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Chemistry: Post your doubts here!

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its a nucleophilic substitution bcoz d C atom bonded to the hydroxyl grp will carry a partially positive charge (diff in electronegativity of O n C).
This makes it open to nucleophilic attack. ie the partially -ve halogen atom in hydrogen halide will attack the bond btw the C n hydroxyl grp..
Hope i helped!!;)
yaaa that helped..!! A LOOT!!
(i kinda tend to miss the most obvious stuff..!!:()
thnx once again:)
 
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Ammonium nitrate, NH4NO3, can decompose explosively when heated.
NH4NO3 → N2O + 2H2O
What are the changes in the oxidation numbers of the two nitrogen atoms in NH4NO3 when this
reaction proceeds?
A –2, –4 B +2, +6 C +4, –6 D +4, –4
 
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Anyone explain these two questions to me please? Thanks first! :Yahoo!:
FYI, the answer given for Q10 is D whereas for Q11 is D.
image.jpg

image.jpg
For Question 11 you can see that the equilibrium concentration of Z decreases as the temperature is increased. This means that increasing the temperature lowers the forward reaction (or more simply the Kc for the reaction), and you must remember that Kc for exothermic reaction decreases with increasing temperature (because exothermic gives out heat energy)
Therefore answer is D.
 
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Ammonium nitrate, NH4NO3, can decompose explosively when heated.
NH4NO3 → N2O + 2H2O
What are the changes in the oxidation numbers of the two nitrogen atoms in NH4NO3 when this
reaction proceeds?
A –2, –4 B +2, +6 C +4, –6 D +4, –4

Answer is D.
First check the oxidation of Nitrogen atom in NH4(+1)
x+4=1 so x= -3
Oxidation of Nitrogen in Ammonium Ion = -3

Now Oxidation of Nitrogen in NO3(-1)
x-6=-1 so x= 5
Oxidation of Nitrogen in Nitrate Ion is 5

Now Check the Oxidation State of Nitrogen in N20.
2x-2=0 so x=1
So Oxidation of Nitrogen in N20 is 1

Final Step :
Calculate the change : from -3 to +1 ( change of +4)
from 5 to +1 (change of -4)
Therefore answer is D :)
 
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For 8, find the mass of Cl2 ie 5.287 - 2.920 = 2.367g
thn find the no of moles of Cl2 ie ( 2.367/71) o.o33 moles
we know the ratio of moles of X : Cl2 is 1:1 thus no of moles of X is also 0.033
then simply substitute moles n mass in Moles = Mass/ Mr , we get Mr = 87.6 which is the mass no of Strontium...so D is the ans..
 
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For 9, 1 mole of gas = 24 dm3
x moles of gas = 3 dm3....ie 0.125 moles = 3 dm3
Now find the no of moles of all the gases given... Mass/Mr
the ans is C
 
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For 10, look at the pH values given for X n Y...
This shows that X is an acid - pH =pH below 7, n Y is a base pH abv 7.
Student P says that X is a strong acid which is completely wrong, as strong acids do not have such a high pH..
However Q says tht Y dissociates more, n since Y is a base, we shud know tht the greater the value of pH, the stronger the acid..
Y is 2 nos greater thn 7, n X is only 1 no lesser thn 7...this shows tht Y is a stronger base n dissociates more..
Hence Q only is correct..
 
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Ammonium nitrate, NH4NO3, can decompose explosively when heated.
NH4NO3 → N2O + 2H2O
What are the changes in the oxidation numbers of the two nitrogen atoms in NH4NO3 when this
reaction proceeds?
A –2, –4 B +2, +6 C +4, –6 D +4, –4

leosco1995 had answerd this..
Figure out the oxidation numbers in both N atoms in NH4NO3 and compare it with the oxidation number of N in N2O. Like so:

You split up NH4NO3 into the NH4+ and NO3- ions.

In NH4+, the charge on Nitrogen is 1 - 4 = -3.
In NO3-, the charge on Nitrogen is -1 + 6 = +5.

And in N2O, the charge on nitrogen is 2/2 = +1.

And the changes in these are +4 and -4 respectively, meaning D is right.
 
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For 10, look at the pH values given for X n Y...
This shows that X is an acid - pH =pH below 7, n Y is a base pH abv 7.
Student P says that X is a strong acid which is completely wrong, as strong acids do not have such a high pH..
However Q says tht Y dissociates more, n since Y is a base, we shud know tht the greater the value of pH, the stronger the acid..
Y is 2 nos greater thn 7, n X is only 1 no lesser thn 7...this shows tht Y is a stronger base n dissociates more..
Hence Q only is correct..
the greater the ph value the weaker the acid..rit?
 
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Did it for you (sorry, diagram doesn't really look good) :p-
UntitledCHEM.jpg


Then
DAVSDF.jpg
Ya noww i get it. well you know you asked this one at school and you drew the whole thing. only problem was i didnt think there would be any other double bond in the chain but only in the cyclohexene ring. But it was supposed to be the opposite. well thanks.

P.S. diagram's not too bad!:p
 
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Concentrated sulfuric acid can behave both as a strong acid and as an oxidising agent.

With which compound does concentrated sulfuric acid react in this way?

A. Ethanol
B. Magnesium Carbonate
C. Propanenitrile
D. Sodium Bromide

Why?

---

In the graph of acidity of period 2 oxides, acidity decreases down the period... But is the acidity of P4O10, SO3, and Cl2O7 the same, or does it decrease as well?
 
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For question 2, 2 double bonds in he compound were removed, thus 4 mole of hydrogen was required (since 2 hydrogens are added to the chain once you break a double bond). If you notice, CH2 was changed to CH3 thus one more mole os Hydrogen was required. So in total, 5 mole of hydrogen was required.

Question 3, first of all find the Mr of P2O5, which is (31*2)+(16*5)= 142.
Now find the amount of phosphorus present in this amount, which is (31*2)/142= 0.4366...
The question said, only 30% of it dissolves, so 0.4366*30= 13.09, which is almost equal to 13.1, hence answer is B.

Question 4-
Ethanol will not react with NaOH. Since a hydroxyl group is present in both of them, no nucleophilic substitution will happen, so it has to be ethanoic acid.

Question 5-
This question is hell tricky, and I've been trying this for half an hour now, and I don't see how to differentiate between A and D, both of 1 mol of A and D, will require 2 mol of HCN, and both will change the color of potassium dichromate.
I will try to brain storm this question with one of my friends, and she might come up with something. :p
Till then I'll be grateful if someone can reason out why it should be D, not A, please?
Here's the question:
attachment.php
A ketone doesn't change the color of potassium dichromate (because it can't be further oxidized), so it can't be A.
 
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Concentrated sulfuric acid can behave both as a strong acid and as an oxidising agent.

With which compound does concentrated sulfuric acid react in this way?

A. Ethanol
B. Magnesium Carbonate
C. Propanenitrile
D. Sodium Bromide

Why?

---

In the graph of acidity of period 2 oxides, acidity decreases down the period... But is the acidity of P4O10, SO3, and Cl2O7 the same, or does it decrease as well?

Well the first answer shud be D (sodium bromide)
beacasue bromide ions are oxidised form Br- to Br2. (Oxidising power of halogens decreases down the group whereas reducing power increases


Cl2O7 is the most acidic . U have misinterpreted or probably theres some misconception :)
 
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