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Chemistry: Post your doubts here!

daredevil

daredevil

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littlecloud11 said:
No of moles of CO = 96/24 = 4mols
Fe2O3 Mr =160
No of moles of Fe2O3 = 320/160= 2
2 mols Fe2O3 requires 6 moles CO for complete reaction but only 4 moles of CO are present, and is therefore limiting.
So, 3 mols CO = 112 g Fe
4 mols CO =149.3 g Fe (ans)
Click to expand...
thanx :) but 112g of Fe ?? where did that come from?? the Mr?? o_O
 
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Fahrial Alam

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Hi I have a serious problem. umm apparently i need to have some significant AS level chemistry knowledge for my A2s. I tried solving some past papers and i was faced with many AS level questions, which i couldnt answer . Can any1 tell me which AS level chapters i must focus on to giv my A2s?
 
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PhyZac

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Fahrial Alam said:
Hi I have a serious problem. umm apparently i need to have some significant AS level chemistry knowledge for my A2s. I tried solving some past papers and i was faced with many AS level questions, which i couldnt answer . Can any1 tell me which AS level chapters i must focus on to giv my A2s?
Click to expand...
Organic chemistry mostly. Equilibria too i believe !
 
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PhyZac

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Ahmedraza73 said:
Ethanol is much more soluble in water than EthylEthanoate.
Which statement help to account for this?
A: A hydrogen bond forms between the hydrogen of the -OH group in ethanol and the hydrogen of a water molecule.
B: A hydrogen bond forms between the hydrogen of the -OH group in ethanol and the Oxygen of a water molecule.
C: Ethanol is a polar molecule ,but ethylethanoate is non-polar.
D: Ethanol is able to dissocaite into hydrogen ions and ethoxide ions,but ethylethanoate is not able to dissociate

Please some one answer this question Briefly?
Click to expand...
Hydrogen bonding is between H and O
thus B is correct...between H of -Oh and O of water...
800px-Hydrogen-bonding-in-water-2D.png
 
littlecloud11

littlecloud11

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Ahmedraza73 said:
Ethanol is much more soluble in water than EthylEthanoate.
Which statement help to account for this?
A: A hydrogen bond forms between the hydrogen of the -OH group in ethanol and the hydrogen of a water molecule.
B: A hydrogen bond forms between the hydrogen of the -OH group in ethanol and the Oxygen of a water molecule.
C: Ethanol is a polar molecule ,but ethylethanoate is non-polar.
D: Ethanol is able to dissocaite into hydrogen ions and ethoxide ions,but ethylethanoate is not able to dissociate

Please some one answer this question Briefly?
Click to expand...

Ethylehtanoate is non-polar but ethanol is polar, hence it will be more soluble in a polar solvent such as water. This is due to the presence of hydrogen bonds which are formed between the ethanol and water molecules. The hydrogen atom in -OH which is less electronegative compared to oxygen has a partial positive charge and is able to form a hydrogen bond with the oxygen atom of water which has a partial negative charge due to it's high electronegativity and it's lone pair. So, your answer is B.
The answer can't be A because H atom can't have a hydrogen bond with another hydrogen atom as they are both partially positive.
 
daredevil

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littlecloud11 said:
Ethylehtanoate is non-polar but ethanol is polar, hence it will be more soluble in a polar solvent such as water. This is due to the presence of hydrogen bonds which are formed between the ethanol and water molecules. The hydrogen atom in -OH which is less electronegative compared to oxygen has a partial positive charge and is able to form a hydrogen bond with the oxygen atom of water which has a partial negative charge due to it's high electronegativity and it's lone pair. So, your answer is B.
The answer can't be A because H atom can't have a hydrogen bond with another hydrogen atom as they are both partially positive.
Click to expand...
so why is the answer not C?? if ethanol is polar and ethylethanoate non-polar?? o_O :confused:
 
Ahmedraza73

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daredevil said:
so why is the answer not C?? if ethanol is polar and ethylethanoate non-polar?? o_O :confused:
Click to expand...
The question is about :Ethanol is much more soluble in water than EthylEthanoate
So we have to give the answer according to the question tht: why the ethanol is more soluble in water than ehtylehthanoate? hope u understand now :cool:
 
daredevil

daredevil

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Ahmedraza73 said:
The question is about :Ethanol is much more soluble in water than EthylEthanoate
So we have to give the answer according to the question tht: why the ethanol is more soluble in water than ehtylehthanoate? hope u understand now :cool:
Click to expand...
ooo ryt..... its not about IF it is soluble or not.. its about HOW soluble it is.... correct if i'm wrong and thansk
 
