Question

class 7 chapter 5 science important notes please send me on this time I will follow you and thanks u​

Answer 1

Acids and Bases

Acids

• Acids are substances that taste sour and are corrosive in nature.
• It turns blue litmus paper to red.
• These substances are chemically acidic in nature .E.g.:-orange juice, curd, vinegar, hydrochloric acid etc.

Bases

• Bases are substances that, in aqueous solution, are slippery to the touch and bitter in taste.
• It turns red litmus paper to blue.
• These substances are chemically basic in nature. Eg:- soap, ammonium hydroxide, calcium hydroxide, etc.

Neutralisation Reaction

• When an acid and base react with each other to form a salt, water and heat then such reaction is known as neutralisation reaction.
• In this reaction, the acidic and basic nature of the acid and base respectively are destroyed.
• The reaction between hydrochloric acid and sodium hydroxide is a classic neutralisation reaction where sodium chloride is formed.
• HCl+NaOH→NaCl(salt)+H2O

Salts

• Salt is the product formed from the neutralisation reaction of acids and bases.
• In the reaction between hydrochloric acid and sodium hydroxide the salt formed is sodium chloride.

      HCl+NaOH→NaCl+H2O

• Salt can be acidic, basic or neutral in nature.

Visual Indicators

• Indicators
• Substances, which are used to test whether a substance is acidic or basic are called indicators.

                  Acidic Solution Basic Solution

Red litmus No change Turns blue

Blue litmus Turns red No change

Natural Indicators

• Plants or plant parts contain useful chemicals that are used for testing an acidic or basic property of a solution are termed as natural indicators. China Rose and turmeric are examples of natural indicators.

Litmus

• Litmus is a naturally occurring purple indicator, which is extracted from lichens.
• When added to an acidic solution, it turns red and when added to a basic solution, it turns blue.
• It is available in the form of a solution or as strips of paper known as litmus paper.

(A) Red litmus turns blue indicating a basic solution

(B) Blue litmus turns red indicating an acidic solution

Phenolphthalein

• Phenolphthalein is an acid-base indicator which is colourless in acid solution but turns pink to red as the solution becomes alkaline.
• It is a synthetic indicator and is used for the neutralisation experiment.

Olfactory Indicators

• Olfactory indicators are substances whose smell changes whether they are mixed with an acidic or a basic solution.
• Onion, clove oil and vanilla extract are examples of such indicators.

Visual Indicators

• Visual Indicators are substances used to show visually (as by a change in colour) the condition of a solution with respect to the presence of a particular material (as a free acid or base).
• Common examples are litmus, red cabbage, phenolphthalein, etc

Neutralization

Neutralisation in Daily Life

• During indigestion, taking milk of magnesia (magnesium hydroxide) gives us relief as it neutralizes the effect of excess acid produced inside the stomach.
• The effect of ant sting which is caused by formic acid can be neutralized by rubbing moist baking soda (basic in nature).
• To ensure that plants can grow well, the soil is treated with either acids or bases depending if it’s basic or acidic in nature.
• Factory wastes, generally being acidic in nature can cause environmental damage, are treated with basic substances before discharge.

Recap of Concepts

• Safety Measures While Using Acids
• When diluting acids, pour the acid into the water, NOT water into acid as this may cause spattering of the acid.
• Safety gloves are to be worn whenever working with acids or bases.

Uses and Applications

• pH of Soil
• Excessive use of chemical fertilisers changes the pH of the soil.
• Plants do not grow well when the soil is either too acidic or too basic.
• Hence substances are added to bring the pH at a neutral level.

Uses of Acids and Bases

• Food preservation – Citric acid.
• Aerated drinks – Carbonic acid.
• Baking powder – Tartaric acid.
• Cooking – Acetic acid(vinegar)
• Manufacture of soaps – Sodium hydroxide.
• Manufacture of bleaching powder – Calcium hydroxide
• As a foaming agent in fire extinguishers – Aluminium hydroxide.