Physics, Chemistry and Biology: Post your doubts here!

[Abu mota]

Thx alot ..If u dnt mind in w02 paper 1 chemistry could u explain questions 24,25 n 30??

Hi, srry for the late reply.
for Q.24 he is saying which will not remove the colour of bromine i.e which will bromine willnot be able to displace and these are itself and chlorine and so the answer is A
for Q.25 copper doesnt react with water at all ,zinc and iron have to be heated to react with steam producing their oxides as they arent very reactive, however as calcium is alot more reactive it can react with cold water directly producing it's hydroxide so it is A
for Q.30 it is D because oxides of nitrogen doesnt come from the fuel, it is caused by the very high temperature not by the fuel, but the other are caused by the combustion of the fuel.
if u dont understand ask again

 

[Abu mota]

plz help biology paper 1 2008 november question 39
how come the answer is "A" i mean 650 multiply by 5 =3250 which is less than "D" THAT IS 420 multiplied by 43 = 18060 so doesnt that cause more pollution also
question 3 i thought the answer is plant Q bcause in the drwaing the flower has only four stamens righ? and question 29
didn't the camel gain "fresh mass" because of the water so it has grown so why is the answe no growth occured?

Hi, srry also for the late reply
for Q.3 actually in the question it says half of the flower and so it only shows half the number of stamens i.e it has more stamens and the answer is D btw
for Q.29 the answer is D because growth is defined as the increase in dry mass, u never use fresh mass because the amount of water varies alot.
for Q. 39 the answer is A because 5x650=3250 while in B it was 8400 and in C it was 6800 and in D it was 18,060. and the question is asking for which is more polluted i.e which has the least animals and this is A
If u dont understand ask again

 

[kainat husain]

Here..
9 : By showing two atoms together they are representing diatomic elements ,the third one is definately oxygen as it has double bond and is diatomic & the second one is hydrogen so water has both of them H2 and O2.
11: This is because in electrplating the positive electrode should have the metal with which it is plated.
19: Well, Copper being lower in reactivity series than hydrogen cannot displace it but its hydroxide and carbonate will react..

ok thank you sooo much but i still didnt get 11th one

 

[kainat husain]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s07_qp_1.pdf
q1 y is it D m not getting :/
q7 how will we knw the answer is C :/
q11 the answer is B but how to do :/
q15 :/ the answer is B
q16 how do we knw which is redox :/ answer is C
q28 answer is B how do we know if Gold occurs native or not
PLEASE HELP

 

[Abu mota]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s07_qp_1.pdf
q1 y is it D m not getting :/
q7 how will we knw the answer is C :/
q11 the answer is B but how to do :/
q15 :/ the answer is B
q16 how do we knw which is redox :/ answer is C
q28 answer is B how do we know if Gold occurs native or not
PLEASE HELP

for Q.1 inorder to smell something it has to diffuse into your nose and so the further away it diffuses the easier it will be to smell it
for Q.7 the answer is C because the carbon shares 4 electrons and hydrogen each share one electron and so 4+(4x1)=8
for Q.11 well u need the formula for the ethanoic acid which is CH3COOH and count how many atoms u have and u will get 8 and then u can find the Mr easily by multiplying 12 by 2 and 16 by 2 and 1 by 4 and add them together to get 60 and so the answer is B
for Q.15 which process isnot exothermic i.e which process is endothermic and so it will be B because inorder to get lime u need to thermally decompose the limestone i.e endothermic, however for the others they are actually a source of energy and so their reactions must be exothermic.
for Q. 16 redox is quite hard for me for some reason but i will try my best to explain it to u, if u looked at the first one S and O2 have oxidation states of 0, but in SO2, the oxygen must have oxidation state of -4 and S +4, for reaction number 2 SO3 the oxidation state of oxygen will be -6 while the oxidation state of sulfur is +6 and so their oxidation numbers changed but in the last reaction no change in the number of oxidation and so it is not a redox reaction. and so the answer is C. ( if u still dont understand it ask again as i didnt explain in full details )
for Q.28 if it is below hydrogen in the reactivity then it is native and this means that it wont react with sulfuric acid as it wont be able to displace the hydrogen atoms and so the answer is B

 

[Abu mota]

ok thank you sooo much but i still didnt get 11th one

for Q.11 copper is below hydrogen in reactivity and so it will be deposited on the electrode, however sodium is above hydrogen in the reactivity and so hydrogen will be produced instead of the metal (this cancels out 3 and 4) leaving 1 and 2 will it be the anode or the cathode? will it must be the cathode because in electrolysis the metal is always deposited on the cathode and the answer is 2 which is C

 

[kainat husain]

for Q.11 copper is below hydrogen in reactivity and so it will be deposited on the electrode, however sodium is above hydrogen in the reactivity and so hydrogen will be produced instead of the metal (this cancels out 3 and 4) leaving 1 and 2 will it be the anode or the cathode? will it must be the cathode because in electrolysis the metal is always deposited on the cathode and the answer is 2 which is C

thank u soo much but well how can it cancel 3 and 4 when copper sulfate solution is for 1 and 2 electrodes its too confusing :/

 

[Abu mota]

thank u soo much but well how can it cancel 3 and 4 when copper sulfate solution is for 1 and 2 electrodes its too confusing :/

when i do multiple choice i do it by eliminating the wrong answers and so i eliminated 3 and 4 as in the sodium solution hydrogen will be produced and not the sodium metal, however in the copper solution, the metal will be produced and it isnt 1 because in electrolysis the metal is deposited on the cathode which is 2 and so the answer is C.

