7/28/2019 Group 1 Slides 29082012

1/23

Group 1: Alkali metalsLi, Na, K, Rb and Cs3Li: [He] 2s1 ;37Rb: [Kr] 5s1 ;11Na: [Ne] 3s1 ;

55

Cs: [Xe] 6s1

;19

K: [Ar] 4s1

;Fr: [Rn] 7s1

7/28/2019 Group 1 Slides 29082012

2/23

General remarks

They are body centered cubic structure and atoms are

surrounded by 8 nearest neighbours with six more atoms

at a distance

metals are extremely reactive and electropositive (prone

to lose electrons) and exist in combination with other

elements or radicals as positive ions, e.g. NaCl, K2SO4.

All alkali metal atoms have one electron in the outer shell

preceded by a closed shell containing eight electrons -

except for lithium which has a closed shell of two.

7/28/2019 Group 1 Slides 29082012

3/23

Cont

The alkali metals have lower ionisation energies than

any other group of elements

The atoms and ions of the alkali metals increase in sizewith increasing atomic number, since each succeeding

member has an extra closed shell of electrons.

Question:

Why Li ion have high NEP:b/c Li being smaller thanthose of other alkali metals it is strongly hydrated in

aqueous solution and it becomes a better reducing

agent than group 1 metals in aqueous solution.

The value = {Li++(aq) + e Li(s) E = -3.04 V Oxdn = +3.04V}

7/28/2019 Group 1 Slides 29082012

4/23

Properties of the alkali metals

Phys ical propert ies

The metals are soft and silvery colored; they are

extremely good conductors of heat and electricity.

Lithium, sodium and potassium are less dense and

rubidium and cesium more dense than water. Because

they rapidly tarnish and lose their silvery appearance in

air, and they are generally stored under oil.

7/28/2019 Group 1 Slides 29082012

5/23

Chemical properties

The metals are very reactive, increasingly so with increasing atomic number;

thus lithium reacts quietly with water,2Li(s) + 2H2O (l) 2LiOH (aq) + H2 (g)

sodium and potassium react with increasing vigour (strength), and rubidium

and cesium with exceptional violence. In all cases an alkali and hydrogen are

produced, e.g.

2K(s) + 2H2O(l) 2KOH(aq) + H2(g)

They react with a variety of non-metals when heated to give oxides, sulphides,

halides, hydrides, etc., e.g.

4Li(s) + O2(g) 2(Li)2O(s)

2Na(s) + S(s) (Na)2S(s)

2K(s) + Cl2(g) 2KCl(s)

2Rb(s) + H2(g) 2RbH(s)

7/28/2019 Group 1 Slides 29082012

6/23

7/28/2019 Group 1 Slides 29082012

7/23

7/28/2019 Group 1 Slides 29082012

8/23

The hydroxide of sodium and

potassium by Castner-Kellner process and the Gibbs diaphragm cell

process.

Saturated solution ofsodium chloride flows through the cell inthe same direction as a shallow stream of mercury which

constitutes the cathode; the anode consists of a number oftitanium blocks. On electrolysis chlorine is discharged at theanode and sodium at the cathode, where it dissolves in themercury and is removed from the cell. The sodium amalgamis passed through water the sodium reacts to form 50%

sodium hydroxide solution of high purity, the reaction beingcatalysed by the presence of iron grids. The mercury is thenreturned to the cell. The products are thus sodium hydroxide(NaOH), chlorine (Cl2) and hydrogen (H2).

7/28/2019 Group 1 Slides 29082012

9/23

7/28/2019 Group 1 Slides 29082012

10/23

Cathode Anode Na+ discharge NaCl Cl- discharge

..................................................................................................................................

2Na+ + 2e 2Na H2O H+ + OH- 2Cl- Cl + 2e

Na + Hg Na/Hg 2Na/Hg + 2H2O 2NaOH + H2 + 2Hg

Sodium is discharged in preference to hydrogen in the cell,since hydrogen has a high overvoltage at a mercuryelectrode. This amounts to saying that mercury is a poorcatalyst for either or both the discharge of hydrogen ions and

the combination of hydrogen to H2. Since the sodiumdissolves in the mercury which is circulated through the cell,the formation of sodium hydroxide and hydrogen in theelectrolytic cell itself is prevented.

