CBSE Class 10 Science Past Paper PDF 2019-2020

Chap 2 : Acid Bases and Salts www.cbse.online File Revision Date : 10 July 2019 CBSE Previous Years Chapterwise Questions Exam 2019-2020 CLASS : 10th...

Chap 2 : Acid Bases and Salts www.cbse.online File Revision Date : 10 July 2019 CBSE Previous Years Chapterwise Questions Exam 2019-2020 CLASS : 10th CHAPTER 2 SUB : Science For more subject visit www.cbse.online or whatsapp at 8905629969 Acid Bases and Salts 1. ONE MARK QUESTIONS H+(aq) ions in a solution have on pH of solution? Ans : [CBSE 2013,2009] Increase in H+ concentration will lead to decrease in 1. Write chemical equation for the reaction of zinc metal pH, on sodium hydroxide. Ans : [CBSE 2016] 10. Name a gas evolved when dilute HCl reacts with Heat sodium hydrogen carbonate. How is it recognised? Zn(s) + 2NaOH(aq) Na2ZnO2(aq) + H2(g) Ans : [CBSE 2013] 2. Three acidic solutions A, B and C have pH = 0, 3 and Carbon dioxide, it turns lime water milky. In this way, 5 respectively. CO2 gas is recognised. a. Which solution has the highest concentration of H+ ions? 11. What are olfactory indicators? b. Which solution has the lowest concentration of Ans : [CBSE 2013] H+ ions? Those indicators whose smell changes in acidic and Ans : [CBSE 2015] basic solutions. a. The solution with pH = 0 has highest concentration of H+ ions. 12. Why does 1 M HCl solution have a high concentration b. The solution with pH = 5 has lowest concentration of H+ ions than 1 M CH3COOH solution? of H+ ions. Ans : [CBSE 2013,2009] It is because 1M HCl is a strong acid and it is completely 3. What is meant by p and H in pH? ionised in aqueous solution whereas CH3COOH is a Ans : [CBSE 2014] weak acid, so it is only partially ionised. p stands for ‘potenz’ in German meaning power, H NO NEED TO PURCHASE ANY BOOKS stands of hydrogen. For session 2019-2020 free pdf will be available at 4. Define alkalies and give an example. www.cbse.online for Ans : [CBSE 2014] 1. Previous 15 Years Exams Chapter-wise Question Water soluble bases are called alkalies e.g., NaOH. Bank 2. Previous Ten Years Exam Paper (Paper-wise). 5. Mention the range of pH for identification of a base. 3. 20 Model Paper (All Solved). Ans : [CBSE 2014] 4. NCERT Solutions All material will be solved and free pdf. It will be 7.1 to 14 is the pH range for bases. provided by 30 September and will be updated regularly. Disclaimer : www.cbse.online is not affiliated to Central Board of Secondary Education, 6. How chloride of lime differs from calcium chloride? New Delhi in any manner. www.cbse.online is a private organization which provide free study material pdfs to students. At www.cbse.online CBSE stands for Canny Books Ans : [CBSE 2014] For School Education CaOCl2 is the chloride of lime whereas CaCl2 calcium chloride. 13. Write the chemical equation representing the action of atmospheric CO2 gas on bleaching powder when left 7. What is meant by water of crystallisation in a exposed in open. substance? Ans : [CBSE 2013] Ans : [CBSE 2014] CaOCl2 + CO2 $ CaCO3 + Cl2 The water molecules associated with a crystalline solid are called water of crystallisation. 14. How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal? 8. Write the chemical name and chemical formula of washing soda. Ans : [CBSE 2012,2009] Ans : [CBSE 2014] Bring a burning matchstick near the gas. If it is burnt with ‘pop’ sound, the gas is H2. Na2CO3.10H2O, sodium carbonate deca-hydrate is washing soda. 15. How is the pH of solution of an acid influenced when 9. What effect does an increase in concentration of Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 11 Chap 2 : Acid Bases and Salts www.cbse.online it is diluted? family. Ans : [CBSE 2012] Ans : [CBSE 2011] pH of the solution increases when it is diluted. NaCl, Na2CO3 are two salts belonging to sodium family. 