1.

One litre of a mixture of O_(2) and O_(3) at NTP was allowed to react with an excess of acidified solution of KI. The iodine liberated required 40 mL of M/10 sodium thiosulphate solution for titration. The weight percent of ozone in the mixture is

Answer»

0.0557
0.0657
0.0757
0.0857

Solution :`O_(3) rarr O_(2)+O`
`{:(2 KI+H_(2)SO_(4)+(O)rarr K_(2)SO_(4)+H_(2)O+I_(2)),(2 Na_(2)SO_(3)+I_(2) rarr Na_(2)S_(4)O_(6)+2" NAI"),(bar(2 Na_(2)S_(2)O_(3)+2 KI+O_(3)+H_(2)SO_(4) rarr O_(2)+K_(2)SO_(4)+H_(2)O+Na_(2)S_(4)O_(6)+2" NaI")):}`
2 moles of `Na_(2)S_(2)O_(3)` react with one MOLE of `O_(3)` No. of moles `Na_(2)S_(2)O_(3)` in 40 ml of `M/10 Na_(2)S_(2)O_(3)`
`=1/10xx1/1000xx40=4xx10^(-3)` mole
`:. O_(3)` reacted (present) `=2xx10^(-3)` mole
VOLUME of `O_(3)=2xx10^(-3)xx22.4 L=0.0448 L`
`:.` Volume of `O_(2)=1-0.0448=0.9552 L`
Weight of `O_(3)=2xx10^(-3)xx48=0.096 g`
Weight of `O_(2) =(0.9552)/22.4xx32=1.3646 g`
`:.` Weight of mixture `=0.096+1.3646`
`=1.4606 g`
`:.` % of `O_(3)` by weight `=0.096/1.4606xx100=6.573%`.


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