Chapter
10
The s-Block Elements Solutions SECTION - A Objective Type Questions 1.
The correct increasing order of densities of alkali metals is (1) Li < Na < K < Rb < Cs
(2)
Cs < Rb < K < Na < Li
(3) Li < K < Na < Rb < Cs
(4)
K < Na < Li < Rb < Cs
Sol. Answer (3) Density =
Mass Volume
The anomaly is in the densities of K and Na. This is because as we move from Na to K the mass is increased but volume has increased unusually more. So, the volume of K is lower than Na. 2.
Which one of the following alkali metals is the most metallic? (1) Li
(2)
Na
(3)
K
(4)
Cs
Sol. Answer (4) Due to increase in size down the group. The ionisation enthalpy decreases and hence the metallic character increases. 3.
The metallic lusture exhibited by sodium is due to (1) Diffusion of Na+ ions (2) Oscillation of loose electrons (3) Excitation of free protons (4) Existence of body centred cubic lattice
Sol. Answer (2) Due to oscillations of loose electrons, energy is emitted during transition which corresponds to a specific wavelength that is responsible for its appearance. When light falls on metals such as sodium, the free electrons oscillate at their mean position and get excited to higher levels. On returning back to lower levels, they emit light (energy). Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
22 4.
The s-Block Elements
Solution of Assignment (Set-2)
Which one of the following ions has the largest size in aqueous solution? (1) Rb+
(2)
Na+
(3)
K+
(4)
Li+
Sol. Answer (4) Smaller the ion more is the extent of hydration. The hydration enthalpies of alkali metal ions decrease with increase in ionic size Li+ > Na+ > K+ > Rb+ > Cs+ Li+ has the maximum degree of hydration. 5.
Which among the following is the strongest reducing agent? (1) K
(2)
Na
(3)
Al
(4)
Mg
Sol. Answer (1) Potassium has the highest negative value of E° amongst the given elements, thus it is the strongest reducing agent. 6.
Sodium chloride gives a golden yellow colour to the bunsen flame, which is due to (1) Sublimation of metallic sodium to give yellow vapour (2) Photosensitivity of sodium (3) Low ionization potential of sodium (4) Emission of excess of energy absorbed as a radiation in the visible region
Sol. Answer (4) The heat from the flame excites the outermost orbital electron to a higher energy level. When the excited electron comes back to the ground state, there is emission of radiation in the visible region. 7.
Which of the following oxides is the most basic in nature? (1) Na2O
(2)
BeO
(3)
Li2O
(4)
H2O
Sol. Answer (1) The larger the metallic character of the element, more is the basic nature of the oxide. 8.
Which of the following hydride is the most stable? (1) LiH
(2)
KH
(3)
NaH
(4)
CsH
Sol. Answer (1) Hydrides of alkali metals contain hydrogen as an anion and are represented as M+H–. Hydrogen, in these compounds gets liberated at the anode, on electrolysis. The hydrides are not very stable. They react with water readily liberating hydrogen. These hydrides are, therefore used as reducing agents. Li[AlH4] is a strong reducing agent. 9.
Na2CO3 can be manufactured by Solvay’s process but K2CO3 cannot be prepared because (1) K2CO3 is more soluble
(2)
K2CO3 is less soluble
(3) KHCO3 is more soluble than NaHCO3
(4)
KHCO3 is less soluble than NaHCO3
Sol. Answer (3) KHCO3 is more soluble than NaHCO3 is correct as the electropositive character increases on moving down the group, the stability of bicarbonates increases in the same order. NaHCO3 is made by saturating a solution of sodium carbonate with carbon dioxide. The white crystalline powder of NaHCO3, being less soluble, gets separated out
Na 2CO 3 + H 2O + CO 2 2NaHCO 3 Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
Solution of Assignment (Set-2)
The s-Block Elements
23
10. Which hydroxide decomposes on heating? (1) NaOH
(2)
KOH
(3)
LiOH
(4)
RbOH
Sol. Answer (3) Lithium hydroxide decomposes on heating (650°C) to produce lithium oxide and water. All the water hydroxides are comparatively stable to heat 2LiOH(s) Li 2O(s) + H 2O(g)
11. Solvay’s process is used for the manufacture of (1) Sodium metal
(2)
Washing soda
(3)
Bleaching powder
(4)
Quick lime
Sol. Answer (2) Na2CO3.10H2O (washing soda) is prepared by Solvay process, which exploits the low solubility of sodium hydrogen carbonate whereby it gets precipitated in the reaction of sodium chloride with ammonium hydrogen carbonate. 12. In the manufacture of sodium hydroxide, by product obtained is (1) O2
(2)
Cl2
(3)
Na2CO3
(4)
NaCl
Sol. Answer (2) A brine solution is electrolysed using a mercury cathode and a carbon anode. Sodium metal discharged at the cathode combines with mercury to form sodium amalgam. Chlorine gas is evolved at the anode Mg Cathode : Na + + e – Sodium amalgam
– Anode : Cl
1 Cl + e – 2 2
13. Which of the following alkali metal bicarbonates readily decomposes? (1) LiHCO3
(2)
KHCO3
(3)
CsHCO3
(4)
NaHCO3
Sol. Answer (1) As the electropositive character increases on moving down the group, the stability of bicarbonates increases in the same order. This LiHCO3 will readily decompose. 14. The polarizing power of magnesium is nearly same as (1) Lithium
