Important Notes for CBSE Class 7 Science Chapter 5 – Acids Bases and Salts. Acids Bases and Salts Class 7 Notes and Study Material Download in PDF form.
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Acids Bases and Salts Class 7 Notes
Tongue has taste buds which helps up identify if a substances taste sour, bitter, sweet and salty.
Acids:
- The word acid has its origin from the Latin language acer which means sour.
- Many acids are natural substances which taste sour.
- Examples of acidic substances include Curd, lemon juice, orange juice and vinegar
Bases:
- The substances which taste bitter, feel soapy to touch are called bases.
- Example of base is baking soda.
Indicator:
- It is the substance used to check if a substance is acidic and basic.
- Indicators change color when they come in contact with an acid or base.
- Examples of natural indicators are Turmeric, litmus, China rose petals.
I. Litmus:
- Litmus is a natural substance extracted from lichens and has purple color in distilled water.
- Litmus changes its color to red when it comes in contact with an acidic solution and turns blue when it comes in contact with basic solution.
- Generally, red and blue litmus paper strips are available to check if a substance is acidic and basic nature
II. Phenolphthalein:
- It is a colorless solution at neutral Ph.
- Phenolphthaleinwhen comes in contact with a basic solution turns the solution pink.
- On mixing with an acid Phenolphthalein does not change color.
III. Turmeric:
- It is a natural indicator.
- Turmeric turns red when mixed with a basic solution.
IV. China Rose:
- It is obtained when China rose petals are socked in water and after which the water is collected and used as the indicator.
- China rose solution when mixed with acidic solutions gives a dark pink color and green color when mixed with basic solutions.
ACID RAINS:
- Air pollutants like carbon dioxide, Sulphur dioxide and Nitrogen dioxide get mixed with rain water, acids like form carbonic acid, sulphuric acid and nitric acid are formed.
- Such rain is termed as acid rains and cause substantial damage to animals, plants and buildings
- Acids and basesare corrosive in nature. They may be harmful or may serve as an irritant to the skin.
NUTRILIZATION:
- When an acid is mixed with a base, it leads to formation of salt and water.
- The acid and base in the solution cancel out each other’s effect, so the solution obtained after mixing is neutral.
- Heat is released after neutralization.
- The salt formed can either be acidic, basic or neutral nature.
- Example: When Hydrochloric acid (HCl) is mixed with Sodiumhydroxide (NaOH), Sodium chloride (NaCl) and Water (H2O) is formed.
COMMON NEUTRALISATION REACTION:
- Indigestion:
- The HCl present in the stomach helps in digesting food.
- If the amount of acid in the stomach increases it leads to painful indigestion.
- Antacid contain bases like magnesium hydroxide are known to neutralize the excess acid of the stomach.
Ant bite:
- Ants have acidic glands in their mouth which contains formic acid.
- When ants’ bites, it injects formic acid in the skin. This acid can be neutralized by applying paste of sodium hydrogen carbonate commonly known as baking soda.
- Calamine or zinc solution can also be used.
Factory wastes:
- Waste water from factories contains acids.
- This water must be treated before it leaves the factories and is mixed with the surrounding water bodies as it is toxic for fishes and other aquatic organisms.
- Such acid water is neutralized by adding basic substance to it.
Soil treatment:
- The soil turns acidic on addition of chemical fertilizers.
- Such soil is not suitable for plant growth.
- Acidic soil is treated with bases like calcium oxide or calcium hydroxide to make it neutral.
- Basic soil can be treated with organic matter (compost) to make it neutral.
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