16. At what pH rain water is said to be acidic ? Ans : [CBSE 2012] 26. Which among distilled water, tap water and sea water is the best conductor of electricity? When pH < 5.5, the rain water becomes acidic. Ans : [CBSE 2010, 2011] 17. Which gas is evolved when dilute hydrochloric acid Sea water is a better conductor due to the presence reacts with zinc metal? Write the molecular formula of ions. of this gas. Ans : [CBSE 2012] 27. Name the acids present in (i) nettle sting, (ti) curd. Dihydrogen gas, H2. Ans : [CBSE 2010] (i) HCOOH, Formic acid, 18. Dry HCl gas does not change the colour of dry blue (ii) Lactic acid, CH3-CH(OH)-COOH litmus. Give reason to justify it. Ans : [CBSE 2012] 28. Name a salt which does not contain water of crystallisation. Dry HCl (g) does not form ions, therefore it does not affect dry blue litmus. Ans : [CBSE 2010] NaHCO3 is a salt that does not contain water of 19. Why is HCl a stronger acid than acetic acid? crystallisation. Ans : [CBSE 2012] 29. Write the name and chemical formula of the product HCl is completely ionised in aqueous solution whereas formed by heating gypsum at 373 K. acetic acid is only partially ionised in aqueous solution. Ans : [CBSE 2010] 20. Name the chemicals used in acid fire extinguisher and Plaster of Paris, CaSO. H2O1 4 2 the gas evolved from it when it is used? Ans : [CBSE 2012, 2011] 30. The pH of a sample of vegetable soup was found to be 6.5. How is this soup likely to taste? NaHCO3 (Sodium hydrogen carbonate) and H2SO4 (Sulphuric acid). The gas evolved is carbon dioxide. Ans : [CBSE 2010] It will be sour in taste. 21. Which is a stronger acid, with pH = 5 or with pH=2? Ans : [CBSE 2011] 31. Which bases are called alkalies? Give one example of alkali. The acid with pH = 2 is a stronger acid. Ans : [CBSE 2010,2009] 22. A compound which is prepared from gypsum has Those bases which are soluble in water are called the property of hardening when mixed with a proper alkalies e.g., NaOH, KOH. quantity of water. Identify the compound and write its chemical formula. 32. Write the name and chemical formula of the product Ans : [CBSE 2011] formed by action of chlorine on slaked lime. CaSO4. 12 H2O (Plaster of Paris), Calcium sulphate Ans : [CBSE 2010] hemihydrate. CaOCl2, Bleaching powder, Calcium oxy-chloride. 23. What is meant by term pH of solution? The pH of 33. Write a balanced chemical equation for the reaction rain water collected from two cities A’ and ‘B’ were between sodium carbonate and hydrochloric acid found to be 6.0 and 5.0 respectively. The water of indicating the physical state of reactants and the which city will be more acidic? products. Ans : [CBSE 2011] Ans : [CBSE 2010] pH of solution is defined as negative logarithm of H+ Na 2 CO 3 (s) + 2HCl (dill) $ 2NaCl (aq) + CO 2 (g) + H 2 O (l) ion concentration. It determines the strength of acid and base. Rainwater with pH = 5 is more acidic. 34. Name the acid and base that have constituted the salt ammonium nitrate. 24. A few drops of sulphuric acid are added to water Ans : [CBSE 2010] before electrolysis, why? Acid: HNO3, Ans : [CBSE 2011] Base: NH4OH (i.e., Nitric acid, Ammonium hydroxide). Water is not a good conductor of electricity. Few drops of sulphuric acid makes it better conductor of 35. Suggest one way to reduce alkaline nature of the soil. electricity. Ans : [CBSE 2010] Add ammonium nitrate (Acidic salt) to neutralise 25. Write the names of two salts belonging to sodium alkaline nature of soil. Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 12 Chap 2 : Acid Bases and Salts www.cbse.online 36. Oxides of metals are basic while those of non-metals 46. How does the pH change when solution of a base is are acidic. Explain. diluted? Ans : [CBSE 2010] Ans : [CBSE 2008] Metal oxides dissolve in water to form base basic in When solution of a base is diluted, its pH decreases. nature. On the other hand non-metals dissolve in water to form acids, acidic in nature. 47. Arrange the following in an increasing order of their pH values: NaOH solution, Blood, Lemon juice. 