# how do you calculate the molecular formula for 3-methylpentane??????? help

Watch
Announcements
#1
helooooooooo
0
#2
helppppppppp
0
2 years ago
#3
Draw it and count the atoms?
0
2 years ago
#4
It says pentane and you have a mthyl group attached to the 3rd carbon hence the name 3-methylpentane. Can you draw the structure firstly? If you are able to draw the structure, then you will be able to spot the formula by just counting the number of atoms of each element.
0
#5
(Original post by marupe)
Draw it and count the atoms?
idk
0
2 years ago
#6
CH3-CH2-CH2(CH3)-CH2-CH3

5 Carbons in a chain with a CH3 methyl group attached to the 3rd carbon.
0
2 years ago
#7
Pent= 5 carbon chain
ane= no unusual functional group, just CnH2n+2 (excuse my lack of subscript)

on the third carbon, add a methyl group (meth is the prefix for one carbon chain, so methyl must be CH3)
but carbon can only have a valence of four, so remove one hydrogen off the above carbon.

Then count the C's and H's

(Original post by hujikolp)
idk
0
#8
(Original post by marupe)
Pent= 5 carbon chain
ane= no unusual functional group, just CnH2n+2 (excuse my lack of subscript)

on the third carbon, add a methyl group (meth is the prefix for one carbon chain, so methyl must be CH3)
but carbon can only have a valence of four, so remove one hydrogen off the above carbon.

Then count the C's and H's
I still dont get it lol can u pm ??
0
#9
(Original post by Volibear)
...have you not gone over the basics in your lessons?
Nope
0
2 years ago
#10
(Original post by hujikolp)
I still dont get it lol can u pm ??
Your longest carbon chain is the pentane, given in the question. Pent means 5 (pentagon etc) and ane is the suffix for just a hydrocarbon chain- there are no functional groups, such as alcohol etc

Each carbon can have 4 bonds. Each carbon will bond to the carbon next to it, so you have 2 carbons on the ends, 3 in the middle. Because the carbons at the end only bond with one other carbon, they must have three hydrogens giving a total of 4 bonds (1+3). The carbons in the middle will have two hydrogens.
So pentane is C5H(3+3+2+2+2) which is C5H12

You need to add a methyl group.

First you label the carbon atoms, and you label the longest chain. In this case it is just a pentane, and you can label the carbons 1 to 5 either way it doesn't matter. The middle carbon (carbon number 3, hence 3-methyl) you will add a methyl (methane minus a hydrogen, CH3) group. But carbon can only have 4 bonds, so by adding a CH3 group you will need to take away one hydrogen.

So C5H12 +CH3 - H =C6H14
0
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### Should there be a new university admissions system that ditches predicted grades?

No, I think predicted grades should still be used to make offers (641)
33.51%
Yes, I like the idea of applying to uni after I received my grades (PQA) (808)
42.24%
Yes, I like the idea of receiving offers only after I receive my grades (PQO) (378)
19.76%
I think there is a better option than the ones suggested (let us know in the thread!) (86)
4.5%