A solution of unknown concentration. NaOH against 0.150 M HCl and 22.0 mL of acid was needed to reach the endpoint of the titration. How many moles of the base were in the solution?

Answer 1

The endpoint of the titration is where moles of H+ = moles of OH– added to the reaction. So to know how many moles of OH–, we need to calculate how many moles of H+ were initially present.

M is the unit for molarity, which is moles of solute per liter of solvent. Since we have 22 mL of a 0.150 M solution of HCl (which is 0.150 mol HCl / 1 L of solution), we can do simple dimensional analysis to calculate how many moles of H+ are in this solutions:

22 mL x (1 L / 1000 mL) x (0.150 mol HCl / 1 L) x (1 mol H+ / 1 mol HCl)

= (22 x 0.150) / 1000 = 0.0033 mol H+ in the acid solution.

Therefore, we will need to add 0.0033 mol of OH– to neutralize the acid. Since there is a 1:1 ratio of OH- to NaOH formula units, the answer is 0.0033 mol NaOH.