chemistry word problem

Question

The exact neutralization of 10.00 mL of 0.1282 M H2SO4(aq) requires 24.94 mL of NaOH.

Part A

What must be the molarity of the NaOH(aq)?
H2SO4(aq)+2NaOH(aq)→Na2SO4(aq)+2H2O(l)

Answer 1

Hello Amy,

 

In systems such as this where strong acids are exactly neutralized by strong bases (or the reverse scenario), it is important that the number of moles of each species is the same taking into account the stoichiometry of the reaction. The first step is to use the given concentration (M = mol L^-1) and volume of H₂SO₄ (in liters!) to determine the number of moles of H₂SO₄:

 

1.  H₂SO₄: (0.0100 L) x (0.1282 mol L^-1) = 0.001282 mol H₂SO₄

 

The next step is to use the balanced chemical reaction that was given in order to determine the stoichiometry of the reaction, which is the ratio of reacting species. Because 2 moles of NaOH are required for every 1 mole of H₂SO₄, we must multiply the number of moles of H₂SO₄ calculated above by 2:

 

2.  NaOH: (0.001282 mol H₂SO₄) x (2 mol NaOH)/(1 mol H₂SO₄) = 0.002564 mol NaOH

 

You have calculated the number of moles of NaOH required to exactly neutralize the H₂SO₄ in problem. The last step is to convert this to concentration by dividing by the volume of NaOH (again, in liters):

 

3.  (0.002564 mol NaOH)/(0.02494 L NaOH) = 0.1028 M NaOH

 

A note on significant figures: Please ignore this (for now) if you have not discussed significant figures in class. Note that all of the numbers given in the problem have four significant figures. Because the operations to obtain the answer to this problem were exclusively multiplication/division, your final answer will also have four significant figures.

 

Best,

- Avery