9. What is the colour of phenolphthalein acidic and basic media?
10. Explain why factory waste should be neutralized before disposing it into the water bodies?
11. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
12. Give examples of some acid and bases.
13. How does rain becomes acidic?
14. Name the source from which litmus solution is obtained. What is the use of this solution?
15.Explain the process of neutralization with example. Red litmus paper is dipped in a solution; it remains red, what is the nature of the solution?
16.What are chemical reactions? Differentiate between combination and decomposition reaction.
17. What is displacement reaction? Give example.
18. Differentiate between physical and chemical change. Give example.
19. (a)Explain two methods by which rusting can be prevented .(b) Burning of a candle may be considered as showing physical and chemical changes occurring simultaneously. Explain.
20.Explain an activity to show that chemical change is irreversible and permanent.
Answers
Phenolphthalein is often used as an indicator in acid–base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions. It belongs to class of dyes known as Pthalein dyes
The factory wastes are neutralized before disposing into water bodies because, factory wastes often contain acid. if it reaches a river, the acid will kill aquatic life. this is prevented by adding a base called slaked lime.
Ammonia is basic in nature as it turns the colour of red litmus paper to blue.
Acids in food such as vinegar (acetic acid), soda water (carbonic acid) and lemon juice (citric acid) are weak acids hydrochloric acid etc
Ammonia is another familiar base, used for cleaning oils and grease from windows. Baking soda (sodium bicarbonate) is another base found in the kitchen, used because it reacts with acids to produce carbon dioxide gas sodium hydroxide
Acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.
Litmus solution is obtained from lichens. This solution is used as an indicator to distinguish between acids and bases. Acids turn blue litmus solution red aijd bases turn red litmus solution blue.
.The reaction between an acid and a base is known as neutralization. Salts and water are produced in this process with the evolution of heat.
Acids + Bases -à Salt + water
HCl + NaOHàNaCl + H2O.