Biology; Chemistry; Physics: Post your doubts here!

[tdk]

www.freeexampapers.com
check it out here???

I got some papers there BUT not older than year 2000. AND some had only QP and no Mark Schemes. I want to get at least as old as 1990 with Mark Schemes as well. If possible plz give me the older ones. Thanks for your cooperation.

 

[asma tareen]

I got some papers there BUT not older than year 2000. AND some had only QP and no Mark Schemes. I want to get at least as old as 1990 with Mark Schemes as well. If possible plz give me the older ones. Thanks for your cooperation.

sorry never practised that old

 

[TheStallion-Reborn]

Atlast after a hell lot of chemistry, I have a biology question "How do we identify by looking at the petals, anthers and stigma of a plant if it's wind pollinated or insect pollinated?" there are a lot of questions regarding this, and most of the time I fail to answer them correctly!

 

[TheStallion-Reborn]

CHMEISTRY!
I'd be more than thankful for any sort of help provided.
http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_s09_qp_1.pdf
Question 10; the marking scheme says it's B (Nitrogen) but HOW??
Question 12; no clue how to do it. Help please
Question 14; Why D (Sulphuric Acid) ??
Question 35; Though I got this right but I wasn't sure of why I chose the correct answer, so if someone could kindly explain the phenomenon.
Question 38; I wish I could have the slightest idea about it.
For convenience, here is the marking scheme; http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_s09_ms_1.pdf

 

[ijlalm]

seems like C to me due to the fact that Cu should require less electricity as it is +2, compared to +3. So,
(64/3)/2 *3 = 32. Do tell the answer if you know it

Yes its correct..BTW it was the question of the year 1975!!

 

[ijlalm]

CHMEISTRY!
I'd be more than thankful for any sort of help provided.
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s09_qp_1.pdf
Question 10; the marking scheme says it's B (Nitrogen) but HOW??
Question 12; no clue how to do it. Help please
Question 14; Why D (Sulphuric Acid) ??
Question 35; Though I got this right but I wasn't sure of why I chose the correct answer, so if someone could kindly explain the phenomenon.
Question 38; I wish I could have the slightest idea about it.
For convenience, here is the marking scheme; http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s09_ms_1.pdf

For Question 10, as you know that 14 g of nitrogen contains 14/28=0.5 moles and 9g of water also contains 9/18=0.5 moles, hence option B is the correct option.
For Question 12, In the choices C and D, the valency of the metal is +1 or +2.Choice D is not possible because in this case the Ar of the metal wud be 74.5-71=3.5. Option C wud be correct as the Ar of the metal is then 74.5-35.5=39, i.e Ar of potassium which has only one valence electron.
14) The others (A, B,C) are weak electrolytes because they do not completely dissociate ions in an aqueous solution whereas H2SO4 readily breaks into its ions when present in an aqueous solution..
38) I'm not quite sure of this though, but i think C is the possible option, as isomers have different structures compared to the original one but has the same chemical formula.. As C is not branched but is chained so its not an isomer.Wish i could explain more clearly but don't know how..

 

[TheLeagueofShadows]

CHMEISTRY!
I'd be more than thankful for any sort of help provided.
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s09_qp_1.pdf
Question 10; the marking scheme says it's B (Nitrogen) but HOW??
Question 12; no clue how to do it. Help please
Question 14; Why D (Sulphuric Acid) ??
Question 35; Though I got this right but I wasn't sure of why I chose the correct answer,we so if someone could kindly explain the phenomenon.
Question 38; I wish I could have the slightest idea about it.
For convenience, here is the marking scheme; http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s09_ms_1.pdf

For q10, we have been the mass of water which is 9g. We can find the no. of moles of water by dividing with the molar mass.(9/18=.5) Now, in the q, it is written that WHICH GAS?
Nitrogen gas has formula N2, so its no. of moles are ( 14 / 28 28 due to to 2 nitrogens)= 0.5. As the no. of moles are same,there is your answer.
For 12, you just have to make an equation and put values. As the mass is given, we make equation( 74.5= 1(no of moles in q) * (?cl + ?y).
74.5= ?cl + ?y
Cl2 is not possible as if we minus 71(35.5*2) the no will be in decimals.
So now we know that there is 1 cl so we minus it from 74.5 to get 39. y2 not possible as (39/2) will be in fractions. NOW WE KNOW THAT IT IS EITHER Y=39 OR Y3=39 > y=12. there is no mass in periodic table as 13 so 39 is y. 39 is in 1st group and has valency 1. and cl too needs 1 electron. so we know that formula will be kcl or ycl.
For 14, I'm not sure. but it guess it is due to it being a strong acid.
35 is long and we will have to make separate equations for all reactions.
For 38, we are asked of the isomers. ALWAYS REMEMBER THAT AN ISOMER HAS BRANCHES IN IT, MEANING THAT 1 PATH IS DIVIDED INTO 2 PARTS. C is the only one which is not being divided.
I hope you got it.

