Acids, Bases and Salts Revision Notes

Acids have a sour taste, turn blue litmus red when mixed with water, and dissolve in water to release hydrogen ions. Bases have a bitter taste, a soapy feel, turn red litmus blue, and produce hydroxide ions (OH^–) in water. Salts are ionic substances that are formed when an acid and a base react to neutralise each other. Salts have no electrical charge. Salts come in a variety of forms, but sodium chloride is the most prevalent. Table salt or common salt are both terms for sodium chloride. Sodium chloride is used to make meals taste better.

Keyterms: Acid, Salt, Base, Water, Hydrogen, Ion, Hydroxide, Sodium chloride, Aqueous solution

---

Acids 

[Click Here for Sample Questions]

Acids have a sour taste, turn blue litmus red when mixed with water, and dissolve in water to release hydrogen ions.

Example: Sulphuric acid (H₂SO₄), Nitric Acid (HNO₃), Acetic Acid (CH₃COOH), etc.

Properties of Acids

• Acids have a sour taste.
• Blue litmus turns red.
• Electricity can be conducted through an acidic solution.
• In an aqueous solution, release H⁺ ions.

Reactions of Acids

1. Reaction of Acid with Metal

Acid + Metal → Salt + Hydrogen gas

Mg + H₂SO₄ → H₂ + MgSO₄

2. Reaction of Acid with Carbonates

Na₂ CO₃ (s) + 2HCl (aq) → 2NaCl (aq) + H₂O(l) + CO₂(g)

3. Reaction of Acid with Bicarbonates

NaHCO₃ (s) + HCl (aq) → NaCl(aq) + H₂O (l) + CO₂ (g)

Types of Acids

(i) Natural Acids: Natural acids, often known as organic acids, are acids derived from natural sources.

Examples:

Methanoic acid (HCOOH)

Acetic acid (CH₃COOH)

Oxalic acid (C₂H₂O₄) etc.

(ii) Mineral Acids: Acids that are prepared from minerals are known as Mineral Acids Example; Inorganic acids, man-made acids, or synthetic acids are also known as Mineral Acids.

Example:

Hydrochloric acid (HCl)

Sulphuric acid (H₂SO₄)

Nitric acid (HNO₃)

Carbonic acid (H₂CO₃)

Phosphoric acid (H₃PO₄) etc.

(iii) Strong Acids: Strong acids are acids that totally dissociate into ions. H₂SO₄ and HCl are two examples.

(iv) Weak Acids: Weak acids are acids that do not entirely break down into ions. Citric acid and acetic acid are two examples.

Read more : Dipole Moment

---

Bases

[Click Here for Sample Questions]

Bases have a bitter taste, a soapy feel, turn red litmus blue, and produce hydroxide ions (OH^–) in water.

Examples: Sodium hydroxide (caustic soda) – NaOH

Calcium hydroxide – Ca(OH)₂

Potassium hydroxide (caustic potash) – (KOH)

Properties of Bases

• Bases have a harsh flavour and are less commonly found in foods than acids.
• Indicators' colours are also changed by bases.
• Acids react with metals in the same way that bases do not.
• Salt and water are produced when bases react with acids.

Reactions of Bases

1. Reaction with Metals

When the base reacts with metals, hydrogen gas is produced.

2NaOH + Zn → Na₂ → Na₂ZnO₂ + H₂

2. Reaction with Acids

Salts are formed when a base combines with an acid. As an example,

KOH + HCl → KCl + H₂O

3. Reaction with Non-metallic Oxides

Salt and water are formed when the base interacts with non-metallic oxides.

2NaOH + CO₂ → CO_2­ → Na₂CO₃ + H₂O

Strength of Acid and Base: Strong acids are those in which the hydrogen ion has completely dissociated. Strong Bases, on the other hand, are bases that completely dissociate the hydroxide ion. Hydrogen ions dissociate entirely in mineral acids such as hydrochloric acid, sulphuric acid, nitric acid, and others, making them strong acids.

Because the hydrogen ions in inorganic acids do not entirely dissociate, they are weak acids.

For water/neutral solutions : pH = 7

For acidic solutions : pH < 7

For basic solution : pH > 7

Universal Indicator: Litmus paper, phenolphthalein, methyl orange, and other indicators do not give an indication of acid or basic strength. A universal indicator is used to determine the strength, as well as the acidic and basic characteristics of a given solution. A universal indicator is included with the colour matching chart, which indicates the varied colours for different pH values.

pH Scale: A scale for estimating the concentration of hydrogen ions in a solution is known as the pH scale.

