You are given solutions of HCl and NaOH and must determine their concentrations. You use 30.0 mL of NaOH to neutralize 100.0 mL of HCl, and 20.0 mL of NaOH to neutralize 50.0 mL of 0.361 M H2SO4. What is the concentration of the HCl solution? Enter your answer in units of M to three significant figures.

0.542M HCl

Explanation:

The reaction of H₂SO₄ with NaOH is:

H₂SO₄ + 2 NaOH → 2H₂O + Na₂SO₄

Where 1 mole of acid reacts with 2 moles of NaOH

Moles of H₂SO₄ are:

0.0500L × (0.361mol / L) = 0.01805 moles H₂SO₄

Thus, moles of NaOH that neutralize this acid are:

0.01805 moles H₂SO₄ × (2 mol NaOH / 1 mol H₂SO₄) = 0.0361 moles NaOH

And concentration is:

0.0361 moles NaOH / 0.0200L = 1.805M

And, reaction of NaOH with HCl is:

NaOH + HCl → H₂O + NaCl

Where 1 mole of NaOH reacts per mole of NaOH

As you use 30.0mL = 0.0300L of NaOH to neutralize the HCl acid, moles of acid are:

0.0300L × (1.805mol / L) = 0.05415 moles NaOH = moles HCl

In 0.1000L:

0.05415 moles HCl / 0.1000L = 0.542M HCl