Question

A beaker contains 0.1 M $H_{2}S{O}_4$ solution; of 100 ml. Another 100 ml, 0.1 M $HCl$ of it is added to the beaker.

(I) What is the initial number of millimoles of $H^{+}$ ions?

​(II) What is the final concentration of $H^{+}$ ions?

• A. 20, 40
• B. 30, 20
• C. 20, 30
• D. 30, 40

Answer 1

The correct option is C

20, 30

Firstly, Let's consider the situation before HCl is added.
We have 0.1 M $H_{2}S{O}_4$ of 100 ml.
We know, No. of moles = Molarity $\times$ volume
($H_{2}S{O}_4$)

$\therefore$ No. of millimoles of $H^{+}=2\times 0.1\times 100=20$
After adding HCl, there in an increase in $H^{+}$ ions.
Similarly, No. of millimoles of $H^{+}$ in HCl = 100 $\times$ 0.1 = 10

$\therefore$ Final number = 20 + 10 = 30

Finaly concentration = 30 millimoles / 200 ml = 0.75 M