Chemistry: Post your doubts here!

[gary221]

the greater the ph value the weaker the acid..rit?

yup

 

[umarashraf]

Defend nhin kr rhi..
mujhey pata tha k aap ko yehi lagey ga

han han... sixth sense achi hai kaafi aapki... paper ki guesses bnaya karo beth k... profit...)

 

[xxfarhaxx]

Need help for 6 questions of paper 1. The correct answer are circled.
View attachment 8533

Q3- total mr of P2O5= (31*2)+(16*5)
=142
mr of P in P2O5=31*2
62
% = 62/142
= 43.66%

thrfr 30.0% of 43.66= (30.0/100)*43.66
=13.09 appr =13.1

 

[thunderingthunder]

I

han han... sixth sense achi hai kaafi aapki... paper ki guesses bnaya karo beth k... profit...)

Bs kya karien
Guesses banae main jitna tym lagon gey us se acha hai k parh lun..agar guesses sahi na huey to kam az kam kuch to aata ho na!

 

[Ashique]

Need help for 6 questions of paper 1. The correct answer are circled.
View attachment 8533

For question 2, 2 double bonds in he compound were removed, thus 4 mole of hydrogen was required (since 2 hydrogens are added to the chain once you break a double bond). If you notice, CH2 was changed to CH3 thus one more mole os Hydrogen was required. So in total, 5 mole of hydrogen was required.

Question 3, first of all find the Mr of P2O5, which is (31*2)+(16*5)= 142.
Now find the amount of phosphorus present in this amount, which is (31*2)/142= 0.4366...
The question said, only 30% of it dissolves, so 0.4366*30= 13.09, which is almost equal to 13.1, hence answer is B.

Question 4-
Ethanol will not react with NaOH. Since a hydroxyl group is present in both of them, no nucleophilic substitution will happen, so it has to be ethanoic acid.

Question 5-
This question is hell tricky, and I've been trying this for half an hour now, and I don't see how to differentiate between A and D, both of 1 mol of A and D, will require 2 mol of HCN, and both will change the color of potassium dichromate.
I will try to brain storm this question with one of my friends, and she might come up with something.
Till then I'll be grateful if someone can reason out why it should be D, not A, please?
Here's the question:

 

[Casablanca]

Concentrated sulfuric acid can behave both as a strong acid and as an oxidising agent.

With which compound does concentrated sulfuric acid react in this way?

A. Ethanol
B. Magnesium Carbonate
C. Propanenitrile
D. Sodium Bromide

Why?

---

In the graph of acidity of period 2 oxides, acidity decreases down the period... But is the acidity of P4O10, SO3, and Cl2O7 the same, or does it decrease as well?

 

[leosco1995]

For question 2, 2 double bonds in he compound were removed, thus 4 mole of hydrogen was required (since 2 hydrogens are added to the chain once you break a double bond). If you notice, CH2 was changed to CH3 thus one more mole os Hydrogen was required. So in total, 5 mole of hydrogen was required.

Question 3, first of all find the Mr of P2O5, which is (31*2)+(16*5)= 142.
Now find the amount of phosphorus present in this amount, which is (31*2)/142= 0.4366...
The question said, only 30% of it dissolves, so 0.4366*30= 13.09, which is almost equal to 13.1, hence answer is B.

Question 4-
Ethanol will not react with NaOH. Since a hydroxyl group is present in both of them, no nucleophilic substitution will happen, so it has to be ethanoic acid.

Question 5-
This question is hell tricky, and I've been trying this for half an hour now, and I don't see how to differentiate between A and D, both of 1 mol of A and D, will require 2 mol of HCN, and both will change the color of potassium dichromate.
I will try to brain storm this question with one of my friends, and she might come up with something.
Till then I'll be grateful if someone can reason out why it should be D, not A, please?
Here's the question:

A ketone doesn't change the color of potassium dichromate (because it can't be further oxidized), so it can't be A.

