Sodium: is found in group 1 period III on the periodic table. It has an atomic number of 11 and an atomic mass of 23.
It does not occur as a free element in nature because it is very reactive. However, it is found mainly in the combined state as sodium chloride in sea water, and as rock salt (Halite) in underground deposits.
It is extracted from fused sodium chloride by electrolysis using the Dawn's Cell. a little amount of CaCl2 is added to lower the melting point (from about 801 to 600)
Chemistry of the reaction
at the cathode
At the cathode: - the sodium ions migrate to the cathode where they gain an electron each to become reduced to metallic sodium
Na+(l) + e- → Na(s)
At the anode: - the chloride ions migrate to the anode where they loss their excess charge and become reduced to atomic chlorine
Cl- → Cl + e-
the chlorine atom combines with another chlorine atom and is discharged as chlorine gas
Cl + Cl → Cl2(g)
Properties of Sodium:
i. Sodium is soft and can easily be cut with a knife.
ii. It has a of 0.968g/cm3
iii. It has a silvery-white appearance.
iv. It has a low melting point.
v. It has a boiling point.
v. Sodium is a good conductor of electricity.
Chemical Properties
i) Reaction with air or oxygen: - Sodium metal tarnishes on exposure to air
4Na(s) + O2(g) →2Na2O(s)
Na2O(s) + H2O(l) → 2NaOH (s)
NaOH(aq) + CO2 → Na2CO3
In excess air or oxygen, it burns with a golden yellow flame to yield sodium peroxide Na2O2,
2 Na(s) + O2(g) → Na2O2(s)
In limited supply of air sodium oxide (Na2O) is formed.
Na(s) + O2(g) → 2Na2O(s)
Because of its reactivity sodium is stored under paraffin oil or other organic solvents like naphtha or toluene.
ii. Reaction with water: - It reacts violently with cold water to yield sodium hydroxide and hydrogen with large amount of heat.
Na(s) + H2O(l) → NaOH(aq) + H2(g)
iii. Reaction with acids: - It reacts explosively to form a salt and hydrogen gas
iv. Na(s) + HCl(aq) →NaCl(aq) + H2(g)
Na(s) H2SO4(aq) → Na2SO4(aq) + H2(g)
This reaction is highly dangerous and should not be carried out in the school laboratory.
Reaction with non-metals: - sodium combines directly with the following non-metals when heated to form binary compounds.
Na(s) + S(s) →Na2S(s)
Na(s) + H2 → NaH(s)
Na(s) +P(s) → Na3P(s)
Na(s) + Cl(g) → NaCl(s)
Sodium does not react with carbon, boron and nitrogen
Reaction with mercury: - Sodium forms various stable mixture with mercury known as sodium amalgam of varying composition such as NaHg, Na2Hg, Na3Hg etc.
Sodium amalgam reacts with water to yield hydrogen.
Na(s) + Hg(l) →NaHg(l)
v. Reaction with ammonia: - Sodium reacts with ammonia to form sodamide and hydrogen gas.
Na(s) + NH3(g) → NaNH2(s) + H2(g)
As a reducing agent: - Sodium act as a strong reducing agent. It reduces some metallic chlorides and oxides to their metals.
Na(s) + BeCl2(s) → NaCl(s) + Be(s)
Test for sodium ions
i). Flame test: when sodium compounds give a bright or golden yellow flame when burnt in a non-luminous flame
Uses of Sodium:
-i). Sodium is used in the manufacture of other compounds like sodamide, sodium peroxide.
ii). Sodium alloys like NaK(sodium-potassium alloy), are used as coolant in nuclear reactors.
iii). Sodium vapor lamps are commonly used for street lighting
iv) It is used in the manufacture of tetraethyl lead (C2H5)4Pb, which is used as an antiknock agent in petrol.
v) It is used as a laboratory reagent (Lassaigne's extract).
vii). It is used for producing amalgams used as reducing agents.
viii) Sodium used as a catalyst in the preparation of artificial rubber and also as a deoxidizer in the preparation of light alloys.
