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30 January, 03:47

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?

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  1. 30 January, 04:09
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    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

    Vi = 8.3 ml
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