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 can use the concept of neutralization, where the number of moles of H2SO4 and NaOH reacted will be equal.
First, let's calculate the number of moles of H2SO4 used in the titration:
Initial volume of H2SO4 = 13.28 mL
Final volume of H2SO4 = 28.29 mL
Volume of H2SO4 used = Final volume - Initial volume = 28.29 mL - 13.28 mL = 15.01 mL
Now, we need to convert this volume to liters:
Volume of H2SO4 used = 15.01 mL = 15.01 mL * (1 L / 1000 mL) = 0.01501 L
Next, we can calculate the number of moles of H2SO4 using its concentration:
Molarity of H2SO4 = unknown (we need to calculate it!)
Number of moles of H2SO4 = Molarity * Volume
Now, let's find the number of moles of H2SO4.
Number of moles of H2SO4 = Molarity * Volume
Number of moles of H2SO4 = unknown * 0.01501 L
Now, let's calculate the number of moles of NaOH using the balanced chemical equation for the neutralization reaction:
H2SO4 + 2NaOH -> Na2SO4 + 2H2O
From the equation, we can see that 1 mole of H2SO4 reacts with 2 moles of NaOH. Therefore, the number of moles of NaOH is half the number of moles of H2SO4 that reacted.
Number of moles of NaOH = 1/2 * Number of moles of H2SO4
At the equivalence point (when the solution turns slightly pink), the moles of NaOH and H2SO4 reacted are equal.
Number of moles of NaOH = Number of moles of H2SO4
1/2 * Number of moles of H2SO4 = Number of moles of H2SO4
1/2 = 1
Now, we can solve for the unknown concentration of NaOH.
unknown * 0.01501 L = 0.5 * unknown * 0.01501 L
Simplifying the equation:
0.01501 L = 0.5 * unknown * 0.01501 L
1 = 0.5 * unknown
unknown = 1 / 0.5
unknown = 2
Therefore, the concentration of NaOH is 2 M (2 moles per liter).