Acids, Bases and Salts Class 7 Science Notes - Chapter 5
Acids, Bases and Salts Class 7 Science Notes - Chapter 5
Preview of the chapter
We use a variety of edible substances in our daily lives, such as lemon, baking soda, tamarind, common salt, sugar, curd and vinegar. Acids, bases and salts are the three important groups of chemical substances used by us in different ways. Some acids, bases and salts occur in nature and can also be made artificially in factories.
Acids and Bases
Acids
- Acid is derived from the Latin word 'acidus' which means'sour'.
- It turns blue litmus paper to red.
- Substances like lemon juice, orange juice, unripe mango and curd taste sour because they contain acids, which are natural acids.
Bases
- Bases are substances that are bitter in taste and feel soapy on touch
- It turns red litmus paper to blue.
- They have no acids and are known as bases because they have no acids in them.
Indicators
- Indicators are special substances that have different colours in acidic and basic mediums.
- Litmus, turmeric, China rose petals (gudhal) and red cabbage juice are natural indicators used to test whether a substance is acidic or basic in nature.
Neutralisation
- Acids and bases are chemically opposite substances, so when an acid is mixed with a base, they neutralise the effect of each other.
- his reaction is known as neutralisation, and salt and water are produced with the evolution of heat.
- The resulting solution is neither acidic nor basic.
The salt that results from the reaction could be acidic, basic, or neutral. The reaction mixture's temperature is increased by the heat that is evolved.
Salt + Water + Acid + Base = Heat, for example. Water + Sodium chloride (NaCl) + Hydrochloric acid (HCl) (Acid) + Sodium hydroxide (NaOH) (Base) (H2O)
Neutralisations in Everyday Life
Neutralisation reactions involve acids and bases, which are essential for many everyday tasks, such as treating an ant's sting, indigestion, soil treatment, and factory waste.
Indigestion
- The stomach produces hydrochloric acid, which can cause indigestion.
- to relieve this, we take an antacid such as milk of magnesia, which contains magnesium hydroxide, which neutralises the excess acid and cures indigestion.
- Baking soda also contains sodium hydrogen carbonate.
Ant Bite
- Ants inject an acidic liquid into the skin of the person, which can be neutralised by rubbing baking soda solution or calamine solution,
- which contain zinc carbonate. This neutralises the acidic liquid injected by the ant and cancels its effect.
Soil Treatment
- The soil in a place can be either acidic or basic.
- Excessive use of chemical fertilisers can make the soil acidic, which is treated with bases like quicklime or slaked lime to reduce its acidic nature.
- Organic matter, such as manure or compost, releases acids to neutralise the excess bases and reduce its basic nature.
Factory Wastes
- The waste substances discharged by many factories contain acids
- Factory wastes should be neutralised by adding basic substances before discharging them into water bodies to prevent the acid from killing fish and other organisms.
Salt
Salt is a type of chemical compound that is formed when an acid reacts with a base. It is made up of two parts - a positively charged part and a negatively charged part. The positively charged part is usually a metal, and the negatively charged part is usually a non-metal.
For example, table salt (sodium chloride) is made up of the metal sodium (Na+) and the non-metal chlorine (Cl-). Salt is commonly used in cooking as a seasoning, and is also used in many other applications such as water softening and fertilizer production.
In summary, salt is a type of chemical compound that is formed from the reaction between an acid and a base, and it has many practical uses in our daily lives.
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