THE PHYSICAL PROPERTIES OF TWO TYPES OF SOLIDS

OBJECTIVE: to study some physical properties of two types of solids - molecular and ionic.

INTRODUCTION: Some solids consist of molecules held together by the covalent bonds. However, other solids are formed from positive and negative ions, which are attracted together in order to produce ionic bonds. In this experiment, we will examine four physical properties (odour, hardness, melting point, and solubility) of a molecular and an ionic solid. We will try to establish a link between the properties and the forces of attraction. The two solids are salt (chlorine and sodium) and camphor (carbon, hydrogen, and oxygen).

MATERIALS: metal ring, watch glass, stand, Bunsen burner, crucible lid, depression plate, porcelain triangle, graduated cylinder (10 ml), spatula, salt, camphor, propanol-2

PROCEDURE: A. Fill out the table for the results, as each of the following parts is completed.

physical properties / sodium chloride / camphor
odour (part B)
Rigidity (part C)
High or Low Melting point (part D)
Solubility in water (part E)
(water is almost ionic)
solubility in propanol-2
(propanol-2 is molecular)
(part E)
Conducts electricity when dissolved? (part F)

B. Place on a watch glass, a small quantity (the size of a pencil eraser) of camphor and sodium chloride. Observe the odour of the two solids by wafting the odours with a hand.

C. Rub a small quantity of each solid between the fingers. Observe and compare the hardness of both. Verify by crushing some crystals of each solid with the spatula on the watch glass.

D. Place some sodium chloride crystals and some camphor crystals on the crucible lid, one solid at each end. Put the lid on the porcelain triangle on the metal ring and gently heat the two solids. One of the solids will probably melt and catch fire.

E. Divide the remaining sodium chloride crystals between two depressions. Do the same with the camphor. To one of the depression with sodium chloride, add 3 drops of water and wait. To the other depression with sodium chloride, add 3 drops of propanol-2. Repeat with camphor.

F. Your teacher will test the conductivity of the dissolved substances. Record the results in the table

QUESTIONS

The strong odour of one of the substances indicates that the particles of that solid leave its surface easily. Which substance has the strongest odour? Is there a strong or weak attraction for these particles?

According to the answer for the previous question, is rigidity also connected to the attraction of the particles? (Think about which substance is soft because its particles have less attraction?)

The melting point can also indicate the force of attraction. Which substance has a low melting point? Are these particles strongly attracted to each other?

Which substance is ionic? Which substance is molecular?

What is the link between solubility and the type of bond (ionic or covalent)?