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Chemistry: Post your doubts here!

A

Aishayasin

Messages
42
Reaction score
6
Points
18
25 If the starting material is iodoethane, which sequence of reactions will produce propanoic acid as
the main final product in good yield?
A add NaOH(aq), isolate the organic product, add acidified K2Cr2O7 and boil under reflux
B add NaOH(aq), isolate the organic product, add H2SO4(aq) and boil under reflux
C heat with HCN in ethanol, isolate the organic product, add H2SO4(aq) and boil under reflux
D heat with KCN in ethanol, isolate the organic product, add H2SO4(aq) and boil under reflux

the answer is D can anyone explain me why not C
 
Last edited:
qwertypoiu

qwertypoiu

Messages
924
Reaction score
1,096
Points
153
Aishayasin said:
25 If the starting material is iodoethane, which sequence of reactions will produce propanoic acid as
the main final product in good yield?
A add NaOH(aq), isolate the organic product, add acidified K2Cr2O7 and boil under reflux
B add NaOH(aq), isolate the organic product, add H2SO4(aq) and boil under reflux
C heat with HCN in ethanol, isolate the organic product, add H2SO4(aq) and boil under reflux
D heat with KCN in ethanol, isolate the organic product, add H2SO4(aq) and boil under reflux

the answer is D can anyone explain me why not C
Click to expand...
HCN is the reagent used to form hydroxynitriles from carbonyl compounds (aledehyde and ketone).
When attempting to form nitriles from HALOGENOLAKES, you should use KCN.
 
Eugene99

Eugene99

Messages
340
Reaction score
339
Points
73
Aishayasin said:
25 If the starting material is iodoethane, which sequence of reactions will produce propanoic acid as
the main final product in good yield?
A add NaOH(aq), isolate the organic product, add acidified K2Cr2O7 and boil under reflux
B add NaOH(aq), isolate the organic product, add H2SO4(aq) and boil under reflux
C heat with HCN in ethanol, isolate the organic product, add H2SO4(aq) and boil under reflux
D heat with KCN in ethanol, isolate the organic product, add H2SO4(aq) and boil under reflux

the answer is D can anyone explain me why not C
Click to expand...

It's KCN that undergoes nucleophilic substitution with halogenalkanes to form propanenitrile which is then reduced with H2SO4 to form propanoic acid.
HCN, on the other hand, only reacts with aldehydes and ketones. It's not used in reactions with halogenalkanes
 
A

Aishayasin

Messages
42
Reaction score
6
Points
18
Use of the Data Booklet is relevant to this question.
The compound S2O7 is hydrolysed by water to produce sulfuric acid and oxygen only.
Which volume of oxygen, measured at room temperature and pressure, is evolved when 0.352 g
of S2O7 is hydrolysed?
A 12 cm3 B 24 cm3 C 48 cm3 D 96 cm3
answer is b how
 
qwertypoiu

qwertypoiu

Messages
924
Reaction score
1,096
Points
153
Aishayasin said:
Use of the Data Booklet is relevant to this question.
The compound S2O7 is hydrolysed by water to produce sulfuric acid and oxygen only.
Which volume of oxygen, measured at room temperature and pressure, is evolved when 0.352 g
of S2O7 is hydrolysed?
A 12 cm3 B 24 cm3 C 48 cm3 D 96 cm3
answer is b how
Click to expand...
S2O7 + 2H2O ----> 2H2SO4 + (1/2)O2

Moles of S2O7 = 0.352g / Mr = 0.001998mol
Moles of O2 evolved = 1/2 * Ans = 0.0009989mol
Volume = 24,000 * Ans = 24
 
A

Aishayasin

Messages
42
Reaction score
6
Points
18
A mixture of nitrogen and hydrogen gases, at a temperature of 500 K, was put into an evacuated
vessel of volume 6.0 dm3. The vessel was then sealed.
N2(g) + 3H2(g) 2NH3(g)
The mixture was allowed to reach equilibrium. It was found that 7.2 mol of N2 and 12.0 mol of H2
were present in the equilibrium mixture. The value of the equilibrium constant, Kc, for this
equilibrium is 6.0 × 10–2 at 500 K.
What is the concentration of ammonia present in the equilibrium mixture at 500 K?
A 0.58 mol dm–3
B 0.76 mol dm–3
C 3.5 mol dm–3
D 27 mol dm–3
answer is b
 
cute97

cute97

Messages
105
Reaction score
222
Points
53
Aishayasin said:
A mixture of nitrogen and hydrogen gases, at a temperature of 500 K, was put into an evacuated
vessel of volume 6.0 dm3. The vessel was then sealed.
N2(g) + 3H2(g) 2NH3(g)
The mixture was allowed to reach equilibrium. It was found that 7.2 mol of N2 and 12.0 mol of H2
were present in the equilibrium mixture. The value of the equilibrium constant, Kc, for this
equilibrium is 6.0 × 10–2 at 500 K.
What is the concentration of ammonia present in the equilibrium mixture at 500 K?
A 0.58 mol dm–3
B 0.76 mol dm–3
C 3.5 mol dm–3
D 27 mol dm–3
answer is b
Click to expand...
N2(g) + 3H2(g) 2NH3(g)
N2 = 7.2g/6dm3 = 1.2 mol/dm3
H2 = 12g/6dm3 = 2 mol/dm3

Kc= (NH3)^2/((H2)^3*(N2))
6*10^-2= x^2/ (2^3* 1.2)
x=0758=0.76 which is B
 
A

Aishayasin

Messages
42
Reaction score
6
Points
18
Ammonia is made by the Haber process. The reactants are nitrogen and hydrogen.
N2(g) + 3H2(g) 2NH3(g) ΔH –ve
What will increase the rate of the forward reaction?
A adding argon to the mixture but keeping the total volume constant
B decreasing the temperature
C increasing the total pressure by reducing the total volume at constant temperature
D removing ammonia as it is made but keeping the total volume of the mixture the same
the answer is c why not b
 
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