CBSE Class 9 Chemistry Hydrogen Notes

CBSE Class 9 Chemistry-Hydrogen. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.

Hydrogen

ImportantQuestions

1.Write the names of isotopes of hydrogen.

2.Why hydrogen molecule is unreactive at room temperature?

3.Whydoes hydrogen occur in a diatomic form rather than in a monoatomicf orm under normal conditions?

4.What do you understand by the term auto-protolysis of water?

5.What properties of water make it useful as a solvent?

6.Does heavy water can be used for drinking purposes?

7.How does hydrogen peroxide behave as a bleaching agent?

8.Why is hydrogen peroxide stored in waxlined bottles?

9.Why does water show high boiling point as compared to hydrogen sulphide?

Answers

1.Protium,deuterium and tritium

2.Due to high enthalpy of H-H bond.

3.To attain the stable inert gas configuration of helium, it shares its single electron with electron of other hydrogen atom to form a stable diatomic molecule.

4.Self ionisation of water is termed as auto-protolysis of water.

5.Water has high dielectric constant and high dipole moment.

6.No as it slows down the rates of reactions occurring in human beings, plants and animals.

7.Bleaching action of hydrogen peroxide due to oxidation of colouring matter by nascent oxygen which it liberates on decomposition.

8.Hydrogen peroxide is decomposed by rough surfaces of glass, alkali oxides present in it and

light to form water and oxygen.

H₂O₂------------>H₂O + O

9.Due to H-bonding in water.

1.What is meant by demineralised water? Is it useful for drinking purposes?

2.Among NH₃, H₂O and HF, which would you expect to have highest magnitude of hydrogen bonding and why?

3.Consider the reaction of water with F2 and suggest, in terms of oxidation and reduction, which species are oxidised and reduced?

4.Write chemical reactions to show the amphoteric nature of water.

5.Write chemical reactions to justify that hydrogen peroxide function as an oxidising as well as reducing agent.

6. What causes the temporary and permanent hardness of water?

Answer

1. Water which is free from all cations and anions is called demineralised water. It is not useful for drinking purposes since it does not contain even useful minerals. 

2. HF has highest magnitude of hydrogen bonding since F is the most electronegative among N, O and F.

3. F₂ + H₂O --- O₂ + H⁺ + F^-

3. F₂ + H₂O --- O₃ + H⁺ + F^-

these reaction , water act as reducing agent and itself oxidised to either O₂ or O₃ while F₂ acts as an oxidising agent and itself reduced to F- ion.

4. H₂O + H₂S ---- H₃O⁺ + HS^-(Water act as base)

H₂O + NH₃ ---- NH+₄ +  + OH-(Water act as acid)

5. Oxidising agent

Fe²⁺ + H⁺ + H₂O₂ ----------- Fe³⁺ + H₂O

MnO4- + H⁺ + H₂O₂ -------- Mn²⁺ + H₂O + O₂

6. Temporary hardness is due to presence of soluble bicarbonates of calcium and Magnesium and permanent hardness is due to chlorides and sulphates of calcium and magnesium.

1. Hard water is unsuitable for laundry, washing and dyeing. Explain.

2. What do you understand by (i) electron-deficient, (ii) electron-precise, and (iii) electron-rich compounds of hydrogen? Provide justification with suitable examples.

Answers

1. Since we know that the soap are the sodium salts of higher fatty acids like stearic acid

(C₁₇H₃₅COOH), oleic acid (C₁₇H₃₃COOH) or palmitic acid (C₁₇H₃₁COOH). When soap is added to hard water, the anions of soap combine with Ca+2 and Mg+2 ions to form calcium and magnesium salt which are insoluble in water.

M ⁺² + 2C₁₇H₃₅COONa → (C₁₇H₃₅COO)₂M(ppt) + 2Na

Therefore, no lather is produce until all the calcium and magnesium ions are precipitated. This also results into wastage of lot of soap. So hard water is unsuitable for laundry, washing and dyeing.

2. [a]Electron deficient:- The hydrides which do not have sufficient number of electrons to form normal covalent bonds is called electron deficient hydride. For example, hydride of group 13 (BH₃, AlH₃, etc.).

[b] Electron precise:-The hydrides which have sufficient number of electrons required for forming covalent bonds is called electron precise hydride. For example, hydrides of group 14

(CH₄, SiH₄, GeH₄, SnH_4, PbH₄ etc.) they have tetrahedral geometry.

[c] Electron rich hydrides:-The hydrides which have excess electrons as required to form normal covalent bonds is called electron rich hydride. For example, hydrides of group 15 to 17 (NH₃, PH₃, H₂O, H₂S, H₂Se, H₂Te, HF etc.)

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