Calculate the mass of KHP present using the molarity and volume of NaOH, the mol

Question

Calculate the mass of KHP present using the molarity and volume of NaOH, the molecular weight of KHP, and the balanced chemical equation for the reaction of KHP and NaOH. Use this mass and the mass of your unknown to calculate the % purity of KHP in your unknown.

1.2889 M NaOH used

Trial #1: 2.1936g of unknown and 29.9mL of NaOH used to reach endpoint

Trial #2: 2.2105g of unknown and 28.7mL of NaOH used to reach endpoint

Trial #1: 2.2125g of unknown and 27.9mL of NaOH used to reach endpoint

Trial #1: 2.1885g of unknown and 27.2mL of NaOH used to reach endpoint

Explanation / Answer

Balanced equation:
NaOH(aq) + KHC8H4O4(aq) ====> KNaC8H4O4(aq) + H2O(l)
Reaction type: double replacement

Trial 1

Volume of NaOH = 29.9 ml

Concentration of NaOH = 1.2889 ml

Moles of NaOH = 29.9 x 1.2889 / 1000 = 0.038538 Moles

Moles of KHP = 0.038538 Moles

molar mass of KHP = 204.22 gm/mol

Mass of KHP present = 0.038538 x 204.22 = 7.87 gm

hence 7.87gm of KHP is needed to neutralize  29.9mL of 1.2889 M NaOH. But 2.1936 gm is mentioned. I hope mistake is there. Please correct it.  

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