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Chemistry: Post your doubts here!

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Q15. This is a similar to question Q14 of 2006.

Group II nitrates decompose based on the equation below:

2 X(NO3)2 (s) --> 2 XO (s) + 4 NO2 (g) +O2(g)
1.32 g is mass of NO2 and O2 gas, the left over mass 0.68 g is XO.

Mass of XO = 0.68g
Moles of XO = 0.68/ (Mr of X + 16)

Mass of X(NO3)2 = 2 g
Moles of X(NO3)2 = 2/(Mr of X + 62)

since moles of X(NO3)2 = moles of XO
2/(Mr of X + 124) = 0.68/ (Mr of X + 16)

We can solve for Mr of X using the normal maths approach, but it might be faster to do trial and error from the Mr of the four options.
Be : 2/(9 + 124) does not equal to 0.68/ (9 + 16)
Ca: 2/(40 + 124) = 0.68/ (40+ 16)
Therefore, answer is Ca.

Q17. At RTP, 1 mol of gas (assume ideal) occupies 24 000 cm3.

mole of O2 = 300 /24 000 = 0.0125 mol

2Ca + O2 --> 2 CaO
2Mg + O2 --> 2 MgO
4K + O2 --> 2K2O
4Na + O2 --> 2 Na2O

0.0125 mol of O2 will react with:
0.025 mol of Ca (1 g)
0.05 mol of Mg (1.2 g)
0.05 mol of K (1.95 g)
0.05 mol of Na (1.15 g)


Thanks a lot! I appreciate all ur help :)
 
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0451d-3e0d5a31-50c0-419b-90fb-e7035208b37e.png


Answer is C.... why? :S
 
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http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_qp_1.pdf
Q4
Q19
Q21 i have difficulty on finding a ciral carbon from rings any tips?
Q33 what about 3? more the concentration lower the activation energy?
Q35 waht about2 won't CO2 and O2 be made with it?
Q39 how do we make out that it reacts with sodium :(
Help please

Q4. The top number is mass number (proton + neutron), to find the protons, you need to refer to Periodic Table

A. Bi : 83 protons, 126 neutrons
B. Pb : 82 protons, 126 neutrons
C. Po : 84 protons, 126 neutrons
D. Tl : 81 protons, 127 neutrons
So Tl is "unstable" as it does not contain 126 neutrons.

Q19. Form the equation based on the information given.

(NH4)2SO4 +
4O2 --> H2SO4 + 2HNO3 + 2H2O

Q21. The carbons on the "ring" are benzene carbons, they do not have 4 bonds to bond to 4 different groups, so we need not
check them for "chirality".

Q35. CaCo3 --> CaO + CO2

Q39. The hydroxyl (OH) group reacts with sodium to from hydrogen gas.
 
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But they also said distillation ! So plz tell me under which condition will an aldehyde form?
Honestly, I do see some flaws in the question set.

I believe they intend for students to interpret in this manner.
1st part of experiment: Reflux to oxidize alcohol to acid.

2nd part of experiment: Distillation to separate mixture of alcohol and acid.
 
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