NCERT solutions for Class 10th Science Acids, Bases and Salts
Updated on June 1, 2025 | By Learnzy Academy
Q1. State differences between acids and bases.
Differences between Acids and Bases:
- Taste:
- Acids taste sour.
- Bases taste bitter.
- Touch:
- Acids are corrosive.
- Bases feel soapy to touch.
- Effect on Litmus Paper:
- Acids turn blue litmus red.
- Bases turn red litmus blue.
- pH Value:
- Acids have pH less than 7.
- Bases have pH more than 7.
- Ions Produced in Water:
- Acids produce hydrogen ions (H⁺).
- Bases produce hydroxide ions (OH⁻).
- Reaction with Metals:
- Acids react with metals to produce hydrogen gas.
- Bases generally do not react with metals.
- Examples:
- Acids: Hydrochloric acid (HCl), Sulfuric acid (H₂SO₄)
- Bases: Sodium hydroxide (NaOH), Calcium hydroxide (Ca(OH)₂)
Q2. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Ammonia is basic in nature because it produces hydroxide ions in water and turns red litmus blue.
Q3. Name the source from which litmus solution is obtained. What is the use of this solution?
Source of Litmus Solution:
Litmus solution is obtained from lichen, a natural plant-like organism.
Use of Litmus Solution:
Litmus solution is used as an acid-base indicator. It helps to check whether a substance is acidic or basic.
- Acids turn blue litmus red.
- Bases turn red litmus blue.
Q4. Is the distilled water acidic/basic/neutral? How would you verify it?
Distilled water is neutral.
How to verify: - You can verify it using litmus paper:
- Dip red litmus paper into distilled water – it remains red.
- Dip blue litmus paper into distilled water – it remains blue.
Since there is no change in color, it means distilled water is neither acidic nor basic, i.e., it is neutral.
Q5. Describe the process of neutralisation with the help of an example.
Neutralisation is a reaction in which an acid reacts with a base to form salt and water.
Example:
When hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), the products are sodium chloride (NaCl) and water (H₂O).
HCl + NaOH → NaCl + H₂O
This reaction is called a neutralisation reaction because the acid and base cancel each other's effect.
Q6. Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?
Dorji can use litmus paper to test each soft drink and find out whether it is acidic, basic, or neutral.
Steps Dorji can follow:
- Take a drop of each drink and put it on blue and red litmus papers.
- Observe the color change:
- If the blue litmus turns red, the drink is acidic.
- If the red litmus turns blue, the drink is basic.
- If no color change in either litmus, the drink is neutral.
Q7. Explain why: (a) An antacid tablet is taken when you suffer from acidity (b) Calamine solution is applied on the skin when an ant bites. (c) Factory waste is neutralised before disposing it into the water bodies.
(a) An antacid tablet is taken when you suffer from acidity:
When you have acidity, your stomach has excess acid, which causes discomfort. An antacid tablet is a base, and it neutralises the excess acid in your stomach. This neutralisation reaction helps to reduce the pain and discomfort caused by acidity.
(b) Calamine solution is applied on the skin when an ant bites:
Ant bites inject acid into the skin, causing pain and irritation. Calamine solution is basic in nature. When applied, it neutralises the acid from the ant bite, soothing the skin and reducing irritation.
(c) Factory waste is neutralised before disposing it into water bodies:
Factory waste may contain harmful acids or bases. If these wastes enter water bodies without treatment, they can harm aquatic life and pollute water. Neutralising the waste by adding suitable acids or bases makes it neutral and safer to dispose of in water.
Q8. Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.
Step 1: Dip turmeric paper in each liquid.
- If turmeric paper turns red or reddish-brown, the liquid is a base.
- If turmeric paper does not change color (stays yellow), the liquid is either acid or neutral.
Step 2: Identify liquids.
- Hydrochloric acid will not change the color of turmeric paper (stays yellow) because it is an acid.
- Sodium hydroxide will turn turmeric paper red or reddish-brown because it is a base.
- Sugar solution will not change the color of turmeric paper (stays yellow) because it is neutral.
Q9. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
If blue litmus paper is dipped in a solution and it stays blue, then the solution is either basic or neutral. Blue litmus paper turns red only in acidic solutions. Since it did not change color, the solution is not acidic.
To know if it is basic or neutral, you can test with red litmus paper:
- If red litmus paper stays red, the solution is neutral.
- If red litmus paper turns blue, the solution is basic.