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 e−→ 2Na ( Reduction at cathode )
Alkali metals compounds
From the commonly known sodium compounds : Sodium hydroxide NaOH and Sodium carbonate Na2CO3 .
Sodium hydroxide NaOH
The most important properties of sodium hydroxide
- It is a white hygroscopic solid compound , Hygroscobic substance is a substance which absorbs the water vapour from the atmospheric air .
- It has a soapy feel and corrosive effect on skin .
- 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 .
- 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
- It is used in many important industries , such as soap , synthetic silk and paper .
- It is used to purify petroleum from the acidic impurities .
- 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
- White powder , easily dissolves in water and its solution has an alkaline effect .
- It is thermal stable compound , it melts by heat without decomposition .
- 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
- It is used in many important industries , such as manufacture of glass , paper industry & textile industry .
- 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
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 .
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 .