4. If you mix 20.0 mL of a 3.20M NaOH solution with 35.0 mL of a 5.80M NaOH solution, what is the molarity of the final solution?  ?

4.
Assume that the volume of NaOH solution is additive.

Moles of NaOH
= (3.20 mol/L) × (20.0/1000 L) + (5.80 mol/L) × (35.0/1000 L)
= 0.267 mol

Final volume of the final solution
= (20.0 + 35.0) mL
= 55.0 mL
= 0.0550 L

Molarity of the final solution
= (0.267 mol) / (0.0550 L)
= 4.85 M