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denis23 [38]
3 years ago
7

A chemist must prepare 200.0 mL of hydrochloric acid solution with a pH of 0.60 at 25 °C. He will do this in three steps: • Fill

a 200.0 mL volumetric flask about halfway with distilled water. • Measure out a small volume of concentrated (6.0M) stock hydrochloric acid solution and add it to the flask. • Fill the flask to the mark with distilled water. Calculate the volume of concentrated hydrochloric acid that the chemist must measure out in the second step. Round your answer to 2 significant digits. mL X 5 ?
Chemistry
1 answer:
Likurg_2 [28]3 years ago
5 0

Answer:

In the second step, the chemist must measure 8.3 ml of concentrated acid

Explanation:

The concentration of the final solution can be obtained using the pH value:

pH = -log[H] = 0.60

[H] = 10^(-0.60) = 0.25 M

Then, the final concentration of HCl will be 0.25 M because HCl is a monoprotic acid, which means that HCl only has one hydrolyzable proton. Therefore: [HCl] = [H].

The number of moles of HCl in the final solution will be equal to the number of moles present in the volume taken from the stock solution:

n° of moles in the volume taken from stock solution = n° moles in the final solution.

The number of moles can be calculated as follows:

number of moles = concentration * volume

Then:

Ci * Vi = Cf * Vf

where

Ci = concentration of the stock solution

Vi = volume taken from the stock solution

Cf = concentration of the final solution

Vf = volume of the final solution

Replacing with the data, we can obtain Vi:

6.0 M * Vi = 0.25 M * 200.0 ml

<u>Vi = 8.3 ml</u>

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Answer: the pH of the solution is 4.52

Explanation:

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the Henderson -Haselbach equation can be expressed as;

pH = pKa + log( [A⁻] / [HA])

the weak acid is dissociated into H⁺ and A⁻ ions in the solution.

now the conjugate base of the weak acid HA is

HA(aq) {weak acid}     H⁺(aq)  +  A⁻(aq) {conjugate base}

so now we calculate the value of Kₐ as well as pH value by substituting the values of the concentrations into the equation;

pKₐ = -logKₐ

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now thw pH is

pH = pKₐ  + log( [A⁻] / [HA])

pH = 4.13 + log( [0.540] / [0.220])

pH = 4.13 + 0.3899

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Explanation:

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For this reaction the balanced chemical equation is

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