37. What is the difference between slaked lime and lime Ans : [CBSE 2008] water? Lemon juice < Blood < NaOH solution. Ans : [CBSE 2010] The solid Ca(OH)2 is slaked lime whereas clear 48. At what pH in the mouth is tooth decay faster and solution of Ca(OH)2 in water is lime water. why? Ans : [CBSE 2008] 38. Write a balanced chemical equation for the At pH lower than 5.5, tooth decay becomes faster neutralisation reaction, mentioning the physical state because calcium phosphate (enamel) reacts with acid of reactants and products. and gets corroded. Ans : [CBSE 2010] NaOH(aq) + HCl(aq) $ NaCl(aq) + H2O(l) TWO MARKS QUESTIONS 39. During summer season, a milkman usually adds a very small amount of baking soda to fresh milk. Give one reason. 49. A white chemical compound becomes hard on mixing proper quantity of water. It is also used to maintain Ans : [CBSE Sample Paper 2009] joints in fixed position. Name the chemical compound Baking soda is basic in nature, it will not allow milk and write its chemical formula. Write the chemical to turn sour due to the formation of lactic acid. equation to show what happens when water is added to this compound in proper quantity. 40. Curd is not kept in copper and brass utensils, why? Ans : [CBSE Sample Paper 2018, CBSE 2016] Ans : [CBSE 2009C] CaSO4. 12 H2O is the formula of the compound. The Curd contains lactic acid which can make poisonous name of compound is ‘Plaster of Paris’ (Calcium compounds with brass and copper vessels. sulphate hemihydrate). 41. Fresh milk has pH = 6. When it changes to curd will CaSO 4 $ 12 H 2 O + 32 H 2 O $ CaSO 4 $ 2H 2 O (Plaster of Paris) (Gypsum) its pH value increase or decrease? 50. Two solutions ‘A’ and ‘B’ have pH value 3.0 and 10.5 Ans : [CBSE 2009] respectively. Which of these will turn pH value will decrease when milk changes to curd. a. Blue litmus solution to red, b. Phenolphthalein from colourless to pink? Justify 42. What would be the colour of litmus in a solution of your answer in each case. sodium carbonate? Ans : [CBSE 2016] Ans : [CBSE 2009] a. ‘A’ with pH = 3, will turn blue litmus red because The red litmus will turn blue in Na2CO3 solution. it is acidic in nature. b. “B’ with pH = 10.5, will turn phenolphthalein 43. What is the colour of litmus in a solution of ammonium colourless to pink because ‘B’ is basic in nature. hydroxide? Ans : [CBSE 2009] 51. The pH of soil ‘A’ is 7.5, while that of soil “B is 4.5. Which of the two soils A or B should be treated with Red litmus will turn blue green colour in a solution of powdered chalk to adjust the pH and why? ammonium hydroxide. Ans : [CBSE 2016] 44. On adding dilute hydrochloric acid to copper oxide Soil ‘B’ is acidic, therefore it needs to be treated with powder, the solution formed is blue green. Predict the powdered chalk to adjust its pH because chalk is basic, new compound formed which imparts a blue green which will make soil neutral. colour to the solution. Ans : [CBSE 2008] 52. Write the chemical equation to describe how baking soda is produced on a large scale. Also write the Copper chloride imparts blue green colour to the chemical name of the products formed in the reaction. solution. Ans : [CBSE 2016] 45. How does flow of acid rain water into river makes the NH 3 + H 2 O + CO 2 + NaCl $ NaHCO 3 + NH 4 Cl survival of aquatic life in the river difficult? (Sodium hydrogen (Ammonium carbonate) chloride) Ans : [CBSE 2008] Acidic water makes aquatic species uncomfortable. 53. What is chlor-alkali process? Write a balanced Aquatic species are more comfortable in the pH 7 to chemical equation for the reaction involved in this 7.8. Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 13 Chap 2 : Acid Bases and Salts www.cbse.online process, to justify your answer. Ans : [CBSE 2016] Ans : [CBSE 2016] a. Green precipitate of Fe(OH)2 will be formed: When brine solution is electrolysed we get alkali FeSO 4 (aq) + 2NaOH (aq) $ Fe (OH) 2. Na 2 SO 4 (aq) (Green ppt) (NaOH) and chlorine (Cl2) gas, this process is called chlor-alkali process. b. White precipitate of Al(OH)3 will be formed: 2NaCl (aq) + 2H 2 O (l) $ 2NaOH (aq) + H 2 (g) + Cl 2 (g) AlCl (aq) + 3NaOH $ Al (OH) 3 (s) + 3NaCl (aq) (White ppt) 54. What is meant by the term water of crystallisation? 