Question

24.0 mL of a 0.120 M Ca(OH)2 solution is required to titrate 160 mL of an HCl solution to its equivalence point. Find the moles of HCl and its concentration in molarity.

Answer 1

The balanced reaction is as follows;
Ca(OH)₂ + 2HCl ---> CaCl₂ + 2H₂O
  stoichiometry of Ca(OH)₂ to HCl is 1:2
number of moles of Ca(OH)₂ reacted = 0.120 mol/L x 0.0240 L = 0.00288 mol according to molar ratio of 1:2 number of HCl moles reacted = twice the number of Ca(OH)₂ moles reacted
number of HCl moles reacted = 0.00288 mol x 2 = 0.00576 mol
number of HCl moles in 160 mL - 0.00576 mol
therefore number of HCl moles in 1000 mL - 0.00576 mol / 160 mL x 1000 mL = 0.036 mol
molarity of HCl = 0.036 M

Answer 2

Answer: The molarity of HCl is 0.036 M and moles of HCl is 5.76 moles.

Explanation:

• To calculate the molarity of HCl used to titrate $Ca(OH)_2$, we use the equation:

$n_1M_1V_1=n_2M_2V_2$

where,

$n_1,M_1\text{ and }V_1$ is the n-factor, molarity and volume of calcium hydroxide.

$n_2,M_2\text{ and }V_2$ is the n-factor, molarity and volume of hydrochloric acid.

We are given:

$n_1=2\\M_1=0.120M\\V_1=24mL\\n_2=1\\M_2=?M\\V_2=160mL$

Putting values in above equation, we get:

$2\times 0.120\times 24=1\times M_2\times 160\\M_2=0.036M$

• Now, to calculate the number of moles, we use the equation:

$\text{Molarity}=\frac{\text{Number of moles}}{\text{Volume}}$

Molarity of HCl = 0.036 mol/mL

Volume of HCl = 160 mL

Putting values in above equation, we get:

$0.036=\frac{\text{Number of moles}}{160}\\\\\text{Number of moles of HCl}=5.76mol$

Hence, the molarity of HCl is 0.036 M and moles of HCl is 5.76 moles.