Chemistry MCQ thread...

[sweetiepie]

Answer is D

CO2 + H2----> CO + H2O
-283+ -286 = X + -44
-569 = X + -44
X = -44 + 569
= +525

i hope u have get it....

 

[MHHaider707]

CO2 + H2----> CO + H2O
-283+ -286 = X + -44
-569 = X + -44
X = -44 + 569
= +525

i hope u have get it....

How did u get it???

i think C is the rite ans!!

 

[abdullah181994]

Can anyone explian this to me,please.

 

[histephenson007]

someone show the calculations for this question

Is the answer C ??

I hope I could draw to show my explanation...

CO2+H2---->CO+H20(g) *** notice the H2O (g)

If we draw a different pathway for the reaction...

C+H2+O2---(-283)--> CO2+H2-----(x)--->CO+H2O(g)-----(-44)--->CO+H20(l) <----(-286) H2+O2

So, -283+x-44=-286
therefore x = -286+44+283

= 41

 

[MHHaider707]

someone show the calculations for this question

Is the answer C ??

I hope I could draw to show my explanation...

CO2+H2---->CO+H20(g) *** notice the H2O (g)

If we draw a different pathway for the reaction...

C+H2+O2---(-283)--> CO2+H2-----(x)--->CO+H2O(g)-----(-44)--->CO+H20(l) <----(-286) H2+O2

So, -283+x-44=-286
therefore x = -286+44+283

= 41

Yeah rite!!!

 

[histephenson007]

Can anyone explian this to me,please.

m=0.23
V= 120 cm^3 =====> 120/1000 dm^3

n = V/24 (gas)
= (120/1000) / 24
= 0.005

Therefore, we can get Mr..

Mr = m/n
= 0.23/0.005
= 46
Then, u just try putting in each values of N(14) and O (16)
Answer : B

 

[histephenson007]

someone show the calculations for this question

Is the answer C ??

I hope I could draw to show my explanation...

CO2+H2---->CO+H20(g) *** notice the H2O (g)

If we draw a different pathway for the reaction...

C+H2+O2---(-283)--> CO2+H2-----(x)--->CO+H2O(g)-----(-44)--->CO+H20(l) <----(-286) H2+O2

So, -283+x-44=-286
therefore x = -286+44+283

= 41

Yeah rite!!!

But one thing I notice about this question is that the enthalpy change of formation of carbon monoxide in the product of the equation isn't considered?? could u plz explain why?

 

[kirashinagami]

Hi pros here.. please help me

3 The foul smell that skunks spray is due to a number of thiols, one of which is methanethiol,
CH3SH, which burns as follows.
CH3SH + 3O2 → CO2 + SO2 + 2H2O
A sample of 10 cm3 of methanethiol was exploded with 60 cm3 of oxygen.
What would be the final volume of the resultant mixture of gases when cooled to room
temperature?
A 20 cm3 B 30 cm3 C 50 cm3 D 70 cm3

19 Ammonium sulphate in nitrogenous fertilisers in the soil can be slowly oxidised by air producing
sulphuric acid, nitric acid and water.
How many moles of oxygen are needed to oxidise completely one mole of ammonium sulphate?
A 1 B 2 C 3 D 4

and please help me with oct nov 04 no 10 11 12 and 21.. i cant paste it here because there are pictures and tables..
thanks a lot

 

[histephenson007]

Hi pros here.. please help me

3 The foul smell that skunks spray is due to a number of thiols, one of which is methanethiol,
CH3SH, which burns as follows.
CH3SH + 3O2 → CO2 + SO2 + 2H2O
A sample of 10 cm3 of methanethiol was exploded with 60 cm3 of oxygen.
What would be the final volume of the resultant mixture of gases when cooled to room
temperature?
A 20 cm3 B 30 cm3 C 50 cm3 D 70 cm3

19 Ammonium sulphate in nitrogenous fertilisers in the soil can be slowly oxidised by air producing
sulphuric acid, nitric acid and water.
How many moles of oxygen are needed to oxidise completely one mole of ammonium sulphate?
A 1 B 2 C 3 D 4

and please help me with oct nov 04 no 10 11 12 and 21.. i cant paste it here because there are pictures and tables..
thanks a lot

Is the answer for 3... A?

 

[abdullah181994]

please explian this

 

[histephenson007]

Answer is D.

Facts :
- liberated gas is NH3 (turns damp litmus paper blue)
- options B and C are eliminated because they aren't nitrates!! (question mentions that it is a solid nitrate)
- ammonium salts react with alkalis to produce ammonium gas ( a new knowledge I've learned from this very MCQ thread ^^ )
- the empirical formula of ammonium nitrate is NH4NO3 --- N2H4O3

 

[abdullah181994]

Answer is D.

Facts :
- liberated gas is NH3 (turns damp litmus paper blue)
- options B and C are eliminated because they aren't nitrates!! (question mentions that it is a solid nitrate)
- ammonium salts react with alkalis to produce ammonium gas ( a new knowledge I've learned from this very MCQ thread ^^ )
- the empirical formula of ammonium nitrate is NH4NO3

Thanks .

 

[abdullah181994]

@Histephenson007 please explian about option B and C i did not get it why they are not nitrates

 

[abdullah181994]

26 An alcohol with molecular formula CnH2n+1OH has a chiral carbon atom but does not react with
MnO4 / H+.
What is the least number of carbon atoms such an alcohol could possess?
A 5 B 6 C 7 D 8

 

[abdullah181994]

PLease explian the above question i shall be thankful to u.

 

[histephenson007]

@Histephenson007 please explian about option B and C i did not get it why they are not nitrates

ah... I forgot that they are shown as empirical formula ...
So, B IS a nitrate, but C isn't because nitrate is NO3 and C has only one atom of oxygen.

 

[histephenson007]

For 26, is C right???

 

[xHazeMx]

For 26, is C right???

yeah

 

[Zishi]

someone show the calculations for this question

I reckon that it's C. Tell me if I'm correct, then I'll post the solution.

 

[histephenson007]

yea I guess its correct plz continue with ur explanation...