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Tuesday, October 9, 2007

Chemistry Question - Acids/Bases

Q) Which of the following statements is true of the hydroxide ion?

A)It is a product of reaction btw hydrogen and oxygen
B)It is present in aqueous ammonia
C)It is present in pure alcohol
D)It is present in pure water

Show your explainations.

Rgds,
Sean
SimpleChemConcepts
"Learning Experience with A Difference"

7 comments:

LinwooD said...

i think the answer is C, its due to the formula of alcohol which is CnH2n+1OH, therefore, pure alcohol contains hydroxide ion.

I don't think A is the answer because the product of reaction btw hydrogen and oxygen is pure water.

I also don't think it is B because aqueous ammonia is NH3 and it has hydrogen ion only when it reacts with a soluble salt to form an insoluble XOH white ppt.

D is obviously not the answer cause pure water doesn't contain hydroxide ion which is OH-.

lijun(: said...

i think the answer should be B.

it cannot be A,
2H2 + O2 -> 2H20
pure water do not have ions, as it is a covalent compound.

aqueous ammonia is always ammonium hydroxide, which is NH4OH.
hence, the ions present are NH4+ and OH-.

in alcohol, the functional group is -O-H. but the functional group is not the hydroxide ion.

in pure water, there's no ions, since it's a covalent compound. hence there can't be any ions present.


*hydroxide ions are usually found in alkalis, alcohol is not an alkali. the -O-H functional group is definitely NOT the hydroxide ion.

lijun(: said...

sorry.
i meant aqueous ammonia is ALSO ammonium hydroxide.

huge typo err. =/

Sean Chua said...

Hi,

Answer is B, Aqeuous Ammonia like what lijun has explained.

It has a formulae of NH4OH which in water (since aqeoues),will dissociates to form NH4+ and OH- ions.

Hope that helps.

Rgds
Sean
SimpleChemConcepts

LinwooD said...

oh yea! lol.

jeez! i didnt see its AQUEOUS ammonia. haha. thanks for correcting me :D

Sean Chua said...

Hi Linwood,

In O LEVEL exams, a lot of time you might have already known the concepts and understanding. Always note to look after those small details, cos if you dont take care of it..it might become "careless mistakes" to hunt you later...

Happy preparation...

Sean
SimpleChemConcepts

Zayd said...

The answer is D since in pure water there are H+ an OH- ions.