A chemist must prepare 400.0 mL of hydrobromic acid solution with a pH of 0.90 a

Question

A chemist must prepare 400.0 mL of hydrobromic acid solution with a pH of 0.90 at 25 °C He will do this in three steps: Fill a 400.0 mL volumetric flask about halfway with distilled water. Measure out a small volume of concentrated (9.0M) 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 2 significant digits 0 ml.

Explanation / Answer

pH = 0.9

pH = -log[H3O+]

0.9 = -logx

x = 0.126

so that, molarity of HBr = 0.126 M

M2 = molarity of dil.HBr = 0.126 M

V2 = volume of DIL.HBr = 400 ml

M1 = Concentrated HBr = 0.9 M

v1 = Volume of Concentrated HBr = x ml

dilution formula,

    M1V1 = M2V2

(0.9*v1) = (0.126*400)

v1 = 56 ml

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