Exercises
1. State differences between acids and bases.
Answer:
- Acids: Taste sour, turn blue litmus red, and are found in substances like lemon juice and vinegar.
- Bases: Taste bitter, feel soapy, turn red litmus blue, and are found in substances like soap and baking soda.
2. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Answer: Ammonia is basic in nature.
3. Name the source from which litmus solution is obtained. What is the use of this solution?
Answer:
- Source: Litmus is obtained from lichens.
- Use: It is used as an indicator to test whether a solution is acidic or basic.
4. Is distilled water acidic, basic, or neutral? How would you verify it?
Answer: Distilled water is neutral. You can verify it by using litmus paper. It does not change the color of red or blue litmus paper.
5. Describe the process of neutralization with the help of an example.
Answer: Neutralization is the reaction between an acid and a base to form salt, water, and heat.
Example: Hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) to form sodium chloride (salt), water, and heat.
6. Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) Nitric acid turns red litmus blue. (F)
(ii) Sodium hydroxide turns blue litmus red. (F)
(iii) Sodium hydroxide and hydrochloric acid neutralize each other and form salt and water. (T)
(iv) Indicator is a substance that shows different colors in acidic and basic solutions. (T)
(v) Tooth decay is caused by the presence of a base. (F)
7. Dorji has a few bottles of soft drink in his restaurant, but they are not labeled. How will he decide which drink is acidic, basic, or neutral?
Answer: Dorji can use litmus paper:
- Acidic drinks turn blue litmus red.
- Basic drinks turn red litmus blue.
- Neutral drinks do not change the color of litmus paper.
8. Explain why:
(a) An antacid tablet is taken when you suffer from acidity.
Answer: Antacid tablets contain bases that neutralize excess stomach acid and relieve acidity.
(b) Calamine solution is applied on the skin when an ant bites.
Answer: Calamine contains zinc carbonate, which neutralizes the formic acid injected by the ant.
(c) Factory waste is neutralized before disposing it into water bodies.
Answer: Factory waste often contains acids that can harm aquatic life. Neutralizing them with bases makes the waste safe.
9. How will you identify hydrochloric acid, sodium hydroxide, and sugar solution using turmeric indicator?
Answer:
- Hydrochloric acid: No color change (turmeric remains yellow).
- Sodium hydroxide: Turns turmeric red.
- Sugar solution: No color change (turmeric remains yellow).
10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution?
Answer: The solution is either neutral or basic because it does not turn the blue litmus red.
11. Consider the following statements and identify which are correct:
(a) Both acids and bases change the color of all indicators.
(b) If an indicator gives a color change with an acid, it does not give a change with a base.
(c) If an indicator changes color with a base, it does not change color with an acid.
(d) Change of color in an acid and a base depends on the type of the indicator.
Answer: The correct statement is (d).
Extended Learning — Activities and Projects
1. Write a secret message with baking soda and beetroot.
- Mix baking soda with water and use a cotton bud to write a message on white paper.
- Rub a slice of fresh beetroot over the paper. The message will appear due to a reaction between baking soda and beetroot juice.
2. Use red cabbage juice as an indicator and test acidic and basic solutions.
- Boil red cabbage in water to prepare the juice.
- Test:
- Acidic solutions turn the juice red.
- Basic solutions turn it green.
- Neutral solutions do not change its color.
3. Test the soil of your area.
- Bring a soil sample and mix it with water to make a solution.
- Test with litmus or red cabbage juice.
- If the soil is acidic, add lime.
- If it is basic, add organic compost.
4. Visit a doctor to learn about acidity treatment.
- Doctors often prescribe antacids containing bases like magnesium hydroxide.
- To prevent acidity: Avoid spicy foods, eat meals on time, and stay hydrated.
1. What is an acid?
Answer: Substances that taste sour and turn blue litmus red are called acids. They are acidic in nature.
2. What is a base?
Answer: Substances that taste bitter, feel soapy, and turn red litmus blue are called bases. They are basic in nature.
3. What is an indicator?
Answer: Substances that change their color in the presence of an acid or a base are called indicators.
4. Name two natural indicators.
Answer: Litmus and turmeric.
5. What is litmus made from?
Answer: Litmus is extracted from lichens.
6. What happens when litmus is added to an acidic solution?
Answer: It turns red.
7. What happens when litmus is added to a basic solution?
Answer: It turns blue.
8. Name the acid present in lemon.
Answer: Citric acid.
9. Which base is present in lime water?
Answer: Calcium hydroxide.
10. What is neutralization?
Answer: The reaction between an acid and a base to form salt and water with the evolution of heat is called neutralization.
11. What is the product of neutralization?
Answer: Salt, water, and heat.
12. Why is milk of magnesia used for indigestion?
Answer: It contains magnesium hydroxide, which neutralizes excess stomach acid.
13. What is the acid present in vinegar?
Answer: Acetic acid.
14. Why do turmeric stains turn red with soap?
Answer: Soap is basic, and turmeric reacts with it to turn red.
15. What happens when an ant bites?
Answer: The ant injects formic acid, which can be neutralized by applying moist baking soda or calamine solution.
16. What is acid rain?
Answer: Rain that contains excess acids like carbonic acid, sulphuric acid, and nitric acid due to air pollution.
17. Why is acid rain harmful?
Answer: It damages buildings, historical monuments, plants, and animals.
18. Name a substance that can neutralize acidic soil.
Answer: Quick lime (calcium oxide) or slaked lime (calcium hydroxide).
19. Why are factory wastes neutralized before disposal?
Answer: Factory wastes often contain acids that can harm aquatic life, so they are neutralized with bases.
20. What happens when baking soda solution is added to vinegar?
Answer: A neutralization reaction occurs, producing carbon dioxide gas, salt, and water.
21. What color does China rose indicator turn in acidic solutions?
Answer: Dark pink (magenta).
22. What color does China rose indicator turn in basic solutions?
Answer: Green.
23. Name the acid present in curd.
Answer: Lactic acid.
24. What is the nature of substances that do not affect red or blue litmus?
Answer: Neutral.
25. What is the importance of a neutral substance in our daily life?
Answer: Neutral substances, like water, are essential for maintaining balance in many chemical processes.
26. Name two common salts.
Answer: Sodium chloride (table salt) and baking soda (sodium bicarbonate).
27. What is the pH of neutral substances?
Answer: Neutral substances have a pH of 7.
28. Why do white paper stains from turmeric turn red when washed with soap?
Answer: Soap is basic and reacts with turmeric to change its color to red.
29. Name a substance used to treat basic soil.
Answer: Organic matter or compost.
30. Why are the outer walls of houses in hot climates painted white?
Answer: White reflects heat and helps keep the house cool.
No Responses