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Chemistry: Post your doubts here!

amina1300

amina1300

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Holmes said:
Tipssss!
Stay Calm and relaxed. My teacher advise me to solve the organic part of the paper before because that gives us confidence about the paper. If you are good at Organic then you can do the same. :)
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I HATE ORGANIC CHEMISTRY I ALWAYS KEEP FORGETTING THE REACTIONS >_<
 
Holmes

Holmes

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amina1300 said:
http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_s16_qp_11.pdf
Q4 I dont understand what Np Pu means??
Q6 ??
Q17 ??
Q30??

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_s16_qp_13.pdf
Q9 ???
Q21 ??
Q33 Statement 2 ; No particles have zero energy at either temperature. ?? What does this mean in context?
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Q17 ??
CaCO3 + 2HCl ------> CaCl2 + CO2 + H2O
moles of HCl = (36*0.500)/1000
= 0.018 moles
Moles of CaCO3 = 0.009 moles
Mr of CaCO3 = 100
Mass of CaCO3 =100*0.009
= 0.9 g
% of CaCO3 in 2.00 g mass:
= (0.9/2) * 100
= 45%

Hope I helped :)
 
M

Metallic9896

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techgeek said:
View attachment 62483
how are we supposed to know if the reaction is endothermic?
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Hmm if the solution does form that means water molecules felt more comfortable forming bonds with the anhydrous aluminium chloride than they did with themselves. All systems want to achieve a lower and lower energy state that gives out heat so they become more stable. If they DID like forming bonds with anhydrous aluminium choride, this means that the energy released when they formed these bonds was MORE than the energy needed to break the water molecules' bonds with themselves, which means that there was a net release of energy, i.e. reaction was exothermic, not endothermic. That leaves only C as the correct choice cause all other options contain statement 1 and we just got rid of it. Without even thinking about 2 and 3 you can choose C. But, you should know about 2 and 3 from the book and the chapter of periodicity where we are told to know reactions of water and period 3 chlorides. Hope I helped. :)

EDIT: Anything that successfully dissolves, you can be sure it's an exothermic process.
 
D

darks

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Metallic9896 said:
Hmm if the solution does form that means water molecules felt more comfortable forming bonds with the anhydrous aluminium chloride than they did with themselves. All systems want to achieve a lower and lower energy state that gives out heat so they become more stable. If they DID like forming bonds with anhydrous aluminium choride, this means that the energy released when they formed these bonds was MORE than the energy needed to break the water molecules' bonds with themselves, which means that there was a net release of energy, i.e. reaction was exothermic, not endothermic. That leaves only C as the correct choice cause all other options contain statement 1 and we just got rid of it. Without even thinking about 2 and 3 you can choose C. But, you should know about 2 and 3 from the book and the chapter of periodicity where we are told to know reactions of water and period 3 chlorides. Hope I helped. :)

EDIT: Anything that successfully dissolves, you can be sure it's an exothermic process.
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So i gave the wrong answer :p my prep not looking too good :/ You explained really well here. (y)(y)(y)
 
M

Metallic9896

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darks said:
So i gave the wrong answer :p my prep not looking too good :/ You explained really well here. (y)(y)(y)
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Haha thanks man but after bio, *sigh* lol anything can happen. Let's just hope tomorrow goes well. I can't afford to lose more than 2 marks tomorrow cause p4 and p3 went bad and need 3 A*s :(
 
M

Metallic9896

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sarmadimran said:
View attachment 62485
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Answered this for another user on here. Here is what I wrote:

Okay so in pentane we have CH3CH2CH2CH2CH3. What came to my mind first was, will it only occur at the terminals (-CH3) or in the middle too? I concluded that it occurs in the middle too by looking at the options. First option is 2. This MAY look like it means that it only occurs at -CH3 ends, but that would mean 1 possible propogation, not 2, because it's the same thing from both sides. Since 1 isn't an option, it MUST mean that propagation can occur on ANY carbon. Now you just have to see how many unique propagations can occur. One is CH3, second is at the CH2 next to it, and third is at the middle CH2. The fourth CH2 is the same as the second and fifth CH3 is the same as the first, so UNIQUE propagation steps are only 3. Answer is B. Notice how I cleared my concept using the answer options. You're going to have to keep an open mind like this.

EDIT: the equation they gave is of methane only to show a demonstration of what happens, they are asking about PENTANE.
 
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Z

zellyman

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sarmadimran said:
anyone plz
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A more proper way to represent these carbonates is in the form of BaCO3.CaCo3
CaCo3 is common in all three of these,so the rest must be categorized in order of how much CO2 would be released on decomposition
Mg3(CO3)3 would release more CO2 than just MgCO3 and that in turn would release more CO2 than BaCO3 which is the hardest to decompose.
So the answer is D I assume?
 
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