Which one of the following should have the lowest boiling point?
a) HBr
b) Zn
c) N2
d) CH3OH
e) NO
The answer is (e) NO.
To determine which one of the given substances should have the lowest boiling point, we need to compare their molecular properties. Boiling point is generally influenced by the strength of intermolecular forces between molecules.
a) HBr: HBr is a polar molecule with hydrogen bonding and dipole-dipole interactions. It has strong intermolecular forces, so it should have a higher boiling point compared to some other substances on the list.
b) Zn: Zinc (Zn) is a metal and does not exist as individual molecules. Therefore, it does not have intermolecular forces and does not have a boiling point.
c) N2: Nitrogen (N2) is a nonpolar molecule with London dispersion forces as the only intermolecular force. London dispersion forces are generally weaker than dipole-dipole interactions and hydrogen bonding. Therefore, N2 should have a lower boiling point than HBr.
d) CH3OH: Methanol (CH3OH) is a polar molecule with dipole-dipole interactions and hydrogen bonding. It has stronger intermolecular forces compared to N2 but weaker than HBr. Therefore, CH3OH should have a higher boiling point compared to N2 but lower than HBr.
e) NO: Nitric oxide (NO) is a polar molecule with dipole-dipole interactions. It has weaker intermolecular forces compared to HBr, CH3OH, and N2. Therefore, NO should have the lowest boiling point among all the given substances.
So, the substance with the lowest boiling point among the given options is e) NO.
To determine which substance should have the lowest boiling point, we need to consider the intermolecular forces present in each molecule. The strength of the intermolecular forces directly affects the boiling point.
Let’s analyze each of the given options:
a) HBr: HBr is a polar molecule due to the difference in electronegativity between hydrogen and bromine. It will experience dipole-dipole forces as the intermolecular force. These forces are stronger than the other options without hydrogen bonding.
b) Zn: Zinc (Zn) is a metal, not a molecule. It does not exist as discrete units and therefore does not have intermolecular forces or boiling point.
c) N2: Nitrogen gas (N2) consists of two nitrogen atoms with a triple bond between them. Since nitrogen is non-polar, the intermolecular forces are weak London dispersion forces. These are generally weaker than dipole-dipole forces.
d) CH3OH: Methanol (CH3OH) is a polar molecule due to the electronegativity difference between carbon, oxygen, and hydrogen. It can experience both dipole-dipole forces and hydrogen bonding, which are stronger than London dispersion forces.
e) NO: Nitric oxide (NO) is a linear molecule and is also a radical. It is paramagnetic and does not have a permanent dipole moment, making it non-polar. Therefore, the intermolecular forces present are only London dispersion forces.
Considering the options, NO (Nitric oxide) should have the lowest boiling point since it experiences the weakest intermolecular forces (London dispersion forces).
In summary, the answer is e) NO.