(2)
Sodium
(3)
Potassium
(4)
Cesium
Sol. Answer (1) Lithium and magnesium has similar size of their atoms and ions, comparable atomic radii and electronegativities, due to this the polarizing power of magnesium is nearly same as lithium. 15. In the preparation of sodium carbonate (Na2CO3) which of the following is used as raw material? (1) Slaked lime
(2)
Brine
(3)
Quick lime
(4)
Sodium hydroxide
Sol. Answer (2) Aqueous solution of NaCl (Brine) is used as raw material in the preparation of sodium carbonate (Na2CO3). Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
24
The s-Block Elements
Solution of Assignment (Set-2)
16. Which of the following halides has the highest melting point? (1) NaCl
(2)
NaBr
(3)
NaF
(4)
NaI
Sol. Answer (3) For a given metal fH– always becomes less negative from fluoride to iodide. The melting and boiling popints always follow the trend, fluoride > chloride > bromide > iodide. 17. The first ionisation energies of alkaline earth metals are higher than those of the alkali metals because (1) There is increase in the nuclear charge of the alkaline earth metals (2) There is decrease in the nuclear charge of the alkaline earth metals (3) There is no change is the nuclear charge (4) All of these Sol. Answer (1) The first ionisation enthalpies of the alkaline earth metals are higher than those of the corresponding group of alkali metals. This is due to their small size as compared to corresponding alkali metals. 18. The most electropositive metal among the alkaline earth metal is (1) Be
(2)
Mg
(3)
Ca
(4)
Ba
Sol. Answer (4) The electropositive character increases down the group from Be to Ba. 19. Why does magnesium form Mg2+ and not Mg+? (1) Magnesium (II) is insoluble in water (2) Commonly higher oxidation states are preferred by metals (3) Ionic radius of Mg (II) is smaller than of Mg (I) (4) High hydration energy as well as high lattice energy of divalent magnesium ion Sol. Answer (4) High hydration energy as well as high lattice energy of divalent magnesium ion. 20. Which of the following alkaline earth metal does not impart any colour to flame? (1) Be
(2)
Mg
(3)
Ca
(4)
Sr
(3)
CaCO3
(4)
CaSO4
(4)
LiCl
Sol. Answer (2) 21. Lime water is an aqueous solution of (1) MgSO4
(2)
Ca(OH)2
Sol. Answer (2) Lime water is an aqueous solution of Ca(OH)2. 22. Which one of the following chlorides has maximum tendency to form hydrate? (1) BaCl2
(2)
NaCl
(3)
MgCl2
Sol. Answer (3) The tendency to form hydrate decreases down the group. Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
Solution of Assignment (Set-2)
The s-Block Elements
25
23. Setting of Plaster of Paris involves (1) Oxidation with atmospheric oxygen
(2)
Combination with atmospheric CO2
(3) Dehydration
(4)
Hydration
Sol. Answer (4) When mixed with water the setting of cement takes place which gives a hard mass. This is due to hydration of the molecules of the constituents and their rearrangement. 24. Which of the following is ‘dead burnt plaster’?
(1) CaCO3
(2)
1 CaSO4 · H2O 2
(3)
CaSO4·2H2O
(4)
CaSO4
Sol. Answer (4) Above 393 K, no water of crystallisation is left and anhydrous calcium sulphate, CaSO4 is formed. This is known as ‘dead burnt plaster’. Reaction referred to 2(CaSO4.2H2O) 2(CaSO4).H2O + 3H2O. 25. Identify the unknown product (x) in the following reaction Milk of lime + Cl2 x + CaCl2 + H2O (1) Ca(OCl)2
(2)
Ca(OH)2
(3)
CaO
(4)
CaCO3
(3)
2CaSO4·H2O
(4)
CaSiO3
(4)
Ba(OH)2
Sol. Answer (1) 2Ca(OH)2 + 2Cl2 CaCl2 + Ca(OCl)2 + 2H2O. 26. Formula of Gypsum is
(1) CaSO4·2H2O
(2)
CaSO4·
1 HO 2 2
Sol. Answer (1) CaSO4·2H2O. 27. Which one of the following compounds is the most soluble in water? (1) Mg(OH)2
(2)
Sr(OH)2
(3)
Ca(OH)2
Sol. Answer (4) The solubility, thermal stability and the basic character of hydroxides increase with increasing atomic number from Mg(OH)2 to Ba(OH)2. 28. Which of the following metals is most commonly used in photochemical cells? (1) Lithium
(2)
Calcium
(3)
Caesium
(4)
Francium
Sol. Answer (3) Caesium is used in photochemical cells. Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
26
The s-Block Elements
Solution of Assignment (Set-2)
29. Which of the following is an amphoteric oxide? (1) CaO
(2)
NaOH
(3)
BeO
(4)
LiOH
Sol. Answer (3) BeO + 2HCl BeCl2 + H2O and BeO + 2NaOH + H2O Na2[Be(OH)4](Sodium beryllate) BeO is an amphoteric oxide as it reacts with an acid as well as a base. As the atoms get larger, the ionization energy decreases and the elements also become more basic. BeO is insoluble in water but dissolves in acids to give salts, and in alkalis to give beryllates which on standing precipitate as the hydroxide. 30. Which of the following statement is true for all the alkali metals? (1) Their nitrates decompose on heating to give NO2 and O2 (2) Their carbonates decompose on heating to give CO2 and metal oxide (3) They react with oxygen to give mainly the oxide MO2 (4) They react with halogens to give halides M+X– Sol. Answer (4) Alkali metals react with dry di-hydrogen at about 673 K (Lithium at 1073 K) to form crystalline hydrides which are ionic in nature and have high melting points. Heat 2M + H 2 2M+H – .
