Henry uses 0.150L of 0.500 mol/L NaOH to neutralize 250.0 mL of the hydrochloric acid. What is the concentration of the HCl (aq)?

Answer 1

method 1:
NaOH + HCl ==> NaCl + H2O
mols NaOH = M x L = ?
mols HCl = mols HCl (look at the equation; note 1 mol NaOH = 1 mol HCl)
Then M HCl = mols HCl/L HCl = ?

method 2:
NaOH + HCl ==> NaCl + H2O
Note 1 mol NaOH = 1 mol HCl
mL NaOH x M NaOH = mL HCl x M HCl
Substitute and solve for M HCl.