COMPOUNDS OF SODIUM
Sodium compounds are generally white crystalline salts and are mostly soluble in water.
1. Sodium chloride (NaCl): (table salt) it is found naturally in sea water and in underground deposits as rock salt.
Properties
- It is a white anhydrous crystalline solid
- It has a melting point of 8010C and a boiling point of 14200C.
- The pure form is not deliquescent.
Uses
1. It is used as a food preservative.
2. It is used as an important raw material for the manufacturing of Na, NaOH, Cl2, Na2CO3, NaClO3 and other compounds.
3. It is used for salting out soap
4. It is used in glazing earthenware
5. It is used in regenerating water softener.
2. Sodium hydroxide (NaOH): It is a white crystalline solid, made into flakes or pallets
Properties
-i). It is a white crystalline solid
ii). It is highly deliquescent
iii) It has a melting point of 3200C without decomposing.
iii). It dissolves in water to give a strong alkaline solution with the evolution of heat
Chemical properties
With acids: - NaOH produce salt and water.
2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l)
With acidic oxides: - It form sodium salt. E.g.
NaOH(aq) + SO2(g) → NaHSO3(aq)
With ammonium salts: - When heated with an ammonium salt, ammonia gas is liberated.
NaOH(aq) + NH4Cl(s)→ NaCl(aq) + H2O(l) + NH3(g)
With metals – Al and Zn are amphoteric; they combine with excess NaOH to form the alluminate (III) and respectively with hydrogen gas.
2Al(s) + 2NaOH(aq) + 6H2O(l) → 2NaAl(OH)4(aq) + 3H2(g)
sodium aluminate (III)
Zn(s) + 2NaOH(aq) + 2H2O(l) → Na2Zn(OH)4(aq) + H2(g)
sodium zincate (II)
Therefore, Aluminium or Zinc containers should not be used to store NaOH.
As a precipitating agent: - NaOH solution is most times used to precipitate insoluble hydroxides. E.g
Zn2+(aq) + 2OH-(aq) → Zn(OH)2(s)
Pb2+(aq) + 2OH-(aq) → Pb(OH)2(s)`
Zn(OH)2, Al(HO)3, Sn(OH)2, and Pb(OH)2, are amphoteric and will react excess sodium hydroxide to form complex salts. E.g
Zn(OH)(s) + 2NaOH(aq) → Na2Zn(OH)4(aq)
With non-metals: NaOH reacts with various non-metals to form sodium salts.
Reaction with glass – High concentrations of NaOH attack glass to form sodium trioxosilicate (IV). Hence, glass stoppers are not used to cover reagent bottles containing concentrated sodium hydroxide or burette because they would become stuck. This is called etching.
Uses of NaOH
1. it is used as a strong alkali
2. it is used as an analytical and precipitating reagent
3. it is used for absorbing CO2
4. it is used for making soap, rayon (artificial silk),
5. I is used for making paper
6. it is used for making various compounds like sodium trioxochlorate (V), sodium methanoate and phosphine.
7. it is used for purification of bauxite
8. it is used petroleum refining.
9. it is used for the bleaching of cotton textiles.
3.Sodium tetraoxosulphate (IV) (Na2SO4)
Properties
It occurs both in the anhydrous form called saltcake or as a decahydrate form known as Glauber’s salt which is efflìorescent.
