1 g of fuming H ₂ SO ₄ ( oleum : It is a mixture of concentrated H ₂ SO ₄ saturated with SO ₃ and having formula H ₂ ~S ₂ O ₇ ) is diluted with H ₂ O . This solution is completely neutralised by 26.7 mL of 0.8 N NaOH . Find the percentage of free SO ₃ in the oleum.

Step-by-step solution

H ₂ ~S ₂ O ₇+ H ₂ O 2 H ₂ SO ₄ SO ₃ of H ₂ ~S ₂ O ₇ is converted into H ₂ SO ₄ , hence SO ₃ acts also as a dibasic acid. Eq. wt. ( SO ₃ )= M 2 =40 Let H ₂ SO ₄ in fuming H ₂ SO ₄= xg SO ₃=(1-x) g Equiválent of H ₂ SO ₄= X 49 SO ₃= 1-x 40 Equivalent of NaOH used = 26.7 0.8 1000 =0.02136 x 49 + 1-x 40 =0.02136x=0.7927 gH ₂ SO ₄ in 1 g oleum. Percentage of H ₂ SO ₄=79.27 % SO ₃=20.73 %