60. 15 mL of water and 10 mL of sulphuric acid are to be How would you show that copper sulphate crystals mixed in a beaker contains water of crystallisation? a. State the method that should be followed with Ans : [CBSE 2016] reason. b. What is this process called? The molecules of water associated with a crystalline Ans : [CBSE 2015] substance are called water of crystallisation. When hydrated copper sulphate is heated its colour a. Acid should be added to the water slowly with changes from blue to dirty white and water droplets constant cooling because the reaction is highly are formed. exothermic. CuSO4.5H2O Heat CuSO4 + 5H2O b. This process is called dilution. If we add little water to anhydrous CuSO4, we get blue NO NEED TO PURCHASE ANY BOOKS colour again. It is the presence of molecules of water of crystallisation which was lost on heating. For session 2019-2020 free pdf will be available at CuSO4 + 5H2O $ CuSO4.5H2O www.cbse.online for (Anhydrous) 1. Previous 15 Years Exams Chapter-wise Question Bank 55. Mention the pH of aqueous solution of the following 2. Previous Ten Years Exam Paper (Paper-wise). salts as 7, more than 7, less than 7. 3. 20 Model Paper (All Solved). KCl, Na2CO3, NH4C1, NaNO3 (Sodium nitrate) 4. NCERT Solutions Ans : [CBSE 2016] All material will be solved and free pdf. It will be KCl and NaNO3 has pH = 7 provided by 30 September and will be updated regularly. Disclaimer : www.cbse.online is not affiliated to Central Board of Secondary Education, Na2CO3 has pH > 7 New Delhi in any manner. www.cbse.online is a private organization which provide free study material pdfs to students. At www.cbse.online CBSE stands for Canny Books NH4Cl has pH < 7 For School Education 56. You have two solutions A and B. The pH of solution ‘A’ is 6 and the pH of solution ‘B’ is 8. Which solution 61. Name the acid present in the following: has more hydrogen ion concentration? Which one of a. Tomato, this is acidic and which one is basic? b. Vinegar, Ans : [CBSE 2016] c. Tamarind ‘A’ has more H+ ion concentration. Ans : [CBSE 2015] ‘A’ is acidic while ‘B’ is basic. a. Tomato contains oxalic acid. b. Vinegar contains acetic acid. 57. Give suitable reasons to justify the following statement: c. Tamarind contains tartaric acid. An aqueous solution of sodium chloride is neutral but an aqueous solution of sodium metal is basic. 62. Explain how antacid works. Ans : [CBSE 2016] Ans : [CBSE 2015] Sodium chloride is made up of a strong base, NaOH Antacids are weakly basic in nature. They neutralise and a strong acid, HCl. Therefore, its aqueous solution excess of HCl present in our stomach and gives us is neutral in nature. relief from hyper-acidity. Sodium metal reacts with water to form NaOH(Base) and H2 gas: 63. Equal lengths of magnesium ribbon are taken in test 2Na (s) + 2H 2 O (l) $ 2NaOH (aq) + H 2 (g) tube ‘A’ and ‘B’. Hydrochloric acid (HCl) is added to test tube A’ while acetic acid (CH3COOH) is added 58. What is the action of litmus on to test tube ‘B’. In which test tube, will fizzing occur a. dry ammonia gas more vigorously and why? b. solution of ammonia gas in water? Ans : [CBSE 2015] Ans : [CBSE 2016] The fizzing will occur more vigorously in test tube ‘A’ a. There is no effect of dry litmus on dry ammonia because HCl is a strong acid and reacts faster than gas. acetic acid which is a weak acid. b. Solution of ammonia will turn red litmus blue. 64. State what does pH of solution signify? Three solutions 59. State the observations you would make on adding A, B and C have pH values of 6, 2 and 10 respectively. sodium hydroxide to an aqueous solution of Which one of these solutions is highly acidic? Which a. ferrous sulphate, solution will turn red litmus blue? b. aluminium chloride. Ans : [CBSE 2015] Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 14 Chap 2 : Acid Bases and Salts www.cbse.online pH of solution