7/28/2019 Group 1 Slides 29082012

11/23

Castner Kellner process

7/28/2019 Group 1 Slides 29082012

12/23

Reactions of sodium and potassium hydroxides

Sodium and potassium hydroxides are white deliquescent

solids which are caustic, and slimy to touch; they dissolve

readily in water with the vigorous evolution of heat.

NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)

or OH-(aq) + H+(aq) H2O(l)

NaOH(aq) + NH4Cl(aq) NaCl(aq) + H2O(l) + NH3(g)

or OH-(aq) + NH4+(aq) H2O(l) + NH3(g)

In aqueous solution they react with many salts andprecipitate the corresponding basic hydroxide, e.g.

CuSO4(aq) + 2NaOH(aq) Cu(OH)2(s) + (Na)2SO4(aq)

or Cu2+(aq) + 2OH-(aq) Cu(OH)2(s)

7/28/2019 Group 1 Slides 29082012

13/23

Uses of sodium and potassium hydroxides

Sodium hydroxide is used in the laboratory for absorbingcarbon dioxide and other acidic gases, in a number oforganic reactions involving hydrolysis, and in volumetricanalysis.

Industrially :it is used in the manufacture of soap(essentially sodium stearate) and sodium formate(obtained by heating sodium hydroxide with carbonmonoxide under pressure).

A solution of potassium hydroxide in alcohol is used in

organic chemistry; industrially the main use of potassium hydroxide is in

the manufacture of soft soap.

7/28/2019 Group 1 Slides 29082012

14/23

The manufacture of sodium carbonate - the Solvay

process

CaCO3(s) + 2NaCl(s) (Na)

2CO

3(s) + CaCl

2(s)

The raw materials are sodium chloride, calcium carbonate and ammonia(practically all recovered in the process),plus energy (fuel).The calcium carbonate is strongly heated to give quicklime (CaO) andcarbon dioxide: CaCO3(s) CaO(s) + CO2(g)

NH3(g) + H2O(l) NH3H2O(aq) NH4+(aq) + OH-(aq) Na+(aq) + Cl-(aq) + NH4

+(aq) + OH-(aq) + CO2(g) Na+(aq) + HCO3

-(aq)+ NH4

+(aq) + Cl-(aq)

Na+(aq) + HCO3-(aq) NaHCO3(s)

Sodium hydrogen carbonate which is not very soluble in sodium chloridesolution - the common ion effect - is filtered and heated to producesodium carbonate:

2NaHCO3(s) (Na)2CO3(s) + H2O(l) + CO2(g) :rain water

H2O(l) + CO2(g) H2CO3 (aq)

7/28/2019 Group 1 Slides 29082012

15/23

Cont

The sodium carbonate at this stage is contaminated with

ammonium salts. Ifrequired to be pure, it is dissolved in

water and carbon dioxide is blown through the solution.

The precipitate ofsodium hydrogen carbonate is filtered

and heated to produce pure sodium carbonate;recrystallisation from water produces washing soda,

(Na)2CO310H2O.

(Na)2CO3(aq) + H2O(l) + CO2(g) 2NaHCO3(s)

2NaHCO3(s) (Na)2CO3(s) + H2O(l) + CO2(g)

7/28/2019 Group 1 Slides 29082012

16/23

The manufacture of potassium carbonate

Potassium carbonate cannot be made by the Solvay

process since potassium hydrogen carbonate is rather too

soluble in water to be precipitated. It can, however, be

made by passing carbon dioxide into a solution of

potassium hydroxide; evaporation and subsequent ignitiongive the carbonate:

KOH(aq) + CO2(g) KHCO3(aq)

2KHCO3(aq) (K)2CO3(s) + H2O(l) + CO2(g)

Reaction for bleach

Bleaching powderreaction: Ca(OH)2 + Cl2CaOCl2 + H2

7/28/2019 Group 1 Slides 29082012

17/23

Uses of sodium and potassium carbonates

Reaction:CaCl2(aq) + (Na)2CO3(aq) CaCO3(s) +2NaCl(aq)

Sodium carbonate is often used in the laboratory as avolumetric reagent.

