) In the lab you used oxalic acid dihydrate as a primary standard , a compound t
ID: 946361 • Letter: #
Question
) In the lab you used oxalic acid dihydrate as a primary standard, a compound that can be measured out very carefully and accurately. Potassium hydrogen phthalate, KHC8H4O4, can also be used as a primary standard to determine the molarity of sodium hydroxide solutions. In a titration of 1.3009g KHC8H4O4, the buret reading went from 10.23mL to 51.43mL at the endpoint. What is the molarity of the NaOH(aq)?
KHC8H4O4(s) + NaOH(aq) -> H2O(l) + KNaC8H4O4(aq)
a) 0.1238M b) 0.1546M c) 0.2624M d) 0.3158M e) 0.6227M
Explanation / Answer
answer : b) 0.1546M
KHC8H4O4 molar mass = 204.22 g/mol
mass of KHC8H4O4 = 1.3009 g
moles of KHP = 1.3009 / 204.22 = 6.37 x 10^-3
volume of NaOH = 51.43 - 10.23 = 41.2 mL
moles of NaOH = M x V
moles of KHP = moles of NaOH
6.37 x 10^-3 = M x 41.2 x 10^-3
M = 0.1546 M
Molarity = 0.1546 M
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