Chemistry: Post your doubts here!

[fantastic girl]

http://www.sheir.org/a-level-chemistry-11-june2011.pdf
Question 8?
And in 11 why's D wrong?
13 My answer's D. What did I do wrong in this calculation:
Al2O3: 6HCL
0.02x6= 2xvolume/1000
AND I DONT GET 15 AND 16 AT ALL!

check that video for Q8

 

[Abdul Hanan]

So we have an upcoming chemistry MCQ exam and i keep getting MCQs for organic chemistry wrong
any advice?
Thanks

 

[princess Anu]

Initial moles H2O = 1
Initial moles CO = 1
Eq moles H2O = 1-x
Eq moles CO = 1-x
Eq moles H2 = x
Eq moles CO2 = x

Total moles = (1-x) + (1-x) + x + x = 2
if hydrogen occupies 33% = 2/3 moles hence CO2 is also 2/3 moles and CO and H2O have 1/3 moles

Now put the values into the equilibrium law.

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

 

[Metanoia]

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

You can post the answer scheme here for checking.

This question is familiar, I believe it was answered before.

View attachment 51471

 

[princess Anu]

You can post the answer scheme here for checking.

This question is familiar, I believe it was answered before.

Yeah it was

 

[princess Anu]

..

 

[Metanoia]

You are referring to the line

mole of H2 formed = 33.3/100 *2 ?

The 2 is the total moles of gases, moles of H2 = % of H2 x total moles

 

[princess Anu]

You are referring to the line

mole of H2 formed = 33.3/100 *2 ?

The 2 is the total moles of gases, moles of H2 = % of H2 x total moles

How do we know 2 moles of gas are present at Equilibrium?

 

[Metanoia]

..

Leaving mathematical calculations aside, we can reason it out in this manner.

A <-> B exothermic can also be represented by A <-> B + heat

A <-> B endothermic can also be represented by A + heat <-> B

Changing the temperature (removing or adding heat) will shift the equilibriums above.

Only equilibriums that are neither exothermic nor endothermic will not shift during temperature changes.
In other words, the enthalpy change of such reactions is zero (heat is neither a "reactant" nor a "product".)

 

[Metanoia]

How do we know 2 moles of gas are present at Equilibrium?

total moles = 1- x + 1 -x + x + x = 2 moles

 

[princess Anu]

total moles = 1- x + 1 -x + x + x = 2 moles

thanks a lot

 

[princess Anu]

..

 

[Metanoia]

..

The NH3 molecule is the same before and after the reaction, so we would not expect any change in its oxidation state.

Ag+ + 2NH3 --> [Ag(NH3)2]+

If you do intend to calculate each atoms, you have to be careful.
+1 + 2x + 6 = +1 ( you had -2x instead of +2x)

 

[princess Anu]

which ones are the intermediate for each??

 

[princess Anu]

.

 

[Mahnoorfatima]

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??

 

[Mahnoorfatima]

http://www.sheir.org/a-level-chemistry-13-nov2011.pdf
Q 14 and 15 and 25 anyone?

 

[Xaptor16]

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!!

 

[princess Anu]

http://www.sheir.org/a-level-chemistry-13-nov2011.pdf
Q 14 and 15 and 25 anyone?

check my answers first
14B
15B
25D??

 

[Mahnoorfatima]

check my answers first
14B
15B
25D??

25 is C rest are correct. Can you please explain?