06 Non Metals

NON METALS: THE HALOGENS Introduction Although metals are roughly an 80 % of the elements, non metals are as important as them. Non metals form water (oceans, rivers, clouds, snow), air and living matter almost exclusively. Non metals combined with metals form the rocks and the inner structures of our planet. Their properties are absolutely opposite to those of the metals: they are usually gases or low melting point solids (graphite, diamond and silicon are the only exceptions). Bromine is a liquid. Solid non metals are brittle and opaque and will not conduce electricity (except once again for graphite). Non metals are located past a zigzagging line at the left side of the PT (Periodic Table). In the PT shown, they are shaded yellow. Notice that Hydrogen is the only non metal on the right side (some tables, namely the one used in 2nd e.s.) place H midway between both sides of the PT. From a chemical point of view, their behaviour is also strikingly different: They tend to capture electrons and form anions (negative particles) instead of cations. They are usually reduced (the opposite of being oxidised): non metals usually take electrons from other atoms or eventually they share pairs of electrons among them. The reactivity pattern of non metals is opposite to that of metals. Thus, the most reactive metal is placed at the lower left corner of the Periodic Table, the most reactive non metal lies on the upper right corner of it As in the case of metals, more reactive non metals displace the weaker from their compounds but in a different fashion: taking electrons to form anions Aims To prepare non metals and to study the reactivity of the halogens. Apparatus Boiling tube, a bended glass tube, pierced rubber stoppers, test tubes and rack, a syringe and needle, clamp and retort stand. PREPARATION OF OXYGEN Oxygen can be easily prepared by decomposition of hydrogen peroxide catalysed (speeded up) by manganese (IV) oxide. The density of oxygen is very similar to that of air so it must be collected by displacement using water-filled test tubes in a trough. You will need some skill to operate as quickly as possible. 1- Set the apparatus as shown in the figure.

2- Put a spatula measure of manganese (IV) oxide in the boiling tube. 3- Punch the needle through the stopper into the boiling tube. 4- Fill a syringe sucking 5 ml of hydrogen peroxide 5- Attach the syringe to the needle and gently push the plunger to add the hydrogen peroxide into the tube. 6- Oxygen bubbles off the mixture and goes through the delivery tube into the water filled test tube in the trough. 7- As oxygen is poorly soluble in water oxygen will fill the test tube displacing the water in it. 8- When the tube is filled, change the delivery tube as fast as possible to a second tube and stopper the first one tightly under the water. The first test tube has mostly air so discard it. 9- Collect some four or five samples and keep them tightly closed. THE FOLLOWING TESTS SHOULD BE CARRIED OUT WITH THE TUBE IN THE RACK NOT IN YOUR HANDS. USE SAFETY GLASSES. Burning in oxygen You will test the following elements all by the same method described below 12345-

Place a sample in a combustion spoon. Heat until it gets red hot or a flame appears. Add the hot sample as soon as you can to an oxygen containing tube . Observe and write your observations. Oxides have been formed. Open the test tubes and add some drops of Universal Indicator solution, stopper and shake. 6- Check the pH and write it down. 7- The elements to be tested are: Carbon Sulphur Magnesium Iron 8- Complete the following table:

Element

Metal/nonmetal

How does it burn

Appearance of product

Colour of Indicator

Acidic or alkaline

Acid or base

Carbon Sulphur Magnesiu m Iron

PREPARATION OF CHLORINE GAS WARNING! CHLORINE IS HIGHLY TOXIC AND CORROSIVE. Avoid breathing the vapours and hold to instructions firmly. Chlorine is soluble in alkaline solution, but if acid is added it will quickly bubble off the solution as a pale green, pungent smelling, toxic gas. It is denser than air and will flow down inside a test tube displacing it. 1- Set the apparatus as shown in the figure 2- Put some 15 ml of bleach or chlorine solution in the boiling tube. 3- Punch the needle through the stopper into the boiling tube. 4- Fill a syringe sucking into it some 5 ml of acetic acid. (Avoid touching and smelling). 5- Attach the syringe to the needle and gently push the plunger to add some drops of acetic acid into the tube. 6- Chlorine bubbles vigorously off the mixture and goes through the delivery tube into the dry test tube. 7- As chlorine is denser than air the glass tube outlet should reach the bottom of the test tube. Chlorine vapours will fill the test tube displacing the air in it. 8- After two or three seconds, change the delivery tube as fast as possible and stopper it tightly. 9- Collect some four or five samples and keep them tightly closed. 10- A hood (fuming cupboard) or working outdoors may be necessary to prevent breathing chlorine vapours.

11- Put a strip of damp litmus paper in the first test tube and see what happens. Write down what you see. This is a test for chlorine gas. DISPLACEMENT REACTIONS IN GROUP VII (halogens) 1- Add 2 m of potassium bromide solution to the second chlorine - containing test tube, put the stopper on it and shake. Observe what happens and write down your observations. Is chlorine more reactive than bromine? 2- Do the same to the third test tube but use potassium iodide solution instead of bromide. Observe and record your observations. Is chlorine more reactive than iodine? 3- Now collect 2 ml of sodium chloride solution into two clean test tubes. 4- Add the first one of the tubes prepared in (3) with 2 – 4 drops of bromine water and the second one with 2 – 4 drops of iodine solution. Notice if there is any change and write down your observations. Do any of these elements displace chlorine? Which is the most reactive halogen? 5- Collect 1 ml of potassium iodide in a test tube. 6- Add one or two drops of bromine water to the test tube. Observe and record your observations. Does bromine displace iodine? Which is the second more reactive in the group? 7- Write your results in a chart: Tested with

Anion tested Chloride Bromid e

Iodide

Chlorine Bromine Iodine

8- Write the three halogens in order of increasing reactivity according to your results.