signifies the nature of the solution i.e., place when it is heated. it is weakly acidic, strongly 1 acidic, neutral, weakly Ans : [CBSE 2013, 2008(C)] basic, strongly basic. ‘X’ is NaHCO3, sodium hydrogen carbonate. It is used ‘B’ with pH = 2 is strongly acidic. in cooking and for curing acidity in stomach. ‘C’ with pH = 10 will turn red litmus blue. Heat 2NaHCO3 Na2CO3 + CO2 +H2O 65. Define an acid and a base. Name one weak acid and one strong acid. 72. Crystals of a substance changes their colour on heating in a closed vessel but regained it after sometime, when Ans : [CBSE 2015] they were allowed to cool down. Acid is a substance which gives H+ ions in an aqueous a. Name one such substance. solution. b. Explain the phenomenon involved. Base is substance which gives OH- ions in the aqueous Ans : [CBSE 2012] solution. CH3COOH is a weak acid, H2SO4 is a strong acid. a. CuSO4.5H2O (Hydrated copper sulphate) Heat b. CuSO4.5H2O CuSO4 + 5H2O Blue (Dirty white) 66. What is universal indicator? State the purpose for which this indicator is used. The colour changes due to the loss of molecules of water of crystallisation. Colour is regained by Ans : [CBSE 2015] absorbing water molecules from the atmosphere Universal indicator is a mixture of a number of containing water vapours. indicators. It is used to determine pH of a solution. 73. (a) Write the name given to the bases that are highly 67. Name the natural source of each of the following acid: soluble in water. Give an example. a. Citric acid, (b) Why does bee sting causes pain and irritation? b. Oxalic acid, Rubbing of baking soda on the sting area gives c. Lactic acid, relief. How? d. Tartaric acid. Ans : [CBSE 2012] Ans : [CBSE 2014] (a) Highly soluble bases are called alkalies e.g., KOH. a. Citric acid—Lemon, Orange. (b) Bee sting contains HCOOH, formic acid which b. Oxalic acid—Tomato, Guava causes irritation. Baking soda (basic) neutralises c. Lactic acid—Curd, Sour milk HCOOH, therefore it gives relief from pain on d. Tartaric acid—Tamarind rubbing it on sting area, 68. Explain why sodium hydroxide solution cannot be 74. The pH of the mouth of a person is lower I than 5.5. kept in aluminium containers? Write the equation for What changes will occur in his mouth? How these the reaction that may take place for the same. changes can be controlled? Write any two measures. Ans : [CBSE 2014] Ans : [CBSE 2012, 2011, 2010] It because ‘Al’ reacts with NaOH to form sodium Acid will be formed in the mouth which causes tooth meta-aluminate and hydrogen gas: decay. 2Al + 2NaOH + 2H2O $ NaAlO2+3H2 a. Wash your mouth with water after every meal. b. Brush your teeth after meal. Toothpastes are basic 69. A student detected the pH of four unknown solutions in nature and it will neutralise the acid formed in A, B, C and D as follows: 11, 5, 7 and 2. Predict the mouth. nature of these solutions. Ans : [CBSE 2013] 75. What is a neutralisation reaction? Give one example. pH = 11 is basic Ans : [CBSE 2011 ] pH = 5 is acidic The reaction in which acid reacts with a base to form pH = 7 is neutral salt and water is called neutralisation reaction e.g., pH = 2 is strongly acidic KOH(aq) + HNO3(aq) $ KNO3(aq) + H2O(l) 70. Give two uses of baking soda and washing soda each. 76. Write the chemical name of Plaster of paris. Write Ans : [CBSE 2013] a chemical equation to show the reaction between Plaster of paris and water. Use of baking soda: a. It is used in making of bread, biscuits, cakes. Ans : [CBSE 2011] b. It is used as an antacid. CaSO 4 $ 12 H 2 O (Calcium sulphate hemihydrate) Use of washing soda: a. It is used as a cleansing agent. CaSO 4 $ 12 H 2 O + 32 H 2 O $ CaSO 4 $ 2H 2 O b. It is used to remove hardness of water. 