Lab #20: Observing the Behavior of Electrons Background: In today s lab we will examine the attractive forces that hold molecules together and the disruptive forces that break them apart. The forces between molecules that hold molecules together are called Intermolecular Forces (IMF) and are comprised of: Hydrogen bonds (H-bonding) Dipole-dipole forces London dispersion forces (LDF) All material is held together by attractive forces but there is always some disruptive force present that can break it apart. In solids the attractive forces are greater than the disruptive forces. With gases the disruptive forces are greater than the attractive forces. In liquids the forces of disruption and attraction are on about the same level. Cohesive forces are attractive forces between particles. They are what hold particles together. They are weak in gases and get progressively stronger as we go from liquid to solid. Recall that the force of attraction decreases with increasing distance of separation or decreasing charge. Materials: Acetone (C 3 H 6 O) Hexane (C 6 H 14 ) Water (H 2 0) Ethyl alcohol (C 2 H 6 O) Thermometer Rubber band Penny Procedure: Part 1: Answer the questions below H 2 O Water C 6 H 14 Hexane
C 2 H 6 O (or CH 3 CH 2 OH) Ethanol (C 3 H 6 O) Acetone Part 2: Investigate Evaporation Rate 1. Obtain 4 pieces of filter paper and 4 rubber bands to attach the paper towel to your thermometer. 2. Attach filter paper to end of the thermometer at the bulb with a rubber band and then dip into the test tube containing the compound to be studied (hexane, water, ethanol, or acetone). When the temperature has stabilized, record the temperature while the paper on the thermometer is still submerged in the liquid. This is the measurement for time = 0.0 min. 3. Your time starts when you pull it out of the liquid. Tape the thermometer to the lab bench so that the paper is hanging off the bench and you can read the thermometer. Note: If there is a big drop hanging from the paper when you pull it out then touch the drop to the side of the test tube to get rid of it. 4. Record the temperature to nearest 0.5 degree every thirty seconds 0.0 min Water Ethyl Alcohol Acetone Hexane 0.5 min 1.0 min 1.5 min 2.0 min 2.5 min 3.0 min 3.5 min 4.0 min
Record your data in the graph below. Label axes (with units) and give the graph a title in the y-axis vs. x-axis format. Title: Part 3: Investigate Surface Tension Fill eye dropper with water and carefully lower tip to a penny on the table. Squeeze the bulb slowly and count the number of drops which you are able to fit onto the penny before the liquid spills off. Repeat with Ethyl alcohol, Acetone and finally Hexane. Water Ethyl alcohol Acetone Hexane # of Drops on Penny
Summary Questions: 1. Does a liquid with high IMF evaporate more quickly or less quickly than a liquid with low IMF? Explain why. 2. What is the relationship between strength of intermolecular forces and boiling point? _ 3. What is the rule that governs whether or not one substance will dissolve in another? _ Explain this rule 4. List the following intermolecular forces in order of increasing strength: H-bonds London Forces Dipole Forces 5. Which of the following substances will most like have the highest boiling point? C 6 H 12 C 6 H 11 OH C 4 H 10 C 5 H 8 (OH) 3 6. Which of the following substances will most likely evaporate the fastest? C 5 H 12 H 2 O C 4 H 6 O C 2 H 5 OH 7. Which of the following substances will most likely evaporate the slowest? C 2 H 5 OH C 2 H 6 C 2 H 4 (OH) 2 8. Which of the following substances would be most likely to dissolve in water? CH 4 CH 3 OH C 6 H 6 C 6 H 11 O 9. If you wanted to dissolve grease, a non-polar substance, off your hands, which liquid below would be best? Water, H 2 O Antifreeze, C 2 H 4 (OH) 2 Gasoline, C 8 H 18 Alcohol, C 2 H 5 OH