Biology; Chemistry; Physics: Post your doubts here!

[irfan.kheerdali]

tha

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_w12_ms_21.pdf
You are really great .Thanks a lot once again. Mr Zushid i will be very happy if you could help in a chemistry question which I am having trouble. i really need your help. Small pieces of copper were added to excess concentrated sulfuric acid and the mixture
heated for 30 minutes. A colourless gas Z was formed. When Z was tested with filter paper
dipped into acidified potassium dichromate(VI), there was a colour change from orange to
green.
The reaction mixture was cooled and then diluted with water. A blue solution, Y, was formed.
Aqueous sodium hydroxide was added drop by drop to the blue solution. Eventually a blue
precipitate, X, was formed. On heating the blue precipitate turned black to form compound V.
Analysis of V showed that it contained 79.9 % copper and 20.1 % oxygen by mass.
(a) Name gas Z.
......................................................................................................................................[1]
(b) Name the blue solution Y.
......................................................................................................................................[1]
(c) When aqueous sodium hydroxide was added to the cooled reaction mixture, it initially
reacted with excess sulfuric acid.
Write the ionic equation for this reaction.
[1]
(d) (i) Name the blue precipitate X.
..............................................................................................................................[1]
(ii) Write an ionic equation, including state symbols, to show the formation of this blue
precipitate.
[2]

AND PLEASE GIVE EXPLANATIONS

 

[Zuhsid]

tha
AND PLEASE GIVE EXPLANATIONS

lol, Yar always welcome to help!!

(a) Sulpher dioxide ----->Wehn you add copper into Conc. sulphuric acid, the equation is: Cu + 2H2SO4 = CuSO4 +2H2O +SO2 ----> so supler dioxide is the only gas formed

(b) Copper (II) Sulphate ------> As in the aboveequation, it is formed and is one of the few compounds having a blue colour.

(c) H^+ (aq) + OH^- (aq) = H2O (l) --------------> This is the ionic equation for EVERY acid-base reaction, so learn it by heart!!!

(d)(i) Copper (II) hydroxide -------> As Cu2SO4 is soluble, so the precipitate only appears when it reacts with NaOH: CuSO4 + 2NaOH = Cu(OH)2 + Na2SO4 --------> you should know taht every compound of copper is blue

(ii) Cu^2 (aq)+ +2OH^- (aq) = Cu(OH)2 (s) ---------------> The equation i gave in the part before is simplified into this, as the rule is that when forming an ionic equation, no soluble compounds have to be written, but the compunds left, have to be balanced, so we place ions of the remaining compounds on the other side.

 

[irfan.kheerdali]

lol, Yar always welcome to help!!

(a) Sulpher dioxide ----->Wehn you add copper into Conc. sulphuric acid, the equation is: Cu + 2H2SO4 = CuSO4 +2H2O +SO2 ----> so supler dioxide is the only gas formed

(b) Copper (II) Sulphate ------> As in the aboveequation, it is formed and is one of the few compounds having a blue colour.

(c) H^+ (aq) + OH^- (aq) = H2O (l) --------------> This is the ionic equation for EVERY acid-base reaction, so learn it by heart!!!

(d)(i) Copper (II) hydroxide -------> As Cu2SO4 is soluble, so the precipitate only appears when it reacts with NaOH: CuSO4 + 2NaOH = Cu(OH)2 + Na2SO4 --------> you should know taht every compound of copper is blue

(ii) Cu^2 (aq)+ +2OH^- (aq) = Cu(OH)2 (s) ---------------> The equation i gave in the part before is simplified into this, as the rule is that when forming an ionic equation, no soluble compounds have to be written, but the compunds left, have to be balanced, so we place ions of the remaining compounds on the other side.

Thanks very much you are very helpful. Another question plz .papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_w12_qp_21.pdf quetion n0. 4(b),(c).(with explanations).thanks once again Mr.zushid

 

[irfan.kheerdali]

Explain how it is possible that parents with different blood groups are able to produce
only children with blood groups different from themselves

 

[Zuhsid]

Thanks very much you are very helpful. Another question plz .papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_w12_qp_21.pdf quetion n0. 4(b),(c).(with explanations).thanks once again Mr.zushid

4(b) Water and lenticels --------> As water contains ozygen, there can come a time when the oxygen accumulates, and can form bubbles on any present substance....... lenticels is one of the raised pores in the stem of a woody plant that allow gas exchange between the atmosphere and plant tissues, so the oxygen with in the tissues(produced during photosynthesis) can leak and form bubbles through them.

(c) (Well this answer is basically the explanation i gave above, but.....) As the plant photosynthesises, it prduces oxygen in the chloroplasts of the stem and then travel to other cells and the spaces in between, form which the oxygen diffuses out through the stomata or lenticels and produces bubbles.


Hope it helps.... and please dont call me "Mr.", thank you!!

