Experiment 5 - How do Geckos walk up walls-SP19 PDF

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Experiment 5 How Can Geckos Walk Up Walls?: A lesson on Intermolecular Forces Ben Lyon and Abby Barrett ANALYSIS and DISCUSSION 1. For Part A, determine the polarity and intermolecular force(s) involved in each liquid (water, ethanol, cyclohexane). Use your data (volatility, solubility, surface tension, and capillary action) to support your answer. Water: polar Forces in water are : dispersion, dipole-dipole, hydrogen bonding. Hydrogen bonding is strongest. Ethanol: polar Forces in ethanol are: dispersion, dipole-dipole, and hydrogen bond. Hydrogen bonding is strongest. Cyclohexane: Nonpolar Forces in cyclohexane: Dispersion only Chemica l

Volatility (Minutes)

Solubilit y (In

Surface tension (dyn/cm)

Capillary Action (cm up tube)

Water) Water

22 min

-----------

72.86

2

Soluble

22.8

1.7

Insolubl

25.3

1.5

-------Ethanol

3 min 14 sec

Cyclohe xane

1 min 53 sec

e

2. Identify each unknown liquid and the intermolecular force(s) involved in each liquid. Provide evidence from your experiment that confirms your conclusions. Substance A: Water, because it has a similar density to water in the first experiment. It was soluble in water, we fit a similar amount of drops on the penny, and a similar volatility as water. Intermolecular Forces: dispersion, dipole-dipole, hydrogen bonding. Hydrogen bonding is strongest. (polar) Substance B: Acetone, because our density was similar to acetone (0.791

g/ml). Also, it was soluble in water. Intermolecular Forces: dispersion, and dipole-dipole (polar) Substance C: Hexane, because it was not soluble in water. Also, our density was similar to Hexane (0.659 g/ml). Intermolecular Forces: dispersion (nonpolar) Substance D: Glycerin, because it had a high volatility. Also, the density was similar to Glycerin (1.26 g/ml). Intermolecular Forces: dispersion, dipole-dipole, hydrogen bonding. Hydrogen bonding is strongest. (polar) Substance E: Butanol, because because our density was similar to Butanol (0.81 g/ml). Also, it was slightly soluble in water. Intermolecular Forces: dispersion, dipole-dipole, hydrogen bonding. Hydrogen bonding is strongest. (polar) Unkno Volatilit wn Substance y (Time) ty

Solubili (In

Surfac Density e tension (# of (grams/millilit Drops) er)

water) A

25+

Compl etely Soluble

24

0.96

B

56 sec

Slightly miscible but dissolved over time

16

0.79

C

56 sec

7

0.69

Dissolv ed after being stirred. Slightly miscible

20

1.3

Insolub

17

0.81

min

Insolub le

D

30+ min

E

14 min le

Density: Substance A: 1.92 grams/ 2mL= 0.96 g/ml

3. Fill in the blanks: The stronger the IMF the a. _Higher_(higher/lower) the melting/freezing/boiling points because _The bonds require more energy to break_. b. _Lower_(higher/lower)the vapor pressure because _molecules with strong

IMF’s want to remain in the liquid state _. c. _Higher_(higher/lower) the viscosity because _The individual molecules are able to withstand gravity due to stronger bonds_. d. _Stronger_(stronger/weaker) the surface tension because _the IMF’s hold the molecules together against the force of gravity_. e. _Weaker_(stronger/weaker)the capillary action because _the stronger the IMF the higher the cohesion between the molecules which decreases adhesion forces between the substance and the container_. 4. How can a gecko walk upside-down on a ceiling? Why can geckos walk upside-down on ceilings, while humans cannot? Structures inside the feet of gecko’s contain microtubules which provide the gecko with the ability to alter the IMF’s inside its feet. This gives them the ability to run on surfaces that humans can’t.

Experiment 5: POST-QUESTIONS 1. Explain, using intermolecular forces, why at room temperature, petrol (mainly octane, C8H18) is a liquid, while candle wax (C23H48) is a solid. At room temperature, candle wax is a solid because dispersion forces are stronger.

Dispersion forces are affected by surface area and size of the molecule. Petrol has weaker dispersion forces, therefore at they have a lower melting point (more likely to be a liquid at room temperature).

2. Indicate the molecular interactions for questions a & b below. Polyethylene, a type of plastic found in grocery bags, is made from the monomer H2C=CH2. These monomers interact in two chief ways to make grocery bags: a. These polymer chains fold up on one another forming these weak secondary bonds. - Dipole-Dipole Forces (polar structure) b. They form long chains (polymers) held together by a strong sharing of electrons. - covalent bonding between hydrogen and carbon.

3. For the following, determine the best answer AND justify your decision: I. Determine which substance has the lowest boiling point: B. H2 because it has weak dispersion forces and is extremely light. This lack of weight and IMF’s allows it to be in its gaseous phase at a very low temperature. II. Determine which substance has the lowest vapor pressure at 25°C: a. HF because it has the strongest intermolecular forces (hydrogen bonding) which means it is has a high boiling point, and low vapor pressure. III. Determine which substance has the highest surface tension: B. H2O because the intermolecular forces are strongest. hydrogen bonds when compared to

H 2O

more available

C H 3 C H 2 OH .

4. Molecular iodine would be most soluble in: Molecular Iodine is nonpolar, so carbon tetrachloride would be most soluble. This is because carbon tetrachloride is both nonpolar, meanwhile the other listed chemicals have strong polar bonds which don’t mix with nonpolar molecules. a. Carbon tetrachloride - Nonpolar b. Water - Polar c. Vodka (ethanol and water) - Polar d. Vinegar (acetic acid and water) - Polar...