Class 7 Science Chapter 4 Question Answers - Acids, Base and Salts

Q1. Name any three acids and three bases.
Ans: Acids: Sulphuric acid, acetic acid, hydrochloric acid. Bases: Sodium hydroxide, potassium hydroxide, calcium hydroxide.

Q2. What are acids and bases?
Ans: An acid is a sour substance that turns blue litmus red. In contrast, a base is a bitter substance that feels soapy to the touch and turns red litmus blue.

Q3. Name any two antacids.
Ans: Milk of magnesia and sodium bicarbonate are antacids.

Q4. What is the pH scale?
Ans: The pH scale is used to measure the strength of acids and bases.

Q5. What are the causes of indigestion?
Ans: Indigestion is caused by various factors, including overeating, consuming spicy or fatty foods, eating too quickly, and consuming excessive alcohol or caffeine. Stress and anxiety can also contribute to indigestion.

Q6. What is acid rain?
Ans: Acid rain is a type of precipitation that contains acidic components like carbonic acid, nitric acid, and sulphuric acid. It is formed when pollutants like carbon dioxide, nitrogen dioxide, and sulphur dioxide react with water in the atmosphere.

Q7. What is the use of litmus paper? What is the natural color of litmus paper?
Ans: Litmus paper is used as a chemical indicator to test whether a substance is acidic or basic. The natural color of litmus paper is purple. When placed in an acidic solution, it turns red, and in a basic solution, it turns blue.

Q8. What happens when a drop of dilute sulphuric acid is added to the china rose indicator?
Ans: When a drop of dilute sulphuric acid is added to the china rose indicator, the light pink color of the china rose indicator changes to magenta.

Q9. What happens when a china rose indicator is added to acid and base?
Ans: When a china rose indicator is added to an acidic solution, it turns magenta. In a basic solution, it turns green.

Q10. Why does a farmer add quicklime in the field?
Ans: A farmer adds quicklime (calcium oxide) in the field to neutralize the acidic soil. Soil can become acidic due to the use of certain chemicals and fertilizers, or it can be affected by acid rain. Quicklime helps to raise the pH of the soil, making it less acidic and more suitable for plant growth.

Q11. Name the chemicals added to the acidic soil to make it neutral.
Ans: The chemicals added to acidic soil to make it neutral are calcium carbonate (lime) and magnesium carbonate (dolomite).

Q12. Why is toothpaste alkaline?
Ans: Toothpaste is alkaline because it helps neutralize the acids produced by bacteria in the mouth when they break down food particles. The alkaline nature of toothpaste helps maintain the pH balance in the mouth and prevent acid erosion of the teeth.

Q13. How can you cure an ant sting?
Ans: To cure an ant sting, you can apply calamine lotion or solution to the affected area. Calamine contains zinc carbonate, which acts as a mild base and helps neutralize the formic acid injected by the ant, reducing inflammation and soothing the skin.

Q14. How can you prepare the china rose indicator?
Ans: To prepare the china rose indicator, soak some china rose petals in warm water for a few hours. The red-colored solution obtained from this is used as an indicator to test for the presence of acids, bases, or neutral substances.

Q15. What are an indicator and a universal indicator?
Ans: An indicator is a substance that changes color when it comes into contact with an acidic or basic substance, helping to determine the pH of the solution. A universal indicator is a mixture of several indicators that provides a broader range of colors and can be used to determine the pH of a substance more accurately across a wider pH scale.