Uses Of Na2SO4
i. It is used as a purgative
ii. In producing of sodium sulphide
Iii it is in the manufacture of wood pulp, glass, and detergents
4. Sodium bicarbonate (NaHCO3): (baking soda): - A white it is utilized in cooking and as a leavening agent in baking.
- Sodium carbonate (Na2CO3): Also called soda ash
Properties
-Na2CO3 in form of soda ash (i.e. anhydrous Na2CO3) is a fine white powder, while washing soda (Na2CO3.10H2O) is translucent and crystalline.
i. They both dissolve in water to form an alkaline solution by hydrolysis.
ii. Washing soda is efflorescent
iii. It does not decompose on heating
iii. t reacts with acid to liberate CO2
Uses of Na2CO3
i. It is used in the industrial manufacturing of glass
ii. It is used as a water softener
iii. It is used in manufacturing of detergent
iv. It is used in the manufacturing NaOH, borax, waterglass, soap and paper
iv. It is used in laboratory to standardize acids and as an analytical reagent.
vi. it is used in glass production,
vi. It is used as a pH regulator in various industrial processes
SOLVAY PROCESS: This is the industrial preparation of NaCO3
The raw materials are sodium chloride, ammonia gas and limestone. The reactions are as follows
1.The ammonia gas in brine (conc. sodium chloride) to give a mixture known as ammoniacal brine.
ii. This mixture is then allowed to trickle down a Solvay tower as a stream of carbon (IV) oxide is forced up the tower. It reacts with the ammonia in the mixture to yield ammonium hydrogen trioxocarbonate (IV) (NH4HCO3).
i). NH3(g) + CO2(g) +H2O →NH4HCO3(aq)
The NH4HCO3 reacts with the sodium chloride to give sodium hydrogen trioxocarbonate (IV) (NaHCO3).
ii). NH4HCO3(aq) + NaCl(aq) →NaHCO3(s) + NH4Cl(aq)
The sodium hydrogen trioxocarbonate (IV) is slightly insoluble in water and so precipitates out as a white sludge.
The NaHCO3 is then filtered, rinsed and heated to give anhydrous sodium trioxocarbonate (IV) (soda ash), steam and carbon (IV) oxide
iii). NaHCO3(s) →Na2CO3(s) + H2O(l) + CO2(g)
The anhydrous Na2CO3(s) (soda ash) is redissolved in hot water and recrystallize to give the pure hydrated compound (Na2CO3.10H2O) called washing soda
iv). Na2CO3(s) + 10H2O(l) →Na2CO3.10H2O(s)
some highlights of the process
-Perforated dome-shaped baffle-plates are incorporated into the Solvay tower to slow down the flow rate of the ammoniacal brine so as to allow for proper contact between the ammoniacal brine and the carbon (IV) oxide as well as increase the surface area of reaction
-The concentrated sodium chloride also serves as a carrier for the ammonia gas.
Importance and Economics of the reaction: -
i. All the raw materials required in the Solvay process are quite cheap and are also readily available.
ii. Almost all the carbon (IV) oxide generated during the process from the decomposition of the NaHCO3(s) is recycled, making the process quite economical.
iii. The sodium chloride solution is obtained from sea water or from rock salt deposits,
iv. the carbon (IV) is got from limestone found in rich deposits around.
CaCO3(s) →CaO(s) + CO2(g)
The calcium oxide (CaO) is then reacted with the ammonium chloride to generate ammonia gas, which is also recycled back into the, producing calcium chloride as a by-product from the process.
CaO(s) + NH4Cl(aq)→ CaCl2 +H2O+ NH3(g)
5. Sodium nitrate (NaNO3): It is a white crystalline solid produced when sodium hydroxide reacts with trioxonitrate (V) acids.
Properties
I). it is a white crystalline solid
ii). It has a melting point of 3100C and decomposes on further heating.
Uses
i) it is used primarily as a nitrogenous fertilizer
ii) In making trioxonitrate (V) acid, potassium trioxonitrate (V) and sodium dioxoxnitrate (III).
iii). It is used in the production of explosives and glass.
Objective questions
1.
THEORY QUESTIONS
1. Explain with equations where appropriate the functions of the following substances in the Solvay Process (i) limestone (ii). ammonia (iii). brine.
2. Calculate the mass of sodium trioxocarbonate (IV) produced by the complete decomposition of 16.8g of sodium hydrogen trioxocarbonate (IV). [ H=1, O=16, Na=23, S=33]
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