Chapter 2: Acids, Bases and Salts Revision Notes

Classification of Matter

on the basis of

a) Composition– elements, compounds, and mixes

b) State of matter- Solids, liquids and gases

c) soluble matter – suspensions, colloids, and solutions

• Homogeneous and heterogeneous mixes are two types of mixtures.
• Covalent and ionic compounds are two different types of chemicals.

What Is the Difference Between an Acid and a Base?

Physical examination

There are two physical tests that may be used to determine if an acid or a base is present.

a. Taste

• An acid has a sour flavour, whereas a base has a bitter flavour.
• Because an acid or a base might be polluted or caustic, this way of tasting is not recommended.

b. Effect on Indicators by acids and bases

• When a chemical substance comes into touch with an acid or a base, it changes its physical qualities, most commonly colour or scent.

The following are some regularly used indicators and the many colours they display:

a) Litmus paper

• Purple in a neutral solution
• In an acidic solution, the colour is red.
• Blue is the most basic answer.
• Litmus is also available as paper strips in two colours: red and blue litmus.
• A damp blue litmus paper turns red when exposed to an acid.
• A base changes the colour of wet red litmus paper to blue.

b) Methyl orange

• Orange in a neutral solution
• In an acidic solution, the colour is red.
• Yellow in basic solution

d) Phenolphthalein

• In a colourless neutral solution
• In an acidic solution, the substance stays colourless.
• Pink is the most basic answer.

WATER

• Water contains acids and bases.
• Acids and bases breakdown into their respective ions when introduced to water and aid in the conductivity of electricity.

What is the distinction between a base and an alkali?

• Acids react with bases to neutralise them.
• Metal oxides, metal hydroxides, metal carbonates, and metal bicarbonates make up these compounds.
• The majority of them are water insoluble.
• An alkali is a base in aqueous solution (mainly metallic hydroxides).
• It dissolves in water and then dissociates to produce the OH ion.
• All bases are alkalis, but not all alkalis are bases.

Hydronium ion

• A coordinate covalent bond is created when a hydrogen ion receives a lone pair of electrons from the oxygen atom of a water molecule.

Dilution

• Dilution is the process of decreasing a solution's concentration by adding more solvent (typically water).
• It's a really exothermic reaction.
• Acid must be put to water, not the other way around, to dilute it.

STRENGTH OF ACID AND WATER

• When all molecules of an acid or a base disintegrate entirely in water to produce their corresponding ions, H+(aq) for acid and OH(aq) for base).

Weak acid or base: When just a few molecules of an acid or base dissociate in water to produce their corresponding ions, H+(aq) for acid and OH(aq) for base.

Universal Indicator

• The pH range of a universal indicator is 0 to 14, and it represents the acidity or alkalinity of a solution.
• The pH of a neutral solution is 7.

pH

• The pH scale spans from 0 to 14, with 0 being the most acidic and 14 being the most alkaline.
• If the acidic solution has a pH of 7, it is said to be acidic.
• If the pH is more than 7, use a basic solution.

Importance of pH in everyday life

1. Plant and animal pH sensitivity

• pH affects both plants and animals. At a given pH value, vital life activities such as food digestion, enzyme functioning, and hormone production take place.

2. A soil's pH

• The pH of a soil that is ideal for plant or agricultural growth is 6.5 to 7.0.

3. The digestive system's pH

• In human stomach, digestion takes place at a precise pH range of 1.5 to 4.
• HCl in our stomach influences the pH of enzyme interactions as food is being digested.

4. The role of pH in tooth decay

• When the teeth are exposed to an acidic environment with a pH of 5.5 or lower, tooth decay occurs.

5. The pH of animal and plant self-defense

• Animals and plants employ acidic compounds as a self-defense strategy.
• For self-defense, bees and plants like nettle emit a very acidic chemical. These acidic chemicals released have a specified pH.

SALTS

• A salt is a compound made up of an acid's anion and a base's cation.
• KCl, NaNO3, CaSO4, and other salts are examples.
• The neutralisation reaction of an acid and a base is commonly used to make salts.

Source:

Common salt

• Because it is used in cooking all around the world, sodium chloride (NaCl) is known as common salt.

Family of Salt

• Salts with the same cation or anion are classified as belonging to the same family. NaCl, KCl, and LiCl, for example.

The salts' pH

• In nature, a salt comprising a strong acid and a strong base will be neutral. pH 7.0 (approx.).
• In nature, a salt of a weak acid and a strong base will be basic. pH greater than 7.
• Acidic in nature is a salt comprising a strong acid and a weak base. pH is less than 7.
• A pH test is used to detect the pH of a salt of a weak acid and a weak base.

Bleaching powder

• Bleaching powder produces chlorine when it comes into contact with water, which is responsible for the bleaching effect.

Baking soda

• Sodium hydrogen carbonate is the chemical name for this substance.
• NaHCO3 is the chemical formula.

Uses:

1. Textile manufacturing

2. Paper manufacturing

3. Antiseptic

Washing soda

• Sodium hydrogen carbonate is the chemical name for this substance.
• NaHCO3 is the chemical formula.

Preparation (the Solvay method) –

a. Limestone is heated in the following way: CaCO3 + CaO + CO2

b. CO2 is passed through a concentrated sodium chloride/ammonia solution:

NaHCO3(aq) + NH4Cl = NaCl(aq) + NH3(g) + CO2(g) + H2O(l) (aq)

Uses

In the glass, soap, and paper industries, for example.

2. Water softening

3. A housecleaner

Plaster of paris

• Heating gypsum, CaSO4.2H2O (s) to 100°C (373K) yields CaSO4. 12 H2O and 3/2 H2O.
• Plaster of Paris is made up of CaSO4 and 12 H2O.
• CaSO4. 12 H2O denotes that two CaSO4 formula units share one water molecule.
• Casts are used to help mend fractures.

Source: