A chemistry problem

Question

Consider the following organic molecules.

(a) Which of the substances pictured above would be insoluble in water? Explain in terms of the molecular structure for both the substance and for water.

(b) Would the remaining two substances, once dissolved in water, be considered electrolytes or nonelectrolytes? Explain your reasoning.

(c) If the two substances that are soluble in water are separated via column chromatography, summarize and explain the separation of the two components. Assume the column is packed with highly polar silica gel.  

(d) A chemist uses a 12% by mass solution of ethanol with a known density of 0.789 g/mL. What is the 

molarity of this solution?

Answer 1

(a) Benzene would be insoluble in water. It is a non polar molecule and would not be miscible with the very polar water molecule. Dimethyl ether would only be partially soluble, but since they ask for only 1, it would be benzene.

(b) The other two are considered to be non electrolytes because they don't ionize.

(c) The more non polar ether compound would not be attracted to the column and we be eluted first. The more polar alcohol would be retained by the column and would be eluted later.

(d) Assume 1000 ml of solution. 1000 ml x 0.789 g/ml = 789 g solution

12% is ethanol, so 789 g x 0.12 = 94.68 g ethanol in 1 liter

molar mass ethanol = 46.1 g/mol

94.68 g x 1 mol/46.1 g = 2.05 mol / L = 2.05 M