Chemistry Doubts: IGCSE Paper 3

[wooowooowoo]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w10_qp_31.pdf

Last question!
& also

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s11_qp_31.pdf

Q 5d (iii)

I can't solve anything with numbers!

Finally understood the last part (I had to use a notebook :/)

Alright so use this
C1V1 = C2V2
C= Concetration; V = Volume

C1 = C2V2/V1

C2 = 1
V2 = 20/1000
V1 = 15/1000

C1 = 0.02 * 1 / 0.015

= 1.333

 

[Shivashree]

I just want to check if this is right:
PROTEIN
-NH-[]-CH-C=O-NH-[]-CH-C=O-
NYLON
-C=O-[]-C=O-NH-[]-NH-C=O-[]-C=O-

PLS HELP

 

[kboss]

I just want to check if this is right:
PROTEIN
-NH-[]-CH-C=O-NH-[]-CH-C=O-
NYLON
-C=O-[]-C=O-NH-[]-NH-C=O-[]-C=O-

PLS HELP

O O
its wrong... | | ||
oxygen can only have 2 bonds...i.e - C- N-[]-N-C-[]-
| |
H H

 

[kboss]

anyone with doubts come over here.....http://www.twiddla.com/830008

 

[kboss]

those who click the link above^^^^
pls. notify me
thank u

 

[kanishk]

another problem help me on this
c) A 5.00 g sample of impure lead(II) nitrate was heated. The volume of oxygen formed was
0.16dm3 measured at r.t.p. The impurities did not decompose.
Calculate the percentage of lead(II) nitrate in the sample.
2Pb(NO3)2 → 2PbO + 4NO2 + O2
Number of moles of O2 formed = .......................................
Number of moles of Pb(NO3)2 in the sample = .......................................
Mass of one mole of Pb(NO3)2 = 331 g
Mass of lead(II) nitrate in the sample = ....................................... g
Percentage of lead(II) nitrate in sample = .....................................
tell me how you got each too please

 

[Mustafa omar]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s10_qp_32.pdf
Question 2b

 

[Mustafa omar]

Can someone send me testing paper

 

[Triplet]

What's the answer kanishk?

 

[Mustafa omar]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s10_qp_32.pdf
Q 2) c i , ii

 

[Sajal mehta]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s10_qp_32.pdf
Q 2) c i , ii

i)starch was in saliva which, may have break down the starch into sugar so after 30 mins all the starch was converted and when tested, now starch visible
ii) enzymes denature so nothing breaks down the starch and test gives a positive for starch

 

[kanishk]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s10_qp_32.pdf
Question 2b

i think its this
-O-[]-O-[]-O-

 

[Sajal mehta]

i think its this
-O-[]-O-[]-O-

oops i think thats right...completely forgot natural polymers

 

[Mustafa omar]

Thank kanishk and sajal Mehta

 

[kainat husain]

how could you prove that the percentage of water in an aq solution of sodium chloride is 74%?

 

[Beedo]

Sorry I have a lot of doubts in http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s11_qp_31.pdf

7b
2c
4a-iii
4b
5b
5d-ii
6a-i + ii

please if anyone can explain them to me

 

[Sajal mehta]

u can try this:
measure the mass of the soln and then boil it to 100 degrees untill no more water is evaporated....take the mass again...and calculate the percentage of nacl and then substract that by 100 and u get the percentage of water...
(it shud work)

 

[imperial]

dude id suggest you look at the marking scheme of that paper. if you dont know, the file name would be s11 ms 31. all the answers are there

he said he need an explanation

 

[Beedo]

ok explain 7b & 2c & 5b only please

 

[kainat husain]

u can try this:
measure the mass of the soln and then boil it to 100 degrees untill no more water is evaporated....take the mass again...and calculate the percentage of nacl and then substract that by 100 and u get the percentage of water...
(it shud work)

ok thank u soo much! one more
d- the formula of an acid is either of the type HY or H2Y.How could you find out which one is correct by using Aq.solutions of the acid and of sodium hydroxide. Assume that both solutions have the same concentration, 0.1 mol/dm3
please help!