oxides

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GRADE 11- CHMISTRY
INVESTIGATION investigating the properties of Period 3 oxides

Aim
The purpose of this experiment is to examine the oxides of Period 3 elements and describe their bonding and structure.
Introduction
You carry out an investigation along similar lines to the work you did on the chlorides of the elements in Period 3 (Experiment 4.12). However, you will not be asked to test the oxides with cyclohexane because unlike the covalent chlorides, most of the oxides are not composed of discrete molecules. Therefore they are unlikely to dissolve in cyclohexane and simple experiments cannot distinguish between insolubility and slight solubility.
Requirements
safety spectacles access to a fume cupboard
6 test-tubes test-tube rack
1 measuring cylinder, 10 cm3
1 measuring cylinder, 100 cm3 distilled water thermometer, 0-100 °C
1 spatula universal indicator solution and colour chart teat pipette pH paper splints sodium peroxide, Na2O2 magnesium oxide, MgO aluminium oxide, Al2O3 phosphorus(V) oxide, P4O10 silicon(lV) oxide, SiO2 access to sulphur dioxide cylinder or generator, SO2
Drechsel bottle glass tubing with right-angled bend rubber tubing for connections
HAZARD WARNING

Phosphorus(V) oxide is corrosive and irritates eyes, skin and lungs. Sodium peroxide is also corrosive and a powerful oxidant. Sulphur dioxide is a toxic gas with a chok­ing smell. Therefore you must: do the experiment at the turn® cupboard wear safety spectacles avoid contact with skin.

Procedure Appearance: Part A
1. Examine the oxide samples provided and make observation on physical properties. Record qualitative data Procedure Appearance: Part B on mixing with water
2. Setup six test-tubes, side by side.
3. Into each test-tube pour about 5 cm3 of distilled water.
4. In the first test-tube place a thermometer. a Note the temperature. b Add half a spatula-tip of sodium chloride and very carefully stir with the thermometer. c Note, after about one minute, i) the temperature, ii) whether the solid has dissolved and iii) anything else you see. For example, is gas evolved at any time? If so, is the gas acidic? Can you identify it using a simple test? d Add 2-4 drops of universal indicator solution, or use a piece of pH paper, compare the colour with the chart provided, and note the pH indicated. 5. . Repeat (but with more care!) the above steps 4a-d using, in turn, magnesium oxide, aluminium oxide, silicon ( IV) oxide phosphorus (V) oxide.
6. Measure the pH of the water in the seventh test-tube by adding 2-4 drops of universal indicator solution or by using pH paper, for comparison with the above.
7. . Bubble sulphur dioxide slowly through the water in the sixth test-tube until there is no further change in the colour of the indicator. Note the final pH of the solution. (You will probably be given sulphur dioxide in liquid form in a cylinder. To obtain the gas you carefully open the valve and the sudden decrease in pressure inside the cylinder causes the surface liquid to vaporise. Make sure there is a Drechsel bottle between the cylinder and the water in case of suck-back. Alternatively, your teacher may suggest other ways of generating the gas.)
8. To test the solubility of sulphur dioxide lower the delivery tube from your generator to the bottom of the 100 cm3 measuring cylinder filled with water. Pass a slow steady stream of gas through the water and when the air has been expelled from your apparatus look for a change in the size of the sulphur dioxide gas bubbles as they rise up through the water.

Na2O2A

MgO

AI2O3

SiO2

P4O10

SO2

Appearance

On mixing with water

Initial temperature

Final temperature

Does it dissolve?

pH of solution

Other observation(s) (if any)

Question
1. Use your experimental results, your data book and your textbook(s) if necessary to complete a larger copy of Table 2 below

Table 2
2. Write equations for any reactions which took place when you added the oxides to water.
3. Comment on the change in structure and bonding in the oxides between sodium and chlorine.
4. How does the acid-base nature of the oxides of the elements in Period 3 change with increasing atomic number?
5. Can you relate this change to the change in structure and bonding that takes place along the period?