Question

chemist must prepare of hydrobromic acid solution with a pH of at . He will do this in three steps: Fill a volumetric flask about halfway with distilled water. Measure out a small volume of concentrated () 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.

Answer 1

Answer:

32 mL

Explanation:

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 2 significant digits.

Step 1: Calculate [H⁺] of the dilute solution

pH = -log [H⁺]

[H⁺] = antilog -pH = antilog -0.50 = 0.32 M

Step 2: Calculate [HBr] of the dilute solution

HBr is a strong acid that dissociates according to the following equation.

HBr ⇒ H⁺ + Br⁻

The molar ratio of HBr to H⁺ is 1:1. The concentration of HBr is 1/1 × 0.32 M  = 0.32 M.

Step 3: Calculate the volume of the concentrated HBr solution

We will use the dilution rule.

C₁ × V₁ = C₂ × V₂

V₁ = C₂ × V₂ / C₁

V₁ = 0.32 M × 500.0 mL / 5.0 M

V₁ = 32 mL