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Published on: 28/05/2021
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Questions + Answers key
Take MCQ Chemistry Test1.
Critical temperatures of N2, CO and CH4 is 126, 134 and 190 K respectively. Arrange them in increasing order of adsorption on the surface of charcoal. Give reason.
2.
Zn rod weighing 25 g was kept in 100 mL of 1M copper sulphate solution. After certain time interval, the molarity of Cu2+ was found to be 0.8 M. What is the molarity of SO42- in the resulting solution and what should be the mass of Zn rod after cleaning and drying ?
3.
Name the reagents you will use to bring about the following conversions.
a. Ethane nitrile to ethanal
b. But-2-ene to ethanal
4.
Why is use of aspartame limited to cold foods and drinks?
5.
Enumerate the reactions of D-glucose which cannot be explained by the open chain structure.
6.
Account for the following :
(a) Chlorine water has both oxidising and bleaching properties.
(b) H 3PO2 and H3PO3 act as good reducing agents while H3PO4 does not.
(c) On addition of ozone gas to KI solution, violet vapours are obtained.
7.
How are octahedral complexes with high spin and low spin states formed? what is the condition of their formation?
8.
While studying the decomposition of N2O5(g), it is observed that a plot of logarithm of its partial pressure versus time is linear. what kinetic parameter can be obtained from this ?
9.
Lithium iodide crystal has a face-centred cubic unit cell.If the edge length of the unit cell is 620pm,determine the ionic radius of I-ion.
10.
What is the arrangement of atoms in the lattice structure of diamond and give contribution of each C atom?
11.
Two liquids A and B boil at 145oC and 190oC respectively. Which of them has higher vapour pressure at 80oC ?
12.
Why copper matte is put in silica lined converter?
1.
N2<CO<Ch4
2.
mass of Zn rod = 23.725 g, molarity of SO42- remains same.
3.
a. Tertiary butyl ketone does not give precipitate with sodium bisulphate whereas acetone does.
b. Dialkyl cadmium is considered superior to grignard reagent for the preparation of a ketone from an acid chloride.
4.
It decomposes at baking or cooking temperatures and hence can be used only in cold foods and drinks.
5.
Open structure of D-glucose could not explain the following reactions:
(i) Despite having the aldehyde group, glucose does not give Schiffs test and 2, 4-DNP test.
(ii) Glucose does not react with sodium hydrogen sulphite to form addition product.
(iii) The pentaacetate of glucose does not react with hydroxyl amine showing the absence of free -CHO group.
(iv) When glucose is heated with methanol in the presence of dry HCI gas, it forms two isomeric monomethyl derivatives known as \(\alpha \)-D-glucoside(m.p. = 165°C) and \(\beta \)-D-glucoside (m.p = 107°C). Since only one molecule of methanol is used for the formation of methyl glucoside, these must be hemiacetals.
These results show that glucose does not have open chain form structure.
6.
(a) In presence of moisture or water, Cl2 gives nascent oxygen which is responsible for its oxidising and bleaching properties as shown below :
Cl2 + H2O ⟶ [HCI + HCIO] ⟶ 2 HCI + \(\underset{Nascent\ \ oxygen}{O}\)
(i) It oxidises acidified ferrous sulphate to ferric sulphate
CI2+ H2O ⟶ 2 HCl + O
\(\underline{2 FeSO_4 + H_2SO_4 +O ⟶ Fe_2(SO_4)_3 + H_2O}\)
2 FeSO4 + H2SO4 + Cl2 ⟶ Fe2(SO4)3 + 2 HCl
(Green) (Brown)
(ii) It bleaches vegetable and organic colouring matter to colourless substances by oxidation.
Cl2 + H2O ⟶ 2 HCI + [0]
Vegetable colouring matter +O ⟶ Oxidised colourless substances.
(b) The structures of H3PO2,·H3PO3 and H3PO4 are:
Due to the presence of P - H bonds, both H3PO2 and H3PO3 act as reducing agents. In contrast, H3PO4 does not have any P - H bonds and hence it does not act as a reducing agent.
(c) 03 is a powerful oxidising agent. Therefore, it oxidises aq. Kl to violet vapours of I2
O3 (g) ⟶ 02 (g) + O(g)
\(\underline{2 Kl (aq) + H_2O (I) + O(g) ⟶ 2 KOH (aq) + I_2(s)}\)__________
2 KI (aq) + H2O (I) + O3 (g) ⟶ 2 KOH (aq) + O2 (g) +I2(s)
potassium iodide Idoine
colourless violet
7.
There are three t2g orbitals with lower energy and two eg orbitals with higher energy. Three electrons with parallel spins can first enter into the lower energy three t2g orbitals, i.e., for complexes with d1. d2 and d3 ion. For d 4, d 5, d6 etc. ions, the electrons can either enter into t2g orbitals and pair up or they may enter into eg orbitals. The former gives rise to low spin complex while the latter gives rise to high spin complex. If crystal field splitting energy (difference of energy between t2g and eg orbitals) is large, low spin state is more stable and if it is small, high spin state is more stable.
8.
For a 1st order reaction, \(k=\frac { 2.303 }{ t } \log { \frac { a }{ a-x } } \)
In terms of pressures, \(a\propto { P }_{ 0 }\) (initial pressure)
\(a-x\propto \)(pressure of \({ N }_{ 2 }{ O }_{ 5 }\) at time t)
\(\therefore \ k=\frac { 2.303 }{ t } \log { \frac { { P }_{ 0 } }{ P } } \) or \(\frac { kt }{ 2.303 } =\log { { P }_{ 0 } } -\log { P } \) or \(\log { P } =\frac { kt }{ 2.303 } +\log { { P }_{ 0 } } \)
Thus, plot of \(\log { P } \) vs. t will be linear if the reaction is of 1st order. Further, from the straight line plot, slope\(=-\frac { kt }{ 2.303 } \) and intercept on \(\log { P } axiz=\log { { P }_{ 0 } } \) . Thus, rate constant k and initial pressure \({ P }_{ 0 }\) can be found.
9.
219.17pm
10.
Diamond is a covalent crystal in which each C-atom is sp3 hybridized.Thus, each C-atom is covalently bonded to four other C-atom tetrahedrally.These tetrahedra are linked together into a three dimensional giant molecule.
The structure of diamond is similar to that o Zns.
In diamond, we have C-atoms in place of Zn2+ and S2- ions.Thus, diamond has face-centred cubic structure in which C-atoms are present at the corners as well as face-centres and alternate tetrahedral voids.
Contribution of C-atoms at the corners = \(8\times{1\over 8}=1\)
Contribution of C-atoms at face-centres = \(6\times{1\over 2}=3\)
As four C-atoms are present on the body diagonals i.e., in the alternate voids, their contribution = 4
Total no. of C-atoms in the unit cell = 1 + 3 + 4 = 8
11.
Liquid A with lower boiling point is more volatile and hence will have higher vapour pressure.
12.
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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