ACTIVITY 1

ACTIVITY 1

Comparing Ionic and Covalent Compounds

I.Purpose:
- to compare the physical properties of ionic and covalent compounds
- to determine whether an unknown substance is ionic or covalent

II.Materials:
burner sodium chloride (A)
conductivity apparatus potassium iodide (B)
scoopula potassium chloride (C)
deflagrating spoons - 2 sugar (D)
watchglass benzoic acid (E)
beakers (7) camphor (F)
unknown solid

III.SAFETY PRECAUTIONS:
Safety glasses must be worn. Caution when heating compounds to determine melting point. The molten state may sputter. IT WILL BURN. Follow teacher's directions about conductivity apparatus.

IV.Procedure:
Before beginning the experiment, create a chart for your observations on a new sheet of paper. Determine suitable headings for your columns based on the rest of the method section of this paper. One column should be a prediction of the type of substance - either covalent or ionic.
(1) Try to detect if any of the substances have an odour. Wave your hand over the substance toward your face. Record your observations.
(2) Ignite a burner. Place a small sample of substance (A) into one deflagrating spoon and a small sample of substance (D) into the other. Record the one that melts first as low, and
the other's melting point as high. You do not need to melt the one with the higher melting point. Thoroughly clean the spoons before continuing.
(3) Repeat step (2) for substances (B) and (E).
(4) Repeat step (2) for substances (C) and (F).
(5) Repeat step (2) for your unknown.
(6) Determine whether each substance seems hard or soft. Do this by first rubbing a small sample of each between your fingers. Then try to crush a few crystals of each. Place each compound in the watchglass one at a time, and use a scoopula to try to crush them.
(7) Make a solution of each compound in separate beakers.
(8) Use the conductivity apparatus to test the solutions of each of the seven substances.

V.Observations:
Create a chart for your observations before beginning the lab activity from the instructions. Predict whether the substances are ionic or covalent (see Pre-lab question 1).

VI.Questions/Discussion:
Pre-lab questions:
(1) Based on what you've learned about electronegativity differences and bond types, predict which group of elements (A-C) or (D-F) are ionic and which are covalent.
(2) Outline the procedure in a series of pictures.
Post-lab questions:
(1) Compare the physical properties of ionic and covalent substances.
(2) What is the number of your unknown? Is it an ionic or covalent substance?
(3) Intermolecular forces exist between molecules or ions. Based on this lab, which do you think are stronger i) intermolecular forces between covalent molecules or ii) intermolecular forces between ions?
(4) Covalent compounds can be found as single molecules, but ionic substances can't be found as single ion pairs. What evidence do you have for this fact?
(5) Which type of substance conducted electricity when dissolved in water? What is different between ionic and covalent substances that causes this?

VII. Generalization: