1. Why does the flow of acid rainwater into a river make the survival of aquatic life in the river difficult?
2. Why should water be never added dropwise to concentrated sulphuric acid?
3. Write balanced chemical equations for the reactions taking place when dry blue crystals of copper sulfate are dropped into concentrated sulphuric acid.
4. What is the role of tartaric acid in baking powder?
5. There are two jars A and B containing food materials. Food in jar A is pickled with acetic acid while B is not. Food of which jar will stale first?
6. If soil is acidic which compound would you spread to treat the soil?
7. Write two observations you make when quick lime is added to water.
8. A calcium compound which is yellow-white powder is used as a disinfectant and also in the textile industry. Name the compound. Which gas is released when this compound is left exposed in the air?
9. State the chemical property in each case on which the following uses of baking soda are based
(i) As an antacid (ii) As a constituent of baking powder
10. How is chlorine of lime is chemically different from calcium chloride?
11. Name the acids present in the following foodstuffs which attribute to a sour taste to them
(a) Lemon juice (b) Vinegar (c) Vitamin C tablet (d) Tamarind (e) Sour milk
12. What does pH stand for? What does the pH scale indicate?
13. sweet tooth may lead to tooth decay. Explain, why? What is the role of tooth paste in preventing cavities
14. Write the names of five hydrated salts with their colors and formulae.
15. How are bases different from alkalis? Are all bases alkalies
16. What are strong acids and weak acids? Give two examples.
17. How will you test a gas which is liberated when hydrochloric acid reacts with an active metal?
18. Indicate with the help of a diagram the variation of pH with a change in concentration of hydrogen ion and hydroxide ions showing
(i) Increase of acidic and basic nature. (ii) Increase and decrease of H ion
19. What are the indicators? Give examples and their colour changes in different mediums.
20. How will you prepare 100 times to dilute solution from 1mL of concentrated sulphuric acid solution? What precaution would you suggest and why?
Answers
Answer:
1. Acid rain water, if mixed with river water, lowers its pH below 5.6, i.e., makes river water acidic. But the living body works normally within a pH range of 7-7.8. That's why flow of acid rain water to river makes the survival of aquatic life in the river difficult.
2. This is because the reaction between acid and water is highly exothermic and so produces lot of heat. Hence, when water is added to acid, it results in vigorous boiling of the solution and the amount of heat produced is so large that it splashes the acid out of the container, which can result in acid burns.
3. CuSO4. 5H20 + conc. H2SO4 (aq.) ------> CuSO4 (s) + SO2 (g) + H20 (l) .
4. Tartaric acid is produced from tomato, and it neutralizes the sodium bicarbonate in the baking powder which helps to bake the food quickly and easily with the process of heating.
5. the one in jar B will stale first because acetic acid (commonly called vinegar ) is used to preserve food. jar b will rot first because jar a is pickled with acetic acid which will lower the pH of food and thus not allowing bacteria to grow on it and spoil the food.
6. Calcium carbonate which is basically and will make the nature of soil neutral.
7. (i) A hissing sound is observed. (ii) The mixture starts boiling and lime water is obtained.
8. Bleaching powder or calcium oxychloride (CaOCl2).
9. a. Basic nature of baking soda
b. When baking soda reacts with an acid CO2 gas is liberated which stops the fire.
10. It is usually stoed in air tight/sealed containers because the naturally existing Carbon dioxide in air decomposes chloride of lime forming Chlorine gas and Calcium Cabonate.
Hope it helps you....