I. Multiple choice questions
1. The chemical equation that represents neutralization reaction among the following is
(A) BaCl2 + H2SO4 → BaSO4 + 2HCl
(B) MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
(C) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(D) AgNO3 + HCl → AgCl + HNO3
Ans: (C) 2 NaOH + H2SO4 → Na2SO4 + 2H2O
2. As the pH value of a neutral solution increases,
(A) basic property decreases and number of OH− ions increases
(B) acidic property increases and number of H+ ions decreases
(C) basic property increases and number of OH− ions increases
(D) acidic property decreases and number of H+ ions increases.
Ans: (C) basic property increases and number of OH− ions increases
3. A compound that reacts with both acids as well as bases to produce salts and water is
(A) Aluminium Oxide (B) Copper Oxide
(C) Iron Oxide (D) Sodium Oxide
Ans: (A) Aluminium Oxide
4. The gas liberated when sodium carbonate reacts with dilute hydrochloric acid is
(A) Carbon Dioxide (B) Nitrogen Dioxide
(C) Hydrogen (D) Chlorine
Ans: (A) Carbon dioxide
5. The substance that converts blue litmus paper into red colour is
(A) Lime water
(B) Pure water
(C) Sodium hydroxide solution
(D) Gastric juice
Ans: (D) Gastric juice
6. An acid present in the stinging hair of nettle plant leaves is
(A) Methanoic acid (B) Oxalic acid
(C) Citric acid (D) Lactic acid
Ans: (A) Methanoic acid
7. The compound used to remove the permanent hardness of water is
(A) Sodium carbonate
(B) Sodium hydroxide
(C) Sodium hydrogen carbonate
(D) sodium chloride
Ans: (A) Sodium carbonate
8. The pH value range of an acid.
(A) 0-7 (B) 2-12 (C) 7-14 (D) 12 - 14
Ans: (A) 0-7
9. As the number of hydrogen ions increases in a solution, then it
(A) becomes neutral
(B) increases acidity
(C) Increases the basicity
(D) reduces acidity
Ans: (B) increases acidity
10. Gas released when the dilute sulphuric acid is mixed with lead is
(A) oxygen (B) nitrogen
(C) Hydrogen (D) carbon
Ans: (C) Hydrogen
11. The product obtained when an acid is mixed with a metal is
(A) Metal oxide & water
(B) Salt & water
(C) Metal oxide & hydrogen gas
(D) Salt & hydrogen gas
Ans: (D) Salt & hydrogen gas
12. The molecular formula of lime water is
(A) CaO (B) Ca(OH)2
(C) CaCO3 (D) CO2
Ans: (B) Ca(OH)2
13. When hydrochloric acid is added to a copper oxide solution, its colour turns into blue-green due to
(A) Copper oxide (B) Water
(C) Copper hydroxide (D) Copper chloride
Ans: (C) Copper hydroxide
14. Acid should be added to water, not water to acid. Because it is
(A) Exothermic and may explode.
(B) Endothermic and may explode
(C) It does not mix
(D) Mixes very slowly
Ans: (A) Exothermic and may explode.
15. An acidic salt is to be obtained. Then the kinds of acid and base that have to be reacted with each other are
(A) Weak base and weak acid
(B) Weak acid and strong base
(C) Strong acid and strong base
(D) Strong acid and weak base
Ans: (D) Strong acid and weak base
16. A change that can be observed when red and blue litmus papers are dipped one after the other in two solutions M and N is
(A) If M is a metallic oxide solution, the blue litmus turns red.
(B) If N is a metallic oxide solution, the red litmus does not change colour
(C) If M is a non-metallic oxide solution, the blue litmus turns red
(D) If N is a non-metallic oxide solution, the red litmus turns blue
Ans: (C) If M is a non-metallic oxide solution, the blue litmus turns red
II. Answer the following questions. (1 Mark)
17. What is neutralisation reaction?
Ans: The reaction between an acid and a base to produce salt and water is called neutralization
18. Plaster of Paris should be stored in a moisture-proof container. Give scientific reason. (JUNE 2019)
Ans: Plaster of Paris reacts with moisture and becomes hard.
19. What are amphoteric oxides?
Ans: Metallic oxides that show both acidic and basic behaviour are called amphoteric oxides
20. Can detergents be used to detect the permanent hardness of water? Give reason.
Ans: No. It gives foam in both soft and hard waters.
21. Name the ions responsible for acidic and basic natures of the substances.
Ans: Acidic — H+ / H3O+ / Hydrogen / Hydronium
22. Write any two uses of washing soda.
Ans: i) In glass, soap and paper industries.
ii) In the manufacture of sodium compounds such as borax.