SECTION - B Objective Type Questions 1.
Which of these give oxide on strong heating? (1) LiNO3
(2)
NaNO3
(3)
KNO3
(4)
RbNO3
Sol. Answer (1) Lithium being very small in size polarises a large NO3– ions leading to the formation of oxide 4LiNO3 2Li2O + 4NO2 + O2 2.
Which among the following shows the tendency to form peroxide? (1) Li
(2)
Mg
(3)
Be
(4)
Ba
Sol. Answer (4) Large size of Ba favours the formation of peroxide. 3.
Which one of the following statements is correct? The chlorides of group II metals (1) Are all hygroscopic in nature
(2)
Increase in lattice enthalpy from BeCl2 to BaCl2
(3) Decrease in m.p. from BeCl2 to BaCl2
(4)
Are all insoluble except BaCl2
Sol. Answer (1) Hygroscopic – Absorbing moisture. Therefore the chlorides of group II metals are hygroscopic and the tendency to form halide hydrates gradually decreases, for example MgCl2.8H2O, CaCl2.6H2O, SrCl2.6H2O and BaCl2.2H2O down the group. Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
Solution of Assignment (Set-2)
4.
The s-Block Elements
27
The solubility order of the chlorides of the alkali metals is (1) NaCl > KCl > RbCl > CsCl
(2)
CsCl > RbCl > KCl > NaCl
(3) KCl > NaCl > RbCl > CsCl
(4)
CsCl > RbCl > NaCl > KCl
Sol. Answer (4) The reason why the solubility of most group one metals decreases on descending the group is that the lattice energy only changes slightly, but the free energy of hydration changes rather more. (for e.g.) the difference in lattice energy between NaCl and KCl is 67 kJ mol–1, and yet the difference in G(Hydration) for Na+ and K+ is 76 kJ mol–1. Thus KCl is less soluble than NaCl. 5.
The thermal stability order of the carbonates is (1) Na2CO3 > K2CO3 > BeCO3 > BaCO3
(2)
K2CO3 > Na2CO3 > BaCO3 > BeCO3
(3) BaCO3 > BeCO3 > K2CO3 > Na2CO3
(4)
BeCO3 > Na2CO3 > BaCO3 > K2CO3
Sol. Answer (2) An electropositive character increases down the group, one elements the stability of the carbonates and hydrogen carbonates increases. The carbonates of alkali metals have more stability is more than alkaline earth metals due to their size which is greater. In alkaline earth metals the thermal stability increases with increasing cationic size. 6.
The thermal stability of alkaline earth metal carbonates increases from Be to Ba. This is because (1) Covalent nature decreases and Ionic nature increases (2) Lattice energy increases (3) Electropositive nature decreases (4) None of these
Sol. Answer (1) As the cationic size increases as we go down the group in alkaline earth metals, so does the thermal stability. This indicated the decrease in covalent nature and the increase in ionic nature. 7.
The solubility of sulphates in water decreases from MgSO4 to BaSO4. It is due to the fact that (1) Ionic nature increases
(2)
Size of M2+ ion increases
(3) Lattice energy decreases
(4)
Hydration enthalpy of M2+ ions decreases
Sol. Answer (4) The solubility of sulphates in water decreases from MgSO4 to BaSO4 because of the decrease in hydration enthalpy of M2+ ions. The greater hydration enthalpies of Ba2+ and Mg2+ ions overcome the lattice enthalpy factor and thus their sulphates are soluble in water. 8.
Which of the following order is correct for thermal stability? (1) MgCO3 < CaCO3 < BeCO3
(2)
BeCO3 < MgCO3 < CaCO3
(3) CaCO3 < BeCO3 < MgCO3
(4)
CaCO3 < MgCO3 < BeCO3
Sol. Answer (2) The thermal stability increases with increasing cationic size. Therefore the order would be BeCO < MgCO3 < CaCO3. Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
28 9.
