My professor gave us these question in call and we solved for it in class, however im not sure how we got the answers.
I dunt really understand the concept of intermolecular forces if some can please help me i have a quiz tomorrow.
A. For each pair of substance, identify the key intermolecular force(s) in eacg substance and select the substance with the lower boiling point.
a) MgCl2 or NH3
b) S02 OR C02
c) cis CHCL=CHCL or trans chcl=chcl
B. Which of the following molecules are likely to form hydrogen bonds?
a)CH3CH2OH
b)CH3CHO
c)CH3OCH3
d)CH3COOH
Does the second question mean, "B. Which of the following molecules are likely to form hydrogen bonds [with themselves]?"
You can get different answers depending on whether or not that added part is implied.
Here is my take on these.
a) MgCl2 or NH3 MgCl2 is an ionic bond and that is stronger than hydrogen bonds from NH3 so b.p. should be higher in MgCl2
b) S02 OR C02SO2 is angular, CO2 is linear; therefore, SO2 has a dipole moment whereas CO2 does not. Thus SO2 will have a higher b.p.
c) cis CHCL=CHCL or trans chcl=chclthe cis isomer is polar, the trans isomer is symmetrical and non-polar; therefore, the cis isomer should have a higher b.p.
B. Which of the following molecules are likely to form hydrogen bonds?
a)CH3CH2OH yes
b)CH3CHO yes
c)CH3OCH3 not likely or weak if at all
d)CH3COOH yes.
to drbob222
B. b) it doesnt form h bonds
A. To determine the key intermolecular forces and select the substance with the lower boiling point for each pair, we need to consider the types of intermolecular forces present in each substance.
1) MgCl2 or NH3:
- MgCl2 is an ionic compound composed of magnesium (Mg) and chloride (Cl) ions. The intermolecular forces here would be ion-ion interactions or ionic bonds.
- NH3 is a molecular compound consisting of nitrogen (N) and three hydrogen (H) atoms. The intermolecular forces in NH3 would be hydrogen bonding (between the hydrogen atoms and the lone pair of electrons on the nitrogen atom).
Comparing the two, hydrogen bonding is a stronger intermolecular force than ion-ion interactions, so NH3 would have a lower boiling point than MgCl2.
2) SO2 or CO2:
- SO2 is a molecular compound consisting of sulfur (S) and two oxygen (O) atoms. The intermolecular forces here would be dipole-dipole interactions due to the polar bonds (S-O).
- CO2 is also a molecular compound with carbon (C) and two oxygen (O) atoms. However, the structure of CO2 is linear, resulting in a symmetrical distribution of charges, making it nonpolar. The intermolecular forces here would be London dispersion forces, also known as induced dipole-induced dipole forces.
Comparing the two, dipole-dipole interactions are stronger than London dispersion forces, so SO2 would have a higher boiling point than CO2.
3) cis-CHCl=CHCl or trans-CHCl=CHCl:
- cis-CHCl=CHCl is a cis isomer of dichloroethylene, where the chloride atoms are on the same side of the double bond. Here, the intermolecular forces would be dipole-dipole interactions due to the polar bonds (C-Cl).
- trans-CHCl=CHCl is a trans isomer of dichloroethylene, where the chloride atoms are on opposite sides of the double bond. Similar to the cis isomer, the intermolecular forces would also be dipole-dipole interactions.
Since both the cis and trans isomers have the same type of intermolecular forces, the boiling point would depend on other factors like molecular shape and size. Therefore, we cannot determine which one has a lower boiling point based solely on intermolecular forces.
B. To determine which molecules are likely to form hydrogen bonds, we need to identify the presence of hydrogen-bonding functional groups: hydrogen atoms bonded to electronegative atoms—nitrogen, oxygen, or fluorine.
1) CH3CH2OH (ethanol):
- Ethanol has an -OH group, which is a hydrogen-bonding functional group. Therefore, it is likely to form hydrogen bonds.
2) CH3CHO (acetaldehyde):
- Acetaldehyde has a carbonyl group (C=O), but it does not have any hydrogen-bonding functional groups. Therefore, it is not likely to form hydrogen bonds.
3) CH3OCH3 (dimethyl ether):
- Dimethyl ether does not have any hydrogen-bonding functional groups. Therefore, it is not likely to form hydrogen bonds.
4) CH3COOH (acetic acid):
- Acetic acid has a carboxyl group (COOH), which contains an -OH group that can participate in hydrogen bonding. Therefore, it is likely to form hydrogen bonds.
In summary, molecules with -OH groups, such as CH3CH2OH and CH3COOH, are likely to form hydrogen bonds, while molecules without such groups, such as CH3CHO and CH3OCH3, are less likely to form hydrogen bonds.