notes of acid ,bases and salts ... plz..
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Acids
Acids is defined as the one which produces hydrogen ions in water. For Example, Sulphuric Acid, Hydrochloric Acid etc.
They give sour taste.
Acids turn blue litmus to red. This is used as confirmation test for the presence of acid.
When acids react with metals, gases are evolved.
Reactions with Acids
1. Reaction of Acid with Metal
Acid + Metal → Salt + Hydrogen gas
Mg + H2 SO4 → H2 + Mg SO4
2. Reaction of Acid with Carbonates
Na2 CO3 (s) + 2 HCl (aq) → 2NaCl (aq) + H2O(l) + CO2(g)
3. Reaction of Acid with Bicarbonates
NaHCO3 (s) + HCl (aq) → NaCl(aq) + H2O (l) + CO2 (g)
Similarity between Acids and Bases
Both acids and base react with water. They produce ions in water
Both acids and bases acts as electrolytes, so are good conductors of electricity.
Both of them changes the colour of the litmus paper.
Classification of Acids
Acids are classified as Organic Acids and Mineral Acids. Acids which are derived from plants and animals, they are known as Organic Acids. For Example, Citric Acid from fruit. Mineral acids are inorganic acids such as Sulphuric Acid. They are dangerous to be used, so need more precautions.
Acids are also classified as Strong Acids or Weak Acids. Strong acid is an acid, that completely dissociates into ions in aqueous solutions. For Example, Sulphuric Acid, Hydrochloric Acid.
Weak acid is the one which does not dissociate completely into ions in aqueous solutions. For Example, Acetic Acid.
Acids can also be as Dilute Acid and Concentrated Acids. The one which has low concentration of acids in aqueous solution, they are known as Dilute Acids whereas the one which has high concentration of acids in aqueous solution, are known as Concentrated Acids.
It is advisable to add acid to water and not vice versa because large amount of heat is released if water is added to acid. This released heat is large enough to cause harm.
Acids can also be classified based on number of hydrogen ions. Monoprotic acid is the one which gives one mole of hydrogen ions per mole of acid, such as HCl. Diprotic Acid is the one which produces two mole of hydrogen ions per mole of acid. For Example, H2SO4.
Bases
Bases are the one which produces hydroxide ions in aqueous solutions. Bases which are water soluble they are known as Alkalis.
They turn red litmus to blue.
They have a bitter taste.
They also produced carbon-dioxide when reacted with carbonates.
They also evolved hydrogen gas when bases react with metals.
Reactions of Bases
1. Reaction with Metals
Base reacts with metals and produce hydrogen gas.
2NaOH + Zn → Na2 → Na2ZnO2 + H2
2. Reaction with Acids
Base reacts with acids to form salts. For Example,
KOH + HCl → KCl + H2O
3. Reaction with Non-metallic Oxides
Base reacts with non-metallic oxides to form salt and water.
2NaOH + CO2 → CO2 → Na2CO3 + H2O
Classification of Bases
Bases are classified as Strong Base and Weak Base. Strong base is the one which dissociates completely into its ions in aqueous solution. For Example, NaOH.
Weak base is the one which does not dissociate completely into its ions in aqueous solutions. For Example, Ammonium Hydroxide, NH4OH
Bases are also classified as Dilute Base and Concentrated Base. The solution which has low concentration of base in aqueous solution is defined as Dilute Base whereas the one which has high concentration of base in aqueous solution is known as Concentrated Base.
Strength of Acid or Base Solutions
The dissociation constant of weak acid or weak base can be represented as-
Suppose HA is weak acid, then dissociation constant is represented as-
Strength of an acid or base can be determined using a pH scale. It is a scale to measure the hydrogen ion concentration in a solution. The p stands for ‘potenz’, it is a German word which means power.
If pH is equal to 7, means the solution is neutral.
If pH is greater then 7 means alkaline solution.
If pH is less then 7 means the solution is acidic.
Fig.1. pH scale
Importance of pH
Human body works at a pH of about 7.4.
Stomach has a pH of about 2 due to presence of hydrochloric acid in it. It is needed for the activation of pepsin protein required for protein digestion.
When we eat food containing sugar, then the bacteria present in our mouth break down the sugar to form acids. This acid lowers the pH in the mouth. Tooth decay starts when the pH of acid formed in the mouth falls below 5.5. This is because then the acid becomes strong enough to attack the enamel of our teeth and corrode it. This sets in tooth decay. The best way to prevent tooth decay is to clean the mouth thoroughly after eating food.
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