23. 1ml of acetic acid is mixed with 1ml of sodium hydroxide solution. Determine the nature of the salt forms here with suitable reason.
Ans: It is a basic salt.
because sodium hydroxide is a strong base.
24. How is concentrated acid diluted?
Ans: By adding the acid slowly to the water with constant stirring.
25. How do you detect acid with litmus paper?
Ans: Blue litmus paper turns red when dipped in acid./ Red litmus paper does not change colour when dipped in acid.
26. What is an acid?
Ans: A solution with a pH value ranging from 0 to 7 is called an acid.
27. Write a chemical equation for the reaction of a metal with a base.
Ans: 2NaOH + Zn → Na2ZnO2 + H2
28. What is the reaction product when air is blown into lime water?
Ans: Calcium carbonate (CaCO3)
29. Which is the gas released when acids react with metal carbonate and metal hydrogen carbonate?
Ans: Carbon dioxide
30. Why is a metal oxide called a basic oxide?
Ans: A metal oxide is called a primary oxide because it reacts with an acid like a primary acid to form a salt and water.
31. Why is a non-metal oxide called an acidic oxide?
Ans: Non-metal oxides react with an acid like an acid to form a salt and water.
32. What are bases?
Ans: Have hydroxide ions
33. What is the ion formed when an acid dissolves in water?
Ans: Hydronium ion (H+)
34. What happens as the number of hydroxide ions in a solution increases?
Ans: The basicity of the solution increases. Or the pH value increases.
35. What is the pH value of acid rain?
Ans: Less than 5.5.
36. What is the chemical name of baking powder?
Ans: Calciumoxychloride
37. Write the chemical equation for the preparation of bleaching powder.
Ans: Ca(OH)2 + Cl → CaOCl2 + H2O
38. What is baking powder?
Ans: Baking powder is an edible mixture of baking soda and tartaric acid.
39. Give the molecular formula and chemical name of washing soda.
Ans: NaHCO3 - Sodium hydrogen carbonate
40. Which salt is used in fire extinguishers?
Ans: NaHCO3 - Sodium hydrogen carbonate
41. Why does baking soda swell when mixed with bread dough?
Ans: Because baking soda reacts with water to produce carbon dioxide gas
42. 20 ml of concentrated sodium hydroxide solution is added to a beaker containing 100 ml of water. How does this affect the concentration and the strength of OH- ions in that solution?
Ans: The concentration and the strength of OH- ions in that solution decreases.
43. How are the released gases P and Q detected in the experiments depicted in the following figures?
III. Answer the following questions. (2 Marks)
44. Give scientific reason: While diluting an acid, the acid should be added to water.
If water is added to concentrated acid the heat generated may cause the mixture to splash out and cause burns.
The glass container may also break due to excessive local heating.
(ii) Otherwise, it reacts with moisture and changes to gypsum which is a solid mass.
45. Agricultural scientists have suggested to add a certain amount of lime powder to an agricultural field. What may be the reasons for this? Explain.
Ans:
★ Plants require a specific pH range for their healthy growth.
★ Soil of his land is acidic.
★ Lime powder is a base.
★ So, adding lime powder to the soil, decreases the acidic property / soil is neutralized
46. The PH values of the solutions A, B and C are 5, 6 and 7 respectively. Which of these solutions has the most acidic nature and why?
46. The solution A is acidic because the more concentration of hydrogen ions.
47. State the properties of acids.
Ans:
Properties of Acids
★ Acids have a sour taste
★ Turns blue litmus paper red
★ Have hydrogen ions
★ Acids are good conductors of electricity
48. State the properties of bases.
Ans:
Properties of Bases
★ Bases have a bitter taste
★ Turns red litmus paper to blue
★ Have hydroxide ions,
★ These are insulators
49. You are given three test tubes, one containing distilled water and the other two containing acidic and basic solutions respectively. If you are given only red litmus paper, how will you identify each sample in the test tube?
Ans:
First dip the litmus paper one by one in a test tube and take it out and wash it in neutral water before dipping it in another test tube.
1. If the colour does not change, then distilled water is neutral
2. If the red litmus turns blue, then it is a base
3. If the blue litmus paper turns red, then it is an acid)
50. HCl, HNO3 etc. exhibit acidic properties in aqueous solution but compounds like alcohol and glucose do not exhibit acidic properties. Why?
Ans:
HCl, HNO3 etc. produce hydrogen ions in aqueous solution Compounds like alcohol and glucose contain hydrogen, so they do not produce hydrogen ions, so they do not exhibit acidic properties.
