BASES
BASE
A Base is a substance which gives hydroxide ion OH-when dissolved in water.
Example
NaOH It is a base since it contains OH- ion or hydroxide ion.
Soap contains Sodium hydroxide, Baking soda contains Sodium bicarbonate , Washing soda contains Hydrated sodium carbonate
Bases can be classifies according to strength (degree of ionization) and molecular structure , Bases are classified according to their degree of ionization (dissociation ) into strong bases and weak bases .
Classifications of bases according to strength
(degree of ionization )
Strong bases: Bases which are completely ionized in the water, Their solutions are good conductors
of electricity, They are considered as strong
electrolytes .
Examples : Potassium hydroxide KOH , Sodium hydroxide NaOH , Barium hydroxide Ba(OH)2 .
Weak bases: Bases which are incompletely ionized
in the water, Their solutions are bad conductors
of electricity ,They are considered as weak
electrolytes .
Examples : Ammonium hydroxide NH4OH
Classifications of bases according to molecular structure
Bases are classified according to their molecular structure into :
(a). Metal oxides such as Iron ( II ) oxide FeO and Magnesium oxide MgO.
FeO ( s ) + 2HCl ( aq ) → FeCl2 + H2 O ( l )
(b). Metal hydroxides such as Calcium hydroxide Ca(OH)2 , Sodium hydroxide NaOH .
Ca(OH)2 ( aq ) + H2SO4 ( aq ) → CaSO4 ( aq ) + 2 H2 O ( l )
(c). Metal carbonates such as potassium carbonate K2CO3 and Sodium carbonate Na2CO3 .
K2CO3 ( s ) + 2HCl ( aq ) → 2KCl ( aq ) + H2 O ( l ) + CO2 ( g )
(d). Metal bicarbonates such as potassium bicarbonate KHCO3 and Sodium bicarbonate NaHCO3 .
KHCO3 ( s ) + HCl ( aq ) → KCl ( aq ) + H2 O ( l ) + CO2 ( g )
The bases that dissolve in the water are called Alkalis , Alkali is a base that dissolves in the water and gives hydroxide ion ( OH−), So, the alkalis are a part of the bases and therefore, we can say that : all alkalis are bases and not all bases are alkalis .
Sodium carbonate is from bases because sodium carbonate reacts with acid forming salt and water , Not all bases are alkalis because there are some bases don’t dissolve in the water .
Physical Properties of Alkalis
Alkalis have the following properties:
1.Alkalis have bitter taste and a slippery soapy feel.
2.Alkaline solutions have pH values greater than 7. (More about pH value in the next sub-topic)
3.Alkaline solutions turn red litmus paper blue.
Chemical Properties of Alkalis
There are four common reactions of alkalis:
Neutralisation Reaction
When an alkali reacts with an acid, the reaction is called a neutralisation reaction.
In a neutralisation reaction, only salt and water are produced. Alkali + acid→ salt + water
All neutralisation can be summarized as the following:
Metal oxides: O2−+H+ → H2O , Metal hydroxides: OH− + H+ → H2O
Example of neutralisation reactions:
Zinc oxide and hydrochloric acid: ZnO(s) + 2HCl(aq) → ZnCl2(aq) + H2O(l)
Sodium hydroxide and sulphuric acid: 2NaOH(aq) + H2SO4(aq)→ Na2SO4(aq) + 2H2O(l)
Hydrogen ion, H+, from the acid neutralized by the hydroxide ion, OH-, from the base to base to form the water molecules
Neutralization reaction can be defined as the process in which acid react with a base or an alkali
to form salt and water only.
Or
Hydrogen ion, H+, from the acid is neutralized by the hydroxide ion, OH-, from the base to form the water molecules
Neutralization reaction can be defined as the process in which acid react with a base or an alkali to form salt and water only.
Or
Neutralization is the combination of hydrogen ions, H+, and hydroxide ions, OH-, to form water molecules. A salt is also formed.
Reaction With Ammonia Salts
When a mixture of an alkali and ammonium salt is heated, ammonia gas is given off.
