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Electricity
1. Two students perform the experiments on series and parallel combination of two given resisters R1and R2and plot the following V-I graphs. This of the two graphs correctly represents the labels ‘series and parallel’. Justify your answer.
2. Two metallic wires A and B of the same material are connected in parallel. Wire A has length l and radius r. wire B has length 2l and radius 2r. Calculate the ratio of the equivalent resistance in parallel combination and the resistance of the wire A.
3. You are given two resistors of 5? and 20?, a battery of emf 2.5 V, a key and an ammeter. Draw a circuit diagram of all given components such that ammeter gives a reading of 0.1 A.
4. The electrical resistivity of few materials is given below in ?m. Which one of these materials has the highest electrical conductivity and which has the lowest?
A (6.84x10-8),
B (1.60x10-8),
C (1.00x10-4),
D (2.50x1012),
E(4.40x10-5)
and F (2.30x1017).
5. A piece of wire of resistance 20? is drawn out so that its length is increased to twice its original length. Calculate the resistance of the wire in the new situation.
6. Two resistors with resistances
(i) 5 ? and 10 ?
(ii) 10 ? and 15 ?
respectively are to be connected to a battery of emf
(i) 6 V,
(ii) 12 V so as to obtain
a) minimum current flowing,
b) maximum current flowing.
a. How will you connect these resistances in each coil?
b. Calculate the strength of total current in the circuit in the two cases.
Acids, Bases and Salts
1. During summer season, a milkman usually adds a very small amount of baking soda to milk. Why?
2. Tooth enamel is one of the hardest substances in our body. How does it undergo damage due to eating chocolates and sweets? How do toothpastes prevent this damage?
3. How are all the acids and bases similar? Explain.
4. Baking soda is used in small amounts in making breads and cakes. It helps to make thes4e soft and spongy. An aqueous solution of baking soda turns red litmus blue. It is also used in soda acid fire extinguisher. Use this information to answer the following questions –
i. How does baking soda help to make cakes and breads soft and spongy?
ii. How does it help in extinguishing fire?
iii. Is the pH value of baking soda solution lower than or higher than 7?
5. Dry HCl gas does not turn blue litmus red whereas hydrochloric acid does. Give one reason.
6. A student drooped few pieces of marble in dilute hydrochloric acid contained in a test tube. The evolved gas was passed through lime water. What change would be observed in lime water? Write balanced chemical equation when (i) gas was evolved (ii) gas was passed through lime water.
7. Answer the following questions –
i. Why is the formula of Plaster of Paris written as CaSO4.½H2O? How is it possible to have half of water molecule attached to CaSO4?
ii. Why is sodium bicarbonate an essential ingredient of most antacids?
iii. Sodium bicarbonate is an essential ingredient of baking powder. What is the function of it?
iv. When electricity is passed through aqueous solution of NaCl, three products are obtained. Why this process is called chlor-alkali process?
8. Fresh milk has a pH of 6. When it changes into curd, will its pH value increase or decrease? Why?
9. A compound which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water. Identify the compound. Write the chemical equation for its preparation. For what purpose it is used in hospitals?
10. Why does tooth decay start when the pH of mouth is lower than 5.5?
11. What effect does an increase in concentration of hydrogen ion in a solution have on the pH of the solution?
12. Why does 1 M HCl solution have a higher concentration of H+ions than 1M CH3COOH solution?
13. Write the name and chemical formula of calcium compound used for disinfecting drinking water. How is this compound manufactured?
14. Why are acid not stored in metal containers? Containers made from which materials are safe to store acids?
15. How will you prepare bleaching powder? Give chemical reaction involved. Why is tartaric acid added along with sodium bicarbonate in baking powder?
16. What is pH? How does pH change on changing H+ concentration? How does acidic or basic nature change?
17. Answer the following questions – a. A metal compound ‘A’ reacts with dilute HCl to produce effervescence. The gas evolved extinguishes a burning candle. Write balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
b. Why do HCl, HNO3, etc show acidic characters in aqueous solution while solutions of compounds like alcohol and glucose do not show acidic characters?
c. How is the concentration of hydronium ion affected when a solution of an acid is diluted?
d. What happens when sodium bicarbonate is heated? Write the balanced chemical equation.
18. You have two solutions A and B. the pH of A is 6 and the pH of B is 8. Which solution has more H+ion concentration? Which one is acidic and which one is basic?
19. A milkman adds a very small amount of baking soda to fresh milk. Why does he shift the pH from 6 to slightly alkaline? Why does this milk take a long time to set as curd?
20. Give reasons for the following –
i. While diluting an acid, it is recommended that the acid should be added to the water and not water to acid.
ii. Dry ammonia has no action on litmus paper but a solution of ammonia in water turns red litmus blue.
iii. Plaster of Paris should be stored in a moisture proof container.
iv. Distilled water does not conduct electricity whereas rain water does.
v. Curd and sour substances should not be kept in brass or copper vessels.
vi. Bleaching powder pollutes when left open air.
vii. Acetic acid is a weak acid while hydrochloric acid is a strong acid.
viii. Sodium carbonate is regarded as a basic salt.
