Question

25 mL of 3 M HCl were added to 75 mL of 0.05 M HCl. The molarity of HCl the resulting solution is approximately.

• A. 0.055 M
• B. 0.35 M
• C. 0.787 M
• D. 3.05M

Answer 1

The correct option is C 0.787 M

${\text{M}}_1=3\text{M}$ ${\text{M}}_f=\text{final}\text{molarity}$
${\text{V}}_1=25\text{ml}\text{or}0.025\text{L}$ ${\text{V}}_f=\text{final}\text{volume}$
${\text{M}}_2=0.05\text{M}$
${\text{V}}_2=75\text{ml}\text{or}0.075\text{L}$
Formula used:
${\text{M}}_1{\text{V}}_1+{\text{M}}_2{\text{V}}_2=\text{M}$
${\text{M}}_f=\frac{{\text{M}}_1{\text{V}}_1+{\text{M}}_f{\text{V}}_f}{{\text{V}}_f}$
${\text{V}}_f=0.025+0.075=0.1\text{L}$
${\text{M}}_f=\frac{3\times 0.025+0.05\times 0.075}{0.1}$
${\text{M}}_f=0.787\text{M}$
Thus, option (C) is correct.