 

[Zuhsid]

Explain how it is possible that parents with different blood groups are able to produce
only children with blood groups different from themselves

Were you not able to find the answer in the following marking scheme?
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_w12_ms_21.pdf

 

[irfan.kheerdali]

Were you not able to find the answer in the following marking scheme?
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Biology (5090)/5090_w12_ms_21.pdf

thanks very much. I know that i am asking too much of questions it's because i dont know how to get full marks in o level biology essay questions.i wanted to know how to construct the answers. sorry

 

[irfan.kheerdali]

papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w10_qp_21.pdf
question no.6 and no.10 b(ii),(iii). with explanations

 

[Spidey21]

papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w10_qp_21.pdf
question no.6 and no.10 b(ii),(iii). with explanations

as far as my knowledge goes (been off this Board for some time now)
(ii) Beta particle is the negatively charged particle emitted by the radioactive source, consisting of fast moving electrons.

 

[Zuhsid]

thanks very much. I know that i am asking too much of questions it's because i dont know how to get full marks in o level biology essay questions.i wanted to know how to construct the answers. sorry

It is possible such that, if the genotype for blood of one parent is OO (blood gorp O) and the other has a genotype of AB (blood gorup AB), in this case, after the alleles seperate and the produced gametes fuse together, the resultant possible genotypes are; AO(blood group A), BO(blood group B), AO(blood group A), BO(blood group B). Thus proving that it is possible to have offsprings of only different bood groups.

 

[irfan.kheerdali]

as far as my knowledge goes (been off this Board for some time now)
(ii) Beta particle is the negatively charged particle emitted by the radioactive source, consisting of fast moving electrons.

It is possible such that, if the genotype for blood of one parent is OO (blood gorp O) and the other has a genotype of AB (blood gorup AB), in this case, after the alleles seperate and the produced gametes fuse together, the resultant possible genotypes are; AO(blood group A), BO(blood group B), AO(blood group A), BO(blood group B). Thus proving that it is possible to have offsprings of only different bood groups.

Thanks guys

 

[irfan.kheerdali]

A current of 0.5A is passes through molten lead(ii)nitrate for 150 min.
1)In what state is the lead collected at cathode and why?
Ans:The state collected is solid but why ????

 

[Zuhsid]

A current of 0.5A is passes through molten lead(ii)nitrate for 150 min.
1)In what state is the lead collected at cathode and why?
Ans:The state collected is solid but why ????

I would say that coz lead(II) nitrate is an ionic compound and thus, it has a very strong electrostatic(electrovalent force) between the lead and nitrate ions, thus also has a very high melting point..... so a small current like 0.5A would have no affect in it, no matter for how long it is passed through teh compound!!

Mgr it would be beta to have a second opinion about it first!!

 

[Spidey21]

Thanks guys

Dont mention it

 

[Yazka Shathir]

The questions says
When leaves fall from plants, they are decomposed to return nutrients to the soil. Suggest why the rate of decomposition will be particularly high in a tropical rain forest.
I wrote
a) large number of leaves will fall so more food available
b) to the decomposers, namely bacteria/fungi
c) more trees means, more oxygen produced during photosynthesis for aerobic respiration , by bacteria.

Bullet (c) is not accepted in the marking scheme. Even if so, will it be accepted? Or is it a wrong concept. Thankyou.

 

[Yazka Shathir]

For biology, read read read and read more!
Don't stick to only olevel notes or your school notes. Explore text books as much as possible and learn more, new things and details of the mechanisms. Not just what the syllabus specifies. Extra information comes very handy in Biology

can someone tell me tecniques to get an A* in o level Biology,physics and chemistry.

 

[Nabeel.Ahmad]

The questions says
When leaves fall from plants, they are decomposed to return nutrients to the soil. Suggest why the rate of decomposition will be particularly high in a tropical rain forest.
I wrote
a) large number of leaves will fall so more food available
b) to the decomposers, namely bacteria/fungi
c) more trees means, more oxygen produced during photosynthesis for aerobic respiration , by bacteria.

Bullet (c) is not accepted in the marking scheme. Even if so, will it be accepted? Or is it a wrong concept. Thankyou.

I think in a Tropical rain forest, there will be more trees and thus more Bacteria. They will replicate and reproduce because of a good oxygen supply and this will lead to high decomposition.

 

[Yazka Shathir]

Marking scheme talks about more leaves falling so more food, then the temperature ( warm ), moist. bacteria.
Nothing about oxygen. :/

I think in a Tropical rain forest, there will be more trees and thus more Bacteria. They will replicate and reproduce because of a good oxygen supply and this will lead to high decomposition.

 

[Nabeel.Ahmad]

Marking scheme talks about more leaves falling so more food, then the temperature ( warm ), moist. bacteria.
Nothing about oxygen. :/

Yeah, more leaves, more food for respiration and more Binary Fission and replication so more decomposition.
How many marks is this question?
Can't we just mention this one point about leaves falling and get full?

 

[Yazka Shathir]

3 marks.



large amount of detritus / leaf litter / organic material available;

ref / bacteria / fungi;

ref. warm;

moist / damp (conditions);

ref. increased + enzyme action.

Yeah, more leaves, more food for respiration and more Binary Fission and replication so more decomposition.
How many marks is this question?
Can't we just mention this one point about leaves falling and get full?