Question

A chemist must prepare 550 mL of hydrochloric acid solution with a pH of 1.60 at 25°C .
He will do this in three steps:
-Fill a 550.0 mL volumetric flask about halfway with distilled water.
-Measure out a small volume of concentrated (8.0M) 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 significant digits.

Answer 1

Answer: The volume of concentrated hydrochloric acid solution is 1.73 mL

Explanation:

To calculate the hydrogen ion concentration of the solution, we use the equation:

$pH=-\log[H^+]$

We are given:

pH = 1.60

Putting values in above equation, we get:

$1.60=-\log [H^+]$

$[H^+]=10^{-1.60}=0.0251M$

To calculate the volume of the concentrated solution, we use the equation:

$M_1V_1=M_2V_2$

where,

$M_1\text{ and }V_1$ are the molarity and volume of the concentrated HCl solution

$M_2\text{ and }V_2$ are the molarity and volume of diluted HCl solution

We are given:

$M_1=8.0M\\V_1=?mL\\M_2=0.0251M\\V_2=550mL$

Putting values in above equation, we get:

$8.0\times V_1=0.0251\times 550.0\\\\V_1=\frac{0.0251\times 550}{8.0}=1.73mL$

Hence, the volume of concentrated hydrochloric acid solution is 1.73 mL