Structured Inquiry Intermolecular Attractions, Polarity, Ion Dipole

Purpose: to investigate and describe the intermolecular forces acting between molecules in various types of molecular substances.

Materials: Small Bottles of water, ethanol,1- Butanol, 1- Propanol , polyethylene plate, micro-wells, ruler, glass capillary tubes, Micro-Titrator or .50 microtip Small Beral Pipettes,computer Vernier computer interface, Logger Pro ,6 pieces of filter paper (2.5 cm x 2.5 cm) 2 small rubber bands , masking tape

Procedure:

  1. Measure a .050 ml drop of liquid on the non- polar polyethylene plate. Measure the drops width on the plate.
  2. Rank the liquids in order for each drop to completely evaporate.
  3. Count the # of drops it takes to fill a micro-well for each liquid.
  4. Take a capillary tube and place it in each well. Remove the glass capillary tube and determine the liquid level rise in each Glass capillary tube
  5. Connect the probes to the computer interface. Prepare the computer for data collection by opening the file “09 Evaporation” from the Chemistry with Vernier folder.
  6. Wrap Probe 1 and Probe 2 with square pieces of filter paper secured by small rubber bands as shown in Figure 1. Roll the filter paper around the probe tip in the shape of a cylinder. Hint: First slip the rubber band up on the probe, wrap the paper around the probe, and then finally slip the rubber band over the wrapped paper. The paper should be even with the probe end.
  7. Stand Probe 1 in the ethanol container and Probe 2 in the 1-propanol container. Make sure the containers do not tip over.
  8. Prepare 2 pieces of masking tape, each about 10 cm long, to be used to tape the probes in position during Step 6.
  9. After the probes have been in the liquids for at least 30 seconds, begin data collection by clicking . Monitor the temperature for 15 seconds to establish the initial temperature of each liquid. Then simultaneously remove the probes from the liquids and tape them so the probe tips extend 5 cm over the edge of the table top as shown in Figure 1.
  10. When both temperatures have reached minimums and have begun to increase, click to end data collection. Click the Statistics button, , then click to display a box for both probes. Record the maximum(t1) and minimum(t2) values for Temperature 1 (ethanol) and Temperature 2 (1-propanol).
  11. For each liquid, subtract the minimum temperature from the maximum temperature to determine t, the temperature change during evaporation.
  12. Repeat the experiment for water and 1- butanol

Data:

Substance / Molecular
Formula / Molar Mass / Width of Drop / Change in Temp
During evap. / Number of Drops to fill well / Height in Capillary Tube
Water / H2O
Ethanol / CH3CH2OH
1-Propanol / CH3 CH2CH2 OH
1-Butanol / CH3 CH2 CH2CH2OH

Questions

  1. Which of the substances had the drop that was least attracted to the surface? How could you tell that this was true?
  1. Which of the drops was the flattest and widest? What does this mean about the attraction of the molecule to itself relative to the surface?
  1. Which liquid had the greatest change in temperature when it was evaporating? What does this imply about the attraction of the molecules to each other?
  1. Which took the most drops to fill the well to the point it spills ? What does that mean about the size of those drops? If gravity is constant, the dropper type is the same, what does that mean about the attraction of those molecules to each other?
  1. When you compare the size of the molecules of water and Ethanol, which is bigger? How does this compare to the size of the drops?
  1. Can you determine whether the polyethylene is made of polar or non-polar molecules?
  1. The glass capillary tube contains ions, based on this fact which molecule shows the greatest Ion –Dipole attraction.
  1. Can you rank these substances from weakest intermolecular attraction to strongest intermolecular attractions and justify your answer?

Additional Research

Determine the following Information about each of the following using the Internet.

Please paste the link resource.

Substance / Molecular
Formula / Boiling Point / Vapor Pressure at 298 Kelvin / Dipole Moment / Density at same temp.
Water / H2O
Ethanol / CH3CH2OH
1-Propanol / CH3 CH 2CH2 OH
1-Butanol / CH3 CH2 CH2CH2OH

Graphical Analysis using Logger Pro

Plot Molar Mass

1. vs Boiling Point

2. vs Vapor Pressure

Explain Graphical trends based on Molecular structure and IMF

9. Why is the Dipole Moment changing?

Teacher notes:

Science Practices Addressed:

6.1 The student can justify claims with evidence.

6.2 The student can construct explanations of phenomena based on evidence produced

through scientific practices.

6.3 The student can articulate the reasons that scientific explanations and theories are

refined or replaced.

6.4 The student can make claims and predictions about natural phenomena based on

scientific theories and models.

6.5 The student can evaluate alternative scientific explanations.

7.1 The student can connect phenomena and models across spatial and temporal scales.

The objective of this lab is to have students explore

  • How structure and size of the molecule effect IMF.
  • Polarity of a molecule is effected by its size
  • Studentswillmakeobservationswith varioussolutionstodeterminethe connectionbetween:
  • molecularstructureandpolarity
  • hydrogenbondingandstructure
  • capillaryactiontopolarity
  • AngleofcurvaturerelationshiptoIMF
  • Dropsizeand IMF

Capillary height

The height h of a liquid column is given by:[5]

where is the liquid-air surface tension (force/unit length), θ is the contact angle, ρ is the density of liquid (mass/volume), g is local acceleration due to gravity (length/square of time[6]), and r is radius of tube (length). Thus the thinner the space in which the water can travel, the further up it goes.

Drop on the plate

The thickness of a puddle of liquid on a surface whose contact angle is 180° is given by:[7]

where

is the depth of the puddle in centimeters or meters.
is the surface tension of the liquid in dynes per centimeter or newtons per meter.
is the acceleration due to gravity and is equal to 980cm/s2 or 9.8m/s2
is the density of the liquid in grams per cubic centimeter or kilograms per cubic meter

Illustration of how lower contact angle leads to reduction of puddle depth

In reality, the thicknesses of the puddles will be slightly less than what is predicted by the above formula because very few surfaces have a contact angle of 180° with any liquid. When the contact angle is less than 180°, the thickness is given by:[7]

Water

Properties
Molecular formula / H2O
Molar mass / 18.01528(33)g/mol
Appearance / white solid or almost colorless, transparent, with a slight hint of blue, crystalline solid or liquid [2]
Density / 1000kg/m3=1g/cm3, liquid (4°C) (62.4 lb/cu. ft)
917kg/m3, solid
Boiling point / 99.98°C, 211.97°F, 373.13K[3]
Dipole moment / 1.85D

Ethanol

Properties
Molecular formula / C2H6O
Molar mass / 46.07 g mol−1
Appearance / Colorless liquid
Density / 0.789 g/cm3 (at 20°C)
Boiling point / 78.37°C; 173.07°F; 351.52K
Vapor pressure / 5.95 kPa (at 20 °C)
Viscosity / 0.0012 Pa s (at 20 °C), 0.001074 Pa s (at 25 °C)[3]
Dipole moment / 1.69 D[4]

1-Propanol

Properties
Molecular formula / C3H8O
Molar mass / 60.10 g mol−1
Appearance / Colorless liquid
Density / .803 g/mL
Boiling point / 97 to 98°C; 206 to 208°F; 370 to 371K
log P / 0.329
Vapor pressure / 1.99 kPa (at 20 °C)
Viscosity / 1.938 mPa s
Dipole moment / 1.68 D

1- Butanol

Properties
Molecular formula / C4H10O
Molar mass / 74.12 g mol−1
Odor / harsh, alcoholic and sweet
Density / 0.81 g cm-3
Boiling point / 117.7°C; 243.9°F; 390.8K
log P / 0.839
Dipole moment / 1.66 D