AQA AS Chemistry help TQ

A hydrocarbon contains 787.8% by mass of carbon and has a relative molecular mass (Mr) of 82.0
The hydrocarbon decolourises bromine water.

1. Determine the empirical and molecular formulae of the hydrocarbon.
2. Suggest two possible structure for the hydrocarbon.
3. Name the type of reaction taking place when bromine water reacts with the hydrocarbon.

My answer:
Type of reaction is electrophilic addition. I don't know how to find question 1.

Please help! THANK YOU

Reply 1

Pigster

20

Original post by beautiful_tae

A hydrocarbon contains 787.8% by mass of carbon

Jeepers.

Reply 2

beautiful_tae

OP

12

*87.8%

sorry for the error

Original post by Pigster

Jeepers.

Reply 3

Pigster

20

Original post by beautiful_tae

A hydrocarbon contains 787.8% by mass of carbon and has a relative molecular mass (Mr) of 82.0
The hydrocarbon decolourises bromine water.

1. Determine the empirical and molecular formulae of the hydrocarbon.
2. Suggest two possible structure for the hydrocarbon.
3. Name the type of reaction taking place when bromine water reacts with the hydrocarbon.

My answer:
Type of reaction is electrophilic addition. I don't know how to find question 1.

Please help! THANK YOU

87.8% C.
Hydrocarbon.
What percentage is the rest? What is the rest made of?
Empirical formulae is (or was) GCSE content.
Divide the Mr by the Mr of the empirical formula to get how many times the empirical formula you're dealing with.
Br2 test, so you know it isn't cyclical.
You know about structural and E/Z isomerism, so you should know there are loads of possible (a quick check of mine suggests 17) isomers to choose from.

Reply 4

funtz

1

Original post by Pigster

87.8% C.
Hydrocarbon.
What percentage is the rest? What is the rest made of?
Empirical formulae is (or was) GCSE content.
Divide the Mr by the Mr of the empirical formula to get how many times the empirical formula you're dealing with.
Br2 test, so you know it isn't cyclical.
You know about structural and E/Z isomerism, so you should know there are loads of possible (a quick check of mine suggests 17) isomers to choose from.

It can be a cyclic alkene and still show a positive test to bromine water. 87.8/12 then 100-87.8/1 , thats the start of your empirical formula method. Finish it you should get c3h5, Mr is 82, find the multipler, you should get C6h10. Structures could be, cyclohexene, hexene (with 2 double bonds so hex-1-2-diene) etc