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NEET Chemistry Hydrogen

Hydrogen PDF Notes, Important Questions and Synopsis

SYNOPSIS
 


Symbol- H

Electronic configuration-1s1
Position in Periodic Table- Not fixed (sometimes with alkali metals in IA and sometimes with halogens in VIIA group.
Similarities with alkali metals-

  1.  Electronic Configuration- ns1
  2. Electropositive character-

    begin mathsize 12px style table attributes columnalign left end attributes row cell straight H rightwards arrow with straight e to the power of minus on top straight H to the power of plus end cell row cell Li rightwards arrow with straight e to the power of minus on top Li to the power of plus end cell row cell Na rightwards arrow with straight e to the power of minus on top Na to the power of plus end cell end table end style
  3. Valency- Both hydrogen and alkali metals show electrovalency +1.

  4. Oxidation state- Both hydrogen and alkali metals show +1 oxidation state

  5. Affinity for non-metal

  6. Reducing nature


Similarities with Halogens-

  1. Nonmetallic character
  2. Electronic configuration-Both have one electron less than the next inert gas.
  3. Diatomic nature- H2,F2,Cl2,Br2
  4. Electronegative nature-

    begin mathsize 12px style table attributes columnalign left end attributes row cell straight H plus straight e to the power of minus rightwards arrow straight H to the power of minus end cell row cell Cl plus straight e to the power of minus rightwards arrow Cl to the power of minus end cell end table end style
  5.  Ionisation potential- Ionisation position of hydrogen is 13.5eV. The value is nearer to the halogens.
  6. 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 –

Laboratory preparation-

  1. Reaction of granulate zinc with dilute hydrochloric acid
    begin mathsize 12px style text Zn + 2H end text to the power of text + end text end exponent rightwards arrow Zn to the power of plus 2 end exponent plus straight H subscript 2 end style

Reaction of zinc with aqueous alkali
begin mathsize 12px style table attributes columnalign left end attributes row cell Zn plus 2 NaOH rightwards arrow Na subscript 2 ZnO subscript 2 plus straight H subscript 2 end cell row cell text                                end text Sodium text   end text Zincate end cell end table end style
Commercial production-

  1. Electrolysis of acidified water

    begin mathsize 12px style 2 straight H subscript 2 straight O rightwards arrow 2 straight H subscript 2 plus straight O subscript 2 end style
  2. In production of NaOH and Cl2

    begin mathsize 12px style 2 Na to the power of plus plus 2 Cl to the power of minus plus 2 straight H subscript 2 straight O rightwards arrow Cl subscript 2 plus straight H subscript 2 plus 2 Na to the power of plus plus 2 OH to the power of minus end style
  3. Reaction of Steam on hydrocarbons

begin mathsize 12px style table attributes columnalign left end attributes row cell CH subscript 4 plus straight H subscript 2 straight O rightwards arrow from Ni to 1270 straight K of CO plus 3 straight H subscript 2 end cell row cell straight C plus straight H subscript 2 straight O rightwards arrow with 1270 straight K on top CO plus straight H subscript 2 end cell row cell CO plus straight H subscript 2 straight O rightwards arrow with 673 straight K on top CO subscript 2 plus straight H subscript 2 end cell row cell CO plus straight H subscript 2 straight O minus text Water gas\Syn gas end text end cell end table end style

Properties of Dihydrogen, H2 –
Physical properties- Colourless, odourless, tasteless, combustible gas
Chemical properties-

  1. Reaction with halogens-
    begin mathsize 12px style straight H subscript 2 plus straight X subscript 2 rightwards arrow 2 HX text             end text left parenthesis straight X equals straight F comma Cl comma Br comma straight I right parenthesis end style
  2. Reaction with dioxygen-
    begin mathsize 12px style 2 straight H subscript 2 plus straight O subscript 2 rightwards arrow 2 straight H subscript 2 straight O end style
  3. Reaction with dinitrogen
    begin mathsize 12px style straight N subscript 2 plus 3 straight H subscript 2 rightwards arrow 2 NH subscript 3 end style
  4. Reactions with metals
    begin mathsize 12px style straight H subscript 2 plus 2 straight M rightwards arrow 2 MH end style
  5. Reactions with metal ions and metal oxides
    begin mathsize 12px style yH subscript 2 plus straight M subscript straight x straight O subscript straight y rightwards arrow xM plus yH subscript 2 straight O end style
  6. Reactions with organic compounds
    begin mathsize 12px style table attributes columnalign left end attributes row cell straight H subscript 2 plus CO plus RCH equals CH subscript 2 rightwards arrow RCH subscript 2 CH subscript 2 CHO end cell row cell straight H subscript 2 plus RCH subscript 2 CH subscript 2 CHO rightwards arrow RCH subscript 2 CH subscript 2 CH subscript 2 OH end cell end table end style

