Intermolecular forces. In our experiment we want to find out how intermolecular forces are present in our samples, how they interact with each other. We will experiment the relationships between molecular structures and their physical properties: volatili

water

S

S

I

I

S

hexane

I

S

S

S

I

Observations

For our first experiment we had three liquids: n-decane, n-heptane and n-pentane. We placed a drop of each alkane liquid on a dry and clean microscope slide. After waiting for one minute we noticed that n-pentane evaporated first, n-heptane second and n-decane third. Next step of our experiment was very similar but with different type of liquids. We took three different alcohols: n-butanol, n-ethanol and n-methanol. Again we placed a drop of each liquid on a slide and waited which one would be the first to evaporate. N-methanol was the first one to evaporate and n-butanol was the last one. Next we took three different compounds: alkane, alcohol and water. We placed single drop of n-butanol, water and n-pentane on a slide and noticed that n-pentane evaporated first. N-butanol evaporated second and water last.

Second experiment consisted of determining the viscosity of liquids, and their resistance to flow. We placed three compounds: glycerol, n-hexane and deionized water, in three separate tubes. After we boiled water and placed our tubes one by one inside the beaker we noticed that only one compound became very viscous, which was glycerol.

Third experiment was, on determining the solubility of liquids. We took deionized water, n-hexane, ethanol, n-butyl acetate and ethylene glycol and we mixed them one by one with each other. We saw that some liquids were miscible and some were immiscible between each other depending on intermolecular forces and their bonds.

In our last experiment we tested the solubility of solids in liquids, by taking deionized water and n-hexane and mixing them with potassium permanganate, sucrose, iodine, nickel (II) sulfate hexahydrate, and naphthalene. We took twelve small tubes, carefully cleaned them and put water in six of them and n-hexane in another six.

Discussion

From our first experiment we can see that the liquid, n-pentane, which has a shorter chain of carbon molecule in it and a lighter mass evaporated the fastest and a heavier liquid, n-decane, took longest time to evaporate. These compounds are held by dispersion forces which are a type of intermolecular forces. After finishing our second experiment with different liquids, alcohol, we saw that the first one to evaporate was n-methanol and the last was n-butanol. Methanol evaporated first because it is smaller compound with a lighter weight. But we see that these three compounds have different intermolecular forces such as: dispersion forces, dipole-dipole forces and hydrogen bonding. When we finished our last step of our first experiment, n-pentane evaporated first because this liquid does not have any hydrogen bonding comparing to another two liquids.

Second experiment showed us that glycerol was the most viscous out of three liquids and water was least viscous after being placed in boiling water. As we know when the temperature increases, the degree of intermolecular hydrogen bonding increases, and it results in increased viscosity of the liquid.

Third experiment showed us that different types of liquids are not always miscible with each other and the reason for this was their intermolecular force. One of the predominant types of intermolecular forces was hydrogen bonding.

Fourth experiment basically showed us that "like dissolves like", which means that polar solutes dissolve in polar solvents and nonpolar solutes dissolve in a nonpolar solvents. Polar molecules interact through dipole-dipole forces and hydrogen bond and nonpolar have symmetrical arrangement of bonds and there is no dipole. For example: when we added sucrose to water. Sugars have many polar oxygen-hydrogen groups and are overall highly polar. Due to the polar nature of the water, highly polar sucrose was able to dissolve in water. On another hand when we added sucrose to hexane, it did not dissolve because there is no dipole in the molecule.

Questions.

. Calcium chloride is more soluble in methanol because both compound are polar and methanol has hydrogen bonding along with London dispersion forces , on another hand we have carbon tetrachloride which is nonpolar. "Like Dissolves Like"

2. In this mixture iodine will dissolve in n-pentane and sand with sodium chloride will not. We will separate iodine and n-pentane solution from sand and sodium chloride by simply pouring it off. To sand and sodium chloride we would add some water to dissolve sodium chloride, pour off the water solution and we will wash off sodium chloride from sand and wait until sand dry. Water from sodium chloride solution will evaporate and we will end up with sodium chloride.

We will distill the solution of iodine and n-pentane to get iodine and then condense pentane vapor and we will get n-pentane.

3. C=O bond will make it polar just like water and it will be soluble in water and C-C-C chain is nonpolar just like hexane and will make it soluble in it.

4. The reason for different boiling point is that ethanol is a liquid and has a very strong hydrogen bond that's why it requires more energy on another hand it's isomer, dimethyl ether, which is a gas, requires less energy because it has no hydrogen bonding .

Boiling points:

Dimethyl ether: -24 °C, 249 K, -11 °F

Ethanol: 78 °C, 351 K, 172 °F

Conclusion

After we finished all our experiences we identified intermolecular forces within pure substances, as well as attractive forces between different substances in a mixture. We made qualitative comparison of physical properties of liquids and solids such as volatility, viscosity and solubility and correlated trends in physical properties with strength of intermolecular attractive forces.

Reference:

Department of Chemistry (2010). Laboratory Experiments in General Chemistry: Chem 110 and Chem 111, Version 9.0: Towson University