Question #c81fe

1 Answer
May 2, 2016

#"0.1705 mol L"^(-1)#


The problem tells you that the two reactants react in a #1:1# mole ratio, so you can solve this problem without having a balanced chemical equation around.

The #1:1# mole ratio tells you that the reaction will consume one mole of potassium hydrogen phthalate, KHP, for every mole of sodium hydroxide that takes part in the reaction.

This means that if you have the number of moles of KHP that took part in the reaction, you also have the number of moles of sodium hydroxide needed to get to the equivalence point.

Use the molar mass of KHP to determine how many moles you have in that sample

#0.7025 color(red)(cancel(color(black)("g"))) * "1 mole KHP"/(204.22 color(red)(cancel(color(black)("g")))) = "0.003440 moles KHP"#

This of course means that the reaction consumed #0.003440# moles of sodium hydroxide.

Since molarity is defined as moles of solute per liter of solution, and since you know that you used #"20.18 mL"# of your sodium hydroxide solution, you can say that its molarity was

#c = "0.003440 moles"/(20.18 * 10^(-3)"L") = color(green)(|bar(ul(color(white)(a/a)"0.1705 mol L"^(-1)color(white)(a/a)|)))#

The answer is rounded to four sig figs.