Chemistry: Post your doubts here!

[Eugene99]

View attachment 60044answer is c

equation for the decomposition of CaNO3 is:
Ca(NO3)2 >>> 2CaO + 4NO2 +O2
solid residue is CaO
Since there are 4.1 g of calcium nitrate:
Mr of Ca(NO3)2=164
no. of mol of 4.1 g of calcium nitrate = 4.1/164
=0.025 mol
1 mol of Ca(NO3)2 produce 1 mol of CaO so
0.025 mol will produce 0.025 mol

no. of mol of CaO x Mr of CaO = mass in g
0.025 x (40+16)
=1.4 g

 

[qwertypoiu]

equation for the decomposition of CaNO3 is:
CaNO3 >>> CaO + NO2
solid residue is CaO
Since there are 4.1 g of calcium nitrate:
Mr of CaNO3=102
no. of mol of 4.1 g of calcium nitrate = 4.1/102
=0.04 mol
1 mol of CaNO3 produce 1 mol of CaO so
0.04 mol will produce 0.04 mol

no. of mol of CaO x Mr of CaO = mass in g
0.04 x (40+16)
=2.25 g
is the answer D?

Well firstly calcium nitrate is Ca(NO3)2 so your Mr should be a bit higher and number of moles slightly lower. (and thus final mass lower)

And secondly (although the mole ratio is still 1:1) the thermal decomposition of Ca(NO3)2 also produces oxygen:
2Ca(NO3)2 -----> 2CaO + 4NO2 + O2

 

[Eugene99]

Well firstly calcium nitrate is Ca(NO3)2 so your Mr should be a bit higher and number of moles slightly lower. (and thus final mass lower)

And secondly (although the mole ratio is still 1:1) the thermal decomposition of Ca(NO3)2 also produces oxygen:
2Ca(NO3)2 -----> 2CaO + 4NO2 + O2

oh my god! so wrong
thank u for pointing out, I'll edit

 

[holoholo]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w14_qp_51.pdf

Question 1 (a) complete explanation please

 

[Aishayasin]

equation for the decomposition of CaNO3 is:
Ca(NO3)2 >>> 2CaO + 4NO2 +O2
solid residue is CaO
Since there are 4.1 g of calcium nitrate:
Mr of Ca(NO3)2=164
no. of mol of 4.1 g of calcium nitrate = 4.1/164
=0.025 mol
1 mol of Ca(NO3)2 produce 1 mol of CaO so
0.025 mol will produce 0.025 mol

no. of mol of CaO x Mr of CaO = mass in g
0.025 x (40+16)
=1.4 g

no the ANSWER IS C

 

[Eugene99]

no the ANSWER IS C

yes I edited, it's C now

 

[Aishayasin]

equation for the decomposition of CaNO3 is:
Ca(NO3)2 >>> 2CaO + 4NO2 +O2
solid residue is CaO
Since there are 4.1 g of calcium nitrate:
Mr of Ca(NO3)2=164
no. of mol of 4.1 g of calcium nitrate = 4.1/164
=0.025 mol
1 mol of Ca(NO3)2 produce 1 mol of CaO so
0.025 mol will produce 0.025 mol

no. of mol of CaO x Mr of CaO = mass in g
0.025 x (40+16)
=1.4 g

answer is c and the mistake in yours is Ca(NO3)2

 

[nadeen64]

hiii, does anyone have any clue on what is coming in chemistry paper 31 this may/june?

 

[cute97]

hiii, does anyone have any clue on what is coming in chemistry paper 31 this may/june?

Titration
Enthalpy with a metal carbonate
Ketones and Aldehydes identification for Q3

 

[princess Anu]

Can acidic amino acids also from zwitter ions?Or basic amino acids?, for that matter
for example this one ??
Nh3-C(H)(COOH)-Cooh

 

[Shah34]

Q8 anyone
Ans is A

 

[qwertypoiu]

Can acidic amino acids also from zwitter ions?Or basic amino acids?, for that matter
for example this one ??
Nh3-C(H)(COOH)-Cooh

Sorry I'm not too sure what you mean can you rephrase your question?
Amino acids can form zwitterions, but they can also act as acids or base by either donating or accepting a proton.

 

[qwertypoiu]

Q8 anyone
Ans is A

Ive made an attempt at this question here before. Read this too it might help.
As for temperature, of course you should know that lower temp = lower rate.

 

[Rizwan Javed]

Ive made an attempt at this question here before. Read this too it might help.
As for temperature, of course you should know that lower temp = lower rate.

I also think that this is the only possible explanation to this question. When the temperature is less, a higher conc. of OH ions would still increase the rate of reaction. So to keep the reaction rate minimum, we must decrease the conc. of OH ions too along with the temperature. Meaning, we must reduce all the factors which are directly proportional to reaction rate.

 

[Aishayasin]

ANSWER IS B HOW

 

[princess Anu]

Sorry I'm not too sure what you mean can you rephrase your question?
Amino acids can form zwitterions, but they can also act as acids or base by either donating or accepting a proton.

I meant to ask whether acidic amino acids ( those having a carboxylic group as their R group) OR basic amino acids (those having a basic group e.g nh3 as their R group ) can form zwitter ions?

 

[princess Anu]

in NMR, is it true that protons in diff chemical environment have a different energy gap between their two states (i.e parallel and antiparallel) ?
Does the energy gap depend on how much shielded they are?

 

[The Sarcastic Retard]

Thanks qwertypoiu

Today there was exam in my school.
The rate eqation was asked.
One was 1st order other was zero order.
I wrote like this Rate = k * [x]^1[y]^0 will it work i should just write [x]^1 ??

 

[qwertypoiu]

I also think that this is the only possible explanation to this question. When the temperature is less, a higher conc. of OH ions would still increase the rate of reaction. So to keep the reaction rate minimum, we must decrease the conc. of OH ions too along with the temperature. Meaning, we must reduce all the factors which are directly proportional to reaction rate.

Yep agreed.

 

[qwertypoiu]

Thanks qwertypoiu

Today there was exam in my school.
The rate eqation was asked.
One was 1st order other was zero order.
I wrote like this Rate = k * [x]^1[y]^0 will it work i should just write [x]^1 ??

Well mathematically you're correct but why insist on testing the math skills of the examiner?
Make it simple by simple writing rate = k[x]