 

[Muhammad Bin Anis]

Concentrated sulfuric acid can behave both as a strong acid and as an oxidising agent.

With which compound does concentrated sulfuric acid react in this way?

A. Ethanol
B. Magnesium Carbonate
C. Propanenitrile
D. Sodium Bromide

Why?

---

In the graph of acidity of period 2 oxides, acidity decreases down the period... But is the acidity of P4O10, SO3, and Cl2O7 the same, or does it decrease as well?

Well the first answer shud be D (sodium bromide)
beacasue bromide ions are oxidised form Br- to Br2. (Oxidising power of halogens decreases down the group whereas reducing power increases


Cl2O7 is the most acidic . U have misinterpreted or probably theres some misconception

 

[Muhammad Bin Anis]

Someone please
need explanation in the following
jun 07,p1, q35
nov 07, p1, q12

 

[Casablanca]

Well the first answer shud be D (sodium bromide)
beacasue bromide ions are oxidised form Br- to Br2. (Oxidising power of halogens decreases down the group whereas reducing power increases


Cl2O7 is the most acidic . U have misinterpreted or probably theres some misconception

Thank you for the first one.

As for the second one, yes, you are right. I accidentally wrote that acidity decreases, whereas acidity actually increases, but since the graph goes down, I misinterpreted it.

So, yeah, I know Cl2O7 is most acidic, but is it a lot more acidic than SO3 and P4O10? As in, would the graph be at an incline, or straight?

 

[LimeReem]

Guys why is HF3 insoluble in water? please provide reasons! =)

 

[Muhammad Bin Anis]

Thank you for the first one.

As for the second one, yes, you are right. I accidentally wrote that acidity decreases, whereas acidity actually increases, but since the graph goes down, I misinterpreted it.

So, yeah, I know Cl2O7 is most acidic, but is it a lot more acidic than SO3 and P4O10? As in, would the graph be at an incline, or straight?

yup man , because chlorine goes for the highest oxidation (+7) , in Cl2O7. it makes the most acidic of all period three solutions

 

[mominzahid]

Oh, sorry I was wrong there, it does have a +2 charge. :\ Actually, all of the other elements are larger but beryllium is the only one which has the same charge density as Al. You can figure that out from the data booklet, that's why it said "use of the data booklet is relevant to this question".

all these elements belong to group 2. and why cant it be magnesium aluminium is right next to magnesium in periodic table?

 

[KurayamiKimmi]

Guys why is HF3 insoluble in water? please provide reasons! =)

are you sure its HF3 ?
i think you're confusing it with HF and in that case it is soluble

 

[mominzahid]

It is very helpfull. Thanks very much Are you doing AS Chemistry exam in May??

Yes.. sadly yess.. my chemistry sucks lol.. i cant get above 30 in MCQ paper i dont know what im gonna do lol...

 

[LimeReem]

are you sure its HF3 ?
i think you're confusing it with HF and in that case it is soluble

Yes its HF3 , it says its insoluble too.. friend asked me this question

 

[Student12]

The equation below represents the combination of gaseous atoms of non-metal X and of
hydrogen to form gaseous X2H6 molecules.
2X(g) + 6H(g) → X2H6(g) ΔH = –2775 kJ mol–1
The bond energy of an X–H bond is 395 kJ mol–1.

What is the bond energy of an X–X bond?
A – 405.0 kJ mol–1
B – 202.5 kJ mol–1
C +202.5 kJ mol–1
D +405.0 kJ mol–1

How is the answer D ?

 

[KurayamiKimmi]

I need help again
i need help with question no.2,12,16,18,26,and 36
please do try to explain the answers and thank you for any help ^_^
http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s07_qp_1.pdf
http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s07_ms_1.pdf

 

[driggerbilal]

^awesome !thnx

 

[KurayamiKimmi]

Yes its HF3 , it says its insoluble too.. friend asked me this question

The only thing i can find by googling HF3 is headphones and missiles o_o
ask your friend again

lemme try searching again