Complete revision notes for EDEXCEL GCSE ( 9-1) chemistry notes.
Acid , bases and salt
The complete revision notes on :
• Characteristics of acid , bases and salts
• Acid and alkali titrations
• Preparation of salts
• practical knowledge
Acid , bases and salt
Any chemical substance you choose from your lab, it may be an acid, base (or alkali) or a salt.
Properties of all the acids:
• Acid is sour in taste ( do not taste laboratory chemicals !!).
• They are soluble in water( partially or completely).
• They are corrosive.
• Acid changes the colour of indicators( Aqueous solutions can be acid, alkaline or neutral.
Indicators are used to tell if a solution is acidic, alkaline, basic or neutral) . They have the ability
to turn blue litmus paper red.
• In their aqueous solutions, acids act as good conductors of electricity.
Acids
Acids only show their properties when they are in aqueous solution. When acids are in water they
dissociate to form hydrogen ions .These ions are responsible for acid properties.
• An acid is an H+ ion (or proton) donor
• A base is an H+ ion (or proton) acceptor or OH- donor .
Bronsted-Lowry theory
The theory says:
• An acid is a proton (hydrogen ion) donor.
• A base is a proton (hydrogen ion) acceptor.
Any acid can be dissociated as follows :
HA(aq) + H2O(l) → H3O+(aq) + A-(aq)
Acid dissolves to form hydrogen ions. Hydrogen ion is bonded with water to form hydronium ions.
Hydronium ion is unstable and it forms H+ ions and water again.
Example 1: H2O (l) + HCl(aq) → H3O+(aq) + Cl-(aq)
The HCI donates a proton (H+) to the H2O molecule. So the HCI is an acid and H 2O is a base because
it accepts the proton( H+ )
Example 2: NH3(aq) + HCl(aq) → NH4Cl(aq)
Hydrochloric acid donate proton (H+) to ammonia , so hydrochloric acid is a proton donor and
, Complete revision notes for EDEXCEL GCSE ( 9-1) chemistry notes.
ammonia accept the proton to become NH4+ ion in ammonium chloride.
• If an acid to behave as an H + ion donor , there must be an another substance present to accept
the H+ ions.
Example of dissociation of acids in water.
HCl(aq) → H+(aq) + Cl- (aq)
HNO3(aq) → H+(aq) + NO-3(aq)
H2SO4 (aq) → 2H+(aq) + SO42-(aq)
• The acidity of a solution is expressed by the concentration of its H+ ions in the solution . It is
known as the measuring pH of the solutions. The pH scale shows how acidic or alkaline a
solution is.
• The scale pH shows the hydrogen ion concentration of given solutions.
An acidic solution has a pH number less than 7
An alkaline solution has a pH number greater than 7
A neutral solution has a pH number of exactly 7
Strengths of acids
• Acids can be strong or weak.
• The relative strength of an acid is found by comparing one acid with another. The strength of
any acid depends upon how many molecules dissociate when the acid is dissolved in water.
Strong and weak acids
Strong acids
• Strong acids completely dissociate in water .
• pH range of strong acids are 1 to 3.
• All these acids have a high concentration of hydrogen ions in solution (H+(aq)) and have a low
pH.
Example of strong acids:
Hydrochloric acid -HCl
Acid , bases and salt
The complete revision notes on :
• Characteristics of acid , bases and salts
• Acid and alkali titrations
• Preparation of salts
• practical knowledge
Acid , bases and salt
Any chemical substance you choose from your lab, it may be an acid, base (or alkali) or a salt.
Properties of all the acids:
• Acid is sour in taste ( do not taste laboratory chemicals !!).
• They are soluble in water( partially or completely).
• They are corrosive.
• Acid changes the colour of indicators( Aqueous solutions can be acid, alkaline or neutral.
Indicators are used to tell if a solution is acidic, alkaline, basic or neutral) . They have the ability
to turn blue litmus paper red.
• In their aqueous solutions, acids act as good conductors of electricity.
Acids
Acids only show their properties when they are in aqueous solution. When acids are in water they
dissociate to form hydrogen ions .These ions are responsible for acid properties.
• An acid is an H+ ion (or proton) donor
• A base is an H+ ion (or proton) acceptor or OH- donor .
Bronsted-Lowry theory
The theory says:
• An acid is a proton (hydrogen ion) donor.
• A base is a proton (hydrogen ion) acceptor.
Any acid can be dissociated as follows :
HA(aq) + H2O(l) → H3O+(aq) + A-(aq)
Acid dissolves to form hydrogen ions. Hydrogen ion is bonded with water to form hydronium ions.
Hydronium ion is unstable and it forms H+ ions and water again.
Example 1: H2O (l) + HCl(aq) → H3O+(aq) + Cl-(aq)
The HCI donates a proton (H+) to the H2O molecule. So the HCI is an acid and H 2O is a base because
it accepts the proton( H+ )
Example 2: NH3(aq) + HCl(aq) → NH4Cl(aq)
Hydrochloric acid donate proton (H+) to ammonia , so hydrochloric acid is a proton donor and
, Complete revision notes for EDEXCEL GCSE ( 9-1) chemistry notes.
ammonia accept the proton to become NH4+ ion in ammonium chloride.
• If an acid to behave as an H + ion donor , there must be an another substance present to accept
the H+ ions.
Example of dissociation of acids in water.
HCl(aq) → H+(aq) + Cl- (aq)
HNO3(aq) → H+(aq) + NO-3(aq)
H2SO4 (aq) → 2H+(aq) + SO42-(aq)
• The acidity of a solution is expressed by the concentration of its H+ ions in the solution . It is
known as the measuring pH of the solutions. The pH scale shows how acidic or alkaline a
solution is.
• The scale pH shows the hydrogen ion concentration of given solutions.
An acidic solution has a pH number less than 7
An alkaline solution has a pH number greater than 7
A neutral solution has a pH number of exactly 7
Strengths of acids
• Acids can be strong or weak.
• The relative strength of an acid is found by comparing one acid with another. The strength of
any acid depends upon how many molecules dissociate when the acid is dissolved in water.
Strong and weak acids
Strong acids
• Strong acids completely dissociate in water .
• pH range of strong acids are 1 to 3.
• All these acids have a high concentration of hydrogen ions in solution (H+(aq)) and have a low
pH.
Example of strong acids:
Hydrochloric acid -HCl
