Comparing Covalent and Ionic Compounds

Background Information:

The curls and waves of you hair are the result of the much hydrogen, ionic, and covalent bonds between the chains of atoms that make up each hair follicle. Styling hair by wetting it or heating it with a curling iron is an attempt to change these bonds so they will form a new shape. The changes are temporary and as soon as you wash your hair, the style is gone. The solutions in a “permanent”, however, break and reform covalent bonds. This is a “permanent” change that will not wash out.

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 (cation and anion). 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), solubility, and conductivity.

Purpose:

To examine the properties of several compounds, including volatility, ease of melting, solubility, and conductivity. Use these properties to classify the compound as either ionic or covalent.

Materials:

Bunsen burnersodium chloride

Test tube holdersucrose

Test tube starch

potassium iodide

Safety gogglessodium acetate

Stopwatchcalcium chloride

Well plates

Toothpicks

Procedure:

  1. Carefully test the odor of each compound. If you can detect an odor, assume that the compound has a high volatility. Record your observations in the data table.
  2. Place small, equal amounts of each substance in a test tube. Heat the sample over a LOW burner flame and observe the time required melt each sample.
  3. Put a few small crystals of each substance in separate wells on a well plate. Add about 2-5 drops of water on top of the crystals. Stir with a toothpick and record on the solubility in the data table.
  4. Test the conductivity of the one of the solutions. Rinse the tester with water between each test. Record in the data table.

Data Table:

Compound / Volatile (yes/no) / Melting Time / Soluble (yes/no) / Conductive
(yes/no)
Sodium Chloride
Sucrose
Starch
Potassium Iodide
Calcium Chloride
Sodium acetate

Unknowns

Compound
(Describe it) / Volatile (yes/no) / Melting Time / Soluble (yes/no) / Conductive
(yes/no)
1
2
3
4

Post-Lab Questions:

  1. List the compounds which are volatile.
  1. List the compounds that melted quickly.
  1. List the compounds that dissolved easily in water.
  1. Based off your DATA, classify each compound as ionic or covalent.
  2. Based off what you LEARNED IN CLASS, classify which compounds should have been ionic and which should have been covalent.

Analysis:

  1. Water molecules have parts that are negatively charged and parts that are positively charge. Which substances tend to dissolve more easily in water, ionic or covalent? Explain why.
  1. Electricity is the flow of electrons through substances. Which type of bond is a better conductor of electricity? Explain why.

Critical Thinking and Application:

  1. What does your data tell you about melting points of ionic and covalent compounds?
  1. Which do you think would be more dangerous near an open flame: an ionic or covalent compound? Why?
  1. Which type of bond-ionic or covalent-would you expect to have a higher boiling point? Why?
  1. 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?
  1. Explain why hair permanents wash out of your hair

Conclusion:

  1. Identify TWO sources of error that could have caused your results to be incorrect.
  1. Now that you have done the lab, write a good hypothesis for this lab. (remember the “then” part was the goal of the lab and the “if” part if how you got there)