Question

The pH of the resultant solution obtained by mixing 20mL of 0.01M HCl and 20mL of 0.005 M Ca(OH)2, is:
A) 2 B) O C) 1 D) 7 E) 5​

Answer 1

Answer:

Total number of moles present in 10 mL of 0.2 M calcium hydroxide are

1000

10×0.2

=0.002 moles.

Total number of moles present in 25 mL of 0.1 M HCl are

1000

25×2

=0.0025 moles.

Ca(OH)

2

+2HCl→CaCl

2

+2H

2

O

1 mole of calcium hydroxide reacts with 2 moels of HCl.

0.0025 moles of HCl will react with 0.00125 moles of calium hydroxide.

Total number of moles of calcium hydroxide unreacted are 0.002−0.00125=0.00075 moles.

Total volume of the solution is 10+25=35 mL.

The molarity of the solution is

35

0.00075×1000

=0.0214M

[OH

−

]=2×0.0214=0.0428M

pOH=−log0.0428=1.368

pH=14−pOH=14−1.368=12.635