Chemistry: Post your doubts here!

[princess Anu]

I can only find 8 Carbons that'll form a ketone on oxidation...which one is the ninth one? :/

 

[Metanoia]

http://www.sheir.org/a-level-chemistry-11-june2011.pdf
In q 40, how can X be ethanoic acid? The emperical formula is C4 whereas ethanoic has 2 C only??

Option says carboxyllic acid, not ethanoic acid.

 

[The Sarcastic Retard]

but my answer comes wrong if I do it this way
I have the solution for this question with the correct ans but
I don't get why we have to multiply moles of H2 by 2

watz d ans?

 

[Metanoia]

In aqueous solution, the acid HIO disproportionates according to the following equation where m,
n, p and q are simple whole numbers in their lowest ratios.
mHIO → nI2 + pHIO3 + qH2O
This equation can be balanced using oxidation numbers.
What are the values for n and p?
n p
a) 1 2
b) 2 1
c) 4 1
d) 4 2

the answer is B
I know how to figure out the oxidation numbers, but I need explanation on how to balance such equations using oxidation numbers... help please!!

You can try to create the 2 half equations

2HIO + 2H+ + 2e- --> I2 + 2H2O ------ (1)

HIO -+ 2H2O -> HIO3 + 4H+ + 4e- ------ (2)

Before combining the 2 equations, we need to make both equations have the same number of electrons
(2) x 2 + (1)

So ratio of I2 to HIO3 is 2: 1

 

[Metanoia]

I can only find 8 Carbons that'll form a ketone on oxidation...which one is the ninth one? :/View attachment 54134

Question is asking for number of fragment molecules containing the ketone group, not number of ketone groups.

 

[The Sarcastic Retard]

In aqueous solution, the acid HIO disproportionates according to the following equation where m,
n, p and q are simple whole numbers in their lowest ratios.
mHIO → nI2 + pHIO3 + qH2O
This equation can be balanced using oxidation numbers.
What are the values for n and p?
n p
a) 1 2
b) 2 1
c) 4 1
d) 4 2

the answer is B
I know how to figure out the oxidation numbers, but I need explanation on how to balance such equations using oxidation numbers... help please!!

Oxidation state of I in HIO, I2 and HIO3 is +1, 0 and +5 respectively.
Oxidation change from HIO to I2 is -2 (not -1 coz I-I)
Oxidation change from HIO to HIO3 is +4

Interchange the numbers, ie 2 for HIO3 and 4 for I2
2 : 4 ----> 1 : 2
n = 2 p = 1

 

[princess Anu]

so how to find that?

Question is asking for number of fragment molecules containing the ketone group, not number of ketone groups.

 

[Metanoia]

so how to find that?

Where will the cleaving of the molecule occur?

 

[princess Anu]

Where will the cleaving of the molecule occur?

at the double bonds

 

[princess Anu]

.

.

help please

 

[The Sarcastic Retard]

help please

Questions?

 

[Metanoia]

at the double bonds

Correct. Break the molecule and then oxidize the areas you've circled. See how many fragments you get that end up with a ketone group.

 

[princess Anu]

what are the intermediates for each?

 

[princess Anu]

Correct. Break the molecule and then oxidize the areas you've circled. See how many fragments you get that end up with a ketone group.

I end up with 6 :s

 

[Mahnoorfatima]

http://www.sheir.org/a-level-chemistry-13-nov2010.pdf
Question 25 why not A??
And in 12 my ans is A?

 

[Metanoia]

I end up with 6 :s

Thats the wrong answer? Which year is it?

 

[Metanoia]

http://www.sheir.org/a-level-chemistry-13-nov2010.pdf
Question 25 why not A??
And in 12 my ans is A?

Q12
heat absorbed by 200 g of water = 200 x 4.2 x 48 = 40 320
heat released by 1.6 g of fuel = 40320/45 x100 = 89 600
heat released by 1 g of fuel = 89600/1.6 = 56 000

Q25. Option A can give both aldehyde and acid.

 

[Metanoia]

what are the intermediates for each?

Q16. Barium sulfate is not soluble in the acid, whereas barium carbonates reacts with the acid to form a soluble barium compound.

Q26. X represents a halogen atom.
W: CH3CH2XCH3
X: CH3CH(OH)CH3X
Y: CH3CH2XCH3
Z: CH3CH2CH2OH

 

[nehaoscar]

Doesn't Selenium also have 6 unpaired electrons??
So does chromium ... B is correct but then what about D?

 

[nehaoscar]

Ok so using pv=nRT ... I'm getting 60000K .... Answer is B.... How??