Chemistry: Post your doubts here!

[Bishnu Dev]

View attachment 62740

w16 p11

help?

The answer is A....
Take a look at bond angle X, the Nitrogen atom makes three bonds which suggests us that the bond angle should be around 120 degree but don't forget about the lone pair on Nitrogen atom which pushes the bonds even closer to each other as lone pair to bond pair repulsion is more significant. So angle X would be around 107 degrees.
Now If we talk about angle Y, there're are four groups attached to Carbon atom so it makes tetrahedral structure with a bond angle of 109.5 which is greater than X. Look, this one is different from angle X because it doesn't involve any lone pairs; and bond pair to bond pair repulsion is not as significant as lone pair to bond pair.
Angle Z is totally clear, there's no lone pair on carbon atom and it makes only three bonds among which one is double bond so we expect the angle to be around 120 degrees. Hence the answer is A

 

[Coolio_777]

9701/11 w16

answer is B but how

 

[Daniel Jeng]

View attachment 62748

9701/11 w16

answer is B but how

You may have thought that there would only be 3 isomers instead of 4 isomers, however there is an extra twist to this question: there are two isomers for the variation in which 2 chloro groups are next to each other. The chloro groups may bond to neighbouring carbon atoms that have a double bond between them, or a single bond. In addition to the 2 other isomers with 1 carbon in between and 2 carbons in between, you will get 4 isomers instead of 3.

 

[Bishnu Dev]

View attachment 62748

9701/11 w16

answer is B but how

As Daniel Jeng said,

 

[Deeksha Tamang]

When solid ammonium chloride dissociates at a certain temperature in a 0.500dm3 container, ammonia and hydrogen chloride are formed. NH4Cl(s) NH3(g) + HCl(g) The initial amount of ammonium chloride was 1.00mol, and when the system had reached equilibrium there was 0.300mol of ammonium chloride. What is the numerical value of Kc for this reaction under these conditions?
A 0.490 B 1.63 C 1.96 D 3.27
can u plz tell me how to solve it??

 

[Bishnu Dev]

When solid ammonium chloride dissociates at a certain temperature in a 0.500dm3 container, ammonia and hydrogen chloride are formed. NH4Cl(s) NH3(g) + HCl(g) The initial amount of ammonium chloride was 1.00mol, and when the system had reached equilibrium there was 0.300mol of ammonium chloride. What is the numerical value of Kc for this reaction under these conditions?
A 0.490 B 1.63 C 1.96 D 3.27
can u plz tell me how to solve it??

Kc = [NH3] * [HCl] / 1

Don't include the concentration of NH4Cl in Kc equation as it is in solid state....

 

[Deeksha Tamang]

Kc = [NH3] * [HCl] / 1

Don't include the concentration of NH4Cl in Kc equation as it is in solid state....

we don't include concentration of solid in Kc ???

thanks a lot

 

[Bishnu Dev]

we don't include concentration of solid in Kc ???

thanks a lot

no we don't

 

[Unknown202]

The commonest form of iron(II) sulfate is the heptahydrate, FeSO4.7H2O. On heating at 90 C
this loses some of its water of crystallisation to form a different hydrated form of iron(II) sulfate,
FeSO4.xH2O.
3.40 g of FeSO4.xH2O was dissolved in water to form 250 cm3
of solution.
A 25.0 cm3
sample of this solution was acidifi ed and titrated with 0.0200 mol dm–3 potassium
manganate(VII).
In this titration 20.0 cm3
of this potassium manganate(VII) solution was required to react fully with
the Fe2+ ions present in the sample.
(a) The MnO4
–
ions in the potassium manganate(VII) oxidise the Fe2+ ions in the acidifi ed solution.
(i) Explain, in terms of electron transfer, the meaning of the term oxidise in the sentence
above.
.............................................................................................................................................
....................................................................................................................................... [1]
(ii) Complete and balance the ionic equation for the reaction between the manganate(VII)
ions and the iron(II) ions.
MnO4
–
(aq) + 5Fe2+(aq) + .........H+(aq)  .........(aq) + 5Fe3+(aq) + .........H2O(l)
[3]
(b) (i) Calculate the number of moles of manganate(VII) used in the titration.
[1]
(ii) Use the equation in (a)(ii) and your answer to (b)(i) to calculate the number of moles of
Fe2+ present in the 25.0 cm3
sample of solution used.
[1]
(iii) Calculate the number of moles of FeSO4.xH2O in 3.40 g of the compound.
[1]
(iv) Calculate the relative formula mass of FeSO4.xH2O.
[1]
(v) The relative formula mass of anhydrous iron(II) sulfate, FeSO4, is 151.8.
Calculate the value of x in FeSO4.xH2O.
I need help in these question

 

[Unknown202]

) Calculate the number of moles of FeSO4.xH2O in 3.40 g of the compound

In these one why 250/25?!?!

 

[Metanoia]

In these one why 250/25?!?!

3.40 g of the compound was dissolved in 250 cm^3 , and only 25 cm^3 of the 250cm^3 was used in the titration.

So when we need to find the original amount in 250 cm^3 , we need to multiply by a factor of 10

 

[Unknown202]

Hmm multiply by 10?!

 

[A*****]

Hmm multiply by 10?!

Yes multiply by 10 aur by 250/25...both mean the same

 

[Unknown202]

Thx u soon much

 

[Unknown202]

And plz help in question 1 Nov 2011 v11 do I hv to learn the properties?

 

[selrey]

Can someone explain Q2) a) i) for [H+]?

 

[Dhr0003]

What are important chapters to score good marks

 

[Leelaa]

Help please........ the ans is B

Which of these equations represents the reaction of sulphur dioxide with an excess of aqueous

sodium hydroxide?

A SO2 + NaOH ----> NaHSO3

B SO2 + 2NaOH -------> Na2SO3 + H2O

C SO2 + 2NaOH ------> Na2SO4 + H2O

D SO2 + 2NaOH -----> Na2SO4 + H2

Why cant it be reaction C???

Because Na2So4 doesn't exist as a product of that reaction.

However, if you didn't know that, just try looking at the balancing of the equation and see if it works. Out of B and C, only B is correct.

 

[Hamnah Zahoor]

Can anyone help me with this question...Oct Nov 2008 Question:39

 

[Sagar Gupta]

28 Compound X will decolourise a warm acidified solution of manganate(VII) ions and forms orange
crystals on reaction with 2,4-dinitrophenylhydrazine.
What is X?
A CH3CH=CHCH2OH
B CH3COCH2CH3
C CH3CH2CH2CHO
D CH3CH(OH)CH2CO2H

And why?