Hydrides-

  1. Ionic or Saline hydride- NaH,LiH
  2. Covalent hydride- H2O, NH3,CH3
  3. Metallic or Non-Stoichiometric(or Interstitial) Hydride- LaH2.87,YbH2.55,VH0.56

Water-

  1. Colourless, tasteless liquid
  2. High freezing and High boiling point
  3. Bond angle in the water molecule is 104.5°.

Structure of Ice

  1. The crystalline form of water is ice.
  2. At atmospheric pressure, ice crystallises in the hexagonal form, but at very low temperatures, it condenses to the cubic form.

 

Chemical Properties of Water-

  1. Amphoteric nature-

    begin mathsize 12px style straight H subscript straight 2 straight O left parenthesis straight l )+ NH subscript straight 3 left parenthesis aq right parenthesis rightwards arrow OH to the power of straight minus left parenthesis aq ) +  NH subscript straight 4 superscript straight plus left parenthesis aq right parenthesis end style
    begin mathsize 12px style straight H subscript 2 straight O left parenthesis straight l right parenthesis plus straight H subscript 2 straight S left parenthesis aq right parenthesis rightwards arrow straight H subscript 3 straight O to the power of blank to the power of plus end exponent left parenthesis aq right parenthesis plus HS to the power of minus left parenthesis aq right parenthesis end style
  2. Redox Reactions Involving Water-

    begin mathsize 12px style 2 straight H subscript 2 straight O text   end text left parenthesis straight l right parenthesis plus 2 Na text   end text left parenthesis straight s right parenthesis rightwards arrow 2 NaOH text   end text left parenthesis aq right parenthesis plus straight H subscript 2 left parenthesis straight g right parenthesis end style

    begin mathsize 12px style 6 CO subscript 2 left parenthesis straight g right parenthesis plus 12 straight H subscript 2 straight O left parenthesis straight l right parenthesis rightwards arrow straight C subscript 6 straight H subscript 12 straight O subscript 6 left parenthesis aq right parenthesis plus 6 straight H subscript 2 straight O left parenthesis straight l right parenthesis plus 6 straight O subscript 2 left parenthesis straight g right parenthesis end style
  3. Hydrolysis Reaction-
    begin mathsize 12px style table attributes columnalign left end attributes row cell straight P subscript 4 straight O subscript 10 left parenthesis straight s right parenthesis plus 6 straight H subscript 2 straight O left parenthesis straight l right parenthesis rightwards arrow 4 straight H subscript 3 PO subscript 4 left parenthesis aq right parenthesis end cell row cell SiCl subscript 4 left parenthesis straight l right parenthesis plus 2 straight H subscript 2 straight O left parenthesis straight l right parenthesis rightwards arrow SiO subscript 2 left parenthesis straight s right parenthesis plus 4 HCl left parenthesis aq right parenthesis end cell end table end style
  4. Hydrates Formation-
    Coordinated water- begin mathsize 12px style open square brackets Cr left parenthesis straight H subscript 2 straight O right parenthesis subscript 6 close square brackets to the power of 3 plus end exponent text   end text 3 Cl to the power of minus end style
    Interstitial water-begin mathsize 12px style BaCl subscript 2.2 straight H subscript 2 straight O end style
    Hydrogen-bonded water-
    begin mathsize 12px style open square brackets Cu left parenthesis straight H subscript 2 straight O right parenthesis subscript 4 close square brackets to the power of 2 plus end exponent text   end text SO subscript 4 superscript 2 minus end superscript. straight H subscript 2 straight O text    end text in text    end text CuSO subscript 4.5 straight H subscript 2 straight O end style

Hard and Soft Water-

  1. Water free from soluble salts of calcium and magnesium is called soft water. It gives lather with soap.
  2. 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-