The negative logarithm of hydrogen ion concentration in moles per liter is used to calculate the pH of a solution.

pH = -log [H⁺]

pH = -log [H₃O⁺]

where [H⁺] or [H₃O⁺] is hydrogen ion concentrations in a solution.

• A neutral solution has a pH of 7.
• The pH of an acidic solution is lower than 7.
• pH greater than 7 indicates a basic solution.

---

Salts

[Click Here for Sample Questions]

Salts are ionic substances that are formed when an acid and a base react to neutralise each other. Salts have no electrical charge. Salts come in a variety of forms, but sodium chloride is the most prevalent. Table salt or common salt are both terms for sodium chloride. Sodium chloride is used to make meals taste better.

Characteristics of salt

• The majority of the salts are solid crystalline.
• Transparent or opaque salts are available.
• The majority of salts are water-soluble.
• In their molten condition, salt solutions transmit electricity as well.
• Salt can be salty, sour, sweet, bitter, or umami in flavour (savory).
• Neutral salts have no odour.
• Salts may be found Colorless or coloured salts 

Types of salts

(i) Neutral Salt: In nature, salts formed by the interaction of a strong acid and a strong base are neutral. Such salts have a pH of 7, which is considered neutral.

Example: Sodium chloride, Sodium sulphate. Potassium chloride, etc.

(ii) Acidic Salts: Acidic salts are the salts that result from the reaction of a strong acid and a weak base. Acidic salt has a pH value of less than 7. Ammonium sulphate, ammonium chloride, and other ammonium compounds are examples.

(iii) Basic Salts: Acidic salts are the salts that result from the reaction of a strong acid and a weak base. Acidic salt has a pH value of less than 7. Ammonium sulphate, ammonium chloride, and other ammonium compounds are examples.

Formation of acidic, basic & neutral salts

• When a strong acid combines with a weak base, the base cannot neutralise the acid completely. As a result, an acidic salt forms.
• The acid is unable to fully neutralise a strong base when it combines with a weak acid. As a result, a basic salt is generated.
• When an acid and a base of equal strength react, they completely neutralise each other. This results in the formation of a neutral salt.

pH value of salt

• Neutral salt: A neutral salt's pH value is nearly equal to 7.
• Acidic salt: An acidic salt has a pH value of less than 7.
• Basic salt: A basic salt has a pH of greater than 7.

The water of Crystallization: Hydrated salts are a type of salt that contains water molecules. The water of crystallisation is the name given to the water molecule found in salt.

Examples: Pentahydrate of copper sulphate (CuSO₄.5H₂O): Copper sulphate has a blue colour due to the presence of 5 water molecules. When copper sulphate is heated, it loses water molecules and becomes anhydrous copper sulphate, which has a grey-white colour. Anhydrous copper sulphate turns blue again after being 

Common Salt (NaCl) (Sodium Chloride) : 

NaOH + HCl → NaCl + H₂O

2NaCl (Brine) + 2H₂O₂NaOH (Caustic Soda) + Cl₂ + H₂

Baking Soda (NaHCO₃) (Sodium Hydrogencarbonate): 

NaCl + NH₃ + H₂O + CO₂ → NaHCO₃ + NH₄Cl

Bleaching Powder (CaOCl₂) (Calcium Oxychloride) : 

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Slaked Lime

CaOCl₂ + H₂SO₄ → CaSO₄ + Cl₂ + H₂O

The chlorine dioxide (Cl₂) formed by dilute acid functions as a bleaching agent.

Plaster of Paris (P.O.P) (CaSO₄.1/2 H₂O) (Calcium Sulphate Hemihydrate) :

CaSO₄.2H₂O (Gypsum) → (Heat to 100^oC)

CaSO₄.H₂O (Plaster of Paris) + 3/2 H₂O

When wetted with water, it transforms into a hard mass, similar to how gypsum is generated.

CaSO₄.2H₂O = CaSO₄.1/2 H₂O (P.O.P) + 1/2 H₂O (Gypsum set as hard mass)

As a result, P.O.P should be stored in moisture-proof containers, as moisture can hydrate P.O.P and cause it to set slowly.