Question

An aqueous solution contains 0.050 m of methylamine. the concentration of h+ in this solution is __________ m. kb for methylamine is 4.4 × 10-4.

Answer 1

The concentration of hydroxide ion in a solution of methylamine is approximately 9.07 x 10^-7 M.

Step-by-step explanation:

The concentration of hydroxide ion in a solution of methylamine can be found by using the relation:

Kw = [H+][OH-]

Given that the Kb for methylamine is 4.4 x 10-4, we can calculate the concentration of hydroxide ion using the formula:

[OH-] = sqrt(Kw/Kb) = sqrt(1.0 x 10-14/4.4 x 10-4)

Substituting the values and solving, we find that the concentration of hydroxide ion in the solution is approximately 9.07 x 10-7 M.

Answer 2

Methylamine is an amine which is an organic weak base. Its chemical formula is CH₃NH₂. When it undergoes hydrolysis wherein water is acting as an acid, the reaction would be

CH₃NH₂ + H₂O ⇆ CH₃NH₃ + OH⁻

Then, we use the ICE analysis which stands for Initial-Change-Equilibrium.

CH₃NH₂ + H₂O ⇆ CH₃NH₃ + OH⁻
Initial 0.05 - 0 0
Change -x +x +x
----------------------------------------------------------------------------
Equilibrium 0.05-x x x

Then, we use the equation for the equilibrium constant of basicity.

Kb = [CH₃NH₃][OH⁻]/[CH₃NH₂] = 4.4×10⁻⁴
4.4×10⁻⁴ = [x][x]/[0.05-x]
[x] = 4.4756×10⁻³

The variable x here denotes the number of moles of the substance that is involved in the reaction. Since the equilibrium amount of OH⁻ is equal to x, then the concentration of OH⁻ is also 4.4756×10⁻³. Thus,

pOH = -log[OH⁻]
pOH = -log[4.4756×10⁻³] = 2.35
The relationship between pOH and pH is that pH + pOH = 14. Thus,
pH = 14 - 2.35 = 11.65

pH = -log[H⁺]
11.65 = -log[H⁺]
[H⁺] = 2.234 × 10⁻¹² M