A 21.18 mL of 0.250 M NaOH is titrated with a H2SO4 solution. The initial
volume of H2SO4 was 13.28 and the final volume of H2SO4 was 28.29 mL when
the solution turned very slightly pink. What is the concentration of NaOH?
To find the concentration of NaOH, we need to use the concept of stoichiometry and the balanced chemical equation for the reaction between NaOH and H2SO4.
The balanced chemical equation for the reaction is:
2 NaOH + H2SO4 -> Na2SO4 + 2 H2O
From the equation, we can see that it takes 2 moles of NaOH to react with 1 mole of H2SO4.
First, let's calculate the moles of H2SO4 used in the titration:
Volume of H2SO4 used = Final volume - Initial volume = 28.29 mL - 13.28 mL = 15.01 mL
Convert the volume of H2SO4 used to liters: 15.01 mL * (1 L / 1000 mL) = 0.01501 L
Next, we need to determine the moles of H2SO4 used:
Moles of H2SO4 = Concentration of H2SO4 * Volume of H2SO4 used
The concentration of H2SO4 is not given in the question, so we cannot directly calculate the moles of H2SO4 used. We need additional information.
If we assume that the reaction between NaOH and H2SO4 is 1:1, it means that the 15.01 mL of H2SO4 used corresponds to the same number of moles as the moles of NaOH present in the solution.
Now, let's calculate the moles of NaOH:
Moles of NaOH = Concentration of NaOH * Volume of NaOH
Moles of NaOH = 0.250 M * 21.18 mL * (1 L / 1000 mL) = 0.005295 moles
Since the reaction is 1:1, the moles of NaOH are also equal to the moles of H2SO4 used, which we calculated to be 0.005295 moles.
Finally, we can calculate the concentration of NaOH:
Concentration of NaOH = Moles of NaOH / Volume of NaOH
Concentration of NaOH = 0.005295 moles / (21.18 mL * (1 L / 1000 mL)) = 0.250 M
Therefore, the concentration of NaOH is 0.250 M.