(a) Which of the ions Cs + , Sr 2+ , Ba 2+ will have the largest heat of hydration? Which the smallest? (b) Of the two compounds NaF and MgF 2 , which has the stronger intermolecular forces? (c) Of the two compounds NaNO 3 and HF, which has the stronger intermolecular forces?
To determine which ion will have the largest heat of hydration and which will have the smallest, you need to consider the size and charge of the ions.
(a) The heat of hydration is the energy released or absorbed when a gaseous ion is dissolved in water and surrounded by water molecules. In general, smaller ions and/or ions with larger charges tend to have stronger attractions to water molecules, resulting in a larger heat of hydration.
Comparing the ions Cs+, Sr2+, and Ba2+:
- Cs+ is the largest ion and has the lowest charge, so it can easily be hydrated by water molecules. As a result, Cs+ will have the largest heat of hydration.
- Ba2+ is smaller than Sr2+, but it has a larger charge. Therefore, Ba2+ will have a larger heat of hydration than Sr2+.
- Sr2+ is smaller than both Cs+ and Ba2+ and has the highest charge, so it will have the smallest heat of hydration among the three ions.
Therefore, the order of the largest to smallest heat of hydration is Cs+ > Ba2+ > Sr2+.
(b) To determine which compound, NaF or MgF2, has stronger intermolecular forces, you need to compare the charges and sizes of the ions involved.
- NaF consists of Na+ and F- ions. The Na+ ion is larger than the F- ion and has a +1 charge, while the F- ion is smaller and has a -1 charge. The size of the ions affects how closely they can approach each other, and the charges influence the strength of the electrostatic attraction between ions.
- MgF2 consists of Mg2+ and 2 F- ions. The Mg2+ ion is smaller than the Na+ ion but has a larger charge of +2. The F- ions are the same as in NaF.
The larger charge and smaller size of the Mg2+ ion result in stronger intermolecular forces in MgF2 compared to NaF. Therefore, MgF2 has stronger intermolecular forces.
(c) To determine which compound, NaNO3 or HF, has stronger intermolecular forces, you need to consider the types of intermolecular forces present in each compound.
- NaNO3 consists of Na+ and NO3- ions. Na+ is larger than the F- ion and has a +1 charge, while NO3- is a polyatomic ion with a large negative charge. The charges and sizes of these ions result in ionic interactions in NaNO3, which are generally stronger than other intermolecular forces.
- HF consists of H+ and Fâ ions, creating a hydrogen bond between them. Hydrogen bonds are stronger than typical dipole-dipole interactions.
Comparing the two compounds, HF has hydrogen bonding, which is stronger than the ionic interactions present in NaNO3. Therefore, HF has stronger intermolecular forces than NaNO3.
In summary:
(a) The order of the largest to smallest heat of hydration: Cs+ > Ba2+ > Sr2+.
(b) MgF2 has stronger intermolecular forces than NaF.
(c) HF has stronger intermolecular forces than NaNO3.
(a) The heat of hydration is the energy released or absorbed when an ion is surrounded by water molecules in aqueous solution. Generally, the heat of hydration increases as the charge density of the ion increases.
Cs+ has the largest heat of hydration because it has the smallest size and highest charge density among the ions Cs+, Sr2+, and Ba2+. The smaller size of Cs+ allows it to interact more closely with water molecules, resulting in a higher energy release during hydration.
Ba2+ has the smallest heat of hydration because it has the largest size and lowest charge density among the ions Cs+, Sr2+, and Ba2+. The larger size of Ba2+ reduces its ability to interact closely with water molecules, resulting in a lower energy release during hydration.
Therefore, the order of the heat of hydration from highest to lowest is Cs+ > Sr2+ > Ba2+.
(b) The strength of intermolecular forces depends on the type of bonding present in a compound. NaF and MgF2 are both ionic compounds.
NaF has weaker intermolecular forces compared to MgF2. The bond between Na+ and F- in NaF is purely ionic, resulting in weaker intermolecular forces. On the other hand, the bond between Mg2+ and F- in MgF2 is stronger due to the higher charge on the cation, resulting in stronger intermolecular forces.
Therefore, MgF2 has stronger intermolecular forces than NaF.
(c) Similarly, the strength of intermolecular forces depends on the type of bonding present in a compound.
NaNO3 has weaker intermolecular forces compared to HF. NaNO3 is an ionic compound, and the strength of intermolecular forces is determined by the ionic bonds between Na+ and NO3-. These forces are weaker compared to the covalent bond in HF.
HF has stronger intermolecular forces because it has a polar covalent bond between H and F. The electronegativity difference between H and F leads to a partial positive charge on H and a partial negative charge on F, resulting in stronger intermolecular forces compared to NaNO3.
Therefore, HF has stronger intermolecular forces than NaNO3.