Comparing Ionic and Covalent Compounds

Name(s): ______

Comparing Ionic and Covalent Compounds

Compounds are either covalent or ionic depending on the nature of the forces that hold them together. In ionic compounds, the force of attraction is between oppositely charged ions. This attraction is called an ionic bond. In covalent compounds, atoms are held together by an interaction between adjacent nuclei and shared electrons. These different forces account for many of the properties of ionic and covalent compounds, such as the degree of volatility (ability to turn into a gas) and solubility.

In this lab, you will examine the properties of a representative ionic compound (sodium chloride) and a representative covalent compound (paradichlorobenzene – PDB -). The properties studied will be volatility, ease of melting, and solubility in water. You will need to find out how the properties of ionic and covalent compounds are different.

Materials:

Sodium chloride Bunsen burner o-ring

ring stand paradichlorobenzene (PDB) (3) 50 mL beaker

safety goggles (2) test tube test tube clamp

wire mesh

Procedure:

1.  Carefully smell each compound. If you can detect an odor, assume that the compound has a high volatility. Record your observations in the Data Table.

2.  Carefully measure out 4.4 grams of sodium chloride, in the 50 mL beaker, using the triple beam balance.

3.  Carefully measure out 4.4 grams of paradichlorobenzene (PDB) in the second 50 mL beaker.

4.  Set up the Bunsen burner, ring stand, and test tube clamp.

5.  The flame from the Bunsen burner CANNOT be touching the bottom of the test tube. It needs to be adjusted so that it is 5 cm higher than the top of the flame.

6.  Place the sodium chloride from the 50 mL beaker into the test tube. Do not lose any.

7.  Place this test tube in the test tube clamp and make sure you are watching the clock. Heat the sample and observe the time required to melt the substance. As soon as the sodium chloride is melted, record exactly how long it took in the Data Table.

8.  Place the contents of the test tube down the sink and run plenty of water. Clean and dry the test tube. Complete the same process as above except use the paradichlorobenze this time. Record the exact time it took to melt in the Data Table.

9.  Place another 4.4 grams of sodium chloride in one of the 50 mL beakers. Fill one of the 50 mL beakers with exactly 20 mL of water. Add the sodium chloride to the 20 mL of water and be ready to keep track of the time. Carefully, stir the mixture and keep track of how rapidly the substance dissolves. Record the time in the Data Table.

10.  Repeat the procedure from number 9 using the paradichlorobenze and record the time in the Data Table.

Data Table:

11.  Which compound was more volatile?

12.  Which compound melted more quickly?

13.  Which compound dissolved more easily with water?

14.  Explain why the type of bond could determine the volatility of a substance.

15.  Does the strength of the bond have anything to do with the time it takes to melt a substance? Explain.

16.  Water molecules have parts that are negatively charged and parts that are positively charged. Which substances tend to dissolve easier in water—ionic or covalent? Why?

17.  What does your data tell you about the melting points of ionic and covalent compounds? How can you tell?

18.  Which do you think would be more dangerous near an open flame: ionic or a covalent compound? Why?

19.  Which type of compound – ionic or covalent – would you expect to have a higher boiling point? Why?

20.  Suppose you had a sample of two compounds mixed together. Both compounds consist of fine white crystals. You know that one of the compounds is ionic and the other is covalent. How might you separate the two compounds?