chemistry p22 help!!

[paparazzi]

07/on b)ii)
(ii) Draw sketches to show orbital overlap that produces the σ bonding in the H2 and HCl molecules.

thx!!

 

[beacon_of_light]

in H2...two S orbitals will overlap...show that by two round or roughly spherical circles have an overlapping region linearly...
In HCl ..one s orbital of H and one p orbital of Cl will overlap...p orbital has a dumbbell shape...

In both sigma bond is formed...so it is important to show linear overlapp....

 

[paparazzi]

u r very nice.
thank u so much.

 

[paparazzi]

08 october
q5.An organic ester, B, has the empirical formula C2H4O. An experiment by a student in a college gave a value of 87.5 for Mr of B.
(b)In the boxes below, draw the structural formulae of four isomers of B that are esters.

The student hydrolysed his sample of B by heating with aqueous mineral acid and then separating the alcohol, C, that was formed. He heated the alcohol C under reflux with acidified dichromate(VI) ions and collected the product D.
A sample of D gave an orange precipitate with 2,4-dinitrophenylhydrazine reagent. A second sample of D gave no reaction with Tollens’ reagent.

(c) (iii) What is the structural formula of the alcohol C?
(iv) Which of your esters, W, X, Y, or Z has the same structure as that of the ester B?



i really confused abt this kind of qs. can sum1 tell me how 2 do this. plzz.
thank u very much!!

 

[paparazzi]

02 may june

2.Ethanol, C2H5OH, is a most important industrial chemical and is used as a solvent, a fuel and an intermediate in large scale organic synthesis.
Ethanol is prepared industrially by the reaction of ethene and steam in the presence of a catalyst.
C2H4(g) + H2O(g) → C2H5OH(g)
The standard enthalpy change of the reaction can be determined by using the standard enthalpy changes of combustion, ∆Hc, at 298 K.
∆Hc / kJ mol–1
C2H4(g) –1411
C2H5OH(l) –1367

(a) Calculate the standard enthalpy change for the following reaction. C2H4(g) + H2O(l) → C2H5OH(l)


i dont know when use the enthalpy change of forward reaction minus reverse reaction.
or usehe enthalpy change of reverse reaction minus forward reaction.

 

[paparazzi]

4 Sulphuric acid is used in many industrial processes of major importance. The first stage in the manufacture of sulphuric acid is to pass air over burning sulphur.
The emerging gas has the following composition by volume.

sulphur dioxide 10%
sulphur trioxide 0.2%
oxygen 10%
nitrogen etc. 79–80%

ii）Suggest why the air is passed so fast that only half the oxygen is used.

 

[intel1993]

4 Sulphuric acid is used in many industrial processes of major importance. The first stage in the manufacture of sulphuric acid is to pass air over burning sulphur.
The emerging gas has the following composition by volume.

sulphur dioxide 10%
sulphur trioxide 0.2%
oxygen 10%
nitrogen etc. 79–80%

ii）Suggest why the air is passed so fast that only half the oxygen is used.

this is because other half of the oxygen is used for contact stage........(if oxygen used in excess so3 will be produced in the same reaction)

 

[paparazzi]

to:intel1993

thank u so much!!

 

[intel1993]

no problem...the enthalaphy change question is easy bt i think so i wud not be able to explain that here so.....thats why donot answer it./.......if u have any more problems u can ask....>>>

 

[noora]

02 may june

2.Ethanol, C2H5OH, is a most important industrial chemical and is used as a solvent, a fuel and an intermediate in large scale organic synthesis.
Ethanol is prepared industrially by the reaction of ethene and steam in the presence of a catalyst.
C2H4(g) + H2O(g) → C2H5OH(g)
The standard enthalpy change of the reaction can be determined by using the standard enthalpy changes of combustion, ∆Hc, at 298 K.
∆Hc / kJ mol–1
C2H4(g) –1411
C2H5OH(l) –1367

(a) Calculate the standard enthalpy change for the following reaction. C2H4(g) + H2O(l) → C2H5OH(l)


i dont know when use the enthalpy change of forward reaction minus reverse reaction.
or usehe enthalpy change of reverse reaction minus forward reaction.

delta of combustion is given to us so we gona use it to calculate h2
Hcom =H1+H2
-1367-[-1411]=-44kjmol

 

[noora]

08 october
q5.An organic ester, B, has the empirical formula C2H4O. An experiment by a student in a college gave a value of 87.5 for Mr of B.
(b)In the boxes below, draw the structural formulae of four isomers of B that are esters.

The student hydrolysed his sample of B by heating with aqueous mineral acid and then separating the alcohol, C, that was formed. He heated the alcohol C under reflux with acidified dichromate(VI) ions and collected the product D.
A sample of D gave an orange precipitate with 2,4-dinitrophenylhydrazine reagent. A second sample of D gave no reaction with Tollens’ reagent.

