Question

Which of the following compounds would you expect to dissolve in water?

            HI                KCl                CH₃OH             Br₂               CBr₄           CO

Answer 1

For a compound to dissolve in water, which happens to be a polar solvent, the compound needs to be polar too.

Hence, among the given compounds, all the compounds that have non-zero dipole moment can dissolve in water.

Note that since water itself is a polar molecule, the O atom has a partial negative charge and H atom in water has a partial positive charge. Now, a polar molecule also has partial positive end and partial negative end. Hence, they can form strong attractive forces with the opposite partial charges of water molecule. This attractive forces result in them being soluble in water.

Now, among the given molecules:

HI

It contains a polar H-I bond as I is more electronegative than H. Hence, it will dissolve in water.

KCl

K is an electropositive metal and Cl is an electronegative element. Hence, they form strong ionic bond and hydrolyse in water. Hence, KCl will also dissolve in water.

CH₃OH

Methanol is also a polar molecule because of the electronegative O atom.Hence, the C-O and O-H bonds are polar. Hence, H and O atoms of methanol can form strong Hydrogen bonding with water resulting in it being soluble in water. Hence, it will dissolve in water.

Br₂

Br₂ is non-polar as it is a homonuclear diatomic molecule. Hence, it will not be able to dissolve in a polar solvent like water.

CBr₄

It has a tetrahedral structure, which leads to cancellation of individual C-Br bond dipoles, resulting in a non-polar molecule.

Hence, it will not dissolve in water.

CO

Carbon monoxide has a polar C-O bond. Hence, it should dissolve in water. But since it exists primarily as a gas, its solubiility will be low.

Hence, the compounds we will expect to dissolve in water are HI, KCl, CH3OH and CO.