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Chemistry: Post your doubts here!

sidbloom1995

sidbloom1995

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goodluckayesha said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_4.pdf
isnt it supposed to be reduction-oxidation ? markscheme says 0.77-1.36 but shouldn't it be 1.36-0.77?
Click to expand...
one moere thing i would like to add is that in the MS it said to ignore the sign and the flow is from right to left!!
this means that the Left is (+) and Right is (-), it's just that when they give us a diagram like that they follow there equation of [Ecell = Er - El]
overall this suggest that even when you follow your own logic and understanding on the topic and write it as 1.36 - 0.77 you will get a correct answer for it!
(this part shook me up pretty bad as well, having all my concepts jumbled up once again, but once i calmed down and reconfirmed a few things i was fine :p)
 
MiniSacBall

MiniSacBall

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Nibz said:
Mass of 1 cm3 of steam (H20) = 1 g
Mol of H20 = 1g / 18 = 0.0555556
1 mol of H20 occupies 24dm^3 at 298K
0.0556 would occupy = 24 x 0.0556 = 1.33 dm^3
Volume of steam at 298K = 1.33 dm^3
Volume of steam at 1 K = 1.33/298 = 0.00446 dm^3
Volume of steam at 596 K = 0.00446 x 596 = 2.668 dm^3 ~ 2.67 dm^3
Answer C.
Click to expand...

I swear i would have done this question on my own but this thing drives me crazy!
If i take the temperature in C and not in K. What is the difference. I mean why can't i do like this way:

Mass of 1 cm3 of steam (H20) = 1 g
Mol of H20 = 1g / 18 = 0.0555556
1 mol of H20 occupies 24dm^3 at 25C
0.0556 would occupy = 24 x 0.0556 = 1.33 dm^3
Volume of steam at 25C = 1.33 dm^3
Volume of steam at 1C = 1.33/25 = 0.0532 dm^3
Volume of steam at 323C = 0.0532 x 323 = 17.1836 dm^3 <----------- Why am i getting this thing wrong here! Why!

Any body please help me! Why can't i take C instead of K. I mean are bigger unit soo inaccurate or what?
Also the difference between them is extreme inaccurate!
323C - 25C = 298C = 571K
596K - 298K = 298K = 25C
So basically if you have water at 25 C and you raise the temperature to 323 C. According to Kelvins you have raised only 25C.

For those who are wondering here is the question! [ http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_1.pdf ] - Q.6

I am mindfucked here. Or may be i am doing some stupid mistake. I just want you to help me!

Edit: I guess i figured out! These are some special types of unit! they are need added or subtracted to get other unit! So that's why i am having this whole problem.
Hah! Seriously Science. !@#$ Science. This is inaccurate as !@#$. I just can't image how inaccurate science is in this case. This is bullshit! !@#$ science.

So only one question: In exams if i get a question similar to this, i have to take in Kelvins even if the question is in Celsius right?

----------------Totally mind fucked!---------------
 
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sidbloom1995

sidbloom1995

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Faaiz Haque said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s05_qp_2.pdf

Part 2d iii, Show calculations with detailed explanations pleaseee
I don't get the Markscheme, thankss
Click to expand...
the answer is simple! the MS just went round about it!!
we already have our equation for H2S with O2

2H2S + 3O2 ---------> 2H2O + 2SO2

we first find the moles of H2S
n of H2S = [8.65/34.1] = 0.254 mol
use the ratio relation from the equation
2 moles of H2S and 3 moles of O2 are uused
H2S : O2
2 : 3
0.254 : x
thus x = (0.254 x 3)/2 = 0.38 mol

now use the formula, volume = moles X 24
V = 0.38 X 24 = 9.12 dm3
thats it
 
1357911

1357911

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http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_41.pdf
Q-8 cii
Q-3 civ

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_4.pdf
q-10 c

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_43.pdf
Q-7 aiii

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_41.pdf
Q7 cii

Can Anyone help me in these questions please?
 
AbbbbY

AbbbbY

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Faaiz Haque said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s05_qp_2.pdf

Part 2d iii, Show calculations with detailed explanations pleaseee
I don't get the Markscheme, thankss
Click to expand...


H2S + 1.5O2 -> H20 + SO2
8.65/(1+1+32) = 0.254 mols of H2S

1 mol reacts completely with 1.5 mol of O2
0.254 will thus react with 0.254*1.5=0.381 mol of O2.

1 mol of O2 occupies 24dm3
0.381 will occupy 9.15 dm3

ALTERNATE METHOD:

1 mol of H2S = 34g requires 1.5 mol of O2 = 36dm3

so;
34g = 36dm3
8.65g = 9.15dm3
 
papajohn

papajohn

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I had a question in my head about the chemistry practical of titration. The problem is that i performed the experiment and there is huge fluctuation i.e 19 cm3 and 25 cm3. The teacher told me that it should be correct to 0.1 cm3. The problem is that why there is great difference b/w my result. I think i used only two drops of methy orange or i do not mixed throughly mixed the HCl with distill water.
 
F

Faaiz Haque

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sidbloom1995 said:
the answer is simple! the MS just went round about it!!
we already have our equation for H2S with O2

2H2S + 3O2 ---------> 2H2O + 2SO2

we first find the moles of H2S
n of H2S = [8.65/34.1] = 0.254 mol
use the ratio relation from the equation
2 moles of H2S and 3 moles of O2 are uused
H2S : O2
2 : 3
0.254 : x
thus x = (0.254 x 3)/2 = 0.38 mol

now use the formula, volume = moles X 24
V = 0.38 X 24 = 9.12 dm3
thats it
Click to expand...
Omg i'm an idiot, ty!!
 
sidbloom1995

sidbloom1995

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papajohn said:
I had a question in my head about the chemistry practical of titration. The problem is that i performed the experiment and there is huge fluctuation i.e 19 cm3 and 25 cm3. The teacher told me that it should be correct to 0.1 cm3. The problem is that why there is great difference b/w my result. I think i used only two drops of methy orange or i do not mixed throughly mixed the HCl with distill water.
Click to expand...
there could be a lot of reasons!
1. like when you do when finish one tit-ration, you dont rinse the flask thoroughly or you dont dry it and add the next contents in it just like that
2. maybe you observe the color change for some as dark and for some as light!
3. maybe you pour the starting contents very quickly, that too can change your value, pour it slowly and shake it continuesly
4. you should keep the mixture on a light background so that you can observe the change quickly
5. you have to make sure that you tip all of the contents in the flask to the last drop!, because even a single drop can cause a change!
make sure that you dont do any of these sorts of mistakes! if you still dont get the answer right then i dont know of anything else!
 
sidbloom1995

sidbloom1995

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Faaiz Haque said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_2.pdf

Q 2 D
How are we suppose to know these
Click to expand...
well about how should we know this, they are all general equations and you sort of have to remember them!
with phosphorus and iodine, there will be replacement of OH by I
with conc. H2SO4, there will be elimination of water, for that we will take the -OH group from one carbon and the -H from the carbon right next to it, and it will form an alkene
with hot K2Cr2O7, the double bond will dissolve (if any) and the -OH will be oxidised to -COOH, but not in tertiary alcohols!, they wont react!
 
roxylara

roxylara

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0.2 mol of aluminium is burned in oxygen and the product reacted with 2.00 mol/dm-3 HCL. What is the minimum volume of acid required for a complete reaction?

A. 15 cm3
B. 20 cm3
C. 30 cm3
D. 60 cm3

Can someone please explain this to me? :/
 
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