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?

0.043 M

Explanation:

The reaction that takes place is:

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

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:

it means there are 3 atoms of oxygen

the answer would be a