9g water is added into 100g oleum sample labelled as 112 percent h2so4 then the amount of free so3 remaning in the solution is
a.14.93L at STP
b. 7.46L at STP
c.3.78L at STP
d.11.2L at STP

Dear Student,

112% oleum means 100g is the sample and 12g is the water required by sample to completely combine SO3 in the sample. 
And according to reaction 
SO3  +  H2O   =      H2SO4
80g       18g               98g

So, 12g water combines with 53.3g SO3 and hence in 100g sample 53.3g is SO3 and 46.7g is H2SO4.

Now, If another 9g of water is added to it, another 40g of SO3 is converted to H2SO4.
So, remaining free SO3 is 15.3g = 0.2 moles 
At STP, 1 mol has volume 22.4 L. SO, 0.2 moles has volume = 3.78 L.

So, the correct option is C.

Regards

  • 11
intial weight of  H2S2O= 100
The weight of H2SO4 after dilution = 112 gm
Weight of H2O =  12 gm
or moles of H2O = Moles of SO3 = 12/18 = 0.67 gm (approx)
​therefore amount of SOremaining = 0.67 * 80 = 53.6 gm
 
  • -19
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