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

Qualification => Subject Doubts => IGCSE/ GCSE => Sciences => Topic started by: emi on April 23, 2009, 03:23:43 pm

Title: Chemistry help
Post by: emi on April 23, 2009, 03:23:43 pm
could some one please explain the moles Question for me ?

5) calculate the mass of copper(II) sulphate formed when 5g of copper oxide reacts with excess sulphuric acid
     CuO+H2SO4 ----> CuSO4+H2O


i some how cant solve any of these type of Questions, so if u know well please help me out im not saying specifically this Question only i want the steps on how to solve these type of Questions .
or if u have any notes regarding this or e-books,  please share with me
Title: Re: Chemistry help
Post by: mousa on April 23, 2009, 07:06:19 pm
ok,,,,in such type of questions u need to work with(use) the limiting Reactant(the one NOT in Excess),hence in this case its copper oxide :therefore in 5g of copper oxide there are [5/(64+16)=0.0625mol(3.s.f)].

now using the ratio of 1CuO: 1CuSO4...no. of moles of coppersulphate= no. of moles of copperoxide=0.0625;;;;;from this u can easily find the mas using[n*mr}

.......hence we get 0.0625*[64+32+(4*16)].,;;;therefore yeild of coppersulphate crystals =0.0625*160=10g


hope u understood!!!! ???
Title: Re: Chemistry help
Post by: AS girl on April 23, 2009, 07:07:29 pm
Quote from: emi on April 23, 2009, 03:23:43 pm
could some one please explain the moles Question for me ?

5) calculate the mass of copper(II) sulphate formed when 5g of copper oxide reacts with excess sulphuric acid
     CuO+H2SO4 ----> CuSO4+H2O


i some how cant solve any of these type of Questions, so if u know well please help me out im not saying specifically this Question only i want the steps on how to solve these type of Questions .
or if u have any notes regarding this or e-books,  please share with me


Hi Emi, I'll try to do my best to help u solving these kind of questions.
You have to know some basic rules:
No.of moles=molarity*Volume(in dm cube)
OR u can use=Mass given/Mr

For your problem u have to find the Mr for both Cupper(II)Sulphate and Copper Oxide
Use a technique called "cross multiplication"

So for example : Mr of Copper(II) Sulphate=Mr of copper oxide
                                        x               =5 gm

Solve for x. This is by 5*(Mr of copper(II)Sulphate)/Mr of copper oxide

I hope i had explained it well.
Title: Re: Chemistry help
Post by: ronno on April 24, 2009, 04:04:33 am
hey guys..i was jus wondering if anyone had any tips or cud help me out with doing the chemistry paper 6 practicals..i just dont get them especially the ones with the questions of the qualiltative analysis..the question that always come out with the blanks tht u have to fill about the solutions they give u..any tips or any e-books or sumthing tht cud help me understand the whole qualitative anlaysis topic cos the notes for the qualitative analysis in the igcse syllabus is not tht helpful..awaiting ur reply anyone  :) thanks
Title: Re: Chemistry help
Post by: june on April 24, 2009, 05:19:55 pm
In the november 08 paper 3 .. Q4biii) page 6..
can anyone please explain how they moleculer formula of benzene was worked out? ???
Title: Re: Chemistry help
Post by: emi on April 24, 2009, 05:27:08 pm
yes please i want that too
Title: Re: Chemistry help
Post by: sweetsh on April 24, 2009, 05:28:57 pm
The hydrogen percentage is 7.7% so the ratio is:
92.3 : 7.7
92.3/12 : 7.7/1
7.69:7.7
7.69/7.69:7.7/7.69

1:1

so the emprical formula is CH
and the molecular formula will be 78/13 *CH =6CH=C6H6

By the way I got this wrong in my mock exam but my teacher explained it to me. This exam was pretty hard!
Hope thats help!
Title: Re: Chemistry help
Post by: june on April 24, 2009, 06:22:44 pm
Oh i get the first part but i still dont get how u got the molecular formula.. where did  the 13 come from? ;s
Is there like an a formula thats used to work out the molecular formula i mean like speed= distance/time .. molecular formula= ?
Lol i dont know if im making any sense! and yeah its really hard, i hope we get an easy one!! :-\
Title: Re: Chemistry help
Post by: SGVaibhav on April 24, 2009, 06:55:59 pm
13 came from CH
u add the molar mass of elements
(12+1)
Title: Re: Chemistry help
Post by: SGVaibhav on April 24, 2009, 07:00:29 pm
http://www.crampuppy.com/1/IGCSE/chemistry/stoichiometry.shtml

read that.

i will tell u actual formula in sometime.
after reading it in my book!
Title: Re: Chemistry help
Post by: june on April 24, 2009, 09:18:35 pm
ooooh i get it now! thanks a bunch!  :D
Title: Re: Chemistry help
Post by: june on April 24, 2009, 09:20:27 pm
and the formula is : molecular formula = molecular mass/ molar mass of elements!! hehe