Chemistry: Post your doubts here!

[darks]

From where did u got a phrase like Avg. isotopic mass?
The colourless solution produces a grey precipitate of silver, or a silver mirror on the test tube.

ok what about average atomic mass?
and thanks for clearing that tollen's problem.

 

[Sarosh Jameel]

PLZ someone explain me part III and IV ...

 

[awesomaholic101]

No one knows this?? Metanoia awesomaholic101

Sorry no idea ... I never really did many papers and when i did, i didn't focus on the pattern .... So i would like to know as well.

 

[The Sarcastic Retard]

Sorry no idea ... I never really did many papers and when i did, i didn't focus on the pattern .... So i would like to know as well.

Can u solve my doubts?

 

[The Sarcastic Retard]

ok what about average atomic mass?
and thanks for clearing that tollen's problem.

The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance

 

[darks]

The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance

divided by 100? thanks so we write as is?
my teacher was saying definitions like these will come.. so i'm just making sure.

 

[The Sarcastic Retard]

divided by 100? thanks so we write as is?
my teacher was saying definitions like these will come.. so i'm just making sure.

According to me, it should be relative atomic mass that ur talking about.
And yeah, definations are must.

 

[awesomaholic101]

Can u solve my doubts?

I'll try now

 

[Metanoia]

When I solve recent years past papers that is from 2007 to 2015(summer) summer and witner both I use to score always above 50. Now when I look into old years like this paper I ended up at the score of just 46. I have so many doubts in this paper. If anyone can help me out solving, Q1(c)(d), Q2(c)(d), Q5(c), Q7(b)(c) in Q7(b) arent answer in ms for uses of esters? Please do it as soon as possible. Also, When I was solving papers I found that mostly moles thingy are in summer papers, in winter papers its mostly inorganic part and theory. Am I correct? Should I expect 2015 november paper to be easier with moles thingy??

Thank you,
Regards,
XPC member,
The Sarcastic Retard

I believed you have gone through the ms already which I am posting below.

Which part of the answers do you need to clarify?

Q1


Q2


Q5



Q7


As for patterns in setting of questions, I don't really look at it. I seldom encourage "spotting of questions".

 

[awesomaholic101]

I believed you have gone through the ms already which I am posting below.

Which part of the answers do you need to clarify?

Q1
View attachment 57215

Q2
View attachment 57216

Q5
View attachment 57217
View attachment 57218

Q7
View attachment 57219

As for patterns in setting of questions, I don't really look at it. I seldom encourage "spotting of questions".

How do we know which line denotes what atom?
How do we calculate the atomic radii of argon? Some data must be given about it in the data booklet right?

 

[Metanoia]

Can anyone explain to me why the potential of the electrode decreases as [Ag+] decreases?

1)b)ii)

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_qp_4.pdf

Shouldnt it increases because in Ag+ + e => Ag, decreasing Ag+ would shift equilibrium to LHS so increasing the Eo?

Ag+ + e- --> Ag E = + 0.800 V

Shifting the eqm to the right will increase the E value, shifting to the left will decrease the E value.

Since you correctly said the eqm would "shift to LHS", you can see that the E value should decrease.

 

[Metanoia]

How do we know which line denotes what atom?
How do we calculate the atomic radii of argon? Some data must be given about it in the data booklet right?

How do we know which line denotes what atom?
The useful background knowledge required is that chlorine has two main isotopes; Cl- 35 and Cl-37.

So, from left to right, we have Cl-35 , HCl (where the Cl is Cl-35), Cl-37 and HCl (where the Cl is Cl-37).

Even if we do not have that background knowledge, we should be able to deduced that the 4 lines are from
lightest Cl atom, HCl with lighter Cl atom, heavier Cl atom, HCl with heavier Cl atom

How do we calculate the atomic radii of argon?
This can be found in the data booklet. The numbers in the most recent edition might be different from the suggested value in the MS, keeping in mind that the paper was set more than 10 years ago.

 

[darks]

According to me, it should be relative atomic mass that ur talking about.
And yeah, definations are must.

relative atomic mass is
average mass of an atom of element relative to carbon 12. which is exactly 12 units. (ms)

 

[awesomaholic101]

How do we know which line denotes what atom?
The useful background knowledge required is that chlorine has two main isotopes; Cl- 35 and Cl-37.

So, from left to right, we have Cl-35 , HCl (where the Cl is Cl-35), Cl-37 and HCl (where the Cl is Cl-37).

Even if we do not have that background knowledge, we should be able to deduced that the 4 lines are from
lightest Cl atom, HCl with lighter Cl atom, heavier Cl atom, HCl with heavier Cl atom

How do we calculate the atomic radii of argon?
This can be found in the data booklet. The numbers in the most recent edition might be different from the suggested value in the MS, keeping in mind that the paper was set more than 10 years ago.

View attachment 57220

Thank u
Yea I'm sorry about the atomic radius question... Didn't check the data booklet well

 

[The Sarcastic Retard]

relative atomic mass is
average mass of an atom of element relative to carbon 12. which is exactly 12 units. (ms)

Yeah, but he is asking about Avg atomic mass..

 

[The Sarcastic Retard]

I believed you have gone through the ms already which I am posting below.

Which part of the answers do you need to clarify?

Q1
View attachment 57215

Q2
View attachment 57216

Q5
View attachment 57217
View attachment 57218

Q7
View attachment 57219

As for patterns in setting of questions, I don't really look at it. I seldom encourage "spotting of questions".

Every thing Sir.

 

[Saad the Paki]

Can some one share a link to topical papers for chemistry (a thread or a website) Appreciated.

 

[Farheen1201]

No one knows this?? Metanoia awesomaholic101

I believe the doubts with the first question is solved.
As for question 2(c): The radius of the argon atom is given as 0.190 in the data booklet. Then it is a simple substitution to find the volume. To find the volume of 1 mole of argon atoms, you have to simply multiply the volume of one atom to Avogadro's constant. We know that one mole of an ideal gas occupies 24 dm3 of volume. So to find percentage it is, the (volume of 1 mole of argon atoms/24)x100. The answer, as given, is 0.074%. This is very negligible hence the assumption made about ideal gases, that is that the volume of gases is negligible is satisfied by our answer.
2(d) Argon is used to fill light bulbs because it is an inert gas and won't react with the tungsten metal. Other components of the air would react and examples are stated in the ms.
For 5(c)(I) & (ii)The MS explains it explicitly.
for 7(b) and (c) the answers in the MS are correct for the uses and physical properties of esters.

Besides we are the last of this syllabus. According to the exams I have already given, I have a hunch CIE may go easy on us. I mean its not wrong to hope.

 

[Farheen1201]

Can some one share a link to topical papers for chemistry (a thread or a website) Appreciated.

I personally find chemguide.co.uk very helpful for the organic part. Xtremepapers revision section is also available.

 

[The Sarcastic Retard]

Good luck!