5. If 30mL of 0.5M NaOH (aq) was used to neutralize 10mL of HCl (aq), what is the concentration of the acid? Show work.

0.15M

Explanation:

NaOH + HCl - ->NaCl + H2O

moles of NaOH reacted with HCl

(0.5 * 30) / 1000 = 1.5 * 10^ - 3

so the moles of HCl reacted with NaOH

1.5 * 10^ - 3

concentration of HCl = (1.5 * 10^ - 3) / 10 * 1000