Question

A 25.0 mL sample of a saturated C a ( O H ) 2 solution is titrated with 0.029 M H C l , and the equivalence point is reached after 37.3 mL of titrant are dispensed. Based on this data, what is the concentration (M) of the hydroxide ion?

Answer 1

Answer:

0.043 M

Explanation:

The reaction that takes place is:

• Ca(OH)₂ + 2HCl → CaCl₂ + 2H₂O

First we calculate how many HCl moles reacted, using the given concentration and volume required to reach the equivalence point:

• 0.029 M HCl * 37.3 mL = 1.0817 mmol HCl = 1.0817 mmol H⁺

As 1 mol of H⁺ reacts with 1 mol of OH⁻, in the 25.0 mL of the Ca(OH)₂ sample there are 1.0817 mmoles of OH⁻.

With that in mind we can calculate the hydroxide ion concentration in the original sample solution, using the calculated number of moles and given volume:

• 1.0817 mmol OH⁻ / 25.0 mL = 0.043 M