A straight glass tube has two inlets `x` and `y` at two ends. The length of the tube is `200 cm`. `HCl` gas through inlet `x` and `NH_(3)` gas through inlet `y` are allowed to enter the tube at the same time. White flames first appear at a point `P` inside the tube. Find the distance of `P` from `x`.

Explanation

According to Graham.s law of diffusion,
`("Rate of diffusion of HCl")/("Rate of diffusion of "NH_(3))=sqrt(("Molar mass of "NH_(3))/("Molar mass of HCl"))`
`"Molar mass of "NH_(3)=17`,
Let the distance between P and X = d cm
`therefore" Distance between P and Y"=(200-d)cm.`
Let they meet at P in time t.
`"Rate of diffusion of HCl"=(d)/(t)`
`"Rate of diffusion of "NH_(3)=(200-d)/(t)`
`therefore" "(d//t)/((200-d)//t)=sqrt((17)/(36.5))`
`(d)/(200-d)=0.6824`
`d=(200-d)(0.6824)`
`"or "d+0.6824d=200xx0.6824`
`"or "d=(200xx0.6824)/(1.6824)`
`=81.12cm.`