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A chemist must prepare 500.0mL of hydrobromic acid solution with a pH of 0.50 at 25°C. He will do this in three steps: Fill a 500.0mL volumetric flask about halfway with distilled water. Measure out a small volume of concentrated (5.0M) stock hydrobromic acid solution and add it to the flask. Fill the flask to the mark with distilled water. Calculate the volume of concentrated hydrobromic acid that the chemist must measure out in the second step. Round your answer to significant digits.

Respuesta :

IthaloAbreu

Answer:

31.62 mL

Explanation:

To have a pH of 0.50, the concentration of ions H+ must be:

pH = -log[H+]

0.50 = -log[H+]

[H+] = [tex]10^{-0.50}[/tex]

[H+] = 0.31623 mol/L

The hydrobromic acid is strong, so we can assume that it dissociates completely in a solution:

HBr → H+ + Br-

Thus, by the stoichiometry [HBr] = [H+] = 0.31623 mol/L

To dilute a stock solution, we can use:

C1V1 = C2V2

Where C is the concentration, V is the volume, 1 represents the stock solution, and 2 the new solution. So, C1 = 5.0 M, C2 = 0.31623 M, V2 = 500.0 mL:

5.0*V1 = 0.31623*500.0

V1 = 31.62 mL

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