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To determine the factors that affect the solubility of materials

Module by: Siyavula Uploaders. E-mail the author

NATURAL SCIENCES

Form, reaction and alteration of materials

EDUCATOR SECTION

Memorandum

1. In which glass is the sugar dissolved quickest?

  • In the glass with warm water.

2. Explain why this happens.

  • The solubility of a substance is affected by the temperature.

Assignment 13:

  • (Groupwork)
  1. How many teaspoons of sugar could you dissolve into the glass of water?
  • The amount depends on the individual experiment.
  • Discus in your group what you could do to dissolve more sugar into the water.
  • The water (solution) can be heated.
  • The sugar crystals (dissolved substance) and be made finer.

Assignment 14:

Observation: The water has evaporated and small crystals have been formed: copper sulphate crystals. Under the microscope the crystals appear as small blocks or cubes.

Conclusion: When a solution is left to stand the opposite of dissolving occurs. The dissolved substance crystallises into a solid in the form of crystals.

Assignment 15:

  1. Is the amount and type of solvent the same in all three cases?
  • Yes
  • Which substance was dissolved the least after the first teaspoon?
  • Corn meal
  • Is corn meal insoluble?
  • Yes

4. Which substance dissolved best?

  • Salt

Conclusion: Not all substances are equally soluble.

Assignment 16:

  1. What do you see?
  • Oil does not dissolve. You continue to see drops of oil on the water

2. Where is the oil?

  • While you are stirring it seems that the oil is mixed with the water, but the moment that you stop stirring the oil floats to the surface of the water.

3. Can oil dissolve in water?

  • No

4. What is the reason for the answer above?

  • Particles of oil are strongly attracted to each other. Water particles cannot move in between the oil particles, so oil is not soluble in water.

Assignment 17:

1. What happens?

  • The naphthalene flakes do not dissolve in water but do dissolve in mentholated spirits.

2. Can you explain why this happens?

  • Naphthalene flakes are not soluble in water.

3. Complete.

  • Naphthalene is easily dissolved in mentholated spirits but is not soluble in water

LEANER SECTION

Content

ACTIVITY: To determine the factors that affect the solubility of materials [LO 1.1, LO 1.2, LO 1.3]

The solubility of a material is determined by:

  • temperature;
  • type of material; and
  • type of solvent.

ASSIGNMENT 12

To determine how temperature affects solubility.

Requirements: Sugar

A glass of cold water

A glass of warm water

A teaspoon

  • Put one teaspoonful of sugar into the glass of cold water and another into the glass of warm water.
  • Do not stir the water.
  • Observe what happens.

What do you observe?

1. In which glass is the sugar dissolved the quickest?

_____________________________________________________________________

2. Explain why this happens.

_____________________________________________________________________

REMEMBER THE FOLLOWING IN CONNECTION WITH SOLUBILITY

Sugar is SOLUBLE in water.

The sugar is the DISSOLVED substance.

The water is the SOLVENT.

The sugar water is the SOLUTION.

HEAT increases the process of solution.

  • A saturated solution:

Water can only take a certain amount of a dissolved substance like sugar. When the water can not take more of the substance, we say that it is a saturated solution.

This is what a saturated solution looks like:

Figure 1
Figure 1 (graphics1.png)

(Compare the sketch above to the previous sketch and ensure that you understand the difference.)

ASSIGNMENT 13 (GROUP WORK)

To prepare a saturated solution.

Requirements: Glass of tap water

White sugar

A teaspoon

  • Fill the glass half full with tap water.
  • Stir a teaspoonful of sugar into the water until it dissolves.
  • Stir another teaspoonful of sugar into the water.
  • Continue to add sugar to the water, until you observe that the sugar will no longer dissolve.

What do you observe?

1. How many teaspoons of sugar dissolved in the water?

_____________________________________________________________________

2. How are you able to dissolve more sugar in the water? Discuss this in your group.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

ASSIGNMENT 14

To investigate the formation of crystals.

  • Make a saturated solution of copper sulphate and water.
  • Place a small amount of the solution in a saucer and allow it to stand for a day.
  • Write your observations and conclusions. You may use a microscope.

Observation:

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

Conclusion:

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

ASSIGNMENT 15

To determine how the type of substance affects solubility.

Requirements: Three clean glasses

Salt

Maize meal

Sulphur

Three teaspoons

Tap water

  • Place exactly the same amount of water in each glass.
  • Add one teaspoonful of salt to the first glass and stir carefully.
  • Count how many teaspoons of salt can be added before the solution is saturated.
  • Repeat the experiment using maize meal and sulphur instead of salt.

What do you observe?

1. Is the amount of soluble matter the same in each case?

_____________________________________________________________________

2. Which substance dissolved the least after the first teaspoonful?

_____________________________________________________________________

3. Is maize meal soluble?

_____________________________________________________________________

4. Which substance was most soluble?

_____________________________________________________________________

Conclusion:

_____________________________________________________________________

_____________________________________________________________________

  • Not all substances are equally soluble.
  • Solubility depends on the type of substance.

ASSIGNMENT 16

Another experiment to show that not all substances are soluble.

Requirements: A glass of tap water

Cooking oil

A teaspoon

  • Half fill the glass with water.
  • Pour a small amount of oil onto the water.
  • Stir the oil and water for a few minutes.

What do you observe?

1. What do you see?

_____________________________________________________________________

_____________________________________________________________________

2. Where is the oil?

_____________________________________________________________________

3. Can oil be dissolved in water?

_____________________________________________________________________

4. What is the reason for your answer above?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

LIKE WATER OFF A DUCK’S BACK

We say this about people who are not overcome by their problems.

Water just rolls off a duck’s back.

The duck doesn’t get wet at all.

Ducks’ feathers are oily.

Water and oil cannot mix, that is why the water runs off the duck’s back.

Most aquatic birds have oily feathers.

Penguins and other sea birds become very heavy when they are covered with oil. This happens when the sea is polluted with oil. The birds will eventually drown.

To save them, the oil must be washed off their feathers with detergent.

When they have been washed they cannot be put straight back into the sea because they will be soaked and will get very cold.

The birds have to be looked after for two to three weeks until their feathers have regained the special coating of oil.

ASSIGNMENT 17

To determine how a solvent affects solubility.

Requirements: Water

Methylated spirits

Two glass flasks

Naphthalene flakes (or crushed mothballs)

  • Place a small amount of water in one flask and a small amount of spirits in the other.
  • Add a teaspoon of naphthalene flakes to each flask and stir.

What do you observe?

1. What happens?

_____________________________________________________________________

2. Can you explain why this has happened?

_____________________________________________________________________

3. Complete:

Naphthalene dissolves easily in _____________________ but does not

dissolve in ____________________.

REMEMBER:

In all the experiments, except the last one,

we have used only WATER as the solvent.

There are many other solvents that can be used,

like spirits, paraffin etc.

Assessment

Learning Outcome 1:Learners respond confidently to their desire to learn about natural phenomena; they investigate relationships and solve problems within the context of science, technology and the environment.

Assessment Standard 1.1:We know this when the learnerplans investigations: helps to clarify focus questions for investigation and describes the kind of information which would be needed to answer the question;

Assessment Standard 1.2:We know this when the learnerconducts investigations and collects data: conducts simple tests or surveys and records observations or responses;

Assessment Standard 1.3:We know this when the learnerevaluates data and communicates findings: relates observations and responses to the focus question.

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