For the reaction: ch3nh2(aq) + h2o(aq) ⇌ ch3nh3 +(aq) + oh- determine the change in the ph (δph) for the addition of 6.7 m ch3nh3cl salt to a 4.7 m solution of ch3nh2, kb=4.38 x 10-4 . view available hint(s) for the reaction: ch3nh2(aq) + h2o(aq) ⇌ ch3nh3 +(aq) + oh- determine the change in the ph (δph) for the addition of 6.7 m ch3nh3cl salt to a 4.7 m solution of ch3nh2, kb=4.38 x 10-4 . δph=12.66 δph=1.86 δph=10.49 δph=2.17

The change in the pH (ΔpH) is 2,17

Explanation:

The reaction:

CH₃NH₂(aq) + H₂O(aq) ⇌ CH₃NH₃⁺(aq) + OH⁻

(1)

In equilibrium, a solution of CH₃NH₂ 4,7M produces:

[CH₃NH₂] = 4,7 - x

[CH₃NH₃⁺] = x

[OH⁻] = x

Replacing in (1):

x² + 4,38x10⁻⁴x - 2,0586x10⁻³ = 0

The solutions are:

x = -0,0456 No physical sense. There are not negative concentrations.

x = 0,04515 Real answer.

The concentration of [OH⁻] is 0,04515 M.

As pOH = -log [OH⁻] And pH+pOH = 14. The pH of this solution is:

pH = 12,65

The addition of 6,7M produce this changes in concentrations:

[CH₃NH₂] = 4,656 + x

[CH₃NH₃⁺] = 6,74515 - x

[OH⁻] = 0,04515 - x

Replacing in (1) you will obtain:

x² - 6,7907x + 0,3025 = 0

Solving for x:

x = 6,74586 No physical sense

x = 0,04484 Real answer.

Thus, [OH⁻] = 0,04515 - 0,044842 = 3,08x10⁻⁴M

pOH = 3,51.

pH = 10,49

Thus ΔpH is 12,65 - 10,49 = 2,16 ≈ 2,17

I hope it helps!

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