Chemistry: Post your doubts here!

[Anas Abbal]

is the answer D ?

yes how did you get it? working or formula

 

[darks]

Guys i recommend learning the balancing of this equation :
3 Cl2 + 6 NAOH = 5 NACl + NAClO3 + 3 H2O
it can save time.. And comes quite often in calculation Qs.

 

[zellyman]

I did some working and some deduction,
You have to calculate for each of them and see if they match
If D is correct,2 moles of P decompose to give x moles of R in a 1:1 ratio
Q :R forms in a 1:2 ratio
Hence you can put the following equation
2- x (decomposition) + x (R) + 1/2 x (Q) = 2 + 1/2 x

 

[Anas Abbal]

I did some working and some deduction,
You have to calculate for each of them and see if they match
If D is correct,2 moles of P decompose to give x moles of R in a 1:1 ratio
Q :R forms in a 1:2 ratio
Hence you can put the following equation
2- x (decomposition) + x (R) + 1/2 x (Q) = 2 + 1/2 x

ohh but like the only part i dont get is for the rest i took (2- 2x) but for p why are we supposed to to take 2-x in this condition

 

[darks]

FLAME TESTS
Na -golden yellow
K -lilac
Ca -brick red
Mg -white
Li -red
Ba -apple green
Sr -red
Anymore to learn?

 

[SohaibButt]

DARKS GIVE MORE TIPS UR GLOWING MY CHEMISTRY! :')

 

[zellyman]

ohh but like the only part i dont get is for the rest i took (2- 2x) but for p why are we supposed to to take 2-x in this condition

P decomposes to form R at a 1:1 ratio
If X moles of R are formed X moles of P decompose

 

[Anas Abbal]

P decomposes to form R at a 1:1 ratio
If X moles of R are formed X moles of P decompose

ohh yes i finally got it thanks alot man

 

[zellyman]

Solves this ,A friend gave it to me to tell him why,and I honestly have no idea C is the answer

 

[Metallic9896]

View attachment 62492

As zellyman said, P is same in both so in first situation:

P = nRT/V

You don't know n but you do know that n = mass/Mr and you have mass so substitute that in, convert T from C to K, convert V from 0.025 to 0.000025 if you want and R is 8.31 as you know, but keep V in dm^3 anyway cause units will cancel out as you'll be able to see if you're good at maths.

P = mass x R x T/V x Mr
P = (0.1 x 8.31 x 373)/(0.025 x Mr), no need to go any further as the final answer isn't a full answer either. It's enough to see that

P = 0.1 x 8.31 x 373/0.025 x Mr

In second situation:

P = nRT/V

You have n (1), rest as usual.

P = 1 x 8.31 x 273/22.4, again, enough to see that P = 8.31 x 273/22.4

Equate both P and Mr subject of formula:

(8.31 x 273)/(22.4) = (0.1 x 8.31 x 373)/(0.025 x Mr)

0.025 x Mr = 0.1 x 8.31 x 373 x 22.4/8.31 x 273

8.31 cancel out

0.025 x Mr = 0.1 x 373 x 22.4/273

Mr = 0.1 x 373 x 22.4/273 x 0.025

D is the answer.

 

[techgeek]

Why B and not C? what 's the difference?

 

[darks]

came in a latest p2... so can come in p1..
the 2nd equation might also have 3Cl- in products as spectator ions.

 

[SohaibButt]

Wow great job dude!

View attachment 62496
came in a latest p2... so can come in p1..
the 2nd equation might also have 3Cl- in products as spectator ions.

 

[darks]

As zellyman said, P is same in both so in first situation:

P = nRT/V

You don't know n but you do know that n = mass/Mr and you have mass so substitute that in, convert T from C to K, convert V from 0.025 to 0.000025 if you want and R is 8.31 as you know, but keep V in dm^3 anyway cause units will cancel out as you'll be able to see if you're good at maths.

P = mass x R x T/V x Mr
P = (0.1 x 8.31 x 373)/(0.025 x Mr), no need to go any further as the final answer isn't a full answer either. It's enough to see that

P = 0.1 x 8.31 x 373/0.025 x Mr

In second situation:

P = nRT/V

You have n (1), rest as usual.

P = 1 x 8.31 x 273/22.4, again, enough to see that P = 8.31 x 273/22.4

Equate both P and Mr subject of formula:

(8.31 x 273)/(22.4) = (0.1 x 8.31 x 373)/(0.025 x Mr)

0.025 x Mr = 0.1 x 8.31 x 373 x 22.4/8.31 x 273

8.31 cancel out

0.025 x Mr = 0.1 x 373 x 22.4/273

Mr = 0.1 x 373 x 22.4/273 x 0.025

D is the answer.

Thanks a lot! This was really complex for me idk why : / but i got it!

 

[darks]

Why B and not C? what 's the difference?View attachment 62495

As Mn2+ is produced, it catalyses the reaction according to the question. So as reaction proceeds, faster decrease in reactant (MnO4-) is seen. Enough to reach answer.
Then as reaction further proceeds, MnO4- is now no longer in excess or is less, so reactions slows down, eventually coming to a halt.

 

[Metallic9896]

Solves this ,A friend gave it to me to tell him why,and I honestly have no idea C is the answerView attachment 62494

Damn. I talked to a friend (absolute genius) and he pointed out that it's perhaps cause CO doesn't get oxidized in the atmosphere. Which would make sense cause normally you see that when CO is produced, it like, remains in the air ya know. It harms us and stuff. Unlike NO which we do in paper 3 which 'readily oxidized to NO2' when in contact with air. I presume the same goes for sulphur. Hence why carbon is rejected.

 

[Metallic9896]

Guys i recommend learning the balancing of this equation :
3 Cl2 + 6 NAOH = 5 NACl + NAClO3 + 3 H2O
it can save time.. And comes quite often in calculation Qs.

Yeah man awesome notes and tips. This came especially in here. A hard question for anyone unless one knows this equation and the cold one too which is

 

[ughkno]

can one of you help me with this? I can't understand why the answer is B - thanks

 

[Metallic9896]

Classic.

 

[Metallic9896]

can one of you help me with this? I can't understand why the answer is B - thanks

1 is true cause of the COOCH3 branch, it's an ester, so H2SO4 will hydrolyze it.
2 is true cause again, COOCH3 is an ester, alkaline hydrolysis of esters will occur due to NaOH.
3 not true cause no open OH or OOH with which sodium metal can react.