Titration / Stoichometery

Question

You prepared 0.5 g of KHP to determine the concentration of the NaOH. During titration, you slowly add NaOH to KHP and found out that it requires 16ml of NaOH to change the color of KHP to light pink (equivalence point). What is the concentration of NaOH? The molar mass of KHP is 204.22g/mol

Answer 1

KHP = potassium hydrogen phthalate

KHP has ONE ionizable (titratable) hydrogen

KHP + NaOH ==> H₂O + NaKP ... BALANCED EQUATION

First, find the moles of KPH that you have present:

molar mass KHP = 204.2 g / mole

0.5 g KHP x 1 mol / 204.2 g = 2.45x10^-3 moles KHP

Next, use the stoichiometry (1:1) of the balanced equation to find moles of NaOH needed:

2.45x10^-3 mols KHP x 1 mol NaOH / 1 mol KHP = 2.45x10^-3 mols NaOH used

Finally, calculate the concentration of the NaOH solution:

molarity = moles NaOH / liters of solution

moles NaOH = 2.45x10^-3 moles

liters of solution = 16 ml x 1 L / 1000 ml = 0.016 L

Molarity = 2.45x10^-3 mols / 0.016 L = 0.153 M = 0.2 M (only 1 sig. fig. based on 0.5 g having 1 sig. fig.)