Use these data to complete the prelaboratory exercises: A student titrated 1.852

Question

Use these data to complete the prelaboratory exercises: A student titrated 1.852 g of a mixture containing potassium hydrogen phthalate, KHP, with O.163 M NaOH solution. She recorded an initial buret reading of 0.84 mL and a final buret reading of 31.32 mL. REMEMBER: KHP is shorthand for a certain acid. It contains NO phosphorus. For full credit, show the detailed steps of each calculation below. 1. Write the reaction equation for the acid-base neutralization. 2. Name the secondary standard used in the titration of the unknown KHP mixture. 3. Calculate the amount of NaOH (in millimoles) delivered in the titration. 4. Find the mass of KHP neutralized in the reaction. 5. Calculate the mass percent of KHP in the original sample.

Explanation / Answer

1)KHC8H4O4 + NaOH -----> KNaC8H4O4 + H2O

2)Secondary standard: NaOH

3) V = 31.32 - 0.84 =30.48 mL = 0.03048 L

Moles NaOH = moles KHP = 0.163 x 0.03048 = 0.004968


4.) So since total volume = final buret reading - initial reading = 31.32 - 0.84 = 30.48 ml = 0.03048 L

At equivalence pt. the total moles of KHP = total moles of NaOH.

So, moles of NaOH = 0.03048 L x 0.163 M = 0.00497 moles = moles of KHP

Mass of KHP = Moles KHP x molar mass of KHP = 0.00497 mol x 204.22 g per mol = 1.015 g



5.) Mass percent of KHP = (1.015 / 1.852) x 100 = 54.81%

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