5.4.1 - Laboratory Activity : To study the physical properties of ionic and covalent compound

Laboratory Activity 5.4.1: To study the physical properties of ionic and covalent compound

Aim: To compare the physical properties of ionic and covalent compounds

Material: » Sodium chloride » Naphthalene » Lead (II) bromide » Distilled water » Benzene

Apparatus: » Spatula » Battery » Electric bulb » Connecting wires » Crucible » Bunsen burner » Tripod stand » Carbon rods » Glass rod » Wire gauze

Procedure:

	►	The animation below shows the procedures and observation of the experiment.
	►	(A) Melting point 1. Some sodium chloride is heated slowly then strongly in a crucible. 2. The changes in the physical state are recorded. 3. Step 1 – 2 are repeated by using naphthalene.
	►	(B) Solubility 1. A spatula of sodium chloride is placed in two test tubes. 2. Water is added to one test tube and some benzene to the other. 3. Both are then stirred with a glass rod. 4. All observation are recorded. 5. Step 1 – 3 are repeated using naphthalene instead of sodium chloride.
	►	(C) Volatility 1. 2 – 3 drops of sodium chloride solution and benzene are placed in two different watch glasses. 2. Both are observed after 10 minutes.
	►	(D) Electrical conductivity 1. Several spatulas of lead(II) bromide powders are put into a crucible. 2. The switch is turned on and the bulb is checked if it is lighted up. 3. Lead (II) bromide powder is heated up until it melts. The switch is turned on again to check if the bulb is lighted up. 4. Step 1 – 3 are repeated using naphthalene to replace lead(II) bromide. 5. Several spatulas of sodium chloride is paced in a crucible. 6. The switch is turned on and the bulb is checked if it is lighted up. 7. Water is added to the sodium chloride. The mixture is stirred with a glass rod until all the sodium chloride solid dissolve in the water. The switch is turned on again to check if the bulb is lighted up.

Results:

	►	(A) Melting point NaCl Naphthalene No change. High melting point. Melts easily.Low melting point.
	►	(B) Solubility NaCl Naphthalene Soluble in water. Insoluble in benzene. Soluble in benzene. Insoluble in water.
	►	(C) Volatility NaCl Benzene Does not evaporates Evaporates quickly.
	►	(D) Electrical conductivity State of compound PbBr2 Naphthalene NaCl Solid Light bulb does not light up. Light bulb does not light up. Light bulb does not light up. Aqueous solution Bulb lights up. Light bulb does not light up. Bulb lights up.

Discussion:

	►	Sodium chloride does not melt when heated because its melting point is very high. But naphthalene melts at about 8OᵒC . Sodium chloride is an ionic compound. Naphthalene is a covalent compound.
	►	Benzene is an organic solvent. Only naphthalene dissolves in it.
	►	Benzene evaporates quickly.
	►	Lead (II) bromide has a lower melting point (373ᵒC) than sodium chloride(801ᵒC). Lead(II) bromide conduct electricity only in the molten state. It does not conduct electricity in the solid state.

Conclusion:

	►	Ionic compounds are soluble in water but insoluble in organic solvents. Ionic compounds have high melting points, low volatility and can conduct electricity in the molten or aqueous states.
	►	Covalent compounds are insoluble in water but soluble in organic solvents. Covalent compounds have low melting points, high volatility and cannot conduct electricity in all state.

↶ 5.4 Properties of Ionic and Covalent Compounds

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