  1. Temporary hardness
  2. Permanent hardness

Methods to remove Temporary hardness-

  1. Boiling:
    begin mathsize 12px style table attributes columnalign left end attributes row cell Mg open parentheses HCO subscript 3 close parentheses subscript 2 space rightwards arrow with Heating on top Mg open parentheses OH close parentheses subscript 2 downwards arrow 2 CO subscript 2 upwards arrow end cell row cell Ca open parentheses HCO subscript 3 close parentheses subscript 2 rightwards arrow with Heating on top CaCO subscript 3 downwards arrow straight H subscript 2 straight O plus CO subscript 2 upwards arrow end cell end table end style
  2. Clark’s method:
    begin mathsize 12px style Ca open parentheses HCO subscript 3 close parentheses subscript 2 plus Ca open parentheses OH close parentheses subscript 2 rightwards arrow 2 CaCO subscript 3 downwards arrow 2 straight H subscript 2 straight O
Mg open parentheses HCO subscript 3 close parentheses subscript 2 plus 2 Ca open parentheses OH close parentheses subscript 2 rightwards arrow 2 CaCO subscript 3 downwards arrow plus Mg open parentheses OH close parentheses subscript 2 downwards arrow plus 2 straight H subscript 2 straight O end style

Methods to remove permanent hardness-

  1. Treatment with washing soda (sodium carbonate):

    begin mathsize 12px style table attributes columnalign left end attributes row cell text MCl end text subscript text 2 end text end subscript text +Na end text subscript text 2 end text end subscript text CO end text subscript text 3 end text end subscript rightwards arrow text MCO end text subscript text 3 end text end subscript downwards arrow text +2NaCl end text end cell row cell text MSO end text subscript text 4 end text end subscript text +Na end text subscript text 2 end text end subscript text CO end text subscript text 3 end text end subscript rightwards arrow text MCO end text subscript text 3 end text end subscript downwards arrow text +Na end text subscript text 2 end text end subscript text SO end text subscript text 4 end text end subscript end cell end table end style
  2. Calgon’s method:

    begin mathsize 12px style table attributes columnalign left end attributes row cell Na subscript 6 straight P subscript 6 straight O subscript 18 rightwards arrow 2 Na to the power of plus plus Na subscript 4 straight P subscript 6 straight O subscript 18 superscript 2 minus end superscript end cell row cell straight M subscript 2 plus end subscript plus Na subscript 4 straight P subscript 6 straight O subscript 18 superscript 2 minus end superscript rightwards arrow open square brackets Na subscript 2 MP subscript 6 straight O subscript 18 close square brackets to the power of 2 minus end exponent plus 2 Na to the power of plus end cell end table end style
  3. Ion-exchange method:
    begin mathsize 12px style table attributes columnalign left end attributes row cell 2 NaZ left parenthesis straight s right parenthesis plus straight M to the power of 2 minus end exponent left parenthesis aq right parenthesis rightwards arrow MZ subscript 2 left parenthesis straight s right parenthesis plus 2 Na to the power of plus left parenthesis aq right parenthesis end cell row cell text                                                                                                            end text left parenthesis straight M equals Mg comma Ca right parenthesis end cell end table end style
    begin mathsize 12px style MZ subscript 2 left parenthesis straight s right parenthesis plus 2 NaCl text   end text left parenthesis aq right parenthesis rightwards arrow 2 NaZ text   end text left parenthesis straight s right parenthesis plus MCl subscript 2 left parenthesis aq right parenthesis end style

  4. Synthetic resins method:

    begin mathsize 12px style 2 RNa left parenthesis straight s right parenthesis plus straight M to the power of 2 plus end exponent left parenthesis aq right parenthesis rightwards arrow straight R subscript 2 straight M left parenthesis straight s right parenthesis plus 2 Na to the power of plus left parenthesis aq right parenthesis end style

