Class 11th Chemistry - The s-Block Elements Case Study Questions and Answers 2022 - 2023
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The s-Block Elements Case Study Questions With Answer Key
11th Standard CBSE
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Reg.No. :
Chemistry
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Group 1 and group 2 elements are called s-block elements. Their general electronic configuration is ns1 to 2. Group 1 are called alkali metals where as group 2 elements are called alkaline earth metals. They resemble with each other in many respects but differ in some of properties due to difference in valence electrons, electronic configuration and atomic size.
(a) Why are group 1 elements softer than group 2 elements?
(b) Why are group 1 elements more electropositive than group 2?
(c) Why are K, Rb and Cs used in photoelectric cells?
(d) Why is BeCI2 more covalent than LiCI?
(e) Which colour is imparted to flame by Ca2+and Ba2+?(a) -
Study the table and answer the questions based on the table and related studied concepts.
Atomic and Physical Properties of the Alkaline Earth MetalsProperty Beryllium Be Magnesium Mg Calcium Ca Strontium Sr Barium Ba Radium Ra Atomic number 4 12 20 38 56 88 Atomic mass (g mol-1) 9.01 24.31 40.08 87.62 137.33 226.03 Electronic configuration [He]2s2 [Ne]3s2 [Ar] 4s2 [Kr] 5s2 [Xe] 6s2 [Rn] 7s2 Ionization enthalpy (I)/kJ mol-1 899 737 590 549 503 509 Ionization enthalpy (II)/kJ mol-1 1757 1450 1145 1064 965 979 Hydration enthalpy (kJ/mol) - 2494 -1921 -1577 -1443 -1305 - Metallic radius/pm 111 160 197 215 222 - Ionic radius M2+/pm 31 72 100 118 135 148 m.p./K 1560 924 1124 1062 1002 973 b.p/K 2745 1363 1767 1655 2078 (1973) Density / g cm-3 1.84 1.74 1.55 2.63 3.59 (5.5) Standard potential \(\mathbf{E}^{\odot} / \mathbf{V}\) for (M2+/ M) -1.97 -2.36 -2.84 -2.89 - 2.92 -2.92 Occurrence in lithosphere 2* 2.76** 4.6** 384* 390* 10-6* (a) Which is best non-radioactive reducing agent in Group 2? Why?
(b) Why does hydration enthalpy of bivalent cations of group 2 decrease down the group?
(c) Which element of group 2 has lowest melting points and why?
(d) Name a radioactive element of group 2
(e) Which group 2 element has lowest density?(a) -
The first element of each group, lithium in first group and beryllium in the second group differ from rest of the elements but have similar properties to diagonally situated elements. Lithium resembles with Mg and Be resembles with Aluminium. Boron resembles with Silicon.
The compounds of alkali metals are predominantly ionic. The oxides and hydroxides are soluble in water forming strong alkalies. Important compounds of sodium includes sodium carbonate, sodium chloride, sodium hydroxide and NaHCO3 Sodium hydroxide is manufactured by Castner-Kellner process and sodium carbonate by Solvay process.
The oxides and hydroxides of group 2 elements are less basic than group 1, oxides and hydroxides. CaO, Ca(OH)2, \(\mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}, \mathrm{CaCO}_{3}\) and cement are industrially important compounds. Portland cement is an important 2 constructional material. It is manufactured by heating limestone and clay in a rotary kiln. The clinker obtained is mixed with 2 to 3% gypsum.
Na+,K+, Mg2+and Ca2+ are found in large amounts in biological fluids. These ions perform important biological functions such as maintenance of ion balance and nerve impulse conductions.
(a) What is cause of diagonal relationship?
(b) Why does first element of each group differ from rest of the elements?
(c) Name the product formed at anode and cathode on electrolysis of brine solution
(d) Why is BeSO4 soluble in water but BaSO4 in not?
(e) Why is gypsum is added to cement?
(f) What is role of Ca2 + in our body?
(g) What is role of Na+ in blood plasma?(a)
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Answers
The s-Block Elements Case Study Questions With Answer Key Answer Keys
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(a) It is because group 1 elements are bigger in size and have weak metallic bonds.
(b) It is due to lower ionisation enthalpy due to their bigger atomic size.
(c) It is due to their low ionisation enthalpy.
(d) Be2+ is smaller than Li+ and it is bivalent, therefore, more polarising power than Li+.
(e) Ca 2+ imparts brick red, Ba2+ imparts apple green colour to the flame. -
(a) Barium because it has lowest standard reduction potential.
(b) It is due increase in ionic size. Larger ions have less hydration energy.
(c) Mg, it is due to weaker metallic bonds
(d) Radium
(e) Calcium -
(a) It is due to similar ionic radii, e.g., Li+ = 76 pm, Mg2+= 72 pm.
(b) It is due to exceptionally small size, high polarising power (charge/radius ratio)
(c) H2 is formed at cathode, Cl2 is formed at anode.
(d) It is because Be2+has higher hydration energy than Ba2+.
(e) It is done to delay the setting time of cement.
(f) It is present in bones and teeth. It plays important role in neuromuscular functions, interneuronal transmission and blood coagulation.
(g) Na+ are present outside the cell, being located in blood plasma and fluids which surround the cells and these ions help in transmission of nerve signals.
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