Edexcel CHEMISTRY DOUBTS!!!!

[**RoRo**]

I think shorter chain fuels are more useful. The branch can then be explained that when cracking these branched chain alkanes/alkenes they give useful product. The latter is correct. Your concept of intermolecular force is correct.

Gasoline(4-8 Carbon atoms).

I'm sorry, I didn't get your point!

Shorter chains are more useful, as in they're more in demand, yes, I agree - that wasn't related to my question though!

"The branch can then be explained that when cracking these branched chain alkanes/alkenes they give useful product." - What do you mean by this sentence?

The question compares more the difference between a straight-chain molecule and a branched molecule in terms of their efficiency as fuels.

Thanks for trying though, if you can help elaborate any further on your point, that would be great! xD

[Master_Key]

I'm sorry, I didn't get your point!

Shorter chains are more useful, as in they're more in demand, yes, I agree - that wasn't related to my question though!

"The branch can then be explained that when cracking these branched chain alkanes/alkenes they give useful product." - What do you mean by this sentence?

The question compares more the difference between a straight-chain molecule and a branched molecule in terms of their efficiency as fuels.

Thanks for trying though, if you can help elaborate any further on your point, that would be great! xD

Okay then dont consider length of fuels. Branched chain fuels have lower intermolecular forces as you said and if used directly then they are liquids or gases. Enthalpy change of combustion will differ. When they are cracked (heating over hot pumice(Al2O3)) to produce shorter chain alkanes then too they are more efficient and produce suitable alkanes.

[EMO123]

Okay then dont consider length of fuels. Branched chain fuels have lower intermolecular forces as you said and if used directly then they are liquids or gases. Enthalpy change of combustion will differ. When they are cracked (heating over hot pumice(Al2O3)) to produce shorter chain alkanes then too they are more efficient and produce suitable alkanes.

thanx man for me also it is damm worthy

[~ 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

hello there anyone

[~ Miss Relina ~]

the image attached is used to reflux organic compound and we must find two mistakes in the diagram.
In the marking scheme, they havent mentioned anything about the flask being sealed which will lead to pressure build up.
So, if I mention this point in the exam- will it be wrong?

This from June 2011 Unit6b Q4biii

is it June 2011
 post the whole question plz

[~ Miss Relina ~]

the image attached is used to reflux organic compound and we must find two mistakes in the diagram.
In the marking scheme, they havent mentioned anything about the flask being sealed which will lead to pressure build up.
So, if I mention this point in the exam- will it be wrong?

This from June 2011 Unit6b Q4biii

well ithink it should not be sealed because its heating under reflux

[Vampire-Love4ever]

well ithink it should not be sealed because its heating under reflux

Thats what I thought too but the marking scheme doesnt mention it! :/

[NidZ- Hero]

Thats what I thought too but the marking scheme doesnt mention it! :/

R3ad this http://www.rod.beavon.clara.net/reflux.htm

[NidZ- Hero]

Can some tell me the obeservation of the reaction when halide reacts with conc H2SO4

[elemis]

Can some tell me the obeservation of the reaction when halide reacts with conc H2SO4

Depends on the halide ion in the reagent. If its a chloride you would see white fumes of Hydrogen Chloride.

If its Bromide you would see the brown vapour of Bromine and fumes of HBr.

An Iodide would react to give the stinking smell of Hydrogen Sulphide and you would see the purple vapour of I2.

[red_911]

when do we use starch as an indicator n what is sodium thiosulfate ? 

[EMO123]

when do we use starch as an indicator n what is sodium thiosulfate ? 

on adding Iodine to the starch it changes the color to black this shows starch is present in that

and what is sodium thiosulfate is given in the site bellow
http://en.wikipedia.org/wiki/Sodium_thiosulfate

[**RoRo**]

Guys, I still need help in the following questions please that I posted here earlier, can any one help?

3. When 8.4g of sodium hydrogen carbonate are heated 5.30g of solid residue and 1200 cm3 of carbon dioxide are produced and 0.900g of water are evolved. Show that this data is consistent with the following equation.
2NaHCO3 -----> Na2CO3 + CO2 + H2O

How do you prove that?

4. Sulphur dioxide can be removed from the waste gases of a power station by passing it through a slurry of calcium hydroxide. The equation for this reaction is:
SO2(g) + Ca(OH)2(aq)  -----> CaSO3(aq) + H2O(l)
What mass of calcium hydroxide would be needed to deal with 1000dm3 of sulphur dioxide?

I'm getting the answer as 3087.5g, but the answer is supposed to be 324.3 [I'm not sure though, because I copied it down from someone] so can someone please confirm?

5. Chlorine reacts with sodium hydroxide as follows:
Cl2(g) + 6NaOH(aq) -----> 5NaCl(aq) + NaClO3(aq) + 3H2O(l)
What mass of sodium chloride and what mass of sodium(V)chlorate would be produced from 240 cm3 of chlorine gas?
The mass of NaClO3 is 1.065, but for the mass of NaCl, I'm getting it as 2.925g when also in the paper, I copied it as 2.94g, so which one is right and if it's 2.94, how do you arrive to such an answer?

6. When nitrogen reacts with hydrogen in the Haber process only 17% of the nitrogen is converted to ammonia. What volume of nitrogen and what volume of hydrogen would be needed to produce one tonne of ammonia? (1 tonne = 1 x 106 g)

The answer is supposed to be 4.15x106 dm3 of N2 and 12.5x106 dm3 of H2 & I don't know how to arrive to either of the answers!

7. Nitric acid is produced by the following series of reactions:
4NH3     +    5O2                     ----> 4NO      +   3H2O
4NO       +     O2                     ----> 4NO2
4NO2     +    O2     + 2H2O      ----> 4HNO3
What mass of nitric acid would be produced from 17 tonnes of ammonia and what volume of oxygen would be needed in the reaction?
I got the mass right, it's 63 tonnes, but for the volume I'm getting it as 3.05x107dm3 when it's supposed to be 4.8x107dm3!

8. 25cm3 of a solution of an acid HxA containing 0.1 mol dm-3 of the acid in each 1000cm3 of solution reacts with 75cm3 of a solution of 0.1 mol dm-3 NaOH. What is the value of x?
The answer is x=3, I solved this question till I reached to the part where 1 mole of HxA reacts with 3 moles of NaOH, but I don't know how do you decide that x=3?

& now another question:
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.

Thank you!

[elemis]

& now another question:
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.

Thank you!

You ignore the mass of Ammonium Nitrate since you are measure the temperature change of the water.... not the Ammonium Nitrate.

[elemis]

Question 3

Calculate the no. of moles of each quantity as per the data. Check to see if they are consistent with the molar ratio of all the chemicals in the equation.

Question 4

Your answer seems to be correct.

Question 5

Your answer for the mass of NaCl is correct.

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.

Question 7

I seem to be getting the same answer as you.

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.