Strength of Acids and Bases Neutralization is a chemical reaction in which an acid reacts with a base to form salt and water. In this process, a hydrogen ion of the acid combines with a hydroxide ion of the
base to form a water molecule. The anion of the acid combines with the cation of the base to form a salt.
For example when hydrochloric acid reacts with sodium hydroxide the chlorine of hydrochloric acid combines with sodium of sodium hydroxide to form sodium chloride. The hydrogen of hydrochloric acid combines with the hydroxyl part of the sodium hydroxide and forms water.
HCl + NaOH � NaCl + H2O
Strength of acids or bases: Based on extent of ionization acids and bases are classified into strong acids, weak acids and strong bases, weak bases. Strong acids or strong bases ionize completely
(100%) to form ions in the aqueous solution.
Example: Hydrochloric acid ionizes completely to form ions.
HCl(aq)
H+ (aq)+ Cl(aq)
Sodium hydroxide ionizes completely to form ions.
NaOH(aq) Na+(aq)+ OH(aq)
Weak acids or weak bases ionizes partially (<100%) to form ions in the aqueous solution.
Example: Acetic acid ionizes partially in aqueoussolution to form ions.
CH3COOH(aq)
H+ (aq) + CH3COO(aq)
Ammonium hydroxide ionizes partially in aqueous solution to form ions.
NH4OH
NH4+ + OH(aq)
An acid or base is considered as strong or weak depending on the concentration of hydrogen and hydroxide ions within it. This concentration or the power of hydrogen differs from substance to substance and can be measured using a scale, called the pH scale. A solution that has a pH value of less than 7 is acidic and a solution with a pH value of more than 7 is basic. A neutral solution is indicated by a pH value of 7 on the scale. Strong acids will posses pH values between 0-2 and weak acids posses pH values more than 3. Strong bases will posses pH values between 12-14 and weak bases posses pH values less than 12.
pH of some of the acids and bases:
- Hydrochloric acid 0.1 – 1.0
- Sulphuric acid 1.0 – 1.2
- Phosphoric acid 1.3 -1.5
- Acetic acid (Vineger) 2.9 – 3.0
- Carbonic acid 3.8 – 4.0
- Water 6.9 – 7.0
- Ammonia 10.8 – 11.2
- Sodium hydroxide 13 – 14
Applications of neutralization concept in daily life:
Antacids like Milk of Magnesia are mild bases that neutralize the acids in the stomach and aid
digestion. If the pH lowers, the acidity in the mouth increases and leads to tooth decay. Toothpastes
are basic in nature and they counteract the acid in the mouth.
Hydrangea produces pink flowers when the soil has a pH value of 6.8 or higher and blue flowers when the pH value is 6.0 or less. If the soil is acidic, then the applied pesticides, herbicides and fungicides
will not be absorbed by the soil. In order to neutralize the soil, suitable bases are used. Generally,
salts of calcium or magnesium, which are basic are used to neutralize soil acidity.
When a bee stings, formic acid is released. That is what makes the skin burn. Baking soda, which is a base, neutralizes the formic acid and provides relief from the pain. Salts and their Properties
The compounds formed by the reaction bet ween an acids and a bases are known as a salts.
Acid + Base
Salt + Water
Salts are ionic compounds which contain positively charged cations and negatively charged anions. During salt formation cation is coming from base and anion is coming from acid.
Example: In Sodium chloride (NaCl) formation cation sodium is coming from sodium hydroxide
and anion chlorine is coming from hydrochloric acid.
Classification of salts: Based on nature the salts have been classified into different types.
They are:
- Normal salts
- Acidic salts
- Basic salts
- Double salts
- Complex salts
Normal salts: These salts are formed by the complete replacement of hydrogen in acids by other metal cations from the bases.
NaCl is normal salt formed by the reaction of HCl with NaOH.
HCl + NaOH
NaCl + H2O
Acidic salts: Salts which are formed by the partial replacement of hydrogen atoms of acids are called acidic salts.
Example: NaHSO4 is formed when partial replacement of hydrogen atoms by the sodium atoms of base.
