A student masses out 1.3009g of potassium hydrogen phthalate (KHP). KHP has the

Question

A student masses out 1.3009g of potassium hydrogen phthalate (KHP). KHP has the formula KHC8H4O4, where only the first hydrogen is acidic. The student dissolves the sample in about 25-mL of water and titrates the acid with sodium hydroxide solution. If 41.20 mL of NaOH solution are required:

Write a balanced equation for the reaction, calculate the moles of base reacted, and calculate the [NaOH].

The student then uses this standardized NaOH soluiton from above to determine the molar mass of an unknown diprotic acid. If a 1.015g sample dissolved in (25mL water) requres 22.62 mL of the NaOH solution to fully react with it:

Write a balanced equation for this reaction, calculate the moles of acid reacted, and calculate the molar mass of the acid.

Explanation / Answer

NaOH + KHC8H4O4 -----> NaKC8H4O4 + H2O
Molar mass of KHC8H4O4 is 204.24 g/mol
1.3009 g x (1 mol / 204.24 g) = 0.0063695 mol KHP = 0.0063695 mol NaOH because 1 mol KHP reacts with 1 mol NaOH
M NaOH = mol / L = 0.0063695 mol / 0.04120 L = 0.1546 M

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