Class 11th
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6 months agoContributor-Level 10
9.41. (d) Hard water forms scum/precipitate with soap. Soap containing sodium stearate (C17H35COONa) reacts with hard water to precipitate out Ca/Mg stearate.It is, therefore, unsuitable for laundry. It is harmful for boilers as well, because of deposition of salts in the form of scale. This reduces the efficiency of the boiler.
New answer posted
6 months agoContributor-Level 10
9.40. (c) The crystalline form of water is ice. Atatmospheric pressure ice crystallises in the hexagonal form, but at very low temperatures it condenses to cubic form. Density of ice is less than that of water. Therefore, an ice cube floats on water. In winter season ice formed on the surface of a lake provides thermal insulation which ensures the survival of the aquatic life. This fact is of great ecological significance.
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6 months agoContributor-Level 10
9.39. (c) Lithium hydride is rather unreactive atmoderate temperatures with O2 or Cl2. It is, therefore, used in the synthesis of other usefulhydrides, e.g.,
8LiH + Al2Cl6 → 2LiAlH4 + 6LiCl
2LiH + B2H6 → 2LiBH4
New answer posted
6 months agoContributor-Level 10
9.38. (b) Loss of the electron from hydrogen atomresults in nucleus (H+) of ~1.5*10–3 pm size.This is extremely small as compared to normalatomic and ionic sizes of 50 to 200pm. As a consequence, H+ does not exist freely and isalways associated with other atoms ormolecules.
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6 months agoContributor-Level 10
9.37. (a) H2O2 decomposes slowly on exposure to light.
2H2O2 (l) → 2H2O (l) + O2 (g)
In the presence of metal surfaces or traces ofalkali (present in glass containers), the above
reaction is catalysed. It is, therefore, stored inwax-lined glass or plastic vessels in dark.
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6 months agoContributor-Level 10
9.36. (i) Hydrogen economy: The basic principle of hydrogen economy is the storage and transportation of energy in the form of liquid or gaseous dihydrogen.
(ii) Hydrogenation: Hydrogenation means addition of hydrogen across double and triple bonds in presence of catalyst to form saturated compounds.
(iii) Syngas: The mixture of CO and H2 are called synthesis gas or 'syngas'. It can be produced by the reaction of steam on hydrocarbon or coke at high temperature in the presence of nickel catalyst
(iv) Water-gas shift reaction: The amount of hydrogen in the syngas can be increased by the action of CO of syngas m
New answer posted
6 months agoContributor-Level 10
9.35. Bleaching action of H2O2 is due to the oxidation of colouring matter by nascent oxygen.
H2O2→ H2O + O
New answer posted
6 months agoContributor-Level 10
9.34. KCl is a salt of strong acid HCl and strong base KOH. Such salts are neutral in nature and do not undergo hydrolysis. In neutral water, acidic water, and alkaline water, KCl dissociates as
Water
KCl → ?K++Cl−
AlCl3? is a salt of strong acid HCl and weak base Al(OH)3?.
(i) In normal water, it is hydrolyzed.
AlCl3?+3H2?O→Al(OH)3?+3H++3Cl−
(ii) In acidic water, H+ ions react with Al(OH)3? (obtained from the hydrolysis of AlCl3?) forming water and Al3+ ions. Hence it exists as Al3++Cl−
AlCl3? + acidifiedwater? → Al++3Cl−
(iii) In alkaline wa
New answer posted
6 months agoContributor-Level 10
9.33. Atomic number 15 is of phosphorus. The hydride is PH3 and its nature is covalent. Atomic number = 19 is of potassium. The hydride is KH and it is ionic in nature. Atomic number = 23 is of vanadium. The hydride is VH. It is interstitial or metallic. Atomic number =44 is of ruthenium, its hydride is interstitial or metallic.
New answer posted
6 months agoContributor-Level 10
9.32. Saline hydrides (i.e. CaH2 NaH etc.) react with water and form the corresponding metal hydroxide with the liberation of H2 gas. Thus, these hydrides can be used to remove traces of water from the organic compounds.
NaH (s) + H2O (l) → NaOH (aq) + H2 (g)
CaH2 (s) + 2H2O (l) → Ca (OH)2 (aq) + H2 (g)
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