Hydrogen Peroxide (H2O2)-

Preparation-

  1. begin mathsize 12px style BaO subscript 2.8 straight H subscript 2 straight O left parenthesis straight s right parenthesis plus straight H subscript 2 SO subscript 4 left parenthesis aq right parenthesis rightwards arrow BaSO subscript 4 left parenthesis straight s right parenthesis plus straight H subscript 2 straight O subscript 2 left parenthesis aq right parenthesis plus 8 straight H subscript 2 straight O left parenthesis straight l right parenthesis end style
  2. begin mathsize 12px style 2 straight H subscript 2 SO subscript 4 superscript minus left parenthesis aq right parenthesis rightwards arrow with Electrolysis on top HO subscript 3 SOOSO subscript 3 left parenthesis aq right parenthesis rightwards arrow with Hydrolysis on top 2 HSO subscript 4 superscript minus left parenthesis aq right parenthesis plus 2 straight H to the power of plus left parenthesis aq right parenthesis plus straight H subscript 2 straight O subscript 2 left parenthesis aq right parenthesis end style
  3. begin mathsize 12px style 2 minus text ethylanthraquinol end text rightwards arrow over leftwards arrow from text H end text subscript text 2 end text end subscript text /Pd end text to text O end text subscript text 2 end text end subscript text (air) end text of straight H subscript 2 straight O subscript 2 plus left parenthesis oxidised text   end text product right parenthesis end style

Physical Properties

  1. In the pure state, H2O2 is a colourless (very pale blue) liquid.
  2. H2O2 is miscible with water and forms a hydrate H2O2. H2O.

Structure

  1. It has a non-polar open book (skew) structure.
  2. 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.

Chemical properties-

  1. Oxidising action in acidic medium

    begin mathsize 12px style table attributes columnalign left end attributes row cell 2 Fe to the power of 2 plus end exponent left parenthesis aq right parenthesis plus 2 straight H plus left parenthesis aq right parenthesis plus straight H subscript 2 straight O subscript 2 left parenthesis aq right parenthesis rightwards arrow 2 Fe to the power of 3 plus end exponent left parenthesis aq right parenthesis plus 2 straight H subscript 2 straight O left parenthesis straight l right parenthesis end cell row cell PbS left parenthesis straight s right parenthesis plus 4 straight H subscript 2 straight O subscript 2 left parenthesis aq right parenthesis rightwards arrow PbSO subscript 4 left parenthesis straight s right parenthesis plus 4 straight H subscript 2 straight O left parenthesis straight l right parenthesis end cell end table end style
  2. Reducing action in acidic medium

    begin mathsize 12px style table attributes columnalign left end attributes row cell 2 MnO subscript 4 superscript minus plus 6 straight H plus plus 5 straight H subscript 2 straight O subscript 2 rightwards arrow 2 Mn to the power of 2 plus end exponent plus 8 straight H subscript 2 straight O plus 5 straight O subscript 2 end cell row cell HOCl plus straight H subscript 2 straight O subscript 2 rightwards arrow straight H subscript 3 straight O plus plus Cl to the power of minus plus straight O subscript 2 end cell end table end style
  3. Oxidising action in basic medium

    begin mathsize 12px style table attributes columnalign left end attributes row cell 2 Fe subscript 2 plus straight H subscript 2 straight O subscript 2 rightwards arrow 2 Fe to the power of 3 plus end exponent plus 2 OH to the power of minus end cell row cell Mn to the power of 2 plus end exponent plus straight H subscript 2 straight O subscript 2 rightwards arrow Mn to the power of 4 plus end exponent plus 2 OH to the power of minus end cell end table end style
  4. Reducing action in basic medium
    begin mathsize 12px style table attributes columnalign left end attributes row cell straight I subscript 2 plus straight H subscript 2 straight O subscript 2 plus 2 OH to the power of minus rightwards arrow 2 straight I to the power of minus plus 2 straight H subscript 2 straight O plus straight O subscript 2 end cell row cell 2 text   end text MnO subscript 4 superscript minus plus 3 straight H subscript 2 straight O subscript 2 rightwards arrow 2 MnO subscript 2 plus 3 straight O subscript 2 plus 2 straight H subscript 2 straight O plus 2 OH to the power of minus end cell end table end style

Heavy Water (D2O)-

  • It is manufactured by the electrolytic enrichment of normal water. It is used as a moderator in nuclear reactors.

    begin mathsize 12px style table attributes columnalign left end attributes row cell CaC subscript 2 plus 2 straight D subscript 2 straight O rightwards arrow straight C subscript 2 straight O rightwards arrow straight C subscript 2 straight D subscript 2 plus Ca open parentheses OD close parentheses subscript 2 end cell row cell SO subscript 3 plus straight D subscript 2 straight O rightwards arrow straight D subscript 2 SO subscript 4 end cell row cell Al subscript 4 straight C subscript 3 plus 12 straight D subscript 2 straight O rightwards arrow 3 CD subscript 4 plus 4 Al open parentheses OD close parentheses subscript 3 end cell end table end style