H2SO4 + NaOH
NaHSO4 + H2O
In general these salts formed when the reacted base is not sufficient for the neutralisation of acid.
Basic salts: Salts which are formed by the partial replacement of hydroxyl group are called basic salts.
Example: Ca(OH)Cl is formed by the partial replacement of hydroxide group from Ca(OH)2
by chloride ions of acid.
Ca(OH)2 + HCl
Ca(OH)Cl + H2O
In general these salts formed when the reacted acid is not sufficient for the neutralisation of base
Table below giving neutral, acidic and basic salts
Double salts: Salts that are formed by mixing of two simple salts which are obtained crystallisation.
Example: Potash alum – K2SO4 Al2 (SO4)3 .24H2O
Dolomite – CaCO3.MgCO3
Complex salts: The salts which contains different types of metal atoms which on hydrolysis produces complex ions along with simple ions are called complex salts.
Example: [Ag(NH3)2]Cl
[Ag (NH3)2]+ + Cl
Salts in our daily life: Baking soda
Chemical name: Sodium hydrogen carbonate
Molecular formula: NaHCO3
Sodium hydrogen carbonate is commonly called as baking soda.
Sodium hydrogen carbonate is used in baking industry.
It is used in preparation of soda acid.
It is also used in foam type fire extinguishers.
Washing soda:
Molecular formula: Na2CO3.10H2O
Chemical formula: Sodium carbonate-decahydrate
Adding water to sodium carbonate and this allowing this mixture to cool to forms decahydrated
sodium carbonate. This is commonly called as washing soda.
Na2CO3 + 10H2O
Na2CO3.10H2O
In general sodium carbonate is prepared by passing CO2 gas through concentrated NaOH.
2NaOH + CO2
Na2CO3 + H2O
Properties: It is a white crystalline solid. It exists as decahydrate of sodium carbonate.
When exposed to dry air and heating it loses water molecules to change into anhydrous form.
Na2CO3.10H2O + Exposure to open dry air
Na2CO3.H2O + 9H2O
Na2CO3.H2O + Heating
Na2CO3
It is soluble in water and during dilution heat will be released out.
On reaction with acids sodium carbonate releases carbon dioxide along with the formation of sodium salts and water.
Na2CO3 + HCl
2NaCl + H2O + CO2
Sodium carbonate is used to manufacture of glass, cleansing agents, soap, glass and paper.
Bleaching powder (CaOCl2): Bleaching powder chemically known as calciumoxy chloride.
It is prepared by the reaction between chlorine and slaked lime at about 40 oC.
Ca(OH)2 + Cl2
Ca(OCl)Cl + H2O + Cl2
Ca(OH)2 + H2SO4
CaSO4 + H2O + Cl2
It acts a strong oxidising agent to bleach substances.
CaOCl2 + KNO2
CaCl2 + KNO3
CaOCl2 + H2S
CaCl2 + H2O + S
It is used to bleach cotton, linen textiles and wood pulp.
Coloured matter + Bleaching powder
Colourless product
It is also used to disinfect drinking water.
Hydrated salts: The molecules of salts which contain fixed number of water molecules in them are called hydrated salts.
In general they exist as dry in pure form.
These salts on heating lose water molecules in them and forms anhydrous salts.
Example:Ferrous sulphate heptahydrate (FeSO4.7H2O) on heating loses water molecules in it.
FeSO4.7H2O (on heating)
FeSO4 + 7H2O
Some of the hydrated salts along with their chemical formula
Plaster of Paris (CaSO4.12H2O): Plaster of Paris which is chemically called calcium sulphate hemihydrate.
Since it is brought to use from Paris, called as “Plaster of Paris”.
It is prepared by heating of gypsum at 373K.
CaSO4.2H2O
CaSO4 ‰ H2O +1‰ H2O
Gypsum (on heating at 373 K) Plaster of Paris Water
Uses: It is used as a bandage, proofing material, sealing agent.
It is used for making statues, toys and decorative articles. It is also used for smoothening wall surfaces.
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