The s-Block Elements
Solution of Assignment (Set-2)
Which one of the following statements concerning the compounds of Lithium is false? (1) The hydroxide, carbonate, nitrate, decompose to give the oxide on heating (2) It is the most electronegative among alkali metals (3) The hydrogen carbonate cannot be isolated as a stable solid (4) It forms a peroxide but not superoxide
Sol. Answer (4) When heated with excess of air lithium forms normal oxide (Li2O). 10. Which of the following statements is incorrect for Be? (1) Most of its compound are largely covalent (2) BeCl2 has bridged covalent structure and is a linear molecule above 1200 K (3) It has distinctive group properties due to smaller size and high electronegativity (4) It forms Be2+ ions because of the lower value the sum of Ist and 2nd I.E. Sol. Answer (4) Beryllium atom has a small size and the electronic configuration of [He]2S2, the ionization enthalpy is very high, further the ion becomes smaller when the electron is abstracted. Therefore the second ionization enthalpy will be also high but lower than corresponding alkali metal. Thus the sum of ionization enthalpies could not be of lower value. 11. Which of the following is not an acidic salt? (1) NaH2PO2
(2)
NaH2PO3
(3)
NaH2PO4
(4)
Na2HPO4
Sol. Answer (1) H3PO2 is a monobasic acid (i.e., has only one replacable proton) reaction with NaOH is shown below
H 3PO 2 + NaOH NaH 2PO 2 Normal salt
No other hydrogen atom of NaH2PO2 is replacable. 12. Baking soda is (1) NaCl
(2)
NaHCO3
(3)
Na2SO4
(4)
Na2CO3
Kerosene oil
(3)
Water
(4)
Petrol
Sol. Answer (2) NaHCO3 13. Sodium is usually kept under (1) Alcohol
(2)
Sol. Answer (2) Sodium reacts vegorously with oxygen in air and water in air. 14. Metallic Magnesium is prepared by (1) Displacement of Mg by iron from MgSO4 solution (2)
Electrolysis of an aqueous solution of Mg(NO3)2
(3) Electrolysis of molten MgCl2
Reduction of MgO by aluminium
(4)
Sol. Answer (3) Electrolysis of molten MgCl2. Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
Solution of Assignment (Set-2)
The s-Block Elements
29
15. Chemical ‘A’ is used for water softening to remove temporary hardness. ‘A’ reacts with sodium carbonate to generate caustic soda. When carbon dioxide is bubbled through ‘A’, it turns cloudy. What is the chemical formula of ‘A’? (2)
(1) CaCO3
CaO
(3)
Ca(OH)2
(4)
Ca(HCO3)2
(3)
Na
(4)
Cs
Sol. Answer (3) Na2CO3 + Ca(OH)2 2NaOH + CaCO3 Ca(OH)2 + CO2 CaCO3 + H2O 16. Alums are not formed by which alkali metal? (1) Li
(2)
K
Sol. Answer (1) All alkali metals (sulphates) form alums except Li2SO4,Li2SO4 is not isomorphous with other sulphates. 17. Epsom salt’s chemical formula is (1) MgSO4 · 7H2O
(2)
Mg(OH)2
(3)
2CaSO4 · H2O
(4)
BaSO4
(3)
FeSO4 · 7H2O
(4)
Na2SO4 · 10H2O
(4)
Mg and Cl2
Sol. Answer (1) Hydrated magnesium sulphate – MgSO4.7H2O. 18. Molecular formula of Glauber’s salt is (1) MgSO4 · 7H2O
(2)
CuSO4 · 5H2O
Sol. Answer (4) The deca hydrate, Na2SO4 · 10H2O is known as Glauber's salt. 19. The electrolysis of molten KCl · MgCl2 · 6H2O gives (1) Mg only
(2)
K only
(3)
K and Mg only
Sol. Answer (4)
MgCl2 Mg
2+
+ 2Cl
–
Mg Cl2 (Cathode) (Anode) KCl is unaffected by the applied voltage and amperage. 20. Alkaline earth metals form hydrated crystalline solids such as MgCl2 · 6H2O and CaCl2 · 6H2O. This is due to (1) Smaller ionic size
(2)
Increased charge on ions
(3) Higher hydration enthalpies
(4)
High oxidation potential
Sol. Answer (3) The hydration energy of the ions of alkaline earth metals (M2+) is nearly four or five times greater than that of alkali metals because of their small size and increased charge. Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
30
The s-Block Elements
Solution of Assignment (Set-2)
21. Compared with the alkaline earth metals, the alkali metals show (1) Greater hardness
(2)
Higher m.p.
(3) Smaller ionic radii
(4)
Lower ionization energy
Sol. Answer (4) The first ionization enthalpies of the alkaline earth metals are higher than those of the corresponding group/ metals. This is due to their small size as compared to the corresponding alkali metals. 22. Which is not the compound of sodium? (1) Chile salt petre
(2)
Salt petre
(3)
Glauber's salt
(4)
Soda ash
Sol. Answer (2) Salt petre or potassium nitrate is an ionic salt of K+ and NO3–. Chemical formula KNO3.
