NEET Chemistry Study Material 10. The s-block Elements

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1 NEET Chemistry Study Material 10. The s-block Elements 1. Alkali metals are not found in free state due to their highly reactive nature. This is due to their large size and low ionization enthalpy their large size and high ionization enthalpy their low ionization enthalpy and high electron gain enthalpy their tendency to impart colour to the flame. 2. First ionization energy of alkali metals is very low but second ionization energy is very high because alkali metals acquire noble gas configuration after losing one electron. a large amount of energy is required to remove electron from a cation alkali metals can form only univalent ions first group elements can lose only one electron. 3. The mobilities of the alkali metal ions in aqueous solution are Li + < Na + < K + < Rb + < Cs + because greater is the degree of hydration, lesser is the mobility in aqueous medium. larger the size of cation, greater is the mobility in aqueous medium. larger the size of cation, lesser is the mobility of ions in aqueous medium lesser the degree of hydration, lesser is the mobility of ions in aqueous medium. 4. Which is the characteristic flame colouration of Li? Yellow Violet Blue Crimson red 5. Which of the following alkali metals when burnt in air forms a mixture of oxide as well as nitride? K Na Li Cs

2 6. Alkali metals cannot be extracted by reduction of their oxides and other compounds because alkali metals are strong reduction agents alkali metals have low ionization enthalpy alkali metals have high lattice enthalpy alkali metals are strongly basic in nature. 7. In all oxides, peroxides and superoxides, the oxidation state of alkali metals is +1 and and only +1, -1 and When sodium is dropped in small amount of water it catches fire. Which one of the following burns in the process? Na H2O H2 NaOH 9. On reaction with dihydrogen the alkali metals form hydrides which are ionic solids with high melting points form hydrides which are molecular solids with low melting points form hydrides which are ionic solids with low melting points from hydrides which are non-stoichiometric. 10. E for Cl2/Cl - = +1.36, I2/I - = +0.53, Ag + /Ag = +0.79, Na + /Na = and Li + /Li = V. What is the order of decreasing reducing strength for these species? Li > Cl - > Ag > I - > Na Li > Na > I - > Ag > Cl - Cl - > Ag > I - > Na > Li Na > Li > Ag > Cl - > I Superoxides of alkali metals act as oxidizing agents while normal oxides are basic in nature. The oxide which is paramagnetic in nature due to presence of unpaired electron is Na2O2 KO2

3 Na2O K2O2 12. Crystalline sodium chloride is a bad conductor of electricity while molten NaCl and its aqueous solution conduct electricity. This is because crystalline sodium chloride contains molecules only the ions present in it are not free to move in solid state sodium chloride is a covalent crystal solid substances do not conduct electricity. 13. Which of the following materials conducts electricity? Crystalline potassium chloride Fused sulphates Molten sodium chloride Diamond 14. Lithium salts are mostly hydrated like LiCl.2H2O due to maximum ionization enthalpy maximum degree of hydration of Li + maximum hydroscopic nature maximum chemical reactivity 15. Which of the following has lowest thermal stability? Li2CO3 Na2CO3 K2CO3 Rb2CO3 16. Which of the following does not show the anomalous behavior of lithium? Lithium reacts with nitrogen to from a nitride. Lithium carbonate decomposes on heating. Lithium nitrate gives NO2 on heating. Lithium is the strongest reducing agent. 17. In Solvay ammonia process, sodium bicarbonate is precipitated due to Presence of NH3 reaction with CO2 reaction with brine solution reaction with NaOH 18. When washing soda is heated CO is released CO + CO2 is released CO2 is released water vapour is released.

4 19. Which of the following is not true about s-block elements? They have large atomic sizes. They have lower ionization enthalpies. They have variable oxidation state. They form basic oxides. 20. What is the formula of hydrated BeCl2? BeCl2.H2O BeCl2.2H2O BeCl2.3H2O BeCl2.4H2O 21. Baking soda is NaHCO3 NaHCO3.6H2O Na2CO3 Na2CO3.10H2O 22. K2CO3 cannot be prepared by Solvay s process because KHCO3 is less soluble than NaHCO3 KHCO3 is too soluble to be precipitated by KCl and NH4HCO3 K2CO3 is too soluble to be precipitated by KCl K2CO3 is less soluble than Na2CO Which of the following statements is not correct regarding preparation of NaOH? NaOH is prepared by electrolysis of sodium chloride in Castner- Kellner cell. Sodium metal discharged at cathode combines with mercury to form sodium amalgam. Chlorine is evolved at anode. Amalgam is heated to separate Na and Hg. 24. The decreasing order of the second ionization potential of Mg, Ca and Ba is Mg > Ca > Ba Ca > Ba > Mg Ba > Mg > Ca Mg > Ba > Ca

5 25. An oxide of alkaline earth metals (X) reacts with C and Cl2 to give a compound Y. Y is found in polymeric chain structure and is electron deficient molecule. The compound Y is BeO BeCl2 Be(OH)2 BeCO3 26. A certain compound X imparts a golden yellow flame. When zinc powder is heated with concentrated solution of X, H2 gas is evolved. X combines with CO2 to give a salt Y. Y is a hydrated salt which on reaction with HCL or excess of CO2 gives another salt Z which is an important part of baking powder. Identify X,Y and Z. X Y Z NaOH Na2CO3 NaHCO3 HCl NaOH NaHCO3 KOH K2CO3 KHCO3 NaCl Na2CO3 NaOH 27. A metal X reacts with water to produce a highly combustible gas Y, and a solution Z. Another metal P reacts with Z to give the same gas Y. X, Y, Z and P respectively are Zn, H2, Zn(OH)2, Al Na, H2, NaOH, Zn K, H2, KOH, Al Li, H2, LiOH, K 28. Which of the following statements is correct regarding alkaline earth metals? Alkaline earth metals are weaker reducing agents than alkali metals. Alkali earth metals salts are paramagnetic in nature. Alkali earth metal salts are more soluble than corresponding alkali salts. Solubility of sulphates of alkaline earth metals increases from top to bottom in a group. 29. Which of the following is arranged according to increasing basic strength? CaO < MgO < SrO < BaO < BeO BaO < SrO < CaO < MgO < BeO BeO < MgO < CaO < BaO < SrO

