15.0ml of an unknown concentration of hcl reacts completely with 20.00ml of 1.0m naoh. determine the concentration of the acid

Molar mass HCl = 36.5 g/mol  and NaOH = 40.0 g/mol

molarity of NaOH = 1.0 M

Volume of NaOH = 20.00 mL in liters : 20.00 / 1000 = 0.02 L

Number of moles NaOH :

n = M * V

n = 1.0 * 0.02

n =  0.02 moles Of NaOH

Finally Molarity of the acid solution

Volume HCl :  15.0 mL in liters : 15.0 / 1000 = 0.015 L

1 HCl + 1 NaOH = 1 H₂O + 1 NaCl

1 mole HCl 1 mole NaOH
? mole HCl   0.02 moles NaOH

moles HCl = 0.02 * 1 / 1

= 0.02 moles of HCl

M ( HCl) = n / V

= 0.02 / 0.015

= 1.333 M of HCl

hope this helps!