Tiêu đề 10. THE S-BLOCK ELEMENTS.pdf ✅

20 The s-Block Elements Solutions of Assignment Sol. Answer (1) KO2 absorb CO2 and produce O2. 4KO2 + 2CO2  2K2CO3 + 3O2 6. Which of the following carbonate decompose on heating to evolve CO2? (1) Na2CO3 (2) Li2CO3 (3) K2CO3 (4) Rb2CO3 Sol. Answer (2) Li2CO3  Li2O + CO2 It decompose because Li2O have very high lattice energy. 7. Which of the following has the highest solubility product ? (1) KOH (2) CsOH (3) LiOH (4) RbOH Sol. Answer (2) CsOH is highly soluble. 8. Which ions are produced when anhydrous KF is mixed with conc. HF? (1) K+, H+, F– (2) {KF+ (HF–)} (3) KH+, F– (4) K+, HF2 – Sol. Answer (4) KF + HF  KHF2 KHF2 dissociate as K+ and  HF2 . [Note that  HF2 contains symmetric hydrogen bonding [F H F] ]– . 9. The ionic character of alkali metal chlorides follow the order (1) LiCl > KCl > NaCl > CsCl (2) CsCl > KCl > NaCl > LiCl (3) NaCl > KCl > LiCl > CsCl (4) LiCl > CsCl > NaCl > KCl Sol. Answer (2) Fajan’s rule. 10. Which of the following is a hypothetical molecular formula? (1) CsBr3 (2) CsI3 (3) CsCl (4) CsF3 Sol. Answer (4) F2 does not react with F– to form F3 –. [Group-2] 11. BaC2 + N2  (A) CaC2 + N2  (B) The compound (A) and (B) are (1) BaCN2, CaCN2 (2) Ba(CN)2, Ca(CN)2 (3) Ba(CN)2, CaCN2 (4) Ba3N2 + Ca(CN)2
Solutions of Assignment The s-Block Elements 21 Sol. Answer (3) )A( 22 2 NBaC   )CN(Ba  22 2 (B) CaC N CaCN   12. One mole of a substance (X) was treated with an excess of water. Two moles of readily combustile gas was produced along with a solution which when treated with CO2 produced a white turbidity. The substance (X) could be (1) Ca (2) CaH2 (3) Ca(OH)2 (4) Ca(NO3) 2 Sol. Answer (2) CaH2 + 2H2O  Ca(OH)2 + 2H2 Ca(OH)2 + CO2  3 milkiness CaCO + H2O 13. The oxidation state of the most electronegative elements in the products of the reaction, BaO2 with dil. H2SO4 are. (1) 0 and – 1 (2) – 1 and – 2 (3) – 2 and 0 (4) – 2 and + 1 Sol. Answer (2) BaO2 + H2SO4  BaSO4 + H2O2 Oxidation state of O in BaSO4 is –2 and that of O in H2O2 is –1. 14. The compound insoluble in acetic acid is (1) Calcium oxide (2) Calcium carbonate (3) Calcium oxalate (4) Calcium hydroxide Sol. Answer (3) Calcium oxalate is insoluble in acetic acid while other are soluble in CH3COOH. 15. Solubilities of group (II) carbonates, sulphates, phosphates decreases down the group, this is due to (1) Entropy of solution formation (2) Lattice energies of solids (3) Hydration energy of cations (4) Inter-ionic attraction Sol. Answer (3) When hydration energy of ions decrease more rapidly as compared to decrease in lattice energy, then solubility decreases down the group. 16. A compound (X) on heating gives a colourless gas. The residue is dissolved in water to obtain (Y). Excess CO2 is bubbled through aqueous solution of (Y) and formation of (Z) is observed. (Z) on gently heating gives back (X). The compound (X) is (1) CaCO3 (2) Na2CO3 (3) Ca(HCO3) 2 (4) K2CO3 Sol. Answer (1)
22 The s-Block Elements Solutions of Assignment 2 x CaCO3   COCaO  CaO + H2O    y OHCa 2 Ca(OH)2 + excess CO2  z HCOCa 23 )( Ca(HCO3) 2  x CaCO3 + CO2 + H2O 17. Which of the following substances can be used for drying non-acidic gas? (1) Calcium carbonate (2) Sodium carbonate (3) Sodium bicarbonate (4) Calcium oxide Sol. Answer (4) CaO is used as a strong drying agent. 18. The solubility of hydroxides of alkaline earth metals increases down the group because (1) The decrease in lattice energy is more prominent than the decrease in hydration energy (2) The decrease in lattice energy is less prominent than the decrease in hydration energy (3) The salts become less ionic (4) Lattice energy increases and hydration energy decreases as one move from Be2+ to Ba2+ Sol.Answer (1) In alkaline earth metal hydroxides and fluorides decrease in lattice energy is more prominent than decrease in hydration energy. 19. The basic character of the oxides, MgO, SrO, K2O, NiO, Cs2O increases in the order (1) MgO < SrO < K2O < NiO < Cs2O (2) Cs2O < K2O < MgO < SrO < NiO (3) NiO < MgO < SrO < K2O < Cs2O (4) K2O < NiO < MgO < SrO < Cs2O Sol. Answer (3) Cs2O + H2O  CsOH Most soluble in water  Most basic. Cs2O > K2O > SrO > MgO > NiO 20. Which of the following are arranged in increasing order of solubilities? (1) CaCO3 < KHCO3 < NaHCO3 (2) NaHCO3 < KHCO3 < CaCO3 (3) KHCO3 < NaHCO3 < CaCO3 (4) CaCO3 < NaHCO3 < KHCO3 Sol. Answer (4) Alkali metal bicarbonates are soluble in water and solubility increases while descending in the group. However alkaline earth metal carbonates are insoluble in water.