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Chemistry: Post your doubts here!

Mathemagical

Mathemagical

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Abdul Hanan said:
Thanks i do understand 27 and 29 now but can you please explain 22 a bit more? thanks again :)
Click to expand...
The keyword in Question 22 is "followed by". Take Option B, for example. After polymerising it, the alkene becomes saturated and therefore cannot undergo a reaction with cold, dilute KMnO4. Similarly, alkanes, which are also saturated, cannot undergo that reaction.
 
Metanoia

Metanoia

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nehaoscar said:
Q20:
View attachment 54222
The green line shows the main carbon chain. These are the 5 isomers
Click to expand...

Your bottom two isomers are identical.

Instead, find the chiral carbon in the 2nd isomer (top row), indicating that there is an extra optical isomer.

The question has hinted to look for optical isomers, so likely there will be at least one.
 
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Mathemagical

Mathemagical

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Studydayandnight said:
how do we solve this one? :/

Correct answer is C.
Click to expand...

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

qwertypoiu

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nehaoscar said:
View attachment 54230
???
Click to expand...
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
 
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