Alkali + ammonium salt + heat →ammonia gas
The reaction is summarized as:
OH−+NH+4→NH3 + H2OOH−+NH4+→NH3+H2O
Example of such a reaction:
Ammonium chloride and sodium hydroxide: NH4Cl(s) + NaOH(s) →NaCl(s) + NH3(g) + H2O(l)
ammonium sulphate and calcium hydroxide: (NH4)2SO4(s) + Ca(OH2)(s) → CaSO4(s) + 2NH3(g) + 2H2O(l)
Precipitation of Metal Hydroxides
Solutions of alkalis are used to precipitate insoluble metal hydroxides from solutions of their salts.
Mn+(aq) + nOH−(aq) → M(OH)n(s)
Example of such a reaction:
Aqueous sodium hydroxide and aqueous copper(II) sulphate
2NaOH(aq) + CuSO4(aq) → Cu(OH)2(s) + Na2SO4(aq) or Cu2+(aq) + 2OH−(aq) → Cu(OH)2(aq)
A blue precipitate of copper(II) hydroxide is produced.
Aqueous sodium hydroxide and aqueous magnesium chloride
2NaOH(aq) + MgCl2(aq) →
Mg(OH)2(s) +
2NaCl(aq) Or Mg2+(aq) + 2OH−(aq) →
Mg(OH)2(s) .
A white precipate of magnesium hydroxide is produced.
Reaction with metals
Alkalis usually do not react with metals.
Strong alkalis such as sodium hydroxide react with aluminium to give hydrogen.
H+(aq) + OH-(aq) H2O(l)
Uses of Bases
1. Sodium hydroxide (caustic soda) is used in the manufacture of soap. It is used in petroleum-refining; in making medicines, paper, pulp, etc. It is used in making rayon.
2. Calcium hydroxide is also known as slaked lime. It is used to neutralize acid in water supplies; in the manufacture of bleaching powder; as a dressing material for acid burns; as an antidote for food poisoning; in the preparation of fungicides and in the mixture of whitewash. It is mixed with sand and water to make mortar which is used in the construction of buildings. It is also used by farmers on the fields to neutralize the harmful effects of acid rain.
3. Ammonium hydroxide is used to remove ink spots from clothes and to remove grease from window-panes. It is used in the cosmetic industry.
4. Alkalis are used in alkaline batteries. Generally, potassium hydroxide is used in such batteries.
Measurement Of Acidity And Alkalinity (the pH Scale)
pH is a negative logarithm of hydrogen ion concentration, or pH is - log [H+]. pH is a measure of hydrogen ion, H+, concentration. The number 7 on the pH scale represents the condition of exact neutrality. Numbers less than 7, that is, pH 6,5,4 etc indicate increasing acidity as the number decreases. Numbers greater than 7, that is, pH 8,9,10 etc indicate increasing alkalinity as the number increases.
The pH value of a colourless solution can be obtained by adding a universal indicator or by spotting the liquid on a universal indicator paper. In both cases, a colour will appear from which the pH of the liquid can be decided.
Calculation of pH
Example 1
Find the pH of 0.1 mole NaOH
Solution: H2O H+ + OH-
[H+] [OH-] Kw (ionic product of water)
[H+] [OH-] = 10---14
[H+] [10-1] = 10 -14
[H+] = 10-14 = 10-14 x 10-1 = 10-13
10-1
pH = 13
Example 2
Calculate the pH of 0.01M of KOH
[H+] [OH-] Kw (ionic product of water) ; [H+] - [OH]- = 10-14 ; [H+][10-2] = 10-14
[H+] = 10-14 = 10-14+2 = 10-12 = 10-2
pH of the alkaline is 12
Example 3
Calculate the Ph of 0.1M HCl
[H+][OH]- = 10-14 ; [10-1] [OH]- = 10-14 ; [OH-] = 10-14 = 10-14 x 10-1 = 10-13
10-1
pH of the acid is 14-13 = 1
BASE
A Base is a substance which gives hydroxide ion OH-when dissolved in water.