(c) (iii) What is the structural formula of the alcohol C?
(iv) Which of your esters, W, X, Y, or Z has the same structure as that of the ester B?



i really confused abt this kind of qs. can sum1 tell me how 2 do this. plzz.

in first part find da molecular formula of B C4H8O2 . in second part change the places of co2 put in da middle ,first ,last and so on like
HCO2CH2CH2CH3 2. CH3CO2CH2CH3 3. CH3CH2CH2CO2 . and last one make a tertiary branching .
part c da sample was hydrolysed means it break into its intial product alcohol and carboxylic acid .he separated da alcohol and oxidation by potassium dichromate both aldehyde and ketone contain carbonyl group so they gav orang ppt with 2,4 DNPH but only aldehyde show positive test with tollens
primary alcohol oxidized gave us aldehyde
secondary alcohol gav ketone
and in last part look in da isomerism of ester that can gav u ester b and da chiral center is da carbon where four different atoms or groups attach look for it hope dat help just rember me in ur prayers

 

[paparazzi]

02 may june

2.Ethanol, C2H5OH, is a most important industrial chemical and is used as a solvent, a fuel and an intermediate in large scale organic synthesis.
Ethanol is prepared industrially by the reaction of ethene and steam in the presence of a catalyst.
C2H4(g) + H2O(g) → C2H5OH(g)
The standard enthalpy change of the reaction can be determined by using the standard enthalpy changes of combustion, ∆Hc, at 298 K.
∆Hc / kJ mol–1
C2H4(g) –1411
C2H5OH(l) –1367

(a) Calculate the standard enthalpy change for the following reaction. C2H4(g) + H2O(l) → C2H5OH(l)


i dont know when use the enthalpy change of forward reaction minus reverse reaction.
or usehe enthalpy change of reverse reaction minus forward reaction.

delta of combustion is given to us so we gona use it to calculate h2
Hcom =H1+H2
-1367-[-1411]=-44kjmol

In this way the answer is = +44 -1367--1411means -1367+1411=+44

 

[paparazzi]

08 october
q5.An organic ester, B, has the empirical formula C2H4O. An experiment by a student in a college gave a value of 87.5 for Mr of B.
(b)In the boxes below, draw the structural formulae of four isomers of B that are esters.

The student hydrolysed his sample of B by heating with aqueous mineral acid and then separating the alcohol, C, that was formed. He heated the alcohol C under reflux with acidified dichromate(VI) ions and collected the product D.
A sample of D gave an orange precipitate with 2,4-dinitrophenylhydrazine reagent. A second sample of D gave no reaction with Tollens’ reagent.

(c) (iii) What is the structural formula of the alcohol C?
(iv) Which of your esters, W, X, Y, or Z has the same structure as that of the ester B?



i really confused abt this kind of qs. can sum1 tell me how 2 do this. plzz.

in first part find da molecular formula of B C4H8O2 . in second part change the places of co2 put in da middle ,first ,last and so on like
HCO2CH2CH2CH3 2. CH3CO2CH2CH3 3. CH3CH2CH2CO2 . and last one make a tertiary branching .
part c da sample was hydrolysed means it break into its intial product alcohol and carboxylic acid .he separated da alcohol and oxidation by potassium dichromate both aldehyde and ketone contain carbonyl group so they gav orang ppt with 2,4 DNPH but only aldehyde show positive test with tollens
primary alcohol oxidized gave us aldehyde
secondary alcohol gav ketone
and in last part look in da isomerism of ester that can gav u ester b and da chiral center is da carbon where four different atoms or groups attach look for it hope dat help just rember me in ur prayers

i really appreciate it.but i think the structural formula of the alcohol c is CH3CH2OH.
cuz CH3COOH+ CH3CH2OH----------CH3COOCH2CH3 (which is exactly C4H8O2)+H2O ???//

AND why HCO2CH(CH3)2 has the same structure as that of ester B.
How do i know this?????/

 

[CrystalCorpse]

noora wrote:
paparazzi wrote:
08 october
q5.An organic ester, B, has the empirical formula C2H4O. An experiment by a student in a college gave a value of 87.5 for Mr of B.
(b)In the boxes below, draw the structural formulae of four isomers of B that are esters.

The student hydrolysed his sample of B by heating with aqueous mineral acid and then separating the alcohol, C, that was formed. He heated the alcohol C under reflux with acidified dichromate(VI) ions and collected the product D.
A sample of D gave an orange precipitate with 2,4-dinitrophenylhydrazine reagent. A second sample of D gave no reaction with Tollens’ reagent.

