Question

What is the pH of a solution where 250 mL of 0.50 M NaOH is completely neutralized by 175mL of HCl? What are the final concentrations of all ions?

Answer 1

Answer:

pH = 7.0

Final concentration= 0.29 M

Explanation:

1. Find the mols of each reagent:

NaOH:

250 mL = 0.250 L

0.50 M

Molarity = mol NaOH / L solution

0.50 M = mol NaOH / 0.250 L

mol NaOH = 0.125 mol NaOH

2. reaction between HCl and NaOH:

NaOH + HCl = NaCl + H2O

3. If the reaction in completly neutralized, it means that all NaOH mol reacted with HCl:

0.125 mol NaOH = 0.125 mol HCl

4. concentration of HCl solution:

Molarity = mol HCl / L solution

M = 0.125 mol HCl / 0.175 L = 0.71 M

5. Neutralized means all reagent reacted. and pH has to be = 7.

6. Concentration of ions:

Cl-:

0.125 mol HCl = 0.125 mol Cl -

M = 0.125 mol Cl- / (0.250 L + 0.175 L) =0.125 mol Cl-/0.425 L = 0.29 M

Na+ :

0.125 mol Na+

M = 0.125 mol Na+ / 0.425 L = 0.29 M