51. Rain water conducts electric current but distilled water does not. Why?
Ans:
In solution, electric current is carried by ions. Rainwater contains dissolved salts which dissociate into ions and carry electric current, but in distilled water, no electric current flows as ions are not formed.
52. The pH of fresh milk is 6. How does its pH change as it curdles? Explain?
Ans:
As milk curdles, its pH decreases because as milk curdles, the lactose in the milk is converted to lactic acid. Acids have a low pH
53. A milkman adds a small amount of baking soda to fresh milk.
Ans:
To increase the shelf life of milk, the pH of fresh milk is changed to alkaline. Since milk is slightly more alkaline, it takes longer.
54. Write the equations for preparing sodium hydroxide and baking soda from sodium chloride.
Ans:
★ NaCl + H2O → NaOH + H2 + Cl2
★ NaCl + NH3 + H2O + CO2 → NaHCO3 + NH4Cl
55. A solution of baking soda is commonly applied to the area of a honeybee stung area. Justify this action.
Ans:
When a bee stings, it releases methanoic acid. Baking soda is a mild base. Baking soda reacts with the methanoic acid to form salt and water, which reduces inflammation.
56. When an aqueous solution of 'P' is subjected to electrolysis in the chlor-alkali process, then the gases 'Q' and 'R' released at cathode and anode respectively
i) Name P, Q and R.
ii) Write any one use of the gas Q.
Ans:
i) P: Sodium chloride solution
Q: Hydrogen
R: Chlorine
ii) used as a fuel, margarine, ammonia for fertilizers
57. Solutions A, B, C and D have pH values of 5.6, 1.8, 13.5 and 8.1 respectively.
a) Which of these solutions used to neutralize the acidity of the stomach?
b) Predict the change in the concentration of H+ and OH- ions in the solution that forms when solutions B and D are mixed in equal volumes.
Ans:
a) D
b) Concentration of ions decreases.
58. When carbon dioxide is passed through the lime water, then a white precipitate forms first. If passing Carbon dioxide is continued, then precipitate disappears. What is the reason for this effect? Name the final product of this reaction.
Ans:
Calcium hydrogen carbonate is formed and dissolved in water.
59. When an acid is diluted with distilled water what happens on the H+ ions concentration of that solution? Is there any change in the pH value of this solution? Clarify.
Ans:
★ Concentration of H+ ions decreases in the solution.
★ pH value increases
IV. Answer the following questions. (3 Marks)
60. Draw the diagram of arrangement of the apparatus to show the reaction of zinc granules with dilute sulphuric acid and testing hydrogen gas by burning. Label the parts.
Ans:
61. Name the gas liberated when an acid reacts with metal carbonate. Write the chemical equation of the reaction when this gas is passed through lime water. What is the colour of the precipitate obtained in this reaction?
Ans:
★ Carbon dioxide or CO2
★ Ca(OH)2 + CO2 → CaCO3 + H2O
★ White precipitate
62. There is no change in the colour of red litmus and blue litmus paper when dipped into an aqueous solution of sodium chloride. After passing direct current through the same solution, red litmus changes to blue colour. Which product is responsible for this change? Mention any two uses of this product.
Ans:
Sodium hydroxide / NaOH.
(i) De-greasing metals (ii) Soaps and detergents (iii) Paper making (iv) Artificial fibres.
63. What is a strong acid? Explain how tooth decay is caused. How can it be prevented?
Ans:
★ Acid that gives rise to more H+ ions is said to be strong acid.
★ Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. So, the pH in the mouth decreases and the tooth enamel gets corroded.
★ Using toothpastes which are generally basic, for cleaning the teeth.
64. Write the molecular formulae and two uses of each of the following compounds
a) Bleaching powder b) Plaster of Paris.
Ans:
a) Bleaching powder: CaOCl2
Uses
★ for bleaching cotton and linen in the textile industry,
★ for bleaching wood pulp in paper factories and for bleaching washed clothes in laundry.
★ as an oxidizing agent in many chemical industries
★ to make drinking water free from germs.
b) CaSO4. ½H2O
Uses
★ for making toys
★ making materials for decoration
★ for making surfaces smooth.
65. What is neutralisation reaction? Give an example.
Ans:
a) Reaction between acids and bases to form salt and water is called neutralization reaction.
Base + Acid → Salt + water.
Ex: NaOH + HCl → NaCl + H 2 O.