Industrially: it is used in a wide variety of ways, includingthe manufacture of glass, in the preparation of sodiumsalts, in the treatment of hard water, for the manufactureof soap, and in papermaking.

Potassium carbonate, which is more expensive, is usedas a drying agent in organic chemistry since it isdeliquescent (melts);and mixed with sodium carbonate itis used as fusion mixture for getting insoluble salts intosolution during analytical procedures.

R ti f h d b t f di d

7/28/2019 Group 1 Slides 29082012

18/23

Reaction of hydrogen carbonates of sodium and

potassium

It is obtained by passing carbon dioxide through a coldconcentrated solution of the corresponding carbonate, e.g.

(Na)2CO3(aq) + H2O(l) + CO2(g) 2NaHCO3(s)

2KHCO3(aq) (K)2CO3(s) + H2O(l) + CO2(g)

Sodium hydrogen carbonate is much less soluble in waterthan potassium hydrogen carbonate and both solutions arealkaline by hydrolysis, but not to the same extent as thecorresponding carbonates:

HCO3-(aq) + H2O(l) H2CO3(s) + OH

-(l)

Because sodium hydrogen carbonate solution is less alkaline

than sodium carbonate solution, the former is often used toprecipitate normal carbonates which would otherwise beformed as basic carbonates.

Cu2+(aq) + 2HCO3-(aq) CuCO3(s) + H2O(l) + CO2(g)

7/28/2019 Group 1 Slides 29082012

19/23

The nitrates

Sodium nitrate occurs as Chile saltpetre in the desertregions in Chile, along with sodium iodate (NaIO3) (fromwhich iodine is extracted). NaNO3 can be separated fromNaIO3 by recrystallisation from an aqueous solution, as it isless soluble than the iodate.

Both sodium and potassium nitrates are used as nitrogenousfertilizers. The latter is a constituent in gunpowder.

Sodium nitrate is also used as a meat preservative.

When heated, the nitrates decompose to give the nitrite and

oxygen, e.g.

2KNO3(s) 2KNO2(s) + O2(g)

7/28/2019 Group 1 Slides 29082012

20/23

The nitrites

The nitrites can be made by the thermal decomposition

2NaOH(aq) + NO2(g) + NO(g) 2KNO2(aq) + H2O(l)

The nitrites can be purified by crystallisation from water.

Sodium nitrite is used extensively in the production ofdyes.

Sulphates

2NaOH(aq) + H2SO4(aq) Na2SO4(aq) + H2O(l)

Sodium sulphate crystallises as the decahydrateNa2SO410H2O which is efflourescence to give theanhydrous salt; when heated above 32.5C.

7/28/2019 Group 1 Slides 29082012

21/23

Cont

Potassium sulphate crystallises as the anhydrous salt and it is

found as such in the Strassfurt deposits in Germany. It isused formaking up potassium deficiency in soil, as a dryingagent and for making potash alum KAl(SO4)212H2O, which isused as a mordant in dyeing

Hydrolysis of alkali metal salts

alkali metal halides, nitrates and sulphates are neutral in

aqueous solution; but other salts, for example hydrogencarbonates, carbonates, cyanides and sulphides, show analkaline reaction in solution:

CO32-(aq) + H2O(l) HCO3

-(aq) + OH-(aq)

HCO3-(aq) + H2O(l) H2CO3(aq) + OH

-(aq)

CN-(aq) + H2O(l) HCN(aq) + OH-(aq)

S2-(aq) + H2O(l) HS-(aq) + OH-(aq)

HS-(aq) + H2O(l) H2S(aq) + OH-(aq)

Potash alum

7/28/2019 Group 1 Slides 29082012

22/23

Questions

Why is lithium a poor reducing agent

extraction and occurrence

Chemical and physical properties and reactions

Explain of Castner Kellner process

Explain Solvay process and uses of carbonates

Bromides and iodides: reactions

Hydrogen sulphates and hydrolysis of alkali

metals

7/28/2019 Group 1 Slides 29082012

23/23