Chemistry: Post your doubts here!

[I Only ask questions]

How did it come

 

[IN NEED OF HELP]

Guys I did GCSE A-Levels by Cambridge International Examinations and I got 2 C's and 2 D's. However I have good SAT score. I secured 1360 in SAT 1 which includes Mathematics and English. I also did IELTS and secured 6.5 out of 9.0. Is this score good enough to get admitted in USA and getting scholarship?

 

[Unknown202]

Which process does not involve either oxidation or reduction?
A formation of ammonium sulphate from ammonia and sulphuric acid
B formation of nitrogen monoxide from ammonia
C formation of sulphuric acid from sulphur
D formation of zinc from zinc blende (ZnS)
someone help why is it A?

 

[A*****]

Which process does not involve either oxidation or reduction?
A formation of ammonium sulphate from ammonia and sulphuric acid
B formation of nitrogen monoxide from ammonia
C formation of sulphuric acid from sulphur
D formation of zinc from zinc blende (ZnS)
someone help why is it A?

Write down the equation for each one and see in which equation the oxidation state of all the elements is unchanged...that will be the one with no redox reaction

 

[Unknown202]

can someone solve tht?

 

[A*****]

View attachment 64262
can someone solve tht?

Is it "...begin to boil or something?" And is the answer D?

 

[Hamnah Zahoor]

I need some help on this mcq. The answer is 1 and 2


View attachment 64265

Q37 For a molecule to be in same plane it should have an angle of 120 degree in its compound
option A contains a 120 degree angle due to C=C bond.
I think option B have planar structure for it can also exist as cyclopropane which have angle of 120 degree.
From the examination report:
Question 37 The most commonly chosen incorrect answer was C. This suggests that most candidates knew that the three carbon atoms in propane all lie in the same plane. The six carbon atoms in 2,3-dimethylbut-2-ene also all lie in the same plane, since the bond angles at an sp2 hybridised carbon atom are very close to 120°, and the π bond prevents rotation. However, the six carbon atoms in cyclohexane do not lie in the same plane, they are all sp3 hybridised with bond angles close to 109°.

 

[Bishnu Dev]

What is the concept behind a (ii) and a (iii) ???

 

[Hamnah Zahoor]

What is the concept behind a (ii) and a (iii) ???

(ii) As, Ksp = [Ca2+][SO4 2-]
(3*10^-5)= (x)(x)
(3*10^-5)=x^2
x=5.48*10^-3

CaSO4 -----> Ca2+ + SO42-
1 mol of CaSO4 : 1 mol of Ca2+
thus, conc. will be same
[CaSO4] = 5.48*10^-3

(iii) conc.of CaSO4 : conc. of H2SO4 (acid rain)
1 : 1
conc. of H2SO4 (acid rain)= 5.48*10^-3
moles = (5.48*10^-3)*100
0.548 moles
As stated in the question statement that the carbonate is converted into soluble sulphate thus we are supposed to calculate the mass of soluble sulfate that is the mass lost. 1 mol of H2SO4 : 1 mol of CaSO4
0.548*( 40.1+32+(16*4)
74.58 g -------------> that is the mass lost.

 

[Asim Shah]

Does any body have Philip Alan Magazines Chemistry review

 

[Bishnu Dev]

do we have to study about the chemical and physical properties of Group IV elements for the current syllabus? (A2)

 

[qwertypoiu]

Q37 For a molecule to be in same plane it should have an angle of 120 degree in its compound
option A contains a 120 degree angle due to C=C bond.
I think option B have planar structure for it can also exist as cyclopropane which have angle of 120 degree.
From the examination report:
Question 37 The most commonly chosen incorrect answer was C. This suggests that most candidates knew that the three carbon atoms in propane all lie in the same plane. The six carbon atoms in 2,3-dimethylbut-2-ene also all lie in the same plane, since the bond angles at an sp2 hybridised carbon atom are very close to 120°, and the π bond prevents rotation. However, the six carbon atoms in cyclohexane do not lie in the same plane, they are all sp3 hybridised with bond angles close to 109°.

Propane has carbon atoms that lie on a plane because it only has three carbons. It is sp3 hybridised and has bond angles of 109, but the carbon atoms still lie in a plane because any three points in a three dimensional space can be placed on a single plane.

 

[Bishnu Dev]

When calculating Ecell, what is the correct method? Suppose that we have two standard electrode potential values: +1.32, -0.37
These two half cells were coupled together
In that case Ecell = 1.32-(-0.37)? or -0.37-1.32? mark scheme provides only one answer but i think it should differ depending on the terminals to which the voltmeter is connected. Any idea?

 

[anastasia grey113]

When calculating Ecell, what is the correct method? Suppose that we have two standard electrode potential values: +1.32, -0.37
These two half cells were coupled together
In that case Ecell = 1.32-(-0.37)? or -0.37-1.32? mark scheme provides only one answer but i think it should differ depending on the terminals to which the voltmeter is connected. Any idea?

Subtract the smaller one from the larger one.
The answer would be 1.32-(-0.37)

 

[Bishnu Dev]

Subtract the smaller one from the larger one.
The answer would be 1.32-(-0.37)

Is that always the case or CIE prefers this one? What if i connect the voltmeter other way around? The magnitude remains same but the sign changes.

 

[anastasia grey113]

Is that always the case or CIE prefers this one? What if i connect the voltmeter other way around? The magnitude remains same but the sign changes.

This is always the case. A negative value is never considered becuz that shows that the reaction is not feasible.
Usually the voltmeter is connected with + terminal on the higher electrode potential so just remember larger - smaller for all.

Don't use it for feasibilities. It has a different method. Don't confuse it with E of cell.

 

[Bishnu Dev]

This is always the case. A negative value is never considered becuz that shows that the reaction is not feasible.
Usually the voltmeter is connected with + terminal on the higher electrode potential so just remember larger - smaller for all.

Don't use it for feasibilities. It has a different method. Don't confuse it with E of cell.

Well, group IV chlorides are removed from the syllabus, right? I have not done the recent papers but it appears frequently in test papers which were administered before 2016

 

[anastasia grey113]

Well, group IV chlorides are removed from the syllabus, right? I have not done the recent papers but it appears frequently in test papers which were administered before 2016

yes whole of group IV is out of syllabus

 

[Bishnu Dev]

Please explain b)

 

[Sheraz ali]

Iron(III) chloride, FeCl 3, is used to dissolve unwanted copper from printed circuit boards
(PCBs) by the following reaction.
2FeCl 3(aq) + Cu(s) → 2FeCl 2(aq) + CuCl 2(aq)
A solution in which [Fe3+(aq)] was originally equal to 1.50 mol dm–3 was re-used several
times to dissolve copper from the PCBs, and was then titrated as follows.
A 2.50 cm3
sample of the partially-used-up solution was acidifi ed and titrated with
0.0200 mol dm–3 KMnO4.
This oxidised any FeCl 2 in the solution back to FeCl 3.
It was found that 15.0 cm3
How one know that which MnO-4 half equation use

MnO4– + 4H++ 3e– MnO2 + 2H2O +1.67
MnO4– + 8H++ 5e– Mn2+ + 4H2O +1.52