23. CaCO3
A + B(gas) H2O
C
Cl2 40ºC
D
Product D is (1) CaCl2
(2)
Ca(OH)2
(3)
CaCl2.6H2O
(1) BeSO4 > BaSO4
(2)
LiCl > LiF
(3) NaHCO3 < KHCO3
(4)
All of these
(4)
CaOCl2
Sol. Answer (4)
CaCO3
1200 K
CaO + CO2 HO 2
Ca(OH)2
2Ca(OH)2 + 2Cl2 CaCl2 + CaOCl2 + 2H2O. 24. Correct order of solubility
Sol. Answer (4) The lattice energy is almost the same in alkaline earth metal sulphates. The sulphate ion is itself very large that relatively small change in metallic ionic size from Be2+ to Ba2+ does not make any material difference. However hydration energy decreases from Be2+ to Ba2+, hence the solubility of sulphates decrease in this order. The solubility decreases with increase in ionic size. The low solubility of lithium fluoride is due to the greater force of attraction between lithium ions and fluoride ions in the crystal lattice. 25. Among the oxides of group 2, least basic is (1) MgO
(2)
CaO
(3)
SrO
(4)
BaO
Sol. Answer (1) Basicity of an oxide increases with increase in atomic number i.e., down the group. Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
Solution of Assignment (Set-2)
The s-Block Elements
31
26. Beryllium on ignition in air gives (1) BeO
(2)
Be3N2
(3)
Both (1) & (2)
(4)
BeC
Sol. Answer (3) Beryllium in powdered form burns brilliantly and gives BeO and Be3N2. 27. Na2CO3 + H2O + CO2 (A). White crystalline powder (A) on reaction with phenolphthalein gives (1) Pink colour
(2)
Yellow colour
(3)
Orange colour
(4)
No colour
(4)
All of these
Sol. Answer (1) Na2CO3 + H2O + CO2 2NaHCO3 NaHCO3 on reaction with phenolphthalin gives pink colour due to its acidity. 28. Composition of baking soda is (1) Starch
(2)
Ca(H2PO4)2
(3)
NaHCO3
Sol. Answer (3) NaHCO3. 29. Which of the following statement is true? (1) NaHCO3 is strongly basic in nature (2) Pure NaCl is hygroscopic (3) On increasing temperature increase in solubility of NaCl in water occurs (4) All of these Sol. Answer (3) On increasing temperature, increase in solubility of NaCl in water occur but not very much. It has a solubility of 36.0 g in 100 g of water at 273 K. 30. On heating sodium hydrogen carbonate, the product formed is (1) Na2O + CO2 + H2O
(2)
Na2CO3 + CO2
(3) Na2CO3 + H2O + CO2
(4)
Na2CO3 + H2O
Sol. Answer (3) 2NaHCO3 Na2CO3 + CO2 + H2O.
SECTION - C Previous Years Questions 1.
Which of the following statements is false?
[NEET-2016]
(1) Mg2+ ions are important in the green parts of plants (2) Mg2+ ions form a complex with ATP (3) Ca2+ ions are important in blood clotting (4) Ca2+ ions are not important in maintaining the regular beating of the heart Sol. Answer (4) Fact. Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
32 2.
The s-Block Elements
Solution of Assignment (Set-2)
On heating which of the following releases CO2 most easily? (1) MgCO3
(2)
CaCO3
(3)
K2CO3
[Re-AIPMT-2015] (4)
Na2CO3
Sol. Answer (1)
MgCO3 MgO CO2
Polarising power of Mg2+ is maximum amongst Ca2+, Mg2+, K+ and Na+, thus on heating, MgCO3 releases CO2 most easily. 3.
The function of "Sodium pump" is a biological process operating in each and every cell of all animals. Which of the following biologically important ions is also a constituent of the pump? [AIPMT-2015] (1) Fe2+
(2)
Ca2+
(3)
Mg2+
(4)
K+
Sol. Answer (4) K+ and Na+ forms pump. 4.
Solubility of the alkaline earth's metal sulphates in water decreases in the sequence (1) Ba > Mg > Sr > Ca
(2)
Mg > Ca > Sr > Ba
(3)
Ca > Sr > Ba > Mg (4)
[AIPMT-2015] Sr > Ca > Mg > Ba
Sol. Answer (2) Solubility of II group sulphate decreases down the group. 5.
Which one of the alkali metals, forms only, the normal oxide, M2O on heating in air? (1) Li
(2)
Na
(3)
Rb
(4)
[AIPMT (Prelims)-2012] K
Sol. Answer (1) Among all the alkali metals, lithium is least reactive but the strongest reducing agent. When burnt in air it forms mainly monoxide Li2O and the nitride Li3N. 6.