6 BeO < MgO < CaO < SrO < BaO 30. The pair of amphoteric oxides is BeO, ZnO Al2O3, Li2O BeO, BO3 BeO, MgO 31. Which of the following will have lowest value of Ksp at room temperature? Be(OH)2 Mg(OH)2 Ca(OH)2 Ba(OH)2 32. Calcium chloride is used as a dehydrating agent because it has a strong affinity for water it has water of crystalline attached to it it loses water when exposed to air it has a high melting point. 33. When BeCl2 is hydrolysed, white fumes of gas are given out. The intensity of fumes intensifies when a rod dipped in moist ammonia is brought near the mouth of the test tube. The gas which comes out during hydrolysis is Cl2 HCl NH4OH NH4Cl 34. Which is the correct sequence of solubility of carbonates of alkaline earth metals? BaCO3 > SrCO3 > CaCO3 > MgCO3 MgCO3 > CaCO3 > SrCO3 > BaCO3 CaCO3 > BaCO3 > SrCO3 > MgCO3 BaCO3 > CaCO3 > SrCO3 > MgCO3 35. Which of the following compounds are not arranged in correct order as indicated? SrCl2 > CaCl2 < MgCl2 < BeCl2 (increasing order of hydrolysis) SrCl2 < CaCl2 < MgCl2 < BeCl2 (increasing lattice energy) CaSO4 < MgSO4 < BeSO4 (increasing stability) Be(OH)2 < Mg(OH)2 < Ca(OH)2 (increasing solubility) 36. The right order of the solubility of sulphates of alkaline earth metals in water is Be > Ca > Mg > Ba > Sr Mg > Be > Ba > Ca > Sr Be > Mg > Ca > Sr > Ba Mg > Ca > Ba > Be > Sr

7 37. Beryllium shows diagonal relationship with aluminium. Which of the following similarity is incorrect? Be2C like Al4C3 yields methane on hydrolysis. Be like Al is rendered passive by HNO3. Be(OH)2 like Al(OH)3 is basic. Be forms beryllates and Al forms aluminates. 38. Which of the following is not the point of difference between Be and other alkaline earth metals? It has a tendency to form covalent bonds. It dissolves in alkalies with evolution of hydrogen. Its oxides and hydroxides are amphoteric. Its carbide gives acetylence on hydrolysis. 39. Slaked lime reacts with chlorine to give CaCl2 CaO Ca(OCl)2 CaCO3 40. When plaster of Paris comes in contact with water it sets into a hard mass. The composition of the hard mass is CaSO4.H2O CaSO4.Ca(OH)2 CaSO4.2H2O CaSO4.2Ca(OH)2 41. Which of the following is not present in Portland cement? Ca3Al2O6 Ca3SiO5 Ca2SiO4 Ca3(PO4)2 42. Gypsum is added to portland cement to fasten the process of setting slow down the process of setting improve the colour of the cement increase the melting point of cement 43. The metal ion, that plays an important role in muscle contraction, is Be 2+ Mg 2+ Ca 2+ Ba Which of the following metals is required as cofactor by all enzymes utilizing ATP in phosphate transfer? K Ca (C) Na Mg

8 45. The reducing power of metal depends on various factors. Suggest the factor which makes Li, the strongest reducing agent in aqueous solution. Sublimation enthalpy Ionisation enthalpy Hydration enthalpy Electron-gain enthalpy 46. Which of the carbonates given below is unstable in air and is kept in CO2 atmosphere to avoid decomposition? BeCO3 MgCO3 CaCO3 BaCO3 47. Dehydration of hydrates of halides of calcium, barium and strontium i.e., CaCl2.6H2O, BaCl2.2H2O, SrCl2.6H2O, can be achieved by heating. These become wet on keeping in air. Which of the following statements is correct about these halides? Act as dehydrating agent Can absorb moisture from air Tendency to form hydrate decreases from calcium to barium. All of the above. 48. Which of the following statements is true about Ca(OH)2? It is used in the preparation of bleaching powder. It is a light blue solid. It does not possess disinfectant property. It is used in the manufacture of cement. 49. The formula of soda ash is Na2CO3.10H2O Na2CO3.2H2O Na2CO3.H2O Na2CO3 50. The solubility of metal halides depend on their nature, lattice enthalpy and hydration enthalpy of the individual ions. Amongst fluorides of alkali metals, the lowest solubility of LiF in water is due to ionic nature of lithium fluoride high lattice enthalpy high hydration enthalpy for lithium ion. low ionization enthalpy of lithium atom. Prepared By Mr. A. Moorthy, NEET Exam Trainer, Chennai.

CHAPTER THE S-BLOCK ELEMENTS

90 CHAPTER THE S-BLOCK ELEMENTS 1. Which one of the following properties of alkali metals increases in magnitude as the atomic number rises? [1989] (a) Ionic radius (b) Melting point (c) Electronegativity