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Ayala Chemistry

LABS CHEM Chemical Bonds

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Chemical Bond
 
Objectives: 
 Compare the melting points of eight solids
 Determine the conductivity of the solids in water and in ethanol.
 Determine the conductivity of water solutions of the soluble solids.
 Classify the compounds into groups of ionic and covalent compounds.
 Summarize the properties of each group.
Introduction:  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 electron from one atom or group of atoms is transferred to another atom.  Positive and negative ions are created through the transfer.  In covalent compounds no electrons are transferred; instead electrons are shared by the bonded atoms.
  The physical properties of a substance, such as melting point, solubility, and conductivity, can be used to predict the type of bond that binds the atoms of the compound.  In this experiment, you will test eight compounds to determine these properties.  Your compiled data will enable you to classify the substances as either ionic or covalent compounds.
Safety:  Always wear safety goggles and a lab apron to protect eyes and clothing. If you get a chemical in your eyes, immediately flush out at the eye wash station while calling to your teacher. Know the location of the emergency lab shower and eyewash station and the procedure for using them.
  Do not any chemicals. If you get a chemical on your skin or clothing, wash the chemical off at the sink while calling to your teacher. Make sure you carefully read the labels and follow the precautions stated on the label, ask your teacher what precautions you should follow. Do not taste any chemicals or items used in the laboratory. Never return leftovers to their original containers; take only small amounts to avoid wasting supplies.
  Call you teacher in the event of a spill. Spills should be cleaned promptly, according to your teacher’s directions.
  When you use a candle, confine long hair and loose clothing. If your clothing catches on fire, walk to the emergency lab shower, and use it to put out the fire. Do not heat glassware that is broken, chipped or cracked. Use tongs or hot mitt to handle heated glassware and other equipment does not look hot.
  Ethanol is flammable. Make sure there are no flames in the room before you use this chemical.

Materials: -24-well microplate                       -Phenyl salicylate
 -Calcium chloride                                        -Potassium iodide
 -Candle                                                        -Ring Stand
 -Lauric Acid                                                 -Sodium Chloride
 -Conductivity tester                                      -Palmitic Acid
 -Ethanol                                                      -Tin can lid
 -iron ring stand                                             -Thin-stemmed pipets, 2
 
Procedure: 1. Before you begin, write a brief description of each of the six substances in your data table.
 2. Place a can lid on an iron ring attached to a ring stand. Position the ring so that it is just above the tip of a candle flame, as shown in figure A. Light the candle for a moment to check that you have correct height.
 3. Place a few Crystals of Palmitic acid, sodium chloride, Phenyl salicylate, Calcium chloride, lauric acid, and potassium iodide in separate locations on the lid, as shown in figure B. Do not allow the samples of crystals to touch. Draw a diagram that shows the position of each compound.
 4. For this experiment it is not necessary to have exact values for the melting point. The lid will continue to get hotter as it is heated, so the order of melting will give relative melting points. Light the candle and observe. Note the substance that melts first by writing a 1 in the data table. Record the order of the melting for the other substances.
 5. After 2 min, record an n in your data table for each substance that did not melt. Extinguish the candle flame. Allow the tin can lid to cool while you complete the remainder of the experiment.
 6. Put a few crystals of each of the white solids in the top row of your microtitration plate. Repeat with the second row. Add 10 drops of water to each well in the top row. Record the solubility of each substance in your data table.
 7. Add 10 drops of ethanol to each well in the second row of the microtitration plate. Record the solubility of each substance in your data table.
 8. Test the conductivity of each water solution on the top row by dipping both electrodes into each well of the microtitration plate. Be sure to rinse the electrodes and dry them with a paper towel after each test. If the bulb of the conductivity apparatus light up, the solution conducts electricity.
 
Cleanup and Disposal
9. Clean the microplate by rinsing it with water into a pan provided by your teacher. If any wells are difficult to clean, use a cotton swab. Wash your hands thoroughly before you leave the lab and after all work is finished.
DATA TABLE:
Compund       Description   Melting Point    Solubility in water   Solubilility in ethanol   Solution
                                                                                                                                        conductivity
 Calcium
 Chloride
 
 Palmitic
 Acid
 
 Phenyl
 Saclicylate
 
 Potassium
 Iodide
 
 Sodium
 Chloride
 
 Lauric
 Acid
 
 
Calculations
1. Organizing Results: Arrange the substances into two groups according to their
     properties.  Explain the properties used to create the groups.  Experimental groups.
2. Calculate the type of bond formed using the electronegativity data found on page 151, in your textbook.  Group the six compounds according to their bond type. Calcium Chloride  CaCl2,  Palmitic Acid  CH3(CH2)14COOH,  Potassium Iodide KI, Lauric Acid  CH3(CH2)10COOH, 
Sodium Chloride NaCl, Phenyl Salicylate  C6H4(OH) COOC6H5. Theoretical groups.
3. Draw dot diagrams for each of the substances in this experiment, except Phenyl Salicylate
Table of Results: List both groups (experimental and theoretical)

Question 1.  Write a statement to summarize the properties of ionic compounds and another statement to summarize the properties of covalent compounds.