Chemistry Heating Substances

HEATING SUBSTANCES

By the end of this unit you should be able to:
(i) State the three states of matter and their characteristic properties.

(ii) Explain and give examples of physical changes arising from evaporation, melting, freezing and sublimation.
(iii) State the differences between an element, compound and mixture.
(iv) Give examples of chemical changes.
(v) State the differences between a physical change and a chemical change.
(vi) Describe one possible test for water of crystallisation.

With the help of your teachers you should be able to perfom one or more of the following experiments, make accurate observations and draw conclusions.
Activity 1
Experiments to demonstrate physical change
Apparatus
Beakers or glass boiling tubes, tripod stands, wire gauzes/pipe clay triangles and bar magnets.
Other requirements: Candle, iron nails and water.
Procedure
(i) Light a candle and observe the change it goes through. Blow out the candle and allow it to cool.
What do you observe? Has any new substance been formed?
(ii) Pass a magnet over iron nails.
What change do the nails go through?
(iii) Run water from a tap into a beaker or boiling tube and boil it.
State the change that takes place.
Activity 2
Experiment to distinguish between a mixture and compound
Apparatus
Test tube racks, test tubes, bunsen burner (or spirit stove), pair of tongs (or folded paper), magnet, filter papers (or cloth), spatula, petri-dish/paper and a wooden splint.
Other requirements: Sulphur, iron filings, carbon disulphide, water and dilute sulphuric acid.
Procedure
(i) Place two spatula ends full of sulphur on a petri-dish and add some iron filings to it.
What is the product formed here called?
(ii) Take a little of the mixture of iron filings and sulphur in a glass test tube and heat it strongly.
What is the final product formed here called?
(iii) Scrape off the product in (i) (ii) from the test tube and carry out the following tests.

TEST	Observations with product from (i)	Observations with product from (ii)
(a) Pass a magnet over the products
(b) Drop a little of each product in water in a test tube
(c) Take a little carbon disulphide in a test tube and add a little of each product, shake and observe what happens
(d) To a little of each product in a test tube add a little dilute sulphuric acid, identify the smell of the gas and test it with a burning splint

Activity 3
Experiment to carry out effect of heat on substances

Investigate the effect of heat on the following substances:
(i) Ice
(ii) Sulphur
(iii) Wax
(iv) Magnesium
(v) Platinum wire
(vi) Mercury(II) oxide
(vii) Iodine (or aluminium chloride)
Apparatus
Glass test tubes, test tube racks, spatulas, pair of tongs and a heating source.
Other requirements: Samples of substances listed above.
Procedure
Place a little of each of the above substances in a test tube and heat:
first (i) gently
then (ii) strongly and observe what happens.

Figure 1- Sublimation of iodine in experiment (vii)

Questions

(i) What do you observe in each case?

(ii) Classify the change as either (a) permanent or (b) temporary, in each case.

Activity 4

Experiment to show precipitation of solids by reacting solutions

Apparatus

Test tube rack and glass test tubes.

(a) Lead(II) nitrate solution and potassium iodide solution

Procedure
(i) Pour a little lead(II) nitrate solution into a test tube.
(ii) Add an almost equal volume potassium iodide solution. Note what you observe.
(b) Copper(II) sulphate solution and sodium hydroxide solution
Procedure
(i) Pour a little copper(II) sulphate solution into a test tube.
(ii) Add sodium hydroxide solution drop wise until in excess. Note what you observed.

Activity 5
Experiment to show the presence of water of crystallization
By heating hydrated copper(II) sulphate crystals and gently heating iron(II) sulphate crystals.
Demonstrate test for water of crystallization using cobalt(II) chloride paper (blue to pink) or using anhydrous copper(II) sulphate (white to blue).
Apparatus
Test tube rack and glass test tubes.
Other requirements: Copper(II) sulphate crystals, iron(II) sulphate crystals, anhydrous copper(II) sulphate and cobalt(II) chloride test paper.
Procedure
(i) Take a little copper(II) sulphate crystals in a test tube and heat them gently. Note what happens.
(ii) Sprinkle anhydrous copper(II) sulphate onto the colourless liquid that formed at the cooler part of the test tube. What did you observe?
You could use blue cobalt(II) chloride test paper instead of anhydrous copper(II) sulphate. Cobalt chloride paper turns pink when dipped into water. Anhydrous copper(II) sulphate goes blue when water is added to it.

Activity 6
Experiment to separate a mixture of substances by physical means

Make a mixture of iron and sulphur

Use a magnet to separate the iron from the sulphur.

Activity 7
TEST QUESTIONS
1. Define the following terms: (a) Element, (b) Compound
2. Classify each of the following naturally occurring substances as an element, a compound or a mixture:
(a) Petroleum, (b) diamond, (c) sand, (d) common salt and (e) coal.
3. State three differences between a mixture and a compound.
4. Give two examples each of (a) a physical change, (b) a chemical change.
5. State four differences between a physical change and a chemical change.
6. Match the Activity with the nature of Change (physical or chemical)

Activity	Physical change (P)/Chemical change (C)
(a) Sugar dissolves in water
(b) Firewood is burnt
(c) Digestion of food
(d) Heating of ammonium chloride
(e) Burning of scrap iron
(f) Roasting of sugar crystals
(g) Warming meat soup to boiling
(h) Burning magnesium in air
(i) Conversion of carbohydrates to fats
(j) Recovering salt crystals from salt solution

DEFINITIONS
Anions - are negatively charged ions (negatively charged atoms).
Cations - are positively charged ions (positively charged atoms).
Mixture - is a substance that consists of two or more elements or compounds not chemically combined together.
Precipitation - is the formation of a solid substance when two aqueous substances are mixed.
Precipitate - is an insoluble substance that is formed when two aqueous solutions are mixed.
Sublimation - is a change of substance from solid state directly to gaseous state without turning to liquid.
Thermal decomposition - is the breakdown of a substance by heat to form a new substance or substances.
Water of crystallisation - is the specific amount of water that some substances combine with in order to form crystals.
Qualitative analysis - is the carrying out of simple experiments in order to identify the cation (s) and anion(s) in an unknown compound.