C)
Temperature
2
(°C)
24
Average
temperature
(°C)
Solubility
(g/100g
water)
13.
Plot a graph of solubility of potassium chlorate(V) against temperature
(°C) on the graph paper below. Choose a scale which suits the size of the
graph paper based on your results and label the axes with the name of the
quantity and units.
25
Questions
1.
Write a full apparatus and materials list including chemicals for this
experiment.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
________________________________________________________ [4]
2.
Write a risk assessment for this experiment including a potential risks to
you or those around you and the measures you would put in place to
prevent harm.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
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3.
From your graph, state clearly the trend in the results.
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26
4.
Draw a labelled diagram of the assembled apparatus used to carry out this
experiment.
[4]
5.
Use the graph you drew to answer the following questions.
(a)
Determine the solubility of potassium chlorate(V) at 50 °C.
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(b)
Determine the temperature at which the solubility of potassium
chlorate(V) is 40 g/100g water.
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(c)
Calculate the mass of potassium chlorate(V) which is required to saturate
25 g of water at 40 °C.
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________________________________________________________ [2]
(d)
Calculate the mass of potassium chlorate(V) which would crystallise if a
saturated solution containing 20 g of water at 60 °C is cooled to 25 °C.
Mass of potassium chlorate(V) =
27
_______________ g [4]