Question

For 109% labelled oleum if the number of moles of H2So4 and free so3 be x and y respectively then what will be the approximate value of x+y\x-y

Answer 1

Well, there is a simple way to solve it,
As we know that oleum actually a mixture of H2SO4 and  the free SO3
and in the 109% grams oleum there is actually 40 gram of SO3 and  also 60 gram of H2SO4
So in this case, Number of moles of  H2SO4 will be "x'' and it will equal to Mass /molar mass (number of moles= Mass/ molar mass).

So the x will be = Mass/molar mass=  60 / 98 =   0.612 
Similarly number of moles of SO3 will be y and = mass/molar = 40/80 = 0.5=y
Now let's calculate the value of x+y = 0.612 + 0.5 = 1.112 Ans
Similarly x-y = 0.612 - 0.5= 0.112 Ans

Note ;molar mass of H2SO4 is 98 while for SO3 it is 80