Teacher Notes 1 Intermolecular Forces Objectives Students determine the effects of molecular size and shape on the strength of intermolecular forces for different alcohols within the same homologous series and between isomeric pairs. Through this investigation, students: ♦ Explain why evaporation causes a decrease in temperature ♦ Describe the relationship between evaporation rate and the strength of intermolecular forces of attraction among molecules ♦ Describe the relationship between the size of molecules in a homologous series and the strength of intermolecular forces of attraction between them ♦ Describe the influence the shape of a molecule has on its vapor pressure by comparing the evaporation rates of two isomeric alcohol pairs Time Requirement ♦ Preparation time 10 minutes ♦ Lab activity 50 minutes Materials and Equipment For each student or group: ♦ Data collection system ♦ Methanol (CH 3 OH), 5 mL ♦ Stainless steel temperature sensor 1 ♦ Ethanol (C 2 H 5 OH), 5 mL ♦ Graduated cylinder, 10-mL ♦ Propanol (C 3 H 7 OH), 5 mL ♦ Test tubes (6), 15-mm x 100-mm ♦ Butanol (C 4 H 9 OH), 5 mL ♦ Test tube rack ♦ 2-Propanol (C 3 H 7 OH), 5 mL ♦ Stoppers (6), to fit the test tubes ♦ 2-Butanol (C 4 H 9 OH), 5 mL ♦ Wash bottle and waste container ♦ Masking tape (2), 6-cm strips 1 A fast-response temperature sensor is not appropriate for this experiment. Concepts Students Should Already Know Students should be familiar with the following concepts: ♦ Kinetic molecular theory ♦ Bonding ♦ Electronegativity ♦ Polar and non-polar molecules ♦ Average kinetic energy ♦ Pressure
Transcript
Teacher Notes
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Intermolecular Forces
Objectives
Students determine the effects of molecular size and shape on the strength of intermolecular forces for different alcohols within the same homologous series and between isomeric pairs. Through this investigation, students:
♦ Explain why evaporation causes a decrease in temperature
♦ Describe the relationship between evaporation rate and the strength of intermolecular forces of attraction among molecules
♦ Describe the relationship between the size of molecules in a homologous series and the strength of intermolecular forces of attraction between them
♦ Describe the influence the shape of a molecule has on its vapor pressure by comparing the evaporation rates of two isomeric alcohol pairs
Time Requirement
♦ Preparation time 10 minutes
♦ Lab activity 50 minutes
Materials and Equipment
For each student or group:
♦ Data collection system ♦ Methanol (CH3OH), 5 mL
♦ Stainless steel temperature sensor1 ♦ Ethanol (C2H5OH), 5 mL
♦ Graduated cylinder, 10-mL ♦ Propanol (C3H7OH), 5 mL
♦ Test tubes (6), 15-mm x 100-mm ♦ Butanol (C4H9OH), 5 mL
♦ Test tube rack ♦ 2-Propanol (C3H7OH), 5 mL
♦ Stoppers (6), to fit the test tubes ♦ 2-Butanol (C4H9OH), 5 mL
♦ Wash bottle and waste container
♦ Masking tape (2), 6-cm strips 1 A fast-response temperature sensor is not appropriate for this experiment.
Concepts Students Should Already Know
Students should be familiar with the following concepts:
♦ Kinetic molecular theory ♦ Bonding ♦ Electronegativity ♦ Polar and non-polar molecules ♦ Average kinetic energy ♦ Pressure
Intermolecular Forces
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Lab Preparation Although this activity requires no specific lab preparation, allow 10 minutes to gather the equipment needed to conduct the lab.
Teacher Tips:
♦ When performing this lab, make certain to have good ventilation in the room.
♦ If you would like to minimize waste of the alcohols used in this experiment, you can have the first group of students set up and label the test tubes and then re-use the test tubes for each of the remaining class periods. Alternatively, pour small amounts into either 50-mL or 100-mL beakers for the students to measure from. When they are done with evaporating each alcohol they can then pour the unused alcohol back into the beaker for the next group or class.
Safety Add these important safety precautions to your normal laboratory procedures:
♦ Use a wafting motion when smelling chemicals.
♦ Alcohols are flammable. Smother pentanol and 2-butanol fires with sand or a Type B fire extinguisher.
♦ Ensure that there is good ventilation in the room. Butanol and pentanol have strong odors.
