Question

13) A 10.6 g sample of an aqueous solution of perchloric acid contains an unknown amount of the acid. If 18.0 mL of 1.17 M potassium hydroxide are required to neutralize the perchloric acid, what is the percent by mass of perchloric acid in the mixture? % by mass

Answer 1

    KOH + HClO4 ----------------------> KClO4 + H2O

no of moles of KOH = molarity * volume in L

                                   = 1.17*0.018    = 0.02106 moles

from balanced equation

1 mole of KOH react with 1 mole of HClO4

0.02106 moles of KOH react with 0.02106 moles of HClO4

mass of HClO4 = no of moles * gram molar mass

                           = 0.02106*100.5   = 2.12g of HClO4

mass of percentage of HClO4 in the sample = 2.12*100/10.6    = 20% >>>>answer