Question

Describe a method to use equilibria and Le Chatelier’s principle to isolate each of the 3 substances in a mixture of iodine, I2, formic acid, HCOOH (Ka = 1.8×10−4), and ethanol, CH3CH2OH. Support your answer with evidence and reasoning in 8-10 sentences. (Use chromatography, pKa, buffers, conjugates, pH)

Answer 1

First, let us state the Le Chatelier principle which deals with changes in an equilibrium:

The statement is as follows:

If any equilibrium is disturbed, that is, change in conditions such as P,T, concentration, partial pressure, etc.., the system will counterbalance such change in order to favour the system's equilbirium.

• Change in concentration
• Change in pressure
• Change in temperature

Now, let us define the equilibrium constant for any species:

The equilibrium constant will relate product and reactants distribution. It is similar to a ratio

The equilibrium is given by

rReactants -> pProducts

Keq = [products]^p / [reactants]^r

For a specific case:

aA + bB = cC + dD

Keq = [C]^c * [D]^d / ([A]^a * [B]^b)

then

for the acid

I2 + HCOOH + CH3CH2OH

analysis:

a)

I2 is nonpolar, can be extracted in organic media

b)

Formic acid can be neutralized with mild base, such as NaHCO3, then, extracted in aqueous media

c)

Finally, ethanol is likely to be protonated, since OH group will not act readily as an acid, then, due to hihg pKa value, expect this to reac tonly with strong bases such as NH2-