21. Rajesh took sulphur powder on a spatula and heated it. He collected the gas evolved on lowering a test tube over it.
(a). What will be the action of gas in
i. dry litmus paper
ii. Moist litmus paper.
(b). Write balanced chemical equation for the reaction.
22. What are the special properties of plaster of Paris, which makes it useful in hospitals?
23. Which one of the medicines – antibiotic, analgesic, or antacid is used for treating indigestion?
24. Five solutions A, B, C, D and E when tested with universal indicator showed pH 5, 2, 10, 7 and 12 respectively. Arrange the pH in increasing order of hydrogen ion concentration.
25. You must have seen tarnished copper vessel being cleaned with lemon and tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
26. An element reacts with oxygen to give a compound of high melting point. This compound is highly soluble in water. Is this element carbon, calcium, silicon or iron?
27. Which gas is produced in when dilute HCl is added to a reactive metal? Write chemical equation when iron reacts with dilute sulphuric acid.
28. Why is PoP written as CaSO4.½H2O? How is it possible to have half water molecule attached to CaSO4?
29. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic and a basic solution respectively. If you are given only red litmus paper, how will you identify content of each test tube?
30. How are bases different from alkalis? Are all bases alkalis?
31. What are antacids? Give an example. Name the acid produced in our stomach.
32. Mention names of two oxides each which on reacting with water give acids and bases.
33. Explain the role of pH in our digestion and tooth decay.
34. Name the gas evolved when dilute sulphuric acid reacts with sodium carbonate. Give three uses of plaster of Paris.
35. Write the name and the chemical formula of organic compound which is present in vinegar.
36. Name an acid base indicator prepared at home. Which acid is present in vinegar, sour milk or curd, tamarind, lemon, orange and ant sting.
37. What is the colour of methyl orange in baking soda solution?
38. What is the colour of phenolphthalein in dilute HCl, soap solution and baking soda solution?
39. Why does copper not react with dilute sulphuric acid or HCl to give hydrogen gas?
40. What is aqua regia? Name the metals which are soluble in it
41. What are antacids? Give an example. Name the acid produced in our stomach.
42. Mention names of two oxides each which on reacting with water give acids and bases.
43. Explain the role of pH in our digestion and tooth decay.
44. Name the gas evolved when dilute sulphuric acid reacts with sodium carbonate. Give three uses of plaster of Paris.
45. Write the name and the chemical formula of organic compound which is present in vinegar.
46. Name an acid base indicator prepared at home. Which acid is present in vinegar, sour milk or curd, tamarind, lemon, orange and ant sting.
47. What is the colour of methyl orange in baking soda solution?
48. What is the colour of phenolphthalein in dilute HCl, soap solution and baking soda solution?
49. Why does copper not react with dilute sulphuric acid or HCl to give hydrogen gas?
50. What is aqua regia? Name the metals which are soluble in it.
51. What do all
(i). Acids,
(ii). Bases have in common? What is milk of magnesia? Is it a strong or mild base?
52. Which chemical compound is present in our tooth enamel? Is toothpaste acidic or alkaline?
53. Which will have more H+ ion concentration – a solution with pH=0 or a solution with pH=14?
54. Which acid and base are used in the formation of – CuSO4, NaNO3, NaHCO3, and NaHSO4?
55. What is the role of tartaric acid or citric acid present in baking powder?
56. Name an indicator which indicates the various levels of the H+ ion concentration.
57. When the concentrated aqueous solution of a substance ‘X’ is electrolysed sodium hydroxide, chlorine and hydrogen gas are produced. Name the substance ‘X’. What is the special name of this process?
58. When a green iron salt is heated strongly, its colour finally changes to black and odour of burning sulphur is given out. Name the iron salt and type of reaction. Write the chemical equation for the above.
59. Name the acid formed when (i). CO2, (ii). SO2is dissolved in water.
60. A gas highly soluble in water turns colorless solution to pink when a few drops of phenolphthalein solution is added to it. What is the nature of the gas?
61. State for what purpose is bleaching powder used in water treatment plants.
62. A compound ‘Y’ loses water of crystallization when exposed to air. Identify compound and write its formula.
63. A calcium compound yellowish white in colour is used as disinfectant and also in textile industry. Name the compound. How is it prepared? Give chemical reaction involved.
64. When phenolphthalein was added to a solution of ‘X’, it turned pink. After some time pink colour fades away. Identify ‘X’ and give reason for the observation.
65. Define natural, synthetic and olfactory indicators with two examples each.
66. What are the substances called which are used to prevent oxidation?
67. How will you provide the following information in a chemical reaction – aqueous solution, a liquid, evolution of heat, evolution of gas, steam and precipitation?
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