IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => IGCSE/ GCSE => Sciences => Topic started by: Trinion on November 10, 2009, 11:33:18 pm

Title: Urgent Help for IGCSE Chem !
Post by: Trinion on November 10, 2009, 11:33:18 pm
If the compound decomposes, complete the word equation.
If it does not decompose, write "no reaction"

Potassium Hydroxide --->________________
calcium Hydroxide ----> ______________

Complete the equations for the decomposition of their nitrates:

2KNO3----> _____+_____
2Ca(NO3)3 -----> _____+_______+_______


Thanks in advance!
Title: Re: Urgent Help for IGCSE Chem !
Post by: Ghost Of Highbury on November 11, 2009, 01:38:47 am
calcium hydroxide ----> Calcium oxide + water

Potassium hydroxide --> no reaction

Potassium nitrate --> Potassium nitrite + oxygen

Calcium nitrate --> Calcium oxide + nitrogendioxide + oxygen
Title: Re: Urgent Help for IGCSE Chem !
Post by: Trinion on November 11, 2009, 02:07:43 am
Thank you very much!
Can you explain to me why Potassium Hydroxide has no reaction?

This stuff isn't even in the IGCSE syllabus but it came up last year!

Also, does a metal carbonate decompose to form the metal oxide+ carbon dioxide?

Edit: One more question. Do all group 1 and 2 metal ions form a colourless solution in water?
Is it the same for halogen and transitional metals ion?
Title: Re: Urgent Help for IGCSE Chem !
Post by: Ghost Of Highbury on November 11, 2009, 02:12:36 am
potassium hyrdroxide is stable to heat thus doesnt decompose.  most alkali metal hydroxides do not decompose, except lithium hydroxide.

its dere in the IGCSE syl. check for "thermal decomposition"

and yes, metal carbonate --> metal oxide + CO_2
Title: Re: Urgent Help for IGCSE Chem !
Post by: Ghost Of Highbury on November 11, 2009, 02:15:12 am
no not all , few metal ions form a white precipitate, green, blue etc. colorless solution is often formed when excess ammonia is added to zinc salt
Title: Re: Urgent Help for IGCSE Chem !
Post by: Trinion on November 11, 2009, 02:51:39 am
Thank you Adi
I still can't find the thermal decomposition in the syllabus!
it certainly isn;t in my textbook? =(

I think you mistook what I meant, I meant say... Sodium chloride dissolves in water, neither ions in aqueous solutions change the colour of the solution correct?

Is it true for other halogens/transitional metal ions when they dissolve in water?
Title: Re: Urgent Help for IGCSE Chem !
Post by: Ghost Of Highbury on November 11, 2009, 04:39:42 am
i'm not sure abt this but i strongly think that it takes the colour of the ppt. colour formed by the cation

fore.g-> CuSO4 -> Cu2+ + SO4(2-)

when added to water, turns blue. blue = Cu(2+)

same with NaCl

so it takes the colour precipitate of the cation
Title: Re: Urgent Help for IGCSE Chem !
Post by: Trinion on November 11, 2009, 05:25:27 am
Cool =)

What about bromine water/solution

Why is it orange or brown? Is it because of the bromine ions?
Title: Re: Urgent Help for IGCSE Chem !
Post by: Ghost Of Highbury on November 11, 2009, 05:32:33 am
bromine water is simply an aqueous solution of Br2 --> no ions, the colour of Br2 is brown thus bromine water is brown color.
Title: Re: Urgent Help for IGCSE Chem !
Post by: Trinion on November 11, 2009, 05:45:46 am
Adi, doesn't an aqueous solution of an element simply mean its ions are dissolved in it?
Title: Re: Urgent Help for IGCSE Chem !
Post by: Ghost Of Highbury on November 11, 2009, 05:55:42 am
oh yes, sry, Br- ions are which give the brown color, but if its so , then Br- ions give a cream color, but bromine water is brown ..???
Title: Re: Urgent Help for IGCSE Chem !
Post by: @d!_†oX!© on November 11, 2009, 07:23:54 am
see according to what i think....
the bromine ions are brown in colour but,
they form a creamish ppt because of the whole compound lead(II) bromide, and not just Br
so basically i wanna say that the cream colour is due to lead(II) bromide and not just bromide ions
Title: Re: Urgent Help for IGCSE Chem !
Post by: Ghost Of Highbury on November 11, 2009, 10:42:37 am
acutally, my logic says -> lead ->white ppt bromine -> brown ppt --> brown ppt _ white ppt --> cream ppt lol..kidding :P

but adi, its abt bromine water being brown not lead bromide  ;D
Title: Re: Urgent Help for IGCSE Chem !
Post by: @d!_†oX!© on November 11, 2009, 10:44:04 am
1)i did not get ur logic :P
2)i replied to what u had asked about bromide ppt being cream
Title: Re: Urgent Help for IGCSE Chem !
Post by: Ghost Of Highbury on November 11, 2009, 10:49:04 am
bleh! :P
Title: Re: Urgent Help for IGCSE Chem !
Post by: eightAs on November 11, 2009, 10:49:56 am
Bromine is naturally liquid at room temperature and its natural colour is brown.