Chemistry: Post your doubts here!

[Mathemagical]

how do we solve this one? :/

Correct answer is C.

Since this is obviously a decomposition reaction, we can conclude that one mole of N2F4 decomposes into 2 moles of NF2. Therefore, only the N-N bond in the middle is broken, and not the N-F bonds. Option 1 is incorrect.

Option 2 states that the enthalpy change of the reaction is +160kJ/mol. This is the approximate bond enthalpy of the N-N bond, so this is correct.

Since we have concluded that X is NF2, we can now begin to inspect it in detail. A nitrogen atom has 5 valence electrons, and 2 of these are involved in bonding. This leaves 3 other electrons in the valence shell, unbonded. Therefore, the molecule is non-linear. Option 3 is correct.

Since Options 2 and 3 are correct, the answer is C.

 

[qwertypoiu]

http://maxpapers.com/wp-content/uploads/2012/11/9701_w14_qp_13.pdf
Q19: Why is B incorrect?

Calcium carbonate would thermally decompose .

 

[Mathemagical]

Calcium carbonate would thermally decompose .

Doubt it. Calcium carbonate decomposes into calcium oxide and carbon dioxide when heated above 840°C, so gentle heating from a Bunsen burner would not be sufficient.

 

[nehaoscar]

How is it B? when does it increase and then decrease??

 

[qwertypoiu]

View attachment 54230
???

W - MgO
X - CaCO3
Y - CaO
Z - Ca(OH)2

1. MgO + 2HCl ---> MgCl2 + H2O
CaCO3 + 2HCl ---> CaCl2 + H2O + CO2

From the equations there is no obvious difference in amount of acid neutralised.

the relative molecular mass of MgO is lower than CaCO3. Therefore, there will be more moles of W in 1g of it than number of moles of X in 1g. So more acid is neutralized by W.

2. This is incorrect. Ca is more reactive than Mg

3. This is incorrect. pH is increased when acid is neutralized.

So D

 

[nehaoscar]

How is it 3? i can only see 2...?

 

[qwertypoiu]

Doubt it. Calcium carbonate decomposes into calcium oxide and carbon dioxide when heated above 840°C, so gentle heating from a Bunsen burner would not be sufficient.

Oh I see.
I have a question. Would it melt or thermally decompose? Is there a way to make it do one and not the other based on what we wish?

 

[nehaoscar]

Why D? why not C?

 

[nehaoscar]

How is 3 also correct? C has 2 in p and Cl+ has 4 in p right?

 

[qwertypoiu]

View attachment 54234

How is it B? when does it increase and then decrease??

2O2- - 4e- ----> O2
This is oxidation. Electrons are lost. Oxidation state was -2, then became 0. So it increased by 2.

C + O2 ---> CO2
Oxygen is first 0, then becomes -2.

 

[nehaoscar]

How is only number 1 correct?
Ethanoic acid has only 2 Carbons which is less than the empirical formula!?

 

[Mathemagical]

View attachment 54235

How is it 3? i can only see 2...?

One on the CH3 group on the far left, one on the CH2 beside it, the other on either one of the CH3 groups attached to the central carbon atom.

 

[Mathemagical]

View attachment 54238
How is only number 1 correct?
Ethanoic acid has only 2 Carbons which is less than the empirical formula!?

Ethanoic acid dissociates into CH3COO- and H+ ions. Calcium forms Ca2+ ions, so 1 mol of Ca2+ ions will combine with 2 moles of CH3COO- ions.

 

[qwertypoiu]

View attachment 54235

How is it 3? i can only see 2...?

A hydrogen atom must be broken off from the organic compound by homolytic fission. Depending on from where this is done, a different resulting free radical will be formed.

The three methane groups are treated as same. From the ethyl group there are two carbons from which the hydrogen may be stolen

 

[Mathemagical]

View attachment 54237
How is 3 also correct? C has 2 in p and Cl+ has 4 in p right?

That's correct. Carbon has 2 electrons in the p-orbital and the chloride ion has 4 electrons in the p orbital. However, both have 2 unpaired electrons in the orbital, so Option 3 is correct.

 

[qwertypoiu]

View attachment 54236

Why D? why not C?

An OH and H next to it must be given off for dehydration of alcohol. There is no way C can be formed this way. The OH is below so how can the double bond form there?

The correct answer D is confusing at first, but it's flipped to the left. Imagine it flipped back and you'll see how it could be formed.

 

[Mathemagical]

View attachment 54236

Why D? why not C?

Check the structure carefully. The compound is not symmetrical so C would not be the same.

 

[qwertypoiu]

View attachment 54237
How is 3 also correct? C has 2 in p and Cl+ has 4 in p right?

C has two. They're both unpaired.
Cl+ has 4. Two of them are paired, the other two are unpaired.

 

[qwertypoiu]

View attachment 54238
How is only number 1 correct?
Ethanoic acid has only 2 Carbons which is less than the empirical formula!?

Ca has a vacancy of +2. It would form Ca(OH)2, for example.
When Na reacts with acid it's simply like CH3COONa. But Ca will join with two of the anions.
Ca2+ ( CH3COO- )2

Thus the empirical formula has 4 carbon atoms.

 

[fantastic girl]

Assalamu Alaikum
http://studentbounty.com/pastpapers...l/Chemistry (9701)/2007 Nov/9701_w07_qp_1.pdf
Can someone explain me statement 1 of Q33 :/

http://studentbounty.com/pastpapers.../Chemistry (9701)/2012 Jun/9701_s12_qp_11.pdf
Q18 - iam confused...plz help :/

Thanks in advance