BTEC Unit 2 Chemistry Learning Aim A Part 2 Structure and Bonding

Scenario You work for a chemical company as a quality control laboratory technician. It is important to understand how chemical substances are bonded together, in order for you to carry out laboratory tests on products as they are produced and determine what uses they could have. As part of an induction day for new recruits, you will need to present material showing how substances are formed through ionic or covalent bonding, and how their properties are related to their bonding and structure.

Teacher Safety Tips When using magnesium sulfide, please ensure old stock is not used as this may affect the practical results. Sulfur dioxide and chlorine are asthma ‘triggers’ so any asthma sufferers in the group should not be exposed to either trigger. Use small amounts of sodium chloride and magnesium chloride to minimise the risk of chlorine gas.

Investigating the properties of substances Part 1 − Investigating electrical conductivity in the solid state Aim To find out if sodium chloride, magnesium chloride, sulfur and sand conduct electricity in their normal physical state – i.e. as a solid. Apparatus required 4 wires 1 spatula 1 low voltage d.c. power supply 1 watch glass 1 bulb 4 crocodile clips Chemicals required Solids: sodium chloride, magnesium chloride, sulfur and sand. Crocodile clips Test substance

Part 1 − Investigating electrical conductivity in the solid state What to do: 1.Observe each of the substances in turn, and write down their appearance in the results table. 2.Set up the equipment as shown in the diagram. 3.Put a small amount of the solid to be tested into a clean watch glass. Put the crocodile clips on the solid, making sure the clips do not touch each other directly. 4.Test each substance in turn and record your results in the results table at the end. If the bulb lights up then the substance conducts electricity Crocodile clips Test substance

Part 2 − Investigating electrical conductivity in solution Aim To find out if sodium chloride, magnesium chloride, sulfur and sand conduct electricity in solution. Chemicals required Solids: sodium chloride, magnesium chloride, sulfur and sand. Apparatus distilled water 1 beaker 2 graphite rods 1 spatula 4 wires 4 crocodile clips 1 LV d.c. power supply 1 watch glass 1 bulb Safety Wear your eye protection all the time until you, and those around you, have completed their practical work. If you smell chlorine gas, which has a strong bleach smell, turn off the power at once because the gas is TOXIC.

What to do 1Add a very small quantity of sodium chloride (1g) to 50 cm 3 of water in a 100 cm 3 beaker. 2Stir gently and make a note if it dissolves (soluble) or doesn’t dissolve (insoluble). 3Record your results in the results table. 4If the sodium chloride doesn’t dissolve start again with magnesium chloride. 5If the sodium chloride does dissolve, add another half spatula to the beaker. 6When it has all dissolved, test to see if sodium chloride conducts electricity in solution. To do this, you need to use the electric circuit you used in part 1. To each crocodile clip in the circuit, you need to fix a graphite rod. 7Record your result in the results table at the end. Repeat for all four substances Part 2 − Investigating electrical conductivity in solution

Part 3 – Investigating the effect of heat Aim To find out what happens when sodium chloride, magnesium chloride, sulfur and sand are heated. Chemicals required Solids: sodium chloride, magnesium chloride, powdered roll sulfur and sand. Apparatus 1 spatula test tube rack 3 test tubes Bunsen burner mineral wool 1 small ignition tube Safety Wear your eye protection all the time until you, and those around you, have completed their practical work. Sulfur vapour is toxic – this activity should be carried out using the clear instructions for sulfur below.

What to do 1Gently warm one spatula of sodium chloride in a test tube using the Bunsen burner until a change occurs. 2Observe and record any changes that occur. 3Record your results in the results table. 4Repeat steps 1–3 for magnesium chloride and sand. If a substance doesn’t melt or boil then its melting/boiling point is high. Testing sulfur Wearing eye protection, measure a small amount (0.5 g) of powdered roll sulfur in a small ignition tube. Stopper the ignition tube with a mineral wool plug to minimise the escape of vapour and reduce the risk of ignition. Heat the ignition tube slowly using a small Bunsen burner flame with the collar half open. STOP heating when the sulfur is molten/has melted. Leave the sulfur to cool with the plug in place, and record your result in the table. Part 3 – Investigating the effect of heat

Investigating the properties of substances SubstanceAppearanceHardness Is the substance hard/soft/brit tle? Electrical conductivity: does it conduct electricity? Solubility Is it soluble in water? (soluble/ insoluble) Heat Is the melting point high or low? Boiling point Is the boiling point high or low? What kind of bonding is present? In the Solid state? (yes/no) Dissolved in water as a solution? (yes/no) Magnesium chloride Sodium chloride Sulfur Silicon dioxide

Questions 1.This experiment investigated some physical properties of ionic and covalent substances – what were they and what other physical properties of these substances are there? What similarities and differences in physical properties are there when comparing these ionic and covalent substances?

Chemical substances data sheet SubstanceMelting point Boiling point Solubility in water Electrical conductivity of solid Electrical conductivit y of solution Ionic or covalent? Giant or simple structure? Silicon dioxide high insolublenon-conductorinsoluble Magnesium bromide high solublenon-conductorconductor Calcium chloride high solublenon-conductorconductor Propanelow insolublenon-conductorinsoluble Sandhigh insolublenon-conductorinsoluble Carbon tetrachloride low insolublenon-conductorinsoluble