Question #ed2aa

1 Answer
Feb 11, 2018

#"0.08 M"#


The idea here is that in order for the titration to reach its equivalence point, the strong base must be completely neutralized by the strong acid.

In practice, we can determine when the neutralization reaction is complete by looking for the endpoint of the titration, which occurs when the indicator changes color.

If we did a good job at picking the indicator and at performing the titration, then we can use the endpoint and the equivalence point interchangeably.

#overbrace(2"NaOH"_ ((aq)))^(color(blue)("2 moles consumed")) + overbrace("H"_ 2"SO"_ (4(aq)))^(color(blue)("1 mole consumed")) -> "Na"_ 2"SO"_ (4(aq)) + "H"_ 2"O"_ ((l))#

Notice that each mole of sulfuric acid can neutralize #2# moles of sodium hydroxide.

You know that in order to get to the endpoint, the reaction consumed

#40 color(red)(cancel(color(black)("mL"))) * ("0.05 moles H"_2"SO"_4)/(10^3color(red)(cancel(color(black)("mL")))) = "0.0020 moles H"_2"SO"_4#

This means that the sodium hydroxide solution contained

#0.0020 color(red)(cancel(color(black)("moles H"_2"SO"_4))) * "2 moles NaOH"/(1color(red)(cancel(color(black)("mole H"_2"SO"_4)))) = "0.0040 moles NaOH"#

Since you know that the volume of the sodium hydroxide solution was equal to #"50 mL"#, you can say that the molarity of the solution was--don't forget to use the volume of the solution in liters!

#["NaOH"] = "0.0040 moles"/(50 * 10^(-3) quad "L") = color(darkgreen)(ul(color(black)("0.08 M")))#

The answer is rounded to one significant figure.