13. A student carries out an experiment to standardize (determine the exact conc

Question

13. A student carries out an experiment to standardize (determine the exact concentration) of a sodium hydroxide solution. To do this, the student weighs out a 1.3009 sample of potassium hydrogen phthalate (KHCeH404, often abbreviated KHP). KHP (MW-204.22 g/mol) has one acidic hydrogen. The student dissolves the KHP in distilled water, adds phenolphthalein as an indicator, and titrates the resulting solution with the sodium hydroxide solution to the endpoint. The difference between the final and initial buret readings indicates that 41.20 mL of the sodium hydroxide solution is required to react exactly with the 1.3009 g KHP. Calculate the concentration of the sodium hydroxide solution.

Explanation / Answer

The reaction between an acid and base produces salt and water:

NaOH(aq)+KHC8H4O4(aq) = KNaC8H4O4(aq) + H2O(l)

Molarity of KHP=Mass in grams of KHP/ Molar mass of KHP==1.3009/204.22=0.00637M

From the above mentioned chemical equation it is clear that the no.of moles of NaOH and KHP for neutralisation is same i.e. 1:1

Therefore number of moles of NaOH =No. of moles of KHP=0.00637

Molarity of NaOH= No. of moles of NaOH/ Volume in Litres= 0.00637/41.20X10-3 = 0.1546M

Hence concentration of Sodium Hydroxide Solution is 0.1546M

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