AS chem problems here for Oct/Nov session

[sadman]

Guys i have some problems please do help me out here

 

[sadman]

Guys please i need help in this!!

 

[destined007]

6) check for oxidation number of nitrogen before and after the reaction.
before:
let the oxidation number of N in NH4+ be x
x+4(4 Hydrogen)=+1
x=-3

let the oxidation number of N in NO3-1 be y
y+3(-2)(3 oxygen)=-1
y=+5

after ther reaction:
let z be the oxidation of N in N20
2(Z)-2=0
z=+1

therefore the change in N is from -3to+1 and +5to+1,ie, +4 and -4

13) There is no change in oxidation number of any coumpound so sulphuric acid is acting as acid.

16) this is a fact based question. Here you must know the mp and ionization energy of period 3 compounds.

20) the only gas non flammable here is oxygen. All the rest catch fire. (NOTE: oxygen doesn't combust but rather supports it)

21) this is the question about free radical reaction. There are 3 places where chlorine free radical can act.
1) CH3CH2C(2CH3)(CH2Cl) (it will only be 1 possibility because no matter which of 3 CH3 you attack Cl, the molecule remains the same)
2) CH3CHClC(3CH3)
3) CH2ClCH2C(3CH3)

32) Check for change in oxidation number. In this case, only 1st equation shows a change in oxidation number. look at bromine in 1st equation. It changes from -1 to 0. In the rest of the equation there is no change in oxidation number of bromine.

 

[sadman]

for number 6:
since hydrogen is donation 3 electrons so the oxidation number of nitrogen is -3 right???? but then it donates a pair of electron to hydrogen so shoudnt it be +1??? i am sorry i didnt get this part.
please do help
and for redox reaction at this level should always look at oxidation number and nothing else??????

 

[destined007]

There are 2 ions involved. One is NH4+ and the other is NO3-1. Therefore the sum of charges will be equal to +1 and -1 in respectively. As simple as that.

 

[destined007]

Yes for most redox reaction, look at oxidation numbers.

 

[sadman]

NH4+ understood but why NO3+?? isnt nitrate ion negetively charged here???

 

[destined007]

Oh boy! my bad. you are right. it is -1. let me correct it.