[Consider any suitable example]
66. What is the common name of the compound that has molecular formula CaSO4. ½H2O.
Ans:
Calcium sulphate hemihydrate or Plaster of Paris
67. How are concentrated acids and weak acids different? State the precautions to be taken while concentrating an acid.
Ans:
★ An acid that contains more water and less acid is called a concentrated acid. Acids that produce fewer H+ ions are also called weak acids.
★ Be careful when adding acid to water. Always add acid slowly to water with constant stirring.
68. Name the salts used in the following situations and write their molecular formula:
a) To remove permanent hardness of water.
b) To make drinking water free from germs.
c) To support fractured bones in their right position.
Ans:
a. sodium hydroxide
b. bleaching powder
c. plaster of paris
69. The pH values of four solutions are given in the below table.
a) Classify these into acidic and basic solutions:
b) Name the antacid used to neutralise excess of acid in the stomach.
Ans:
a) Acidic solutions- e h
Basic solutions –h g
b) Milk of magnesia / Magnesium hydroxide / Mg (OH) 2
70. Simultaneously red and blue litmus papers are dipped in the brine solution and in the aqueous product produced by subjecting that solution to electrolysis. What changes do you observe in litmus papers? Support your answer with reasons.
Ans:
No colour change is observed in the litmus papers dipped in the brine solution. Because it is a neutral solution. Red litmus paper dipped in aqueous product obtained by electrolysis of brine solution turns to blue colour. Because it is a basic solution
71. Observe the pH values of four solutions given in the following table and answer the questions below.
i) Which solution can be used to prepare an antacid? Why?
ii) Which two solutions can be used to get a neutral salt? Why?
Ans:
i) Solution ‘P’ can be used to prepare an antacid. Because it is a mild base.
ii) Solution ‘Q’ and ‘S’ can be used to get a neutral salt. Because ‘Q’ is a strong base and ‘S’ is a strong acid
72. Name the acid present in the following substances.
i) Curd ii) Gastric juice
Ans:
i) Curd: Lactic acid
ii) Gastric juice: Hydrochloric acid (HCl)
73. Solutions A, B, C and D are having pH values of 2, 6, 8 and 13 respectively. Then,
i) Which solution has more H+ and which solution has more OH− ions concentration? Why?
ii) Which solutions can be made to react each other to get neutral salts?
Ans:
i) Solution ‘A’ has more H + ions concentration.
Reason: If pH value is less, then H+ concentration is more.
Solution ‘D’ has more OH− ions concentration.
Reason: As the pH value increases from 7 to 14, there is an increase in OH− ions concentration.
ii) Solutions ‘A’ and ‘D’. Solutions ‘B’ and ‘C
74. Four solutions A, B, C and D when tested with universal indicator showed pH as 5, 2, 7 and 11 respectively. Which solution
(i) has more hydronium ions?
(ii) is neutral?
(iii) is the strong acid?
Ans:
(i) B
(ii) C
(iii) D
V. Answer the following questions. (4 Marks)
75. Name the products of chlor - alkali process. Write one use of each.
Ans:
(i) The reaction between an acid and a base to give salt and water is known as a neutralization reaction.
(ii) The products of chlor-alkali process are:
★ hydrogen
★ chlorine
★ brine containing NaOH.
Uses of hydrogen:
★ used as a fuel
★ margarine
★ ammonia for fertilizers
Uses of chlorine:
★ used in water treatment
★ used as a cleaning agent in swimming pools
★ used in making PVC, CFCs
★ used as a disinfectant
★ used as a pesticide
Uses of NaOH:
★ used for degreasing metals
★ used for making paper
★ used for making soaps and detergents
★ used for making artificial fibers
76. NaOH, Ca(OH)2, H2 and Cl2 materials are given to you. By using which of these materials you can prepare bleaching powder? Write the chemical name and one use of the bleaching powder.
Ans:
a) Bleaching powder is produced by the action of chlorine on dry slaked lime.
OR
Ca(OH)2 + Cl2 → CaOCl2 + H2O
Uses:
★ For bleaching cotton and linen in the textile industry, wood pulp in paper factories. For bleaching washed clothes in laundry
★ As an oxidizing agent in chemical industry
★ to make drinking water free from germs.
b) The salt solution is a neutral solution.
★ NaOH + HCl → NaCl + H2O.
77. i) How do you identify a solution as basic solution by using blue litmus paper?
ii) Under what condition does a farmer treat the soil of his field with slaked lime.
Ans:
i) The blue litmus paper does not change its colour in basic solution.
ii) When acidic property of soil increases when pH value of soil decreases when the concentration of H +/ H 3O+ ions in soil increases
78. Write the differences between acid and base.
Ans:
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