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PhyZac

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Soldier313 said:
thanx a lot...

qn:

View attachment 22198


ans:
View attachment 22197
Click to expand...
See,
propene is reacted with bromine and chlorine..
so the formula will be C3H6ClBr
now...what is this molecular formula?
will C3H6 is 42
Cl could be 35 or 37 ( two isotopes of clorine)
Br could be 79 or 81 (isotopes of bromine)

If the "42" combined with the 35Cl and 79Br......the Mr wud be 156
If the "42" combined with the 37Cl and 81Br.....the Mr wud be 160
If the "42" combined with the 35Cl and 81Br OR 37Cl and 79Br..the Mr wud be 158

Now see, YOU have to know these isotopes !! They are found in the application booklet !

And for the second part i rely on guess with logic...! so you have to think of radical broken when spectra is found...and should be less than 20 Mr
if you think of bromo chloro propane...u can see CH3 in the side....it has Mr of 15 !
 
littlecloud11

littlecloud11

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Soldier313 said:
reposting my question.....help pleaseeee....
Click to expand...

When propane was subjected to bromine you would expect electrophilic substitution to occur. Since Cl- ions were present it is more likely that the carbocation would accept the Cl- ion more readily than the Br- ion due to it's higher electronegativity. As a result you would end up with a chloro-bromo substituted propane.
Ok, you know that the M: (M+2) ratio for chlorine is 3:1, you can see that the peaks corresponding to this ratio in the table has a much higher m/e value than you would only expect for chlorine ions. As the M:(M+2) ratio for bromine is 1:1 it does not change the height ratio caused by the chlorine isotope.
So, the m/e values of 156 and 160 are caused by the isotopes of both chlorine and bromine together. Once you've figured this out you have to trial out to see which combination fits the m/e values.
156= C3H6(35Cl)(79Br)
160= C3H6(37Cl)(81Br)
Now, when you notice the height ratio for 156 and 158 it's nearly 1:1, so you know this is due to the bromine isotopes. You already know that the peak at
156 is due to C3H6(35Cl)(79Br) so the peak at 158 must be due to C3H6(35Cl)(81Br).
Now, notice how the peak ratio isn't exact 1:1 this is due to the contamination by the chlorine isotope. C3H6(37Cl)(79Br) also has a m/e value of 158 and is responsible for the slight difference in the ratio.

For the second part the peak is due to CH3+ and them/e value is 15. For any organic molecule CH3 is always a highly abundant specie.
 
iKhaled

iKhaled

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Soldier313 said:
thanx a lot...

qn:

View attachment 22198


ans:
View attachment 22197
Click to expand...
ok this question is testing you if you understand,

1. addition reactions of alkenes
2. the mass spectrometry

we have our molecule propene (CH3CH=CH2). when we add it to a solution of bromine and chlorine addition reaction will occur..now we need to identify what species will be formed and we can do that from the m/e given.

we know that bromine has an isotope of Br-81 and chlorine has an isotope of Cl-37 so now lets see which products will be formed..


the products we can have will be CH3CHBrCH2Cl+ , CH3CHBr^81CH2Cl+ , CH3CHBrCH2Cl^37+ , CH3CHClCH2Cl+ , CH3+,and others....i just hope u got the idea of it. now to identify the species just calculate the Mr of the products and see to which m/e it belongs for example

m/e 156: will be CH3CHBrCH2Cl+ to prove that.. 3(12) + 6 + 79 + 35 = 156
m/e 158 : will be either CH3CHBrCH2Cl^37+ or CH3CHBr^81CH2Cl+ lets count their Mr to prove it 3(12) + 6 + 79 + 37 = 158 or 3(12) + 6 + 81 + 35 = 158
m/e 160: will be CH3CHBr^81CH2Cl^37+ the Mr = 3(12) + 6 + 81 + 37 = 160

The specie which has a Mr of less than 20 will obviously be CH3+..it cant be Cl+ or Br+ or any other ion except that. i am trying my best to make it understandable to you. if you still don't get whats going on just tell me.
 
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