Answer Happy

A 0.385 4 g sample gave 0.800 0 g of product. Find the wt% of
piperazine in the sample. (Answer: 86.69%)
EXAMPLE Relating Mass of Product to Mass of Reactant The piperazine content of an impure commercial material can be determined by precipitat- ing and weighing the diacetate: 12 :NH HN: + 2CH,CO,H HUN CNH,CH,CO, (27-6) If you were performing this analysis, it would be important to determine that the impurities in the piperazine do not precipitate-otherwise the result will be high. Piperazine Acetic acid Piperazine diacetate FM 86.136 FM 60.052 FM 206.240 In one experiment, 0.312 6 g of sample was dissolved in 25 mL of acetone, and 1 mL of acetic acid was added. After 5 min, the precipitate was filtered, washed with acetone, dried at 110°C, and found to weigh 0.712 1 g. Find the wt% of piperazine in the sample. Solution For each mole of piperazine in the impure material, 1 mol of product is formed. 0.7121 g Moles of product = = 3.453 X 10-3 mol 206.240 g/mol This many moles of piperazine corresponds to Grams of piperazine = (3.453 x 10-3 mot)( 86.136 mot mot 8 = 0.297 4g 760 CHAPTER 27 Gravimetric and Combustion Analysis which gives 0.297 4g Percentage of piperazine in analyte = x 100 = 95.14% 0.3126 g An alternative (but equivalent) way to work this problem is to realize that 206.240 g (1 mol) of product will be formed for every 86.136 g (1 mol) of piperazine analyzed. Because 0.712 1 g of product was formed, the amount of reactant is given by x g piperazine 86.136 g piperazine 0.712 1 g product 206.240 g product (86.136 g piperazine 0.712 1 g product = 0.297 4 g piperazine →x = 206.240 g product The quantity 86.136/206.240 is the gravimetric factor relating the mass of starting mate- rial to the mass of product. Gravimetric factor: relates mass of product to mass of analyte. TEST YOURSELF A 0.385 4 g sample gave 0.800 0 g of product. Find the wt% of pipera- zine in the sample. (Answer: 86.69%)