EXPERIMENT 4: IONIC AND COVALENT PROPERTIES

Transcription

1 EXPERIMENT 4: IONIC AND COVALENT PROPERTIES PURPOSE To measure and observe properties of various substances. To arrange the substances into groups on the basis of their properties. To learn the properties of ionic and covalent substance. BACKGROUND Chemical compounds are combinations of atoms held together by chemical bonds. These chemical bonds are of two basic types: ionic and covalent. Ionic bonds result when one or more electrons from one atom or group of atoms are transferred to another atom. Positive and negative ions are formed. In covalent compounds the electrons are shared by the bonded atoms. The curls and waves of your hair are the result of many ionic, covalent and hydrogen 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 the hydrogen and ionic bonds so they will form a new shape. The changes are temporary and when you wash your hair, the style is gone. The solution in a "permanent" (or "perm") on the other hand, breaks and reforms covalent bonds. A permanent wave does not wash out when you shampoo your hair. The physical properties of a substance such as melting point, solubility, and conductivity tell us a lot about the type of bond in a compound. In this experiment, you will conduct tests on the properties and compile data enabling you to classify compounds as ionic or covalent. MATERIALS medicine droppers Bunsen burner ethanol conductivity apparatus tin can lid potassium iodide iron ring and stand calcium chloride sodium chloride 2 test tubes citric acid stearic acid sucrose PROCEDURE A - Description 1. Record a detailed description of each substance in your data table. Your observations should be extensive.

2 B - Melting Point 1. Set-up the ring stand with the tin can lid over a Bunsen burner. Place a few crystals (approx. 10) of each of the substances into separate 10 ml beakers. Label the beakers and arrange them around the edge of the tin can lid as shown: 2. Light the burner. Make sure the beakers are approximately the same distance from the flame of the Bunsen burner. Heat for two minutes only. Remove the substances that melt immediately. Notice which substances melt very quickly and which do not melt at all. Record your data. C - Solubility 1. Place a few crystals (approx. 5-10) of one substance into a clean test tube. Add drops of water and gently agitate the test tube for 3-5 minutes. Record your observations. Repeat this procedure for the rest of the substances. 2. Using drops of ethanol instead of water, repeat the above process. Record your observations. NOTE: In procedure 2, be sure that the test tube is clean and DRY for each substance before adding the ethanol. D - Conductivity 1. Using the conductivity tester, test each of the solutions. Record your observations.

3 Sample data table: Compound Melting Point Solubility Conductivity Water Ethanol table. Note: Write the descriptions separately since there may not be enough space on a

4 Name: Date PRE-LAB QUESTIONS 1. Define the terms covalent bonding and ionic bonding. 2. In part B, procedure 2, why should the 10 ml beakers be approximately the same distance from the flame of the Bunsen burner? 3. During which procedure should the Bunsen burner be lit, and how long should it remain lit? 4. In part C, procedure 2, why should the test tubes be dry when testing the solubility of a substance in ethanol? 5. In part B, procedure 1, how are you going to remember where each substance is on the tin can lid? 6. Classify the properties to be tested (description, melting point, solubility, and electrical conductivity) as chemical or physical properties.

5 Name: Date: IONIC AND COVALENT PROPERTIES Compound Description Melting Point Solubility Conductivity Water Ethanol calcium chloride CaCl 2 citric acid C 6 H 8 O 7 stearic acid C 18 H 36 O 2 sodium chloride NaCl potassium iodide KI sucrose C 12 H 22 O 11

6 RESULTS AND POST-LAB QUESTIONS 1. Using the physical property of solubility in water separate the compounds into 2 groups. Group 1 Group 2 Soluble in water Insoluble in water 2. What other physical properties do these groups have in common? Group 1 Group 2 3. Which compounds do not share all the physical properties of these groups? Name the compounds and the unshared physical property. 4. Separate the compounds into 2 groups based on the type of compound (i.e. ionic or molecular). Ionic Molecular

7 5. Describe the general physical properties for ionic compounds. 6. Describe the general physical properties for molecular compounds. 7. Using your data, which physical property best separates the compounds into ionic or molecular? 8. Using your data, which physical property is least helpful in separating the compounds into ionic or molecular? Why? 9. List the physical properties you would predict the following compounds to have. methane - CH 4 acetic acid - HC 2 H 3 O 2 copper(ii) sulfate - CuSO 4