Equimolar solutions of the following substances were prepared separately. Which one of these will record the [AIPMT (Prelims)-2012] highest pH value? (1) LiCl
(2)
BeCl2
(3)
BaCl2
(4)
AlCl3
Sol. Answer (3) 7.
Which of the following compounds has the lowest melting point? (1) CaF2
(2)
CaCl2
(3)
CaBr2
[AIPMT (Prelims)-2011] (4)
CaI2
Sol. Answer (4) Due to the large size of iodine and weaker bond strengths because of lower forces of attraction. The CaI2 will have lowest boiling point. 8.
Which one of the following is present as an active ingredient in bleaching powder for bleaching action? [AIPMT (Prelims)-2011] (1) CaCl2
(2)
CaOCl2
(3)
Ca(OCl)2
(4)
CaO2Cl
Sol. Answer (3) Ca(OCl)2 Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
Solution of Assignment (Set-2)
9.
The s-Block Elements
Which of the following statements is incorrect ?
33
[AIPMT (Mains)-2011]
(1) Aluminium reacts with excess NaOH to give Al(OH)3 (2) NaHCO3 on heating gives Na2CO3 (3) Pure sodium metal dissolves in liquid ammonia to give blue solution (4) NaOH reacts with glass to give sodium silicate Sol. Answer (1) 2Al + 2NaOH + 6H2O 2NaAl(OH)4 + 3H2. 10. Match list-I with list-II for the composition of substances and select the correct answer using the code given below the lists [AIPMT (Mains)-2011] List-I
List-II
(Substances)
(Composition)
(A) Plaster of paris
(i) CaSO4.2H2O
(B) Epsomite
(ii) CaSO4.
(C) Kieserite
(iii) MgSO4. 7H2O
(D) Gypsum
(iv) MgSO4. H2O
(A)
(B)
(C)
(D)
(1) (i)
(ii)
(iii)
(iv)
(2) (iv)
(iii)
(ii)
(i)
(3) (iii)
(iv)
(i)
(ii)
(4) (ii)
(iii)
(iv)
(i)
1 HO 2 2
Sol. Answer (4) Plaster of Paris –
1 CaSO 4 H 2O 2
Epsomite
–
MgSO47H2O
Kiesertie
–
MgSO4H2O
Gypsum
–
CaSO42H2O
11. Which of the following alkaline earth metal sulphates has hydration enthalpy higher than the lattice enthalpy ? [AIPMT (Prelims)-2010] (1) CaSO4
(2)
BeSO4
(3)
BaSO4
(4)
SrSO4
Sol. Answer (2) BeSO4 has hydration enthalpy higher than the lattice enthalpy. 12. Property of the alkaline earth metals that increases with their atomic number
[AIPMT (Prelims)-2010]
(1) Solubility of their hydroxides in water
(2)
Solubility of their sulphates in water
(3) Ionization energy
(4)
Electronegativity
Sol. Answer (1) The hydration enthalpy decreases down the group due to which the extent of solubility of their hydroxides increase down the group. Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
34
The s-Block Elements
Solution of Assignment (Set-2)
13. Which one of the following compounds is a peroxide ? (1) KO2
(2)
BaO2
[AIPMT (Prelims)-2010] (3)
MnO2
(4)
NO2
Sol. Answer (2) Barium peroxide BaO2 is the ionic compound formed when barium metal burns in oxygen. 14. The compound A on heating gives a colourless gas and a residue that is dissolved in water to obtain B. Excess of CO2 is bubbled through aqueous solution of B, C is formed which is recovered in the solid form. Solid C on gentle heating gives back A. The compound is [AIPMT (Mains)-2010] (2)
(1) CaCO3
Na2CO3
(3)
K2CO3
(4)
CaSO4.2H2O
Sol. Answer (1) CaCO 3 CaO + CO 2 Colourless gas
(A)
CaO + H 2O Ca(OH) 2 Residue
(B)
Ca(OH) 2 + 2CO 2 Ca(HCO 3 ) 2 (B)
excess
(C)
Ca(HCO 3 ) 2 CaCO 3 + CO 2 + H 2O (C)
(A)
15. Which of the following oxides is not expected to react with sodium hydroxide ? (1) CaO
(2)
SiO2
(3)
BeO
[AIPMT (Prelims)-2009] (4)
B2O3
Sol. Answer (1) Among the given oxides CaO is the most basic and hence it will not react with NaOH. 16. The alkali metals from salt-like hydrides by the direct synthesis at elevated temperature. The thermal stability of these hydrides decreases in which of the following orders ? [AIPMT (Prelims)-2008] (1) LiH > NaH > KH > RbH > CsH
(2)
CsH > RbH > KH > NaH > LiH
(3) KH > NaH > LiH > CsH > RbH
(4)
NaH > LiH > KH > RbH > CsH
Sol. Answer (1) The ionic character of the bonds in hydrides increase from LiH to CsH so thermal stability of these hydrides decreases from LiH to CsH. 17. In which of the following the hydration energy is higher than the lattice energy ? (1) SrSO4
(2)
BaSO4
(3)
MgSO4
[AIPMT (Prelims)-2007] (4)
RaSO4
Sol. Answer (3) As Mg2+ ion is smallest in size so it will have maximum hydration energy. This is because hydration energy
1 Size
