Organic compound formula = C7H14. It doesn't decolourise bromine water.Which is false

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YasminBedford
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#1
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#1
a) its emperical and molecular formulae are different
b) it is an alkene
c) it is a cycloalkane
d) it is a hydrocarbon
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(Original post by 16AFC)
A is false.
A is true. Emperical formula is CH2
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(Original post by YasminBedford)
a) its emperical and molecular formulae are different
b) it is an alkene
c) it is a cycloalkane
d) it is a hydrocarbon
What does the bromine water decolourisation test tell you about a compound?
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YasminBedford
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(Original post by TutorsChemistry)
What does the bromine water decolourisation test tell you about a compound?
Is it a test to identify if an alkene is present?
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(Original post by YasminBedford)
Is it a test to identify if an alkene is present?
Spot on.

So... if the compound doesn't decolourise bromine water that is a negative test for an alkene.
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YasminBedford
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(Original post by TutorsChemistry)
Spot on.

So... if the compound doesn't decolourise bromine water that is a negative test for an alkene.
So option B is false right?
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(Original post by YasminBedford)
So option B is false right?
Yes
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confusedchildren
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(Original post by YasminBedford)
a) its emperical and molecular formulae are different
b) it is an alkene
c) it is a cycloalkane
d) it is a hydrocarbon
Its C A is true as someone mentioned before. B is true because it is an alkene. The formula for an alkene is cnH2n which is the case in c7H14 and both alkenes and alkanes are hydrocarbons so D is true leaving C remaining. Also, cycloalkane involves the word alkane (cnH2n+2) which means the formula should have been C7H16 but its c7h14 so it is an alkane so C is false.
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confusedchildren
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(Original post by YasminBedford)
a) its emperical and molecular formulae are different
b) it is an alkene
c) it is a cycloalkane
d) it is a hydrocarbon
However it is strange that it doesnt decolourise in bromine water. All alkenes make bromine water go colourless. Maybe there is something wrong with your question?
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Guarddyyy
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(Original post by confusedchildren)
However it is strange that it doesnt decolourise in bromine water. All alkenes make bromine water go colourless. Maybe there is something wrong with your question?
Probably a mistype, it certainly does make bromine water colourless.
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(Original post by confusedchildren)
However it is strange that it doesnt decolourise in bromine water. All alkenes make bromine water go colourless. Maybe there is something wrong with your question?
What is the emperical formula of a cycloalkane? Also CnH2n
Hence C could be true.
The fact that the compound doesn't decolourise bromine water is the give away that B is false whilst C would then be true.
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YasminBedford
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(Original post by Guarddyyy)
Probably a mistype, it certainly does make bromine water colourless.
I know what you mean - I thought all alkenes turned bromine water colourless?
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bozmak
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B is the answer. It is false as alkene will always decolourize bromine water which as the question says, this compound doesn't.A: Its empirical formula is CH2 so thats different than molecular one. So this is true.C: This one is a little tricky to understand but when an alkane becomes a cycloalkane then it loses two hydrogen atoms. So this can be C7H16 alkane converted to C7H14 cycloalkane. So this is also true.D: It is definitely a hydrocarbon. I guess this is self-explanatory. True.
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Guarddyyy
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Maybe you're missing something to the question. C7H14 can either be a cycloalkane (cycloheptane) or an alkene (heptene). If it is a cycloalkane, it will not decolourise bromine water. If it is an alkene, it will decolourise bromine water.
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(Original post by TutorsChemistry)
What is the emperical formula of a cycloalkane? Also CnH2n
Hence C could be true.
The fact that the compound doesn't decolourise bromine water is the give away that B is false whilst C would then be true.
They do.
It's not an alkene

Whenever you see the bromine water test in a question use that to decide whether the substance definitely is or definitely isn't an alkene.
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thotproduct
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Use the fact it doesn't decolourise bromine water to eliminate the option of it being an alkene. So B would be the false statement. Bromine water engages in a reaction mechanism with unsaturated compounds (i.e things with carbon-carbon double bonds, triple, etc), to decolourise the water, and you should know alkenes are unsaturated compounds. The fact that this test provides a negative means that this compound is not an alkene but is a functional group isomer of an alkene, which is an cycloalkane of a sort. These have the same molecular formulae as the alkene form however are alkanes in every other sense, and won't react with bromine water. You know from this statement and what I said earlier that C would be true, and D is true since the compound only contains Carbon and Hydrogen atoms, obviously. So the answer you can both deduct immediately and invalidate the other answers, as B.

(Original post by 16AFC)
A is false.
are you on crack cuz
(Original post by confusedchildren)
However it is strange that it doesnt decolourise in bromine water. All alkenes make bromine water go colourless. Maybe there is something wrong with your question?
and you, pass me your syringe Ms Jade. Cycloalkanes won't decolourise bromine water either, and have the same general form.
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