Which pair will not form an ideal solution ?

Options

A. `C_(2)H_(5)Br and C_(2)H_(5)I`
B. `C_(6)H_(5)Br and C_(6)H_(5)I`
C. `C_(6)H_(6) and C_(6)H_(5)CH_(3)`
D. `C_(2)H_(5)I and C_(2)H_(5)OH`

Answer

To determine which pair of substances will not form an ideal solution, we need to understand the characteristics of ideal solutions. An ideal solution is one where:

1. The change in volume upon mixing (ΔV) is zero. This means that the total volume of the solution is equal to the sum of the volumes of the individual components.
2. The change in enthalpy upon mixing (ΔH) is zero. This indicates that there is no heat absorbed or evolved during the mixing process.

For a solution to be ideal, the interactions between the molecules of the two components must be similar to the interactions between the molecules of each component. This can be expressed mathematically as:

- Interaction of AA molecules + Interaction of BB molecules = Interaction of AB molecules

Where A and B are the two components of the solution.

Now, let's analyze the given pairs:

1. **C2H5Br (ethyl bromide) and C2H5I (ethyl iodide)**: Both are alkyl halides and have similar molecular structures. Thus, they are likely to have similar intermolecular interactions, suggesting they will form an ideal solution.

2. **C6H5Br (bromobenzene) and C6H5Cl (chlorobenzene)**: Both are aryl halides and also have similar molecular structures. Therefore, they are likely to have similar intermolecular interactions, indicating they will form an ideal solution.

3. **C6H6 (benzene) and C7H8 (toluene)**: Both are hydrocarbons and have similar types of intermolecular forces. Hence, they are likely to have similar interactions, suggesting they will form an ideal solution.

4. **C2H5OH (ethyl alcohol) and C2H5I (ethyl iodide)**: Ethyl alcohol is a polar molecule that can form hydrogen bonds, while ethyl iodide is a non-polar molecule. The difference in their intermolecular interactions (hydrogen bonding in alcohol and van der Waals forces in iodide) means that they will not have similar interactions when mixed. Therefore, they will not form an ideal solution.

Based on this analysis, the pair that will not form an ideal solution is:

**C2H5OH (ethyl alcohol) and C2H5I (ethyl iodide)**.