Chemistry: Post your doubts here!

[SohaibButt]

For the 1st one there is 1 lone pair and 2 bond pairs so a near trigonal planar shape would be formed if including the lone pair.The bond angle is hence 120 degrees
For the 2nd one change in oxidation in each Cr ion is -3 ,as two Cr ions are oxidized a total change of -6 is observed,as the reaction is redon 6 Fe ions must be reduced for this to occur
For the 3rd Group 1 metals ALWAYS form +1 ions,so the number of electrons in Na is 10 while this 1 electron is shared between the N3 ion to give a total of 3x7 +1 = 22 electrons
For the 4th just multiply percentage and mass and divide by 100 to get the average density,I assume the answer is D
For the 5th find the moles of oxygen,if it reacts with group 2 metal a molar ratio of 1:2 is used for calculation ,if it reacts with a group 1 metal a molar ratio of 1:4 should be used,both methods should be used to find the Mr ,and one comes off to be 46 which is far from calcium,hence wrong the other is 23 which is the Mr of Sodium

Tysm MAN!

 

[zellyman]

can anyone help me with this i dont get it people are saying there are two methods to solve this but each giving a different result

is the answer D ?

 

[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