Alkali metals compounds properties and uses ( Sodium hydroxide & Sodium carbonate )

Alkali metals are elements that are not found in nature in a free state , but rather in the form of ionic compounds , Because these metals easily lose their valence electron and they are the most powerful reducing agents , Preparing of these metals involves the electrolysis of their molten ( fused ) halides .

Extraction of sodium metal from its ores

By the electrolysis of molten sodium chloride in the presence of a flux substance to decrease the melting point of the halide , Oxidation and reduction reactions occur at anode and cathode , as the following :

2Cl Cl2 + 2e      ( Oxidation at anode )

2Na + + 2 e2Na      ( Reduction at cathode )

Alkali metals compounds

Alkali metals

Alkali metals

From the commonly known sodium compounds : Sodium hydroxide NaOH and Sodium carbonate Na2CO3 .

Sodium hydroxide NaOH

The most important properties of sodium hydroxide 
  1. It is a white hygroscopic solid compound , Hygroscobic substance is a substance which absorbs the water vapour from the atmospheric air .
  2. It has a soapy feel and corrosive effect on skin .
  3. It dissolves easily in water forming an alkaline solution and the reaction is accompanied by the liberation of heat energy as it is an exothermic dissolution .
  4. It reacts with acids forming sodium salt of the acid and water ( Neutralization reaction ) .

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

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

The most important uses of sodium hydroxide
  1. It is used in many important industries , such as soap , synthetic silk and paper .
  2. It is used to purify petroleum from the acidic impurities .
  3. It is used in detection of basic radicals ( cations ) , such as : Cu2+ and Al3+ .
Detection of Cu2+ and Al3+ cations by using sodium hydroxide solutions 

Copper ( II ) cation Cu2+ : Detection by adding sodium hydroxide solution to the cation solution such as copper II sulphate .

Observation : A blue precipitate of copper II hydroxide is formed which turns black on heating , due to forming of copper II oxide .

CuSO4 ( aq ) + 2NaOH ( aq ) Na2SO4 ( aq ) + Cu (OH)2 ( s ) ↓   blue ppt.

Cu(OH)2 ( s ) H2O ( l ) +  CuO ( s ) ↓    black ppt.

Aluminum cation Al3+ : Detection by adding sodium hydroxide solution to the cation solution such as aluminum III chloride .

Observation : A white gelatinous precipitate of aluminum hydroxide is found which dissolves in excess reagent ( NaOH ) , To form sodium meta aluminate ( NaAlO2 ) , which is soluble in water .

AlCl3 ( aq ) + 3NaOH ( aq ) 3NaCl ( aq ) + Al (OH)3 ( s ) ↓   white ppt.

Al(OH)3 ( s ) + NaOH ( aq ) 2 H2O ( l ) + NaAlO2 ( aq ) ↓     sodium meta aluminate

Sodium carbonate Na2CO3

The most important properties of sodium carbonate
  1. White powder , easily dissolves in water and its solution has an alkaline effect .
  2. It is thermal stable compound , it melts by heat without decomposition .
  3. It reacts with acids forming sodium salt of acid and carbon dioxide gas evolves .

 2HCl ( aq ) + Na2CO3 ( s ) 2NaCl ( aq ) + H2O ( l ) + CO2 ( g )

The most important uses of sodium carbonate
  1. It is used in many important industries , such as manufacture of glass , paper industry & textile industry .
  2. It is used in removing water hardness ( water softening ) .
Preparation of sodium carbonate in laboratory

By passing carbon dioxide gas through a hot solution of sodium hydroxide , then the solution is left to cool , white crystals of hydrated sodium carbonate are separated gradually .

CO2 ( g ) + 2NaOH ( aq ) H2O ( l ) + Na2CO3 ( aq )

2NaOH ( aq ) + CO2 ( g ) Na2CO3.10 H2O ( s )Na2CO3 ( s ) + 10 H2O ( v )

The hydrated sodium carbonate Na2CO3.10 H2O is known as washing soda , Because it is used to remove the water hardness which is arised from the presence of soluble Ca2+ and Mg2+ salts in water , where washing soda reacts with these salts forming calcium carbonate and magnesium carbonate which are insoluble in water , so , the water hardness is removed as shown in the following equations :

Na2CO3 ( aq ) + CaCl2 ( g ) CaCO3 ( s ) + 2NaCl ( aq )

Na2CO3 ( aq ) + MgSO4 ( aq ) Na2SO4 ( aq ) + MgCO3 ( s ) 

Preparation of sodium carbonate in industry ( Solvay process )

The scientist solvay had reached a method to prepare sodium carbonate from table salt , by passing ammonia and carbon dioxide gases in a saturated aqueous solution of sodium chloride to produce sodium bicarbonate .

NH3 ( g ) + CO2 ( g ) + NaCl ( aq ) + H2O ( l ) NaHCO3 ( aq ) + NH4Cl ( aq )

Then heating sodium bicarbonate , it will decompose to sodium carbonate , water and carbon dioxide .

2NaHCO3 ( aq ) Na2CO3 ( aq ) + H2O ( v ) + CO2 ( g )

Biochemical role of sodium & potassium ions
Sodium ions

They are considered from the common ions present in the blood plasma & in the intercellular fluids in the body , They are found in many natural sources such as vegetables ( specially celery ) , milk & its products , They have an important role in the vital processes , Because they represent the required medium to transfer the nutrients , such as : glucose and amino acids .

Potassium ions

They are considered from the common ions present in the living cell , They play an important role in oxidation of glucose in the living cell , to produce the required energy for its activity , They are found in many natural sources such as meats , milk , eggs , vegetables & cereals .

Elements of p-block , General properties of group 5A elements ( group 15 )

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