Help chemistry moles q

Help!
So I got 2 marks out of 4 :frown:

(
I understand the first two steps…
But how do I know the formula of the saturated product is C40H78
I mean I thought it was the general formula of an alkane CnH2n+2…
But nope.
So I think it’s something to do with the two rings and branched chain but I’m struggling as to how I would know what the structure looks like in order to determine the 78 Hs

(edited 1 year ago)

Reply 1

callphd

so you are adding H2 to remove 11 double bonds, so you are adding 22 hydrogen atoms. 56+22 =78

Reply 2

Alevelhelp.1

Original post by callphd

so you are adding H2 to remove 11 double bonds, so you are adding 22 hydrogen atoms. 56+22 =78

I get that part… but I don’t get how I know it’s c40H56

Reply 3

Emmmaaaa...

Original post by Alevelhelp.1

I get that part… but I don’t get how I know it’s c40H56

Because you have lost 23 H due to the double bonds, and by having a ring, 2 carbons lose 1 H off of them to create a bond between them - this happens twice as there are 2 rings, so 4 H are lost
Assuming it's an alkane with 40 C, it should have 82 H (using the formula)
82 -22-4=56