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artcher [175]
2 years ago
5

What is the pH of a solution of 0.400 M CH₃NH₂ containing 0.250 M CH₃NH₃I? (Kb of CH₃NH₂ is 4.4 × 10⁻⁴)

Chemistry
1 answer:
Karolina [17]2 years ago
4 0

Answer:

\boxed{\text{10.84}}

Explanation:

A solution of a weak base and its conjugate acid is a buffer.

The equation for the equilibrium is

\rm CH$_3$NH$_2$ + H$_2$O $\, \rightleftharpoons \,$ CH$_3$NH$_2$+ H$_{3}$O$^{+}$\\\text{For ease of typing, let's rewrite this equation as}\\\rm B + H$_2$O $\longrightarrow \,$ BH$^{+}$ + OH$^{-}$; $K_{\text{b}}$ = 4.4 \times 10^{-4}$

The Henderson-Hasselbalch equation for a basic buffer is

\text{pOH} = \text{p}K_{\text{b}} + \log\dfrac{[\text{BH}^{+}]}{\text{[B]}}

Data:

   [B] = 0.400 mol·L⁻¹

[BH⁺] = 0.250 mol·L⁻¹

    Kb = 4.4 × 10⁻⁴

Calculations:

(a) Calculate pKb

pKb = -log(4.4× 10⁻⁴)  = 3.36

(b) Calculate the pH

\text{pOH} = 3.36 + \log \dfrac{0.250}{0.400} = 3.36 + \log 0.625 = 3.36 - 0.204 = 3.16\\\\\text{pH} =14.00 -3.16 = \mathbf{10.84}\\\\\text{The pH of the solution is }\boxed{\textbf{10.84}}

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The K w for water at 0 ∘ C is 0.12 × 10 − 14 M 2 . Calculate the pH of a neutral aqueous solution at 0 ∘ C . p H = Is a pH = 7.2
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Answer:

pH → 7.46

Explanation:

We begin with the autoionization of water. This equilibrium reaction is:

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Kw = [H₃O⁺] . [OH⁻]

We do not consider [H₂O] in the expression for the constant.

[H₃O⁺] = [OH⁻] = √1×10⁻¹⁴   →  1×10⁻⁷ M

Kw depends on the temperature

0.12×10⁻¹⁴ = [H₃O⁺] . [OH⁻]  → [H₃O⁺] = [OH⁻]         at 0°C

√0.12×10⁻¹⁴ = [H₃O⁺] → 3.46×10⁻⁸ M

- log [H₃O⁺] = pH

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A description of the experiment the chemicals were used for.

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A chemical waste label is required to provide information about any hazardous waste present in the container. Some details are mandatory to mention of the chemical waste label to prevent any accident while doing the experiment, that includes:

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A chemical waste label does not mention or describe the experiment for which the chemicals were used for, scientists, teacher or students should have knowledge of the chemical composition by reading their names and evaluate themselves on which chemical should be used for which experiment.

Hence, the correct answer is  "A description of the experiment the chemicals were used for."

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Answer:

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