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Published on: 28/05/2021
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Questions + Answers key
Take MCQ Chemistry Test1.
Enumerate two reactions of glucose which cannot be explained by its open chain structure.
2.
Arreange the following in order of increasing boiling. State reason
CH3CH2CH2OH, CH3CH2CH2CH3, CH3CH2OCH2CH3, CH3CH2CH2CHO
3.
(a) You have the following substances : NH3, O2, Pt and H2O. Write equations for the preparation of N2O from these substances.
(b) Considering the fact that N2 makes up about 79% of the atmosphere, why don't animals use the more abundant N2 instead of O2 for biological reactions.
4.
Write the elementary steps of the reaction 2O3 \(\rightleftharpoons \) 3O2 and hence derive the rate law expression for this reaction. Comment on the order of reaction.
5.
Addition of H2 to acetylene gives ethane in presence of palladium but if BaSO4 and quinoline or sulphur are also added, the product is ethane. Why ?
6.
Lithium borohydride,LiBH4,crystallize in an orthorhombic system with 4 molecules per unit cell.The unit cell dimensions are: a=6.81\(\overset { 0 }{ A } \) ,b=4.43\(\overset{0}{A}\) and c=7.17\(\overset{0}{A}\).Calculate the density of the crystal.Take atomic mass of Li=7,B=11 and H=1 a.m.u.
7.
Why copper matte is put in silica lined converter?
1.
(i) Glucose does not give Schiff‘s Test although it contains aldehyde group.
(ii) Glucose does not form crystaline product with NaHSO3.
2.
CH3CH2CH2CH3 < C2H5OC2H5 < CH3CH2CH2CHO < CH3 (CH2 )2OH
\((hydrocarbon)\overset { (ether) }{ \underset { increase\quad in\quad bond\quad polarity }{ \longrightarrow } } (aldehyde)(alcohol)\).
3.
(a)
\(4N{ H }_{ 3 }\left( g \right) +5{ O }_{ 2 }\left( g \right) \xrightarrow [ 1100K ]{ Pt } 4NO\left( g \right) +6{ H }_{ 2 }O\left( l \right) ;\ 2NO\left( g \right) +{ O }_{ 2 }\left( g \right) \longrightarrow 2{ NO }_{ 2 }\left( g \right) \)
\(\\ 3{ NO }_{ 2 }\left( g \right) +{ H }_{ 2 }O\left( l \right) \longrightarrow 2HN{ O }_{ 3 }\left( aq \right) +NO\left( g \right) ;\ { NH }_{ 3 }\left( g \right) +HN{ O }_{ 3 }\left( aq \right) \longrightarrow { NH }_{ 4 }{ NO }_{ 3 }\left( aq \right) \)
\(\\ { NH }_{ 4 }{ NO }_{ 3 }\left( aq \right) \xrightarrow [ at\ room\quad temperature ]{ Vacuum\ evaporation } { NH }_{ 4 }{ NO }_{ 3 }\left( s \right) ;\ { NH }_{ 4 }{ NO }_{ 3 }\left( s \right) \xrightarrow { 523K } { N }_{ 2 }O\left( g \right) +2{ H }_{ 2 }O\left( l \right) \)
(b) Animals need large amount of energy to move around and maintain the body temperature. Therefore, to obtain the required energy, it is much easier for them to break weaker double bond (493-4 kJ \({mol }^{ -1 }\) ) of \({ O }_{ 2 }\) than breaking the much stronger triple bond (941·4 kJ \({ mol}^{ -1 }\) ) of \({ N }_{ 2 }.\)
4.
\(Step \ 1.{ O }_{ 3 }\rightleftharpoons { O }_{ 2 }+O\quad (fast)\quad \quad \quad ..(i)\)
\(Step \ 2.O+{ O }_{ 3 }\longrightarrow 2{ O }_{ 2 }\quad (slow)\quad \quad \quad...(ii)\)
\(From \ slow \ step, \ Rate \ = \ k\left[ { O }_{ 3 } \right] \left[ O \right] \ \ \ \ \ \ \ \ \ \ \ \ \ ...(iii)\)
\(From \ eqn. \ (i), \ { K }_{ eqm. }=\frac { \left[ { O }_{ 2 } \right] \left[ O \right] }{ \left[ { O }_{ 3 } \right] } or \ \left[ O \right] ={ K }_{ eqm. }\frac { \left[ { O }_{ 3 } \right] }{ \left[ { O }_{ 2 } \right] } \)
Substituting this value in eqn. (iii), we get
\(Rate=k\left[ { O }_{ 3 } \right] \times { K }_{ eqm. }{ \left[ { O }_{ 3 } \right] }/{ \left[ { O }_{ 2 } \right] }=k\prime { \left[ { O }_{ 3 } \right] }^{ 2 }{ \left[ { O }_{ 2 } \right] }^{ -1 }\)
Thus, order w.r.t \({ O }_{ 2 }\) = -1
5.
\(CH=CH+{ H }_{ 2 }\underrightarrow { Pd } { CH }_{ 2 }={ CH }_{ 2 }\overset { { +H }_{ 2 } }{ \underset { Pd }{ \rightarrow } } { CH }_{ 3 }\_ { CH }_{ 3 }\)
\(\\ \quad \quad Acetylene\quad \quad \quad \quad \quad \quad Ethane\quad Ethane\)
\(\\ CH=CH+{ H }_{ 2 }\overset { Pd+Ba{ SO }_{ 4 } }{ \underset { +quinoline/S }{ \longrightarrow } } { CH }_{ 2 }={ CH }_{ 2 }\)
Ethane
BaSO4 + quinoline/S poison the catalyst. Hence, the efficiency of the catalyst decreases and the reaction stops at the first stage of reduction.
6.
0.676g cm-3
7.
Copper matte chiefly consists of Cu2S along with some unchanged FeS. When a blast of hot air is passed through molten matte taken in a silica lined converter, FeS present in matte is oxidised to FeO which combines with silica (SiO2) to form FeSiO3 slag.
\(2FeS+3{ O }_{ 2 }\longrightarrow 2FeO+2S{ O }_{ 2 }\uparrow \quad ;\quad FeO+\underset { Silica }{ Si{ O }_{ 2 } } \longrightarrow \underset { Slag }{ FeSi{ O }_{ 3 } } \)
When whole of iron has been removed as slag, some of the CU2S undergoes oxidation to form Cu 2O which then reacts with more Cu2S to form copper metal.
\(2{ Cu }_{ 2 }S+3{ O }_{ 2 }\longrightarrow 2{ Cu }_{ 2 }S+2S{ O }_{ 2 }\uparrow \quad ;\quad 2{ Cu }_{ 2 }O+{ Cu }_{ 2 }S\longrightarrow 6Cu+2S{ O }_{ 2 }\uparrow \)
Thus, copper matte is heated in silica lined converter to remove FeS present in matte as FeSiO3 slap.
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