 

[TheStallion-Reborn]

For Question 10, as you know that 14 g of nitrogen contains 14/28=0.5 moles and 9g of water also contains 9/18=0.5 moles, hence option B is the correct option.
For Question 12, In the choices C and D, the valency of the metal is +1 or +2.Choice D is not possible because in this case the Ar of the metal wud be 74.5-71=3.5. Option C wud be correct as the Ar of the metal is then 74.5-35.5=39, i.e Ar of potassium which has only one valence electron.
14) The others (A, B,C) are weak electrolytes because they do not completely dissociate ions in an aqueous solution whereas H2SO4 readily breaks into its ions when present in an aqueous solution..
38) I'm not quite sure of this though, but i think C is the possible option, as isomers have different structures compared to the original one but has the same chemical formula.. As C is not branched but is chained so its not an isomer.Wish i could explain more clearly but don't know how..(35) You have to write the balanced equation first C3H6+ 4.5O2= 3CO2 + 3H2O

thankyou! but i didn't get clear about question 12. am i supposed to look for the Ars of all the posible metals and see if any of them could fit in?

 

[TheStallion-Reborn]

For q10, we have been the mass of water which is 9g. We can find the no. of moles of water by dividing with the molar mass.(9/18=.5) Now, in the q, it is written that WHICH GAS?
Nitrogen gas has formula N2, so its no. of moles are ( 14 / 28 28 due to to 2 nitrogens)= 0.5. As the no. of moles are same,there is your answer.
For 12, you just have to make an equation and put values. As the mass is given, we make equation( 74.5= 1(no of moles in q) * (?cl + ?y).
74.5= ?cl + ?y
Cl2 is not possible as if we minus 71(35.5*2) the no will be in decimals.
So now we know that there is 1 cl so we minus it from 74.5 to get 39. y2 not possible as (39/2) will be in fractions. NOW WE KNOW THAT IT IS EITHER Y=39 OR Y3=39 > y=12. there is no mass in periodic table as 13 so 39 is y. 39 is in 1st group and has valency 1. and cl too needs 1 electron. so we know that formula will be kcl or ycl.
For 14, I'm not sure. but it guess it is due to it being a strong acid.
35 is long and we will have to make separate equations for all reactions.
For 38, we are asked of the isomers. ALWAYS REMEMBER THAT AN ISOMER HAS BRANCHES IN IT, MEANING THAT 1 PATH IS DIVIDED INTO 2 PARTS. C is the only one which is not being divided.
I hope you got it.

thankyou for q 35, i adopted a rather unorthodox approach. i was supposed to choose only one option, so I chose the odd one. A, C & D were alkanes while B was an alkene.

 

[usama321]

clash!

Let's just see what the answer is then.

Yes its correct..BTW it was the question of the year 1975!!

TheStallion-Reborn

 

[usama321]

Can anyone help me with ionic equations please? I can do the simpler ones in which there is only one displacement. But when it comes to double displacement, i really suck at them.

 

[asma tareen]

which ones??

 

[usama321]

eg

BaCl2 + H2SO4 = BaSO4 + 2HCl

(by the way i just made it up so an ionic equation of this reaction might not be possible) :O

 

[asma tareen]

:/ can an acid and salt give and acid and salt as product???

 

[usama321]

:/ can an acid and salt give and acid and salt as product???

its a double displacement reaction?

 

[asma tareen]

i guess it would be
BaCl2(aq) + SO4^2-(aq)= BaSO4 (aq) + 2Cl-(aq)

 

[usama321]

i guess it would be
BaCl2(aq) + SO4^2-(aq)= BaSO4 (aq) + 2Cl-(aq)

does it have anything to do with barium sulphate being insoluble? I mean i don't understand how you made this equation

 

[TheStallion-Reborn]

TheStallion-Reborn

hehehe yea...defeat accepteed.

 

[TheStallion-Reborn]

:/ can an acid and salt give and acid and salt as product???

seems immposible

 

[nidz]

Yes, that's why we wash flasks only with water!

Hopefully complicated questions wont come this year