Notesale: Turn your study into money

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HYDROGEN


This element does not fit well into any group in the periodic table
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The observation that
whenever it burned it produced water spurred Lavoisier to name it "hydrogen" which means "water
producer"
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Hence it occurs in compounds such as water, acids and
organic substances
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Of these isotopes, tritium is radioactive and having a half-life of twelve years
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The process involves
passing electricity through acidified water causing it to decompose:

2H2O(l) » 2H2(g) + O2(g)
o

Displacement from water by using a metal
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The very active metals high up in the activity
series (eg K, Ca, Na) liberate hydrogen gas from ordinary cold water e
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2Na(s) +2H2O(l) » 2NaOH(aq) + H2(g)
For moderately active metals eg mg hot water is required
Mg(s) + 2H2O » Mg(OH)2(aq) + H2
The other metals in the activity series above hydrogen (e
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Zn, Fe, Pb) require steam to produce
hydrogen
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o

Displacement from dilute acids by using moderately active metals (e
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Ca, Mg, Zn)
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Hno3 is not used in this method because HNO3 is a strong oxidising agent
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o

Action of steam on hot coke:

C(s) + H2O(g) » CO(g) + H2(g)
The CO2 is removed by means of KOH or any other suitable method
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

Test for hydrogen is carried out by introducing a lighted splint
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

The physical properties are:

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It is a colourless, odourless and tasteless gas
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o

It is much less dense than air (0
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e
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o

It liquefies at -240•C and 13 atm
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o

It does not support ordinary combustion, hence it extinguishes any lighted splint introduced into
its gas with a 'pop sound'
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g
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g
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Because of the extreme combustibility of hydrogen,
helium is used nowadays for this purpose
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o

In the manufacture of ammonia (Haber's Process)
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o

In the synthesis of organic chemicals e
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methanol
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g
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o

For making hydrogen bombs ( from its isotopes)

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