NEET Chemistry Hydrogen
Hydrogen PDF Notes, Important Questions and Synopsis
Position in Periodic Table- Not fixed (sometimes with alkali metals in IA and sometimes with halogens in VIIA group.
Similarities with alkali metals-
- Electronic Configuration- ns1
- Electropositive character-
Valency- Both hydrogen and alkali metals show electrovalency +1.
Oxidation state- Both hydrogen and alkali metals show +1 oxidation state
Affinity for non-metal
Similarities with Halogens-
- Nonmetallic character
- Electronic configuration-Both have one electron less than the next inert gas.
- Diatomic nature- H2,F2,Cl2,Br2
- Electronegative nature-
- Ionisation potential- Ionisation position of hydrogen is 13.5eV. The value is nearer to the halogens.
- Similar covalent compound- CH4 and CCl4, SiH4 and SiCl4.
Discovery and Occurrence-
1. Hydrogen was prepared by Henry Cavendish by the action of acids on metals.
2. Lavoisier named it hydrogen.
3. Hydrogen is most abundant element in the universe.
4. Present in sun’s atmosphere, mineral oils, Organic compounds, alkalies.
Isotopes of Hydrogen-
Protium(1H1), Deuterium(1H2), Tritium(1H3)
Preparation of Dihydrogen, H2 –
- Reaction of granulate zinc with dilute hydrochloric acid
Reaction of zinc with aqueous alkali
- Electrolysis of acidified water
- In production of NaOH and Cl2
- Reaction of Steam on hydrocarbons
Properties of Dihydrogen, H2 –
Physical properties- Colourless, odourless, tasteless, combustible gas
- Reaction with halogens-
- Reaction with dioxygen-
- Reaction with dinitrogen
- Reactions with metals
- Reactions with metal ions and metal oxides
- Reactions with organic compounds
- Ionic or Saline hydride- NaH,LiH
- Covalent hydride- H2O, NH3,CH3
- Metallic or Non-Stoichiometric(or Interstitial) Hydride- LaH2.87,YbH2.55,VH0.56
- Colourless, tasteless liquid
- High freezing and High boiling point
- Bond angle in the water molecule is 104.5°.
Structure of Ice
- The crystalline form of water is ice.
- At atmospheric pressure, ice crystallises in the hexagonal form, but at very low temperatures, it condenses to the cubic form.
Chemical Properties of Water-
- Amphoteric nature-
- Redox Reactions Involving Water-
- Hydrolysis Reaction-
- Hydrates Formation-
Hard and Soft Water-
- Water free from soluble salts of calcium and magnesium is called soft water. It gives lather with soap.
- Water containing soluble salts of calcium and magnesium in the form of hydrogen carbonate, chlorides and sulphates is called hard water. It does not give lather with soap.
Hardness of Water-
- Temporary hardness
- Permanent hardness
Methods to remove Temporary hardness-
- Clark’s method:
Methods to remove permanent hardness-
- Treatment with washing soda (sodium carbonate):
- Calgon’s method:
- Ion-exchange method:
- Synthetic resins method:
Hydrogen Peroxide (H2O2)-
- In the pure state, H2O2 is a colourless (very pale blue) liquid.
- H2O2 is miscible with water and forms a hydrate H2O2. H2O.
- It has a non-polar open book (skew) structure.
- The length of the O–H bond is 95 pm, that of the O–O bond is 147.5 pm and the H–O–H bond angle is 111°5.
- Oxidising action in acidic medium
- Reducing action in acidic medium
- Oxidising action in basic medium
- Reducing action in basic medium
Heavy Water (D2O)-
- It is manufactured by the electrolytic enrichment of normal water. It is used as a moderator in nuclear reactors.
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