Class 11 Chemistry Ch-10 The s-Block Elements (VSQ)

Q.1. Why does a piece of burning magnesium ribbon continues to burn in sulphur dioxide ?

Answer Answer: This is because magnesium has high affinity to combine with oxygen of SO2 to form MgO and S.
2Mg + SO2 → 2MgO + S

Q.2. What is the function of adding gypsum to clinker cement ?

Answer Answer: Gypsum is added to retard the rate of setting of cement. Gypsum reacts with tricalcium aluminate to form calcium sulphoaluminate.
3CaO.Al2O3 + 3CaSO4 + nH2O → 3CaO . Al2O3 .CaSO4 . nH2O

Q.3. Why is anhydrous CaSO4 used as drying agent? Why not plaster of paris ?

Answer Answer: Anhydrous CaSO4 can absorb water to form CaSO4. 2H2O and hence can be used as a drying agent. Plaster of paris is not used as a drying agent because it sets into a hard mass by absorbing water.

Q.4. How the caves are formed in limestone regions ?

Answer Answer: Caves in limestone regions get formed due to the dissolution of calcium carbonate in water containing carbon dioxide.
CaCO3 + H2O → Ca(OH)2 + CO2

Q.5. How is slaked lime prepared ?

Answer Answer: Refer Textbook

Q.6. Why group 2 elements (Mg and Ca) are harder and denser than group 1 elements?

Answer Answer: They have strong metallic bonds due to smaller size and have more number of valence electrons.

Q.7. Why are alkali metals used in photoelectric cells?

Answer Answer: They have low ionisation energy and can lose electrons when light falls on them, that is why they are used in photoelectric cells.

Q.8. Why do alkali metals have low melting and boiling points?

Answer Answer: It is due to weak metallic bonds which is due to bigger atomic size that is why they how low melting and boiling points.

Q.9. Why do alkali metals have low density?

Answer Answer: Due to weak metallic bonds and large atomic size, their density is low.

Q.10. Why are alkali metals soft?

Answer Answer: They are soft metals due to less force of attraction between positively charged kernels and valence electrons cloud and due to large atomic size, i.e., weak metallic bond.

Q.11. Why is second ionisation energy of alkali metals higher than alkaline earth metals?

Answer Answer: Refer theory

Q.12. Which out of K, Mg, Ca and Al form amphoteric oxide?

Answer Answer: Al forms amphoteric oxide, i.e., acidic as well as basic in nature.

Q.13. Complete the reaction : LiI + KF →

Answer Answer: LiI + KF → LiF + KI; larger cation stabilizes larger anion and smaller cation stabilizes smaller anion.

Q.14. The second ionization enthalpy of Ca is higher than first and yet calcium forms CaCl2 and not CaCl, why?

Answer Answer: The hydration energy of Ca2+ overcomes the second ionisation energy of Ca, that is why Ca forms CaCl2 and not CaCl. Ca+ is not stable.

Q.15. Name the metal which floats on water without apparent reaction.

Answer Answer: Beryllium

Q.16. Can we store sodium metal in air or water?

Answer Answer: No, it reacts violently with water and catches fire.

Q.17. Give two uses of sodium carbonate.

Answer Answer: Refer theory

Q.18. Which is more basic, NaOH or Mg(OH)2 ?

Answer Answer: NaOH.

Q.19. Which method is commonly used to extract sodium metal from its ores?

Answer Answer: Electrolytic reduction using Down cell is commonly used for the extraction of sodium metal.

Q.20. The crystalline salts of alkaline earth metals contain more water of crystallisation than the corresponding alkali metal salts, why?

Answer Answer: This is because alkaline earth metals have smaller size and higher nuclear charges as compared to alkali metals.

Q.21. Name the alkali metal which shows diagonal relationship with magnesium?

Answer Answer: Li

Q.22. What happen when crystals of washing soda(Na2CO3.10H2O) are exposed to air?

Answer Answer: Monohydrate (Na2CO3. H2O) is formed as a result of efflorescence.

Q.23. Why is the solution of alkali metals in liquid ammonia conducting in nature?

Answer Answer: Due to ammoniated electrons and cations.

Q.24. What is the oxidation state of K in KO2?

Answer Answer: K is +1.

Q.25. Sodium peroxide forms a white compound when it comes into contact with moist air. Explain.

Answer Answer: Sodium peroxide when exposed to moist air turns white due to formation of NaOH and Na2CO3.
2Na2O2 + 2H2O → 4NaOH + O2
2Na2O2 + 2CO2 → 2Na2CO3 + O2

Q.26. Account for the following :
Be has less negative value of the reduction potential (E°)

Answer Answer: The less negative value for Be arises from the large hydration energy associated with the small size of Be2+ and the relatively large value of the enthalpy of atomization of the metal.

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