Question

You need to use a dilute hydrochloric acid solution in an experiment. However, the only bottle of hydrochloric acid in your lab’s acid‑base cabinet is 8.0 M. Calculate the pH of the solution you prepare by diluting 1.5 mL of the 8.0 M HCl to a final volume of 250 mL with H2O. Use appropriate significant figures in your answer.

Answer 1

The pH of the diluted HCl solution is 1.3.

Explanation:

Given:

The concentrated HCl solution of 8.0 M. The 1.5 mL of 8.0 M HCl is diluted with water to 250 mL volume.

To find:

The pH of the diluted HCl solution.

Solution

• The concentration of the HCl solution before dilution = $M_1=8.0 M$
• The volume of the HCl solution taken for dilution = $V_1=1.5 ml$
• The concentration of the HCl solution after dilution =$M_2=?$
• The volume of the HCl solution after dilution = $V_2=250 mL$

Using the Dilution equation:

$M_1V_1=M_2V_2\\8.0M\times 1.5ml=M_2\times 250 mL\\M_2=\frac{8.0M\times 1.5ml}{250 mL}=0.048 M$

The concentration of diluted HCl solution = 0.048 M

$HCl(aq)\rightarrow H^+(aq)+Cl^-(aq)$

In the 1 M solution of HCl, there are 1 M of hydrogen ion, then the concentration of hydrogen ions in 0.048 M of HCl will be:

$[H^+]=1\times 0.048M=0.048 M$

The pH of the diluted HCl solution :

$pH=-\log [H^+]\\=-\log [0.048M]=1.18 \approx 1.3$

The pH of the diluted HCl solution is 1.3.

Learn more about the dilution equation here:

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