JEE Main Previous Year Papers Questions With Solutions Chemistry Elements of S-Block : Hydrogen,Group 1 and 2

JEE Main Previous Year Papers Questions With Solutions Chemistry  Elements of S-Block : Hydrogen, Group 1 and 2

1.K02(potassium super oxide) is used in oxygen cylinders in space and submarines. This is because it        (2002)
(1)absorbs C02 and increases 02 content
(2)eliminates moisture
(3)absorbs C02 4) produces ozone
Ans.(2) 2KO, + 2H20 —>2KOH + H202 + 02. Eliminates moisture.
2.A metal M readily forms its sulphate MS04which is water soluble. It forms its oxide MO which becomes inert on heating. It forms an insoluble hydroxide M(OH)2 which is soluble in NaOH solution. Then M is     (2002)
(1)Mg 2) Ba 3) Ca 4) Be
Ans.(4) Beryllium shows anomalous properties with alkaline earth metals, due to its small size.
3.In curing cement plasters water is sprinkled from time to time. This helps in           (2003)
(1)developing interlocking needle-like crystals of hydrated silicates.
(2)hydrating sand and gravel mixed with cement
(3)converting sand into silicic acid
(4)keeping it cool
Ans.(1) Cross links are developed during hydration of calcium aluminosilicates.
4.The substance not likely to contain CaC03 is
(1)calcined gypsum 2) sea shells (2003) 3) dolomite 4) a marble statue
Ans.(1) The composition of gypsum is CaS04. 2H20, while others are carbonates.
5.The solubilities of carbonates decrease down the magnesium group. This is due to a decrease in
(1)hydration energies of cations (2003)
(2)inter – ionic attraction
(3)entropy of solution formation
(4)lattice energies of solids
Ans.(1) The solubility is governed by AH soIution
AH solution AHlattjce_ AHHydration.
Due to increase in size, the magnitude of hydration energy decreases and hence the solubility.
6.Several blocks of magnesium are fixed to the bottom of a ship to          (2003)
(1)make the ship lighter
(2)prevent action of water and salt
(3)prevent puncturing by under-sea rocks
(4)keep away the sharks
Ans.(2) Magnesium provides cathodic protection and prevent rusting or corrosion.
7.Which one of the following processes willproduce hard water ?      (2003)
(1)Saturation of water with MgCOa
(2)Saturation of water with CaS04
(3)Addition of Na2S04 to water
(4)Saturation of water with CaC03
Ans.(2) Permanent hardness of water is due to chlorides and sulphates of calcium and magnesium.
8.In hydrogen – oxygen fuel cell, combustion of hydrogen occurs to      (2004)
(1)generate heat
(2)remove adsorbed oxygen from electrode surfaces
(3)produce high purity water
(4)create potential difference between the two electrodes Ans.(4) Heat is converted directlyto electricity.
Ans.(4) Heat is converted directlyto electricity.
9.One mole of magnesium nitride on the reaction with an excess of water gives (2004)
(1)one mole of ammonia
(2)two moles of nitric acid
(3)two moles of ammonia
(4)one mole of nitric acid
Ans.(3) Mg3N2 +6H20——– » 3Mg(OH)2 + 2NH3
10.Hydrogen bomb is based on the principle of
(1)Nuclear fission (2005)
(2) Natural radioactivity
(3) Nuclear fusion
(4)Artificial radioactivity
Ans.(3) Fusion of isotopes of hydrogen.
11.Based on lattice energy and other considerations which one of the following alkali metal chlorides is expected to have the highest melting point.(2005)
1) LiCl       2) NaCl       3) KC1       4) RbCl
Ans.(2) Although lattice energy of LiCl higher than NaCl, but LiCl is covalent in nature and NaCl ionic. There after, the melting point decreases as we move NaCl because the lattice energy decreases as size of alkali metal atom increases. Higher lattice energy denotes higher melting and boiling points.
12.The ionic mobility of alkali metal ions in aqueous solution is maximum for (2006)
1) K+   2) Rb+  3) Li+   4) Na+
Ans.(2) Hydrated Rb+ has small size.
13.In context with the industrial preparation of hydrogen from water gas (CO+H2), Which of  the following is the correct statement ? (2008)
(1)CO and H2 are fractionally separated using differences in their densities
(2)CO is removed by absorption in aqueous Cu2Cl2 solution
(3)H2 is removed through occulsion with Pd
(4)CO is oxidised to C02 with steam in the presence of a catalyst followed by absorption of C02 in alkali
14. Very pure hydrogen (99.9%) can be made by ’ which of the following processes ?   (2012)
(1)Reaction of methane with steam
(2)Mixing natural hydrocarbons of high molecular weight
(3) Elecrolysis of water
(4)Reaction of salt like hydrides with water
15.The first ionization potential of Na is 5.1 eV. The value of electron gain enthalpy of Na+ will be (2013)
1) -2.55 eV                   2) -5.1 eV
3)-10.2 eV                    4) +2.55 eV
Ans.(2) Inisation potential of alkali metal atom and electron affinity of its monocovalent cation are same in magnitude, but with opposite signs.
16.The metal that cannot be obtained by electrolysis of an aqueous solution of its salt is       (2014)
1) Cr 2) Ag 3) Ca 4) Cu
Ans.(3) Ca canot be obtained by the electrolysis of aqueous solution of its salt.
17.In which of the following reactions H202 acts as reducing agent ?     (2014)
a.H202 + 2H+ + 2e- -> 2H20
b.H202 – 2e–> 02 + 2H+
c.H202 + 2e- -> 20H-
d.H202 + 20H- 2e- -> 02 + 2H20
1) (b), (d)    2) (a), (b)      3) (c), (d)    4) (a), (c)
Ans.(1) While acting as reducing agent it gives up electrons and release oxygen gas.
Ans. 4) 2 mol of water softener require one mole of Ca2+
19.Form the following statements regarding H202, choose the incorrect statement (2015)
(1)It can act only as an oxidizing agent
(2)It decompose on exposure to light
(3)It has to be stored in plastic or was lined glass bottles in dark
(4)It has to be kept away form dust
Ans.(1) It is disproportionating agent.
20.Which one of the following alkaline earthmetal sulphates has its hydration enthalpy greater than its lattice enthalpy ?        (2015)
1) CaS04 2) BeS04 3) BaS04 4) SrS04
Ans.(2) Among alkaline earth metal sulphates BeS04 and MgS04 are water soluble due to high hydration enthalpy of Be2+ and Mg2+.

Courtesy : CBSE