Ncert Solutions Chemistry Class 11th
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9.22. What causes the temporary and permanent hardness of water?
9.22. What causes the temporary and permanent hardness of water?
9.22. Temporary hardness of water is due to the presence of bicarbonates of calcium and magnesium in water i.e., Ca (HCO3)2 and Mg (HCO3) in water. Permanent hardness of water is due to the presence of soluble chlorides and sulphates of calcium and magnesium i.e., CaCl2, CaSO4, MgCl2
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9.21. Ice has crystalline structure which is highly ordered due to hydrogen bonding. It has hexagonal form at atmospheric pressure and cubic form at low temperature. Each O atom has tetrahedral geometry and is surrounded by 4 oxygen atoms each at a distance of 276 pm.
Upvote 9.20. Complete the following chemical reactions.
(i) PbS(s) + H2O2 (aq) →
(ii) MnO4– (aq) + H2O2 (aq) →
(iii) CaO(s) + H2O(g) →
(iv) AlCl3(g) + H2O(l)→
(v) Ca3N2(S) + H2O(l) →
Classify the above into (a) hydrolysis, (b) redox and (c) hydration reactions.
9.20. Complete the following chemical reactions.
(i) PbS(s) + H2O2 (aq) →
(ii) MnO4– (aq) + H2O2 (aq) →
(iii) CaO(s) + H2O(g) →
(iv) AlCl3(g) + H2O(l)→
(v) Ca3N2(S) + H2O(l) →
Classify the above into (a) hydrolysis, (b) redox and (c) hydration reactions.
9.20. (i) PbS(s) +4H2O2(aq) → PbSO4(s) + 4H2O(l)
(ii) 2MnO4– (aq) +H2O2(aq) + 6H+(aq) → 2Mn (aq) + 8H2O(l) + 5O2(g)
(iii) CaO(s) + H2O(g) → Ca(OH)2(aq)
(iv) AlCl3(aq) + 3H2O(l) → Al(OH)3(s) + 3HCl (aq)
(v) Ca3N2(s) + H2O(l) → 3Ca(OH)2(aq) + 2NH3(aq)
(a) Hydrolysis reactions, (iii) (iv) and (v)
Upvote 9.19. Consider the reaction of water with F2 and suggest, in terms of oxidation and reduction, which species are oxidised/reduced?
9.19. Consider the reaction of water with F2 and suggest, in terms of oxidation and reduction, which species are oxidised/reduced?
9.19. 2F2 (ag) + 2H2O (l)? O2 (g) + 4H+ (aq) + 4F (aq)
In this reaction water acts as a reducing agent and itself gets oxidised to O2 while F2 acts as an oxidising agent and hence itself reduced to F– ions.
Upvote 9.18. What do you understand by the term ‘auto-protolysis’ of water? What is its significance?
9.18. What do you understand by the term ‘auto-protolysis’ of water? What is its significance?
9.18. Auto-protolysis means self-ionisation of water. It may be represented as
2H2O(l) + H2O(l) ? H3O+(aq) + OH-(aq)
Acid 1 Base 2 Acid 2 Base 1
Due to auto-protolysis nature of water, it can act as a
Upvote 9.17. In water, O is sp3 hybridized. Due to stronger lone pair-lone pair repulsions than bond pair-bond pair repulsions, the HOH bond angle decreases from 109.5° to 104.5°. Thus, water molecule has a bent structure.
Upvote 9.16. Arrange the following:
(i) CaH2, BeH2 and TiH2 in order of increasing electrical conductance.
(ii) LiH, NaH and CsH in order of increasing ionic character.
(iii) H-H, D—D and F—F in order of increasing bond dissociation enthalpy.
(iv) NaH, MgH2 and H2O in order of increasing reducing property.
9.16. Arrange the following:
(i) CaH2, BeH2 and TiH2 in order of increasing electrical conductance.
(ii) LiH, NaH and CsH in order of increasing ionic character.
(iii) H-H, D—D and F—F in order of increasing bond dissociation enthalpy.
(iv) NaH, MgH2 and H2O in order of increasing reducing property.
9.16. (i) BeH2< TiH2 < CaH2
(ii) LiH (iii) F—F < H—H < D—D (iv) H2O < MgH2
Upvote 9.15. Saline hydrides are known to react with water violently producing fire. Can CO2, a well known fire extinguisher, be used in this case? Explain.
9.15. Saline hydrides are known to react with water violently producing fire. Can CO2, a well known fire extinguisher, be used in this case? Explain.
9.15. No. Because if saline hydrides react with water the reaction will be highly exothermic thus the hydrogen evolved in this case can catch fire. CO2 cannot be used as fire extinguisher because CO2 will get absorbed in alkali metal hydroxides.
Upvote 9.14. Among NH3, H2O and HF, which would you expect to have highest magnitude of hydrogen bonding and why?
9.14. Among NH3, H2O and HF, which would you expect to have highest magnitude of hydrogen bonding and why?
9.14. HF is expected to have the highest magnitude of hydrogen bonding since, fluorine is most electronegative. Therefore, HF is the most polar.
Upvote 9.13. How does the atomic hydrogen or oxy-hydrogen torch function for cutting and welding purposes? Explain.
9.13. How does the atomic hydrogen or oxy-hydrogen torch function for cutting and welding purposes? Explain.
9.13. When hydrogen is burnt in oxygen the reaction is highly exothermic, it produces very high temperature nearly 4000°C which is used for cutting and welding purposes.
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