-
Looking for HSC notes and resources? Check out our Notes & Resources page
Hydrocarbons (1 Viewer)
- Thread starter hs17
- Start date
specificagent1
Well-Known Member
- Joined
- Aug 24, 2021
- Messages
- 1,977
- Gender
- Male
- HSC
- 2021
ye i think it should be 14
Note that some of the answers to the Baulkham Hills High School 2019 Chemistry trial exam (where this question appears) are actually incorrect. This was confirmed by CM_Tutor in the thread below:
boredofstudies.org
If the answer stated is 10, whereas you and specificagent1 got 14, then there is a chance that the answer would indeed be 14, i.e. (D).
I hope this helps!
Chemistry question help
Hi guys, if anyone could help me with the attached questions it would be greatly appreciated. The correct answer is highlighted, I just need help with the working out.
boredofstudies.org
If the answer stated is 10, whereas you and specificagent1 got 14, then there is a chance that the answer would indeed be 14, i.e. (D).
I hope this helps!
Eagle Mum
Well-Known Member
- Joined
- Nov 9, 2020
- Messages
- 532
- Gender
- Female
- HSC
- N/A
It is 14 hydrogens (D).
The rationale and a good approach for working it out:
Butane, with 4 carbons would have 2n + 2 = 2x4 + 2 = 10 hydrogens
Butanol, with substitution of a hydrogen (H) attached to C1 for a hydroxyl (-OH) group doesn’t change the number of hydrogens from the base alkanes.
With substitution of each of both hydrogens (H) attached to C2, for a methyl (CH3) group, each substitution increases the number of hydrogens by 3-1 = 2, with two substitutions increasing the total number by 2x2 = 4.
Hence, total number of hydrogens is 10+4 = 14.
The rationale and a good approach for working it out:
Butane, with 4 carbons would have 2n + 2 = 2x4 + 2 = 10 hydrogens
Butanol, with substitution of a hydrogen (H) attached to C1 for a hydroxyl (-OH) group doesn’t change the number of hydrogens from the base alkanes.
With substitution of each of both hydrogens (H) attached to C2, for a methyl (CH3) group, each substitution increases the number of hydrogens by 3-1 = 2, with two substitutions increasing the total number by 2x2 = 4.
Hence, total number of hydrogens is 10+4 = 14.
Firstly, to answer the specific question, the answer is wrong it should be 14.
Although the above method mentioned is correct. It would take too much time to do that in an exam and you would have to memorise something like that for different types of molecules like alcohols, haloalkanes, ketones, esters etc. The faster way to solve this is to draw the molecule and count the number of hydrogens, which would take about 10-20 seconds.
We can see based on drawing and counting the H, there is 14.
Although the above method mentioned is correct. It would take too much time to do that in an exam and you would have to memorise something like that for different types of molecules like alcohols, haloalkanes, ketones, esters etc. The faster way to solve this is to draw the molecule and count the number of hydrogens, which would take about 10-20 seconds.
We can see based on drawing and counting the H, there is 14.