Question

1. What type of intermolecular force is predominant in the following two compounds? H3C -C-CH3 H3C- CH-CH (3 points) 2. Hydrazine (NH2NH2), hydrogen peroxide (HooH), and water (H20) all have higher boiling points in comparison with other substances of comparable molecular weights. What structural property do these substances have in common, and how might that account for (4 points) their high boiling points? 3. The most significant factor which is responsible for the higher boiling point of ethanol C2H5OH, compared to ethane, C2H6, is the (3 points) a. higher molecular mass b. larger size c. stronger dispersion forces d. dipolar forces e. hydrogen bonding forces 4. For each of the following substances, list all of the intermolecular forces expected. Underline (4 points) the most predominant intermolecular force. a. BF3 b. Isopropyl alcohol, CH3CHOHCH3 c. Hydrogen iodide, HI d. Krypton, Kr 5. 1-Propanol, CH3CH2CH2OH, has a molecular weight that is similar to that of acetone, yet acetone boils at 56.50C and 1-propanol boils at 97.20C. Explain the difference. (3 points) 6. Would naphthalene, C10H8, be more soluble in ethanol, C2H50H, or in benzene, C6H6? (3 points) Explain why

Answer 1

1. The intermolecular forces presenet in acetone are : London dispersion forces and dipole dipole forces due to presenc of electronegative oxygen. while in isobutane only Van Der wall forces are present.

2. In all the three mentioned compounds there is formation of hydrogen bond ( Bond between hydrogen and high electronegative element( F, O , N) . Due to Intermolecular hydrogen bonds the molecules are more tightly packed and have high boiling point.

3. In ethanol there is hydrogen bonded to highly electronegative oxygen and which is responsible for hydrogen bonding and hence high boiling point

4. BF3: Weak London dispersion forces
isopropyl alcohol : Hydrogen bond

HI : London Dispersion Forces, Dipole-Dipole

Krypton: London Dispersion Forces