Potassium hydrogen phthalate (abbreviated KHP) has the chemical formula HKCsH404

Question

Potassium hydrogen phthalate (abbreviated KHP) has the chemical formula HKCsH404. What is the molar mass of KHP? A 0.322 g sample of an unknown, monoprotic acid (call it HA) is neutralized by 19.81 mL of a 0.1033 M NaOH solution. 2. a) Write the balanced equation for the reaction of HA with NaOH. b) Calculate the molar mass of HA. Suppose 15.56 mL of NaOH solution are required to reach the first equivalence point for a HsPO, solution. Approximately how many additional mL of NaOH will be required to reach the second equivalence point? 3. 4. Look up, in your text, the acid dissociation constants (K) for the three neutralization steps of H PO,. What are the corresponding pK, values?

Explanation / Answer

1.

HKC8H4O4

Molar mass of KHP = 1 (1 ) + 1 ( 39 ) + 8 ( 12 ) + 4 ( 1 ) + 4 ( 16 ) = 204 g/mol

2.

(a) Balanced equation:

HA (aq.) + NaOH (aq.) ------------> NaA (aq.) + H2O (l)

(b)

Moles of NaOH used = M * V / 1000 = 0.1033 * 19.81 / 1000 = 0.00205 mol

From the balanced equation,

1 mol NaOH neutralises 1 mol HA

Hence moles of HA prsent in unknown = 0.00205 mol

Molar mass = mass / number of moles = 0.322 / 0.00205 = 157. g/mol

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