A student standardized a NaOH solution, following the procedure described in thi

Question

A student standardized a NaOH solution, following the procedure described in this module. The student weighed two samples of KHP and transferred them into two 125-mL Erlenmeyer flasks. She dissolved each sample, using distilled water. After adding phenolphthalein indicator solution to each KHP solution, she titrated the solution with the NaOH solution being standardized. The student's data are given in Table 1 (http://imgur.com/tpPAIFI)

Questions:

(1) Express the volume of NaOH solution used for each titration in liters.

(2) Calculate the number of moles of KHP titrated in each determination.

(3) Calculate the number of moles of NaOH required for each titration.

(4) Calculate the molarity of the NaOH solution, based upon the data for each determination.

(5) Calculate the mean molarity of the NaOH solution.

Explanation / Answer

NaOH + KHP => NaKP + H2O

Determination 1

(1) Volume of NaOH in L = 42.83/1000 = 0.04283 L

(2) Moles of KHP = mass/molar mass of KHP = 3.009/204.22 = 0.01473 mol

(3) Moles of NaOH = moles of KHP = 0.01473 mol

(4) Molarity of NaOH = moles/volume of NaOH = 0.01473/0.04283 = 0.3439 mol/L

Determination 2

(1) Volume of NaOH in L = 45.93/1000 = 0.04593 L

(2) Moles of KHP = mass/molar mass of KHP = 3.246/204.22 = 0.01589 mol

(3) Moles of NaOH = moles of KHP = 0.01589 mol

(4) Molarity of NaOH = moles/volume of NaOH = 0.01589/0.04593 = 0.3460 mol/L

(5) Mean molarity of NaOH = (0.3439 + 0.3460)/2

= 0.3450 mol/L

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