Which one of the following substances has the highest solubility in the specified liquid at a temperature of 298 K and 1 atm pressure?
A. sodium chloride in liquid cyclohexane
B. bromine in liquid hexane
C. hydrogen in liquid water
D. potassium bromide in liquid tetrachloromethane
E. silicon dioxide in liquid water
Background
To determine the answer, we need to find the intermolecular forces of the molecules.
Example:
NaCl : which is an ionic salt. It is made of 2 ions Na^+ and Cl^- which will interact to form ion-dipole attractions with water.
What Happens with Cl^- ion
(-) so attracted to (δ+)
What Happens with Na^+ ions
(+) attracted to (δ-) part of water (oxygen atom)
Oxygen has a higher electronegativity than Hydrogen so there is a net-dipole moment. Oxygen exerts a stronger attraction on electrons in water’s covalent bond between O-H. As a result, the electrons spend more time around oxygen and less time with Hydrogen. This separation of charge makes oxygen partially negative (δ-) and hydrogen partially positive (δ+)
Partial negativity (δ-) is caused when the electrons spend MORE time around the atom than in other regions.
Partial positivity (δ+) is caused when the electrons spend LESS time around the atom than in other regions.
Approach
Polarity is determined by the structure of the molecule (asymmetric = polar), and the difference in electronegativity
Electronegativity Scale
0.0-0.4 (non-polar - covalent bond)
0.4-1.7 (polar - covalent bond)
greater than (>) 1.7 (Ionic bond)
Remember that Like Dissolves like!
Let’s summarize the results:
A. Polar solute ------- Non-polar solvent
B. Non-Polar solute ------- Non-polar solvent
C. Non-Polar solute ------- polar solvent
D. Polar solute ------- Non-polar solvent
E. Non-Polar solute ------- polar solvent
