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Physics, Chemistry and Biology: Post your doubts here!

Phoenix Blood

Phoenix Blood

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My Name said:
Predict the products of the electrolysis of a specified
binary compound in the molten state
wta is that suppose to mean?
Click to expand...
Meaning if you electrolyse a binary compound (A binary compound is a chemical compound that contains exactly two different elements. Eg, NaCl, CaS04, etc) , what products will you get, if the reactants are in the molten state and have no water in it, at the cathode and the anode (?)
For this, you'll need to learn the preferential discharge of anions and cations.
 
M

My Name

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Phoenix Blood said:
Meaning if you electrolyse a binary compound (A binary compound is a chemical compound that contains exactly two different elements. Eg, NaCl, CaS04, etc) , what products will you get, if the reactants are in the molten state and have no water in it, at the cathode and the anode (?)
For this, you'll need to learn the preferential discharge of anions and cations.
Click to expand...
so u mean i shud know wat cums at cathoda and anode
 
Mr.Physics

Mr.Physics

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My Name said:
Describe electrolysis in terms of the ions
present and reactions at the electrodes in
the examples given?
Click to expand...
Hey the question requires you to give ions present in the reaction and what happened at different electrodes when a reaction occured .
So first you should learn the reactivity series of ions. It means that if there is a reaction containing H+and Na+ , then which cation will go towards cathode ?? It will be H+ because it takes less energy to get discharged. However , if the concentration of Na +will be higher, then it will be discharged. The list of reactivity series should be there in your book.

And in the case of electrodes , you have to learn what happenes at different electordds in different reactions.
 
Phoenix Blood

Phoenix Blood

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My Name said:
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s06_qp_1.pdf
questions
16
19
21
39
40

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w06_qp_1.pdf
question 7
Click to expand...

*Remember most oxides, hydroxides, carbonates and hydrogen-carbonates are either alkalis or bases with a Ph above 7

16) D.
What happens to the pH of a solution of hydrochloric acid as an excess of aqueous barium
hydroxide is added?
HCl is acidic, and barium hydroxide is basic. If excess BaOH is added to HCl, we come to understand that more of the base (BaOH) remains after complete neutralization of the HCl. So the solution goes from Ph 1 (HCl) to beyond neutralization, i.e. Ph 14. Neutralization is Ph 7 as we know.

19) C.
Cu + H2SO4 --> Copper does not react with dilute sulphuric acid.
Cu(OH)2 + H2SO4 --> CuSO4 + H2O (not balanced) .....here we have CU2+ ions
CuCO3 + H2SO4 ---> CuSO4 + CO2 + H2O .....here we have CU2+ ions

21) A.
Ionic compounds are formed b/w a metal and a non-metal.
Covalent compounds are formed bw two non-metals.
(Starting 3 groups are metals, last group contains unreactive elements. The remaining elements are non-metals and metalloids. )
W and X are non-metals so they'll form a covalent compound, Y is a metal, and Z unreactive.

39) C
A has double and single bonds.
B has double and single and triple bonds b/w Carbon atoms
C has all double bonds b/w Carbon atoms, and hence all belong to the same homologous series.
D also has varying single and double bonds b/w varying elements.

40) B
When an alkene (Double bonds b/w two carbon atoms) links with another alkene, the double bond breaks in both to join with the other alkene, and all the rest of the atoms stay same and undisturbed.
 
Phoenix Blood

Phoenix Blood

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My Name said:
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w06_qp_1.pdf
question 7
Click to expand...

Covalent compunds are formed b/w a non-metal and another non-metal.
Since the electrons in the outer shell correspond to the group number, we know that elements with a valency of 1 and 2 are metals. A valency of 6 and 7 means they are both non-metals and hence will react to form a covalent compound.

Another way we can use to find out the answer is to know that non-metals for acidic oxides and hences will be in the later groups with valencies of 6, 7 and 8. One element we can know that is being used here is oxygen which will too be in the latter groups.
 
M

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Phoenix Blood said:
Covalent compunds are formed b/w a non-metal and another non-metal.
Since the electrons in the outer shell correspond to the group number, we know that elements with a valency of 1 and 2 are metals. A valency of 6 and 7 means they are both non-metals and hence will react to form a covalent compound.

Another way we can use to find out the answer is to know that non-metals for acidic oxides and hences will be in the later groups with valencies of 6, 7 and 8. One element we can know that is being used here is oxygen which will too be in the latter groups.
Click to expand...
Phoenix Blood said:
*Remember most oxides, hydroxides, carbonates and hydrogen-carbonates are either alkalis or bases with a Ph above 7

16) D.
What happens to the pH of a solution of hydrochloric acid as an excess of aqueous barium
hydroxide is added?
HCl is acidic, and barium hydroxide is basic. If excess BaOH is added to HCl, we come to understand that more of the base (BaOH) remains after complete neutralization of the HCl. So the solution goes from Ph 1 (HCl) to beyond neutralization, i.e. Ph 14. Neutralization is Ph 7 as we know.

19) C.
Cu + H2SO4 --> Copper does not react with dilute sulphuric acid.
Cu(OH)2 + H2SO4 --> CuSO4 + H2O (not balanced) .....here we have CU2+ ions
CuCO3 + H2SO4 ---> CuSO4 + CO2 + H2O .....here we have CU2+ ions

21) A.
Ionic compounds are formed b/w a metal and a non-metal.
Covalent compounds are formed bw two non-metals.
(Starting 3 groups are metals, last group contains unreactive elements. The remaining elements are non-metals and metalloids. )
W and X are non-metals so they'll form a covalent compound, Y is a metal, and Z unreactive.

39) C
A has double and single bonds.
B has double and single and triple bonds b/w Carbon atoms
C has all double bonds b/w Carbon atoms, and hence all belong to the same homologous series.
D also has varying single and double bonds b/w varying elements.

40) B
When an alkene (Double bonds b/w two carbon atoms) links with another alkene, the double bond breaks in both to join with the other alkene, and all the rest of the atoms stay same and undisturbed.
Click to expand...
I FEEL SO DUMB AN DSCRAED!:cry::cry::cry::cry::cry:
 
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