Example
NaOH It is a base since it contains OH- ion or hydroxide ion.
Soap contains Sodium hydroxide, Baking soda contains Sodium bicarbonate , Washing soda contains Hydrated sodium carbonate
Bases can be classifies according to strength (degree of ionization) and molecular structure , Bases are classified according to their degree of ionization (dissociation ) into strong bases and weak bases .
Classifications of bases according to strength
(degree of ionization )
Strong bases: Bases which are completely ionized in the water, Their solutions are good conductors
of electricity, They are considered as strong
electrolytes .
Examples : Potassium hydroxide KOH , Sodium hydroxide NaOH , Barium hydroxide Ba(OH)2 .
Weak bases: Bases which are incompletely ionized
in the water, Their solutions are bad conductors
of electricity ,They are considered as weak
electrolytes .
Examples : Ammonium hydroxide NH4OH
Classifications of bases according to molecular structure
Bases are classified according to their molecular structure into :
(a). Metal oxides such as Iron ( II ) oxide FeO and Magnesium oxide MgO.
FeO ( s ) + 2HCl ( aq ) → FeCl2 + H2 O ( l )
(b). Metal hydroxides such as Calcium hydroxide Ca(OH)2 , Sodium hydroxide NaOH .
Ca(OH)2 ( aq ) + H2SO4 ( aq ) → CaSO4 ( aq ) + 2 H2 O ( l )
(c). Metal carbonates such as potassium carbonate K2CO3 and Sodium carbonate Na2CO3 .
K2CO3 ( s ) + 2HCl ( aq ) → 2KCl ( aq ) + H2 O ( l ) + CO2 ( g )
(d). Metal bicarbonates such as potassium bicarbonate KHCO3 and Sodium bicarbonate NaHCO3 .
KHCO3 ( s ) + HCl ( aq ) → KCl ( aq ) + H2 O ( l ) + CO2 ( g )
The bases that dissolve in the water are called Alkalis , Alkali is a base that dissolves in the water and gives hydroxide ion ( OH−), So, the alkalis are a part of the bases and therefore, we can say that : all alkalis are bases and not all bases are alkalis .
Sodium carbonate is from bases because sodium carbonate reacts with acid forming salt and water , Not all bases are alkalis because there are some bases don’t dissolve in the water .
Physical Properties of Alkalis
Alkalis have the following properties:
1.Alkalis have bitter taste and a slippery soapy feel.
2.Alkaline solutions have pH values greater than 7. (More about pH value in the next sub-topic)
3.Alkaline solutions turn red litmus paper blue.
Chemical Properties of Alkalis
There are four common reactions of alkalis:
Neutralisation Reaction
When an alkali reacts with an acid, the reaction is called a neutralisation reaction.
In a neutralisation reaction, only salt and water are produced. Alkali + acid→ salt + water
All neutralisation can be summarized as the following:
Metal oxides: O2−+H+ → H2O , Metal hydroxides: OH− + H+ → H2O
Example of neutralisation reactions:
Zinc oxide and hydrochloric acid: ZnO(s) + 2HCl(aq) → ZnCl2(aq) + H2O(l)
Sodium hydroxide and sulphuric acid: 2NaOH(aq) + H2SO4(aq)→ Na2SO4(aq) + 2H2O(l)
Hydrogen ion, H+, from the acid neutralized by the hydroxide ion, OH-, from the base to base to form the water molecules
Neutralization reaction can be defined as the process in which acid react with a base or an alkali
to form salt and water only.
Or
Hydrogen ion, H+, from the acid is neutralized by the hydroxide ion, OH-, from the base to form the water molecules
Neutralization reaction can be defined as the process in which acid react with a base or an alkali to form salt and water only.
Or
Neutralization is the combination of hydrogen ions, H+, and hydroxide ions, OH-, to form water molecules. A salt is also formed.
Reaction With Ammonia Salts
When a mixture of an alkali and ammonium salt is heated, ammonia gas is given off.