18. The correct order of increasing thermal stability of K2CO3, MgCO3, CaCO3 and BeCO3 is [AIPMT (Prelims)-2007] (1) K2CO3 < MgCO3 < CaCO3 < BeCO3
(2)
BeCO3 < MgCO3 < K2CO3 < CaCO3
(3) BeCO3 < MgCO3 < CaCO3 < K2CO3
(4)
MgCO3 < BeCO3 < CaCO3 < K2CO3
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Solution of Assignment (Set-2)
The s-Block Elements
35
Sol. Answer (3) Since the thermal stability of IA is more than IIA and on moving down the group thermal stability decreases, so the correct increasing order of thermal stability is, BeCO3, < MgCO3 < CaCO3 < K2CO3. 19. The correct order of the mobility of the alkali metal ions in aqueous solution is +
+
+
+
(1) Li > Na > K > Rb
(2)
+
+
+
+
Na > K > Rb > Li
(3)
+
+
+
[AIPMT (Prelims)-2006] +
K > Rb > Na > Li (4)
Rb+ > K+ > Na+ > Li+
Sol. Answer (4) 20. In Castner-Kellner cell for production of sodium hydroxide : (1) Brine is electrolyzed with Pt electrodes
(2)
Brine is electrolyzed using graphite electrodes
(3) Molten sodium chloride is electrolysed
(4)
Sodium amalgam is formed at mercury cathode
Sol. Answer (4) Anode : 2Cl– Cl2 + 2e– Cathode : Na+(aq) + e– Na(s)
2Na/Hg Sodium amalgam
+ 2H 2O 2Na + + 2OH – + H 2 + 2Hg
21. In the replacement reaction
Cl + MF
CF + MI
The reaction will be most favourable if M happens to be (1) Na
(2)
K
(3)
Rb
(4)
Li
Sol. Answer (3) According to Fajan's rule, the more the size of anion and smaller the size of cation more is the polarizability. Rb has the biggest size due to which the bond strength will be lowest. 22. The solubility in water of sulphate down the Be group is Be > Mg > Ca > Sr > Ba. This is due to (1) Decreasing lattice energy
(2)
High heat of solvation for smaller ions like Be2+
(3) Increase in melting points
(4)
Increasing molecular weight
Sol. Answer (2) The lattice energy is almost the same in alkaline earth metals sulphates. The sulphate ion is itself very large that relatively small change in metallic ionic size from Be2+ to Ba2+ does not make any material difference. However hydration energy decreases from Be2+ to Ba2+, hence the solubility decreases with increase in ionic size. 23. The sodium is made by the electrolysis of a molten mixture of about 40% NaCl and 60% CaCl2 because (1) Ca++ can displace Na from NaCl
(2)
This mixture has a lower melting point than NaCl
(3) CaCl2 helps in conduction of electricity
(4)
Ca++ can reduce NaCl to Na
Sol. Answer (2) The mixture contains 40% NaCl and 60% CaCl2. On comparing it with 100% NaCl, its melting point will be lower. 24. Identify the correct statement (1) Plaster of Paris can be obtained by hydration of gypsum (2) Plaster of Paris is obtained by partial oxidation of gypsum (3) Gypsum contains a lower percentage of calcium than Plaster of Paris (4) Gypsum is obtained by heating Plaster of Paris Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
36
The s-Block Elements
Solution of Assignment (Set-2)
Sol. Answer (3) 1 Gypsum is CaSO42H2O while Plaster of Paris is CaSO 4 H 2O . 2
25. Calcium is obtained by (1) Reduction of calcium chloride with carbon
(2)
Electrolysis of molten anhydrous calcium chloride
(3) Roasting of limestone
(4)
Electrolysis of solution of calcium chloride in H2O
Sol. Answer (2) 2+ – CaCl 2 Ca + 2Cl
At cathode : Ca2+ + 2e– Ca At anode : 2Cl– Cl2 + 2e–. 26. When a substance (a) reacts with water it produces a combustible gas (b) and a solution of substance (c) in water. When another substance (d) reacts with this solution of (c), it also produces the same gas (b) on warming but (d) can produce gas (b) on reaction with dilute sulphuric acid at room temperature. Substance (a) imparts a deep golden yellow colour to a smokeless flame of Bunsen burner. Then (a), (b), (c) and (d) respectively are (1) Ca, H2, Ca(OH)2, Sn
(2)
K, H2, KOH, Al
(3) Na, H2, NaOH, Zn
(4)
CaC2, C2H2, Ca(OH)2, Fe
Sol. Answer (3) (A) Deep golden yellow colour is produced in flame test by sodium only C
A
B
2Na + 2H 2O 2NaOH(aq) + H 2 (g)
H2 is combustible gas. Further aqueous solution of NaOH(C) reacts with Zn to form H2
2NaOH + Zn Na 2 ZnO 2 + H 2
Zn also reacts with dilute H2SO4 to produce H2
Zn + H 2SO 4 ZnSO 4 + H 2
SECTION - D Assertion Reason Type Question 1.