(c) (iii) What is the structural formula of the alcohol C?
(iv) Which of your esters, W, X, Y, or Z has the same structure as that of the ester B?



i really confused abt this kind of qs. can sum1 tell me how 2 do this. plzz.

in first part find da molecular formula of B C4H8O2 . in second part change the places of co2 put in da middle ,first ,last and so on like
HCO2CH2CH2CH3 2. CH3CO2CH2CH3 3. CH3CH2CH2CO2 . and last one make a tertiary branching .
part c da sample was hydrolysed means it break into its intial product alcohol and carboxylic acid .he separated da alcohol and oxidation by potassium dichromate both aldehyde and ketone contain carbonyl group so they gav orang ppt with 2,4 DNPH but only aldehyde show positive test with tollens
primary alcohol oxidized gave us aldehyde
secondary alcohol gav ketone
and in last part look in da isomerism of ester that can gav u ester b and da chiral center is da carbon where four different atoms or groups attach look for it hope dat help just rember me in ur prayers




i really appreciate it.but i think the structural formula of the alcohol c is CH3CH2OH.
cuz CH3COOH+ CH3CH2OH----------CH3COOCH2CH3 (which is exactly C4H8O2)+H2O ???//

AND why HCO2CH(CH3)2 has the same structure as that of ester B.
How do i know this?????/

no, the structural formula of the alcohol is CH(CH3)2OH....thats because this is the secondary alcohol and ketones(which is the compound D here) are formed from secondary alcohol only.....and also to get this structure from ester B, the structure of B has to be HCO2CH(CH3)2

 

[ShudyShab]

Please help me with this question. it is from May?june 2002 Paper 2 question 4c


After each condition explain why this leads to an increased yield of sulphur trioxide.

(i) The catalyst needs to be cooled

(ii) The air used to burn the sulphur must be as clean as possible

 

[DragonCub]

Please help me with this question. it is from May?june 2002 Paper 2 question 4c


After each condition explain why this leads to an increased yield of sulphur trioxide.

(i) The catalyst needs to be cooled

(ii) The air used to burn the sulphur must be as clean as possible

To (i), the delta H is -ve, meaning that the forward reaction is exothermic, i.e. from SO2 + O2 to SO3, heat is given out, raising the temperature of the surroundings. So to favour the forward reaction (i.e. move the equilibrium more towards the products), according to Le Chartlier's Principle, the temperature should be decreased. That can be resulted from cooling the catalyst.

To (ii), the purer the oxygen, the more concentrated it is in the reaction. Again by the Principle, forward reaction is favoured and yield is increased.

 

[aquariangurl]

Please help me with this question. it is from May?june 2002 Paper 2 question 4c


After each condition explain why this leads to an increased yield of sulphur trioxide.

(i) The catalyst needs to be cooled

(ii) The air used to burn the sulphur must be as clean as possible

To (i), the delta H is -ve, meaning that the forward reaction is exothermic, i.e. from SO2 + O2 to SO3, heat is given out, raising the temperature of the surroundings. So to favour the forward reaction (i.e. move the equilibrium more towards the products), according to Le Chartlier's Principle, the temperature should be decreased. That can be resulted from cooling the catalyst.

To (ii), the purer the oxygen, the more concentrated it is in the reaction. Again by the Principle, forward reaction is favoured and yield is increased.

Nah, for the second, the most appropriate answer could be that impure air poisons the catalyst thus decreasing the rate of reaction..thats what our teacher told us.

 

[workinghard]

aquariangurl is rite here
it is 2 avoid poisoning of catalyst!

 

[ShudyShab]

Thank You so Much!!

 

[ShudyShab]

Hi This question from October/November 2010 is something I just can't understand.

Q1:

Davy and Faraday deduced the formula of A by exploding it with an excess of oxygen and
analysing the products of combustion.
(b) Complete and balance the following equation for the complete combustion of a
hydrocarbon with the formula CxHy.
CxHy + (x +y/4)O2 ------> ................................ + ................................

(c) When 10 cm3 of A was mixed at room temperature with 50 cm3 of oxygen (an excess)
and exploded, 40 cm3 of gas remained after cooling the apparatus to room temperature
and pressure.
When this 40 cm3 of gas was shaken with an excess of aqueous potassium hydroxide,
KOH, 30 cm3 of gas still remained.
(i) What is the identity of the 30 cm3 of gas that remained at the end of the
experiment?

(ii) The combustion of A produced a gas that reacted with the KOH(aq).
What is the identity of this gas?

(iii) What volume of the gas you have identified in (ii) was produced by the combustion
of A?

(iv) What volume of oxygen was used up in the combustion of A?


Please Please Help me out with this question