Edexcel CHEMISTRY DOUBTS!!!!

[**RoRo**]

Question 6

N₂  + 3 H₂  ---> 2 NH₃

(1*10^6)/(14+3) = 58823.5 moles of Ammonia.

In a reaction where ALL the Nitrogen reacts this would equate to a need for 29411.8 moles of Nitrogen.

BUT, only 17% of the Nitrogen we put in reacts. Therefore, 83% goes to waste.

We consider the 29411.8 moles of Nitrogen to represent the amount that REACTS i.e. the 17%.

Hence, 0.17*x = 29411.8

Solve for x and you will get the answer you have listed. Use the molar ratio to find the required volume of Hydrogen.

Well, when I solve for x, I get x = 173010.5882 which is the answer that I got earlier, but it's not the same as the answer given, thanks for that, I guess this answer is the right one then, I'll try to meet my teacher soon and confirm with her.

Question 8

The very first question was something along these lines. Apply yourself and think about it. If you cant figure it out I'll help.

I got that, thank you!

Just one more question here,

When 4.0g of ammonium nitrate (NH4NO3) dissolves in 100cm3 of water, the temperature falls by 3.0oC. Calculate the enthalpy change per mole when NH4NO3 dissolves in water under these conditions,

First I find the amount of NH4NO3 used and that's 4/80=0.05 mol
Then I calculate the energy absorbed = m x c x T
Shouldn't m be 104 because it's 100cm3 of water = 100g and 4 g of NH4NO3 so 104g?
My textbook says it should be 100g, why so?
& then I know the rest of the procedure.

[~ Miss Relina ~]

well 1.what is the benedict's solution used for
      2.how to prepare a saturated solution accurately
      3.explain the mean bond enthalpy and distinguissh between ti and the bond enthalpy
Thanks in advance

[The Golden Girl =D]

well 1.what is the benedict's solution used for
      2.how to prepare a saturated solution accurately
      3.explain the mean bond enthalpy and distinguissh between ti and the bond enthalpy
Thanks in advance

1.test for aldehyde and ketone ..... it gives a red ppt for aldehyde and no ppt for ketone

2. Add solute till no more dissolves.

3.don't remember unit 1 -.-

[**RoRo**]

Bond enthalpy of a particular bond is the energy required to break one mole of the bonds in a substance in the gaseous state.
Bond enthalpies are precise values for one kind of bond in different compounds. (e.g. for the C-Cl bond in CH3Cl).
Mean bond enthalpies are average values for one kind of bond in different compounds. (e.g. an average value for the C-Cl bond in all compounds)

[~ Miss Relina ~]

1.test for aldehyde and ketone ..... it gives a red ppt for aldehyde and no ppt for ketone

2. Add solute till no more dissolves.

3.don't remember unit 1 -.-

Thanks

[~ Miss Relina ~]

Bond enthalpy of a particular bond is the energy required to break one mole of the bonds in a substance in the gaseous state.
Bond enthalpies are precise values for one kind of bond in different compounds. (e.g. for the C-Cl bond in CH3Cl).
Mean bond enthalpies are average values for one kind of bond in different compounds. (e.g. an average value for the C-Cl bond in all compounds)

Thanks  

[**RoRo**]

Thanks  

You're welcome!

[**RoRo**]

Another question:

Explain the following statements about oil refining in terms of intermolecular forces.
a) It is possible to separate the hydrocarbons in crude oil into fractions by distillation. [3 marks]
b) Cracking turns a mixture of liquids from crude oil into a mixture of gases. [2 marks]
c) Isomerisation turns straight chain alkanes into alkanes with lower boiling temperatures. [2 marks]

Thank you!

[elemis]

Well, when I solve for x, I get x = 173010.5882 which is the answer that I got earlier, but it's not the same as the answer given, thanks for that, I guess this answer is the right one then, I'll try to meet my teacher soon and confirm with her.

I got that, thank you!

Just one more question here,

Yes, that is the no. of moles of the gas. Now convert to volume.

I've answered it on the previous page.

[**RoRo**]

Yes, that is the no. of moles of the gas. Now convert to volume.

I've answered it on the previous page.

Ahaaa, I got it, thanks a lot and sorry for all the trouble!

[elemis]

Another question:

Explain the following statements about oil refining in terms of intermolecular forces.
a) It is possible to separate the hydrocarbons in crude oil into fractions by distillation. [3 marks]
b) Cracking turns a mixture of liquids from crude oil into a mixture of gases. [2 marks]
c) Isomerisation turns straight chain alkanes into alkanes with lower boiling temperatures. [2 marks]

Thank you!

a) By fractional distillation - yes.
b) Not necessarily. Cracking a long chain alkane may just give you a long change alkene (which is likely to be liquid) and hydrogen, for example.
c) Branched hydrocarbons have weaker van der waals forces of attraction hence lower boiling points.

[**RoRo**]

a) By fractional distillation - yes.
b) Not necessarily. Cracking a long chain alkane may just give you a long change alkene (which is likely to be liquid) and hydrogen, for example.
c) Branched hydrocarbons have weaker van der waals forces of attraction hence lower boiling points.

mmm, what points should be mentioned for part a) to gain the 3 marks?

b) The question says explain the statement in terms of IMF, so how would you answer that?



&&&&
another question, do we need to study the procedure, the equations and the calculations method for the iodine-thiosulfate titrations like
-Finding the purity of potassium Iodate (V)
-Finding the % of Copper in Brass
-Finding the concentration of domestic bleach

[Master_Key]

mmm, what points should be mentioned for part a) to gain the 3 marks?

b) The question says explain the statement in terms of IMF, so how would you answer that?



&&&&
another question, do we need to study the procedure, the equations and the calculations method for the iodine-thiosulfate titrations like
-Finding the purity of potassium Iodate (V)
-Finding the % of Copper in Brass
-Finding the concentration of domestic bleach

I think in iodine-thiosulfate titration you need to calculate the molarity of one of the reactants.

S₂O₈^2- = 2I^-

1:1 Ratio.

1 Mole : 1 Mole

n=cv.

[Mike Benn]

Hey guys..can anyone tell me that How Instantaneous Dipole is produced..?...like how it rises up..?

[SkyPilotage]

Hey guys..can anyone tell me that How Instantaneous Dipole is produced..?...like how it rises up..?

due to the electrons moving around in 3-dimensions..it induces charges on other particles or molecules but its very weak compared to permanent dipoles..