Alkali + ammonium salt + heat →ammonia gas
The reaction is summarized as:
OH−+NH+4→NH3 + H2OOH−+NH4+→NH3+H2O
Example of such a reaction:
Ammonium chloride and sodium hydroxide: NH4Cl(s) + NaOH(s) →NaCl(s) + NH3(g) + H2O(l)
ammonium sulphate and calcium hydroxide: (NH4)2SO4(s) + Ca(OH2)(s) → CaSO4(s) + 2NH3(g) + 2H2O(l)
Precipitation of Metal Hydroxides
Solutions of alkalis are used to precipitate insoluble metal hydroxides from solutions of their salts.
Mn+(aq) + nOH−(aq) → M(OH)n(s)
Example of such a reaction:
Aqueous sodium hydroxide and aqueous copper(II) sulphate
2NaOH(aq) + CuSO4(aq) → Cu(OH)2(s) + Na2SO4(aq) or Cu2+(aq) + 2OH−(aq) → Cu(OH)2(aq)
A blue precipitate of copper(II) hydroxide is produced.
Aqueous sodium hydroxide and aqueous magnesium chloride
2NaOH(aq) + MgCl2(aq) →
Mg(OH)2(s) +
2NaCl(aq) Or Mg2+(aq) + 2OH−(aq) →
Mg(OH)2(s) .
A white precipate of magnesium hydroxide is produced.
Reaction with metals
Alkalis usually do not react with metals.
Strong alkalis such as sodium hydroxide react with aluminium to give hydrogen.
H+(aq) + OH-(aq) H2O(l)
Uses of Bases
1. Sodium hydroxide (caustic soda) is used in the manufacture of soap. It is used in petroleum-refining; in making medicines, paper, pulp, etc. It is used in making rayon.
2. Calcium hydroxide is also known as slaked lime. It is used to neutralize acid in water supplies; in the manufacture of bleaching powder; as a dressing material for acid burns; as an antidote for food poisoning; in the preparation of fungicides and in the mixture of whitewash. It is mixed with sand and water to make mortar which is used in the construction of buildings. It is also used by farmers on the fields to neutralize the harmful effects of acid rain.
3. Ammonium hydroxide is used to remove ink spots from clothes and to remove grease from window-panes. It is used in the cosmetic industry.
4. Alkalis are used in alkaline batteries. Generally, potassium hydroxide is used in such batteries.
Measurement Of Acidity And Alkalinity (the pH Scale)
pH is a negative logarithm of hydrogen ion concentration, or pH is - log [H+]. pH is a measure of hydrogen ion, H+, concentration. The number 7 on the pH scale represents the condition of exact neutrality. Numbers less than 7, that is, pH 6,5,4 etc indicate increasing acidity as the number decreases. Numbers greater than 7, that is, pH 8,9,10 etc indicate increasing alkalinity as the number increases.
The pH value of a colourless solution can be obtained by adding a universal indicator or by spotting the liquid on a universal indicator paper. In both cases, a colour will appear from which the pH of the liquid can be decided.
Calculation of pH
Example 1
Find the pH of 0.1 mole NaOH
Solution: H2O H+ + OH-
[H+] [OH-] Kw (ionic product of water)
[H+] [OH-] = 10---14
[H+] [10-1] = 10 -14
[H+] = 10-14 = 10-14 x 10-1 = 10-13
10-1
pH = 13
Example 2
Calculate the pH of 0.01M of KOH
[H+] [OH-] Kw (ionic product of water) ; [H+] - [OH]- = 10-14 ; [H+][10-2] = 10-14
[H+] = 10-14 = 10-14+2 = 10-12 = 10-2
pH of the alkaline is 12
Example 3
Calculate the Ph of 0.1M HCl
[H+][OH]- = 10-14 ; [10-1] [OH]- = 10-14 ; [OH-] = 10-14 = 10-14 x 10-1 = 10-13
10-1
pH of the acid is 14-13 = 1
Comments
Post a Comment