 

[kainat husain]

for Q.1 inorder to smell something it has to diffuse into your nose and so the further away it diffuses the easier it will be to smell it
for Q.7 the answer is C because the carbon shares 4 electrons and hydrogen each share one electron and so 4+(4x1)=8
for Q.11 well u need the formula for the ethanoic acid which is CH3COOH and count how many atoms u have and u will get 8 and then u can find the Mr easily by multiplying 12 by 2 and 16 by 2 and 1 by 4 and add them together to get 60 and so the answer is B
for Q.15 which process isnot exothermic i.e which process is endothermic and so it will be B because inorder to get lime u need to thermally decompose the limestone i.e endothermic, however for the others they are actually a source of energy and so their reactions must be exothermic.
for Q. 16 redox is quite hard for me for some reason but i will try my best to explain it to u, if u looked at the first one S and O2 have oxidation states of 0, but in SO2, the oxygen must have oxidation state of -4 and S +4, for reaction number 2 SO3 the oxidation state of oxygen will be -6 while the oxidation state of sulfur is +6 and so their oxidation numbers changed but in the last reaction no change in the number of oxidation and so it is not a redox reaction. and so the answer is C. ( if u still dont understand it ask again as i didnt explain in full details )
for Q.28 if it is below hydrogen in the reactivity then it is native and this means that it wont react with sulfuric acid as it wont be able to displace the hydrogen atoms and so the answer is B

thank you sooooo very much for your effort! thank u i have understood evthg except q16 :/
like how S will ahve +4 it should have +2 :/ please explain its hard :/

 

[Abu mota]

thank you sooooo very much for your effort! thank u i have understood evthg except q16 :/
like how S will ahve +4 it should have +2 :/ please explain its hard :/

ok, SO2 is a covalent compound, this means that the atoms must have oxidation states that cancel each other and as oxygen will always be -2 then we need sulfur to cancel it out i.e in SO2 the oxygen has an oxidation state of -4 (-2x2) and so inorder to cancel it we need +4 and so sulfur must be +4, in the other one it is SO3, the oxygen now has oxidation state of -6 (-2x3) and so inorder to balance it we need +6 but in the last one there is no change at all in oxidation numbers and so the answer is 1 and 2

 

[joulie]

Hi, srry also for the late reply
for Q.3 actually in the question it says half of the flower and so it only shows half the number of stamens i.e it has more stamens and the answer is D btw
for Q.29 the answer is D because growth is defined as the increase in dry mass, u never use fresh mass because the amount of water varies alot.
for Q. 39 the answer is A because 5x650=3250 while in B it was 8400 and in C it was 6800 and in D it was 18,060. and the question is asking for which is more polluted i.e which has the least animals and this is A
If u dont understand ask again

thanks alot btw your reply wasn't slow it was fast

 

[kainat husain]

ok, SO2 is a covalent compound, this means that the atoms must have oxidation states that cancel each other and as oxygen will always be -2 then we need sulfur to cancel it out i.e in SO2 the oxygen has an oxidation state of -4 (-2x2) and so inorder to cancel it we need +4 and so sulfur must be +4, in the other one it is SO3, the oxygen now has oxidation state of -6 (-2x3) and so inorder to balance it we need +6 but in the last one there is no change at all in oxidation numbers and so the answer is 1 and 2

okkk thank u sooo very much i got it

 

[kainat husain]

when i do multiple choice i do it by eliminating the wrong answers and so i eliminated 3 and 4 as in the sodium solution hydrogen will be produced and not the sodium metal, however in the copper solution, the metal will be produced and it isnt 1 because in electrolysis the metal is deposited on the cathode which is 2 and so the answer is C.

thank you i got it jazak ALLAH kahiran

 

[Love Islam]

thanks...!!!

 

[joulie]

can someone explaine this plz :-biology paper 1 year 2000 mayjune
question 27 why the increase in mass only occured at the end
and question 17 i dont even understand what is the difference between "p"and "q"
and in year 2001 may june question 38 ??????

 

[za Shadow]

helppp plzzz why is it D not C i can't undersatnad the question all of them r present plzzz help me

 

[khaled talat]

plz from where can i get mark scheme of biology paper 1 1994-1999

 

[sweetsis]

helppp plzzz why is it D not C i can't undersatnad the question all of them r present plzzz help me

hey hydrogen is present but manganese is not present as its symbol is Mn and not Mg like u were probably thinking ......

 

[za Shadow]

hey hydrogen is present but manganese is not present as its symbol is Mn and not Mg like u were probably thinking ......

thanks and yes u were right looolll thanks again

 

[za Shadow]

helppp plzzz plzzz help me​

may 1995
29 why A not D

nov 1997 19 why C not B
25 why A not C
36 why C not D i think the ms is wrong :/

June 1998 4 why D not C
15 its D but i don't understand why i don't understand how did the ms get to the answer :'(

nov 1998
11 why A not D
15 why A not C
35 why A not B
37 why A not D

may 1999
24 why A not B

nov 1999
21 i don't understand the question and what should we think about to get the answer btw its C

j 2000
17 there r 2 answers D and B so why is it D

PLZZZZ HELPP ME I REALLY NEED UR HELPPPP PLZZZZZZ HELP ME :'(