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Chemistry: Post your doubts here!

loveyuan

loveyuan

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savera said:
Sure why not..... can you please be specific. For which chapter are you talking about.
Click to expand...

hi ,
for an example
http://www.cie.org.uk/images/157296-november-2012-question-paper-43.pdf
question number 7 iii

I can solve the 7 i and ii
and from the question i know there will have 2 -CH3 group and 2-CH2 group
and one of the element beside C and H is O

and according to chemical shift ,
there is some group in ~around 1 and 2.5
but everytime i cant find something fit to information

here is the data booklet :
http://fmcapechemistry.weebly.com/uploads/5/6/3/3/5633072/chem_data_booklet.pdf
 
♣♠ Magnanimous ♣♠

♣♠ Magnanimous ♣♠

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Pink Flower said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_1.pdf
Can someone please explain me Question 2???????????
Click to expand...
We have to find concentration of Nitrogen in that solid

Answer ---> First of all we need to know how we can fine concentration
Conc = moles/volume
Units : Mol/dm3
Moles --> moles
Volume --> dm3

According to the ratio given of that solid material we have 15 gram of N per 100 g of fertiliser which means 15% and the usage of fertiliser in 14 g so :
14(15/100) ===> 2.1 grams.

Converting Grams to Moles we get ---> 0.15 moles

We have volume 5 dm3

Now put the values in equation :
Conc : 0.15/ 5 --> 0.03 mol/dm3

I hope you got it :)
 
Pink Flower

Pink Flower

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♣♠ Magnanimous ♣♠ said:
We have to find concentration of Nitrogen in that solid

Answer ---> First of all we need to know how we can fine concentration
Conc = moles/volume
Units : Mol/dm3
Moles --> moles
Volume --> dm3

According to the ratio given of that solid material we have 15 gram of N per 100 g of fertiliser which means 15% and the usage of fertiliser in 14 g so :
14(15/100) ===> 2.1 grams.

Converting Grams to Moles we get ---> 0.15 moles

We have volume 5 dm3

Now put the values in equation :
Conc : 0.15/ 5 --> 0.03 mol/dm3

I hope you got it :)
Click to expand...
How did u convert grams to moles?
 
Pink Flower

Pink Flower

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RoOkaYya G said:
conc in g per dm^3 = conc in mol * Mr
so conc in mol= conc in g per dm^3 / Mr
Click to expand...
♣♠ Magnanimous ♣♠ said:
We have to find concentration of Nitrogen in that solid

Answer ---> First of all we need to know how we can fine concentration
Conc = moles/volume
Units : Mol/dm3
Moles --> moles
Volume --> dm3

According to the ratio given of that solid material we have 15 gram of N per 100 g of fertiliser which means 15% and the usage of fertiliser in 14 g so :
14(15/100) ===> 2.1 grams.

Converting Grams to Moles we get ---> 0.15 moles

We have volume 5 dm3

Now put the values in equation :
Conc : 0.15/ 5 --> 0.03 mol/dm3

I hope you got it :)
Click to expand...
Thank you!
 
Pink Flower

Pink Flower

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♣♠ Magnanimous ♣♠ said:
Umm,

Mass = Moles * Mass of 1 mole (Molar Mass)
So moles = mass / mass of 1 mole right?
now put values simple :)
Click to expand...
Ohh Thanks!
I did not have a good teacher in my AS....and she did not even touch upon the chapter of moles saying that its easy..and just read from the book...I got a C in my May/June session and I am,pretty much self studying, repeating to get a better grade... Thanks for the help.
♣♠ Magnanimous ♣♠ said:
Thoda achi tarah se samjao
Muje bhi samaj nahi aya usko kya ayega :/ :p
Click to expand...
And there are some days that a mind is blank..........
 
♣♠ Magnanimous ♣♠

♣♠ Magnanimous ♣♠

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Pink Flower said:
Ohh Thanks!
I did not have a good teacher in my AS....and she did not even touch upon the chapter of moles saying that its easy..and just read from the book...I got a C in my May/June session and I am,pretty much self studying, repeating to get a better grade... Thanks for the help.

And there are some days that a mind is blank..........
Click to expand...
You have teaceers, I didn't have teacher of chem :( :(
I did everything myself :)
 
Charlotte20102013

Charlotte20102013

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Metanoia said:
Q3.
Ti+ --> Ti3+ + 2e-

moles of Ti+ : moles of e- : moles of VO3-
0.003 moles : ? : 0.002 moles
3 moles : ? moles : 2 moles

Using the half equation, we can see that 3 moles of Ti+ will transfer 6 moles of electrons to 2 moles of VO3-.

In other words, 1 mole of VO3- gains 3 moles of electrons (its oxidation number would decrease by 3 units).

Original oxidation number of vanadium in VO3- is +5, final oxidation number would then be +2 (since it decreases by 3 units).

Q15.
NH3 is a stronger base than H2O, so we have NH3 accepting protons from H2O

NH3 + H2O <--> NH4+ + OH-

Q23.
Using cold dilute KMnO4, we will add OH to each of the carbons across the C=C double bonds.

Q27.
It should be a tertiary alcohol as it is not oxidized. The carbon holding the OH is expected to be joined to 3 other branches containing different number of carbons.

......C
C2-C-C3
.....OH

Q38. Which option are you unsure of? See if you can google for the mechanism of the reaction.

Q39.
Option 1 is correct
CH3CH2CH2OH (alcohol) can be oxidized to CH3CH2CO2H (acid)
CH3CH2CH2OH (alcohol) and CH3CH2CO2H (acid) can undergo esterifcation to form the desired product.

Option 2 is correct
CH3CH2CHO (aldehyde) can be oxidized to CH3CH2CO2H (acid)
CH3CH2CHO (aldehyde) can be reduced to CH3CH2CH2OH (alcohol)
CH3CH2CH2OH (alcohol) and CH3CH2CO2H (acid) can undergo esterifcation to form the desired product.
Click to expand...

Thank you very much! And I can see that you've prepared videos on the past MCQ questions for us A level students too. Thanks for that also, I'm sure it will help a whole lot of students ! :LOL:
 
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