Answer: condenstation.
Justification:
The polymerization by condensation is a well know chemical reaction in which two monomers ("small" molecules), each with (at least) two functional groups, combine and relase water as by-product. Actually, even if the by-product released is not water, yet the reaction is called condenstation, since the mechanism is basically the same.
An example of such reaction is the manufacturing of nylon 6,6, which is produced from adipic acid and 1,6-diamine hexane:
HOOC - [CH₂]₄ - COOH + nH₂N - [CH₂]₆ - NH₂ → - nylon - + nH₂O
I omitted the formula of nylon because it is large, and that is not the core of the question but the fact the kind of reaction: two molecules combine to form is a larger molecule, and water is released
Answer:
pH =3.8
Explanation:
Lets call the monoprotic weak acid HA, the dissociation equilibria in water will be:
HA + H₂O ⇄ H₃O⁺ + A⁻ with Ka = [ H₃O⁺] x [A⁻]/ [HA]
The pH is the negative log of the H₃O⁺ concentration, we know the equilibrium constant, Ka and the original acid concentration. So we will need to find the [H₃O⁺] to solve this question.
In order to do that lets set up the ICE table helper which accounts for the species at equilibrium:
HA H₃O⁺ A⁻
Initial, M 0.40 0 0
Change , M -x +x +x
Equilibrium, M 0.40 - x x x
Lets express these concentrations in terms of the equilibrium constant:
Ka = x² / (0.40 - x )
Now the equilibrium constant is so small ( very little dissociation of HA ) that is safe to approximate 0.40 - x to 0.40,
7.3 x 10⁻⁶ = x² / 0.40 ⇒ x = √( 7.3 x 10⁻⁶ x 0.40 ) = 1.71 x 10⁻³
[H₃O⁺] = 1.71 x 10⁻³
Indeed 1.71 x 10⁻³ is small compared to 0.40 (0.4 %). To be a good approximation our value should be less or equal to 5 %.
pH = - log ( 1.71 x 10⁻³ ) = 3.8
Note: when the aprroximation is greater than 5 % we will need to solve the resulting quadratic equation.
