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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.

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Source:  OpenStax, Natural sciences grade 6. OpenStax CNX. Sep 16, 2009 Download for free at http://cnx.org/content/col11079/1.1
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