A : NaN3 and Na3N both are stable. R : Na when reacted with atmospheric nitrogen at different temperature forms stable NaN3 and Na3N.
Sol. Answer (4) heat 3NaN 3 Na 3N + 4N 2
NaN3 and Na3N are both unstable. The reaction shown is the laboratory method for preparation of nitrogen. Strong triple bond has a small bond length that makes the above compounds unstable. 2.
A : Magnesium sulphate is heptahydrate where as calcium sulphate is dihydrate. R : Mg and Ca belongs to Group II.
Sol. Answer (2) Magnesium sulphate is heptahydrate. Calcium sulphate is dihydrate. Mg and Ca belong to group II. Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
Solution of Assignment (Set-2)
3.
The s-Block Elements
37
A : LiF and CsI both are less soluble in water. R : LiF is with high lattice energy and CsI is with smaller hydration energy.
Sol. Answer (1) LiF with high lattice energy and Csl with smaller hydration energy. Owing to the size of atoms. Due to this LiF and CsI are both less soluble in water. 4.
A : Lithium is less reactive but the strongest reducing agent in aqueous solution. R : Lithium shows positive reduction potential.
Sol. Answer (3) Lithium has a small size due to which electrons are more closely bound making it less reactive and it needs to gain an electron to attain a stable outer shell octet. Which makes it a good reducing agent, reduction potential of Li = –3.04 V. 5.
A : Na and Li are stored under kerosene. R : Na and Li are soluble in kerosene.
Sol. Answer (4) Sodium and potassium are kept in kerosene. They react vigorously with air (oxygen) and moisture in air due to which they are stored in kerosene as no reaction occurs with it. 6.
A : CaCO3 requires more temperature than MgCO3 for decomposition. R : Group II metal carbonates on decomposition gives respective oxide and CO2.
Sol. Answer (2) As the size increases down the group therefore stability will also increase in the same way. This is why 1200K CaCO3 requires more temperature than MgCO3 for decomposition. CaCO 3 CaO + CO 2 . Thus group
II metal carbonates on decomposition gives oxide and CO2. 7.
A : Magnesium and Cesium gives blue colour in flame colouration. R : Mg and Cs are of comparable size.
Sol. Answer (4) Magnesium does not give the blue colour test. Cs gives the blue colour test. Mg occurs in the second position from top of group II element whereas. Cs is present on the second last position of group I elements. 8.
A : Lithium has highest ionization enthalpy among group-1 elements. R : Lithium has highest reducing power in group-1.
Sol. Answer (2) Lithium being the smallest in size has the highest ionization enthalpy. Lithium has the maximum reducing power. 9.
A : On reaction with liquid ammonia, alkali metals give conducting solution. R : Ammoniated e– and ammoniated cations are formed when alkali metals is present in liquid ammonia.
Sol. Answer (1) On reaction with liquid ammonia, alkali metals give conducting solution, this is because ammoniated e– and ammoniated cations are formed when alkaline metals is present in liquid ammonia. Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
38
The s-Block Elements
Solution of Assignment (Set-2)
10. A : LiF has low solubility in water. R : LiF has high hydration energy. Sol. Answer (3) LiF has low solubility in water due to high bond strength. LiF has high lattice energy. 11. A : Solubility of alkaline earth metal carbonates decreases down the group. R : Hydration enthalpy decreases down the group, whereas lattice enthalpy remain almost constant. Sol. Answer (1) Solubility of alkaline earth metals carbonates decreases down the group, as hydration enthalpy decrease down the group, whereas lattice enthalpy remains almost constant as the size of carbonate molecule is too large and the change in metallic ion size does not make any material difference. 12. A : Magnesium do not impart flame colouration. R : The e– in magnesium are too strongly bound to get excited by flame. Sol. Answer (1) Magnesium does not impart flame colouration because its e–s are too strongly bound to get excited by flame. 13. A : Beryllium hydroxide is basic in nature only. R : It reacts with acid only and not with base. Sol. Answer (4)
Be(OH) 2 + 2OH – Be(OH) 4
2–
Beryllate ion
Be(OH) 2 + 2HCl + 2H 2O Be(OH) 4 Cl 2 Beryllium hydroxide is amphoteric in nature. 14. A : Aq. solution of washing soda is alkaline in nature. R : It is salt of weak acid and strong base. Sol. Answer (1) Aq. solution of washing soda is alkaline in nature because it is a salt of weak acid and strong base. 15. A : Be is sp hybridized in BeCl2 at room temperature. R : Be is sp3 hybridized above 1200 K in BeCl2. Sol. Answer (4) The hybridisation of Be in BeCl2 is ‘sp’ in vapour phase.
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