Question

If 10g of a hydrocarbon (molecular mass=54g/mol) reacts completely with 8.30 L (measured at STP) of hydrogen then, the total number of C=C bonds in one molecule of the hydrocarbon is.
Answer it please..​

Answer 1

Hey you are in a great coaching

You are doing those things which are in 11th by now

Anyway I have done all these and 12th also

Any hydrocarbons react with hydrogen to give addition reactions

And it is only possible when the hydrocarbon contains multiple bonds

So it is not possible in alkane or cyclo alkane but possible in alkene , cyclo alkene , alkyne and cycloalkyne, etc

Overall possible in unsaturated hydrocarbons

Now ,

At STP ,

moles of a gas = volume of gas given / 22.4 L

moles of hydrogen which reacts in the reaction = 8.30 L / 22.4 L

= 0.3705 moles

moles of hydrocarbon = given weight / molecular weight = 10 g /54 g = 0.1851 mole

So ratio of mole in which hydrocarbon reacts with hydrogen = moles of hydrocarbon in exhausted in reaction : moles of hydrogen exhausted in reaction

= 0.1851 : 0.3705

= 1:2 (approximately)

Of course here hydrogen means hydrogen gas or H2 , which is used in hydrogenation reactions

So 1 mole of hydrocarbon reacts with two moles of hydrogen molecule

This means two multiple bonds are hydrogenated to form single bond at their place

So there are two possibilities

(1) hydrocarbon contains a triple bond in the molecule which requires two moles of hydrogen per mole of hydrocarbon

(2) hydrocarbon contains two different double bond in the molecule which also requires two moles of hydrogen per mole of hydrocarbon

Answered by an IIT JEE ASPIRANT and all India mathematics OLYMPIAD TOPPER in class 10th