77. State in brief the preparation of washing soda from 71. A compound ‘X’ of sodium is commonly used for baking soda. Write balanced chemical equation of the making crispy pakoras. It is also used for curing reaction involved. acidity in the stomach. Identify ‘X’. Write the formula Ans : [CBSE 2011] and its chemical name. State the reaction which takes When sodium hydrogen carbonate (Baking soda) Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 15 Chap 2 : Acid Bases and Salts www.cbse.online is heated sodium carbonate is formed which on oxychloride crystallisation forms washing soda: Ca(OH)2 + Cl2 $ CaOCl2 + H2O (Dry slaked lime) Heat 2NaHCO 3 Na 2 CO 3 + CO 2 + H 2 O It is used as a disinfectant i.e., it makes water fit for (Baking soda) drinking. Na CO + 10H 2 O $ Na 2 CO 3 $ 10H 2 O 2 3 (Washing soda) 84. What are olfactory indicators? Dry HCl gas does not 78. What is colour of FeSO4.7H2O crystals? How does this change the colour of dry blue litmus. Give reason. colour change upon heating? Give a balanced chemical Ans : [CBSE 2011] equation for the change. Ans : [CBSE 2011] Olfactory indicators: They give different smell in acids and bases. FeSO4.7H2O is pale green in colour. It becomes dirty white on heating. Dry HCl(g) does not form ions, so there is no FeSO4.7H2O $ FeSO4 + 7H2O effect on litmus. If it is heated strongly Fe2O3 and SO2, SO3 gases will NO NEED TO PURCHASE ANY BOOKS be formed. Heat For session 2019-2020 free pdf will be available at 2FeSO4 Fe2O3 + SO2 + SO3 www.cbse.online for 79. Classify the following salts into acidic, basic and 1. Previous 15 Years Exams Chapter-wise Question neutral salts: Potassium sulphate, ammonium chloride, Bank sodium carbonate, sodium chloride 2. Previous Ten Years Exam Paper (Paper-wise). 3. 20 Model Paper (All Solved). Ans : [CBSE 2011] 4. NCERT Solutions Acidic: Ammonium chloride, All material will be solved and free pdf. It will be Basic: Sodium carbonate, provided by 30 September and will be updated regularly. Neutral: Potassium sulphate, sodium chloride. Disclaimer : www.cbse.online is not affiliated to Central Board of Secondary Education, New Delhi in any manner. www.cbse.online is a private organization which provide free study material pdfs to students. At www.cbse.online CBSE stands for Canny Books 80. A student dropped few pieces of marble in dilute HCl For School Education contained in a test tube. The evolved gas was passed through lime water. 85. Answer the following: a. What change would be observed in lime water? a. Why is Plaster of paris written as CaSO 4 $ 12 H 2 O b. Write a balanced chemical equation for the above ? How is it possible to have a half water molecule change. attached with CaSO4? Ans : [CBSE 2011] b. Why is sodium hydrogen carbonate an essential a. Lime water will turn milky. ingredient in antacids? b. Ca(OH)2(aq) + CO2(g) $ CaCO3(s) + H2O(l) Ans : [CBSE 2011,2010] 81. A white powder is added while baking breads and a.It has one molecule of water associated with 2 while making cakes to make them soft and fluffy. molecules of CaSO4. Water molecules are present What is the name of that powder? What are the as water of crystallisation. main ingredients in it? What are the functions of each b. It is a mild base and it can neutralise hyper acidity ingredient? without harming our body. Ans : [CBSE 2011,2010] 86. What happens when chlorine is passed over slaked The powder is baking powder. It consist of sodium lime at 313 K? Write chemical equation of the reaction hydrogen carbonate and tartaric acid. involved and state two uses of the product. NaHCO3 gives CO2 on heating which makes the Ans : [CBSE 2010] bread cake soft and fluffy. Tartaric acid neutralises Bleaching powder, CaOCl2 is formed: Na2CO3 which is bitter in taste. Ca(OH)2 + Cl2 3313 K CaOCl2 + H2O a. It is used as an oxidising agent. 82. HCl and HNO3 show acidic characteristics in aqueous b. It is used as a disinfectant. solution while alcohol and glucose solutions do not. Give reasons. 87. What is meant by ‘water of crystallisation’ of Ans : [CBSE 2011] a substance? Describe an activity to show that HCl and HNO3 form H or H3O ions in aqueous + + blue copper sulphate crystals contains water of solution whereas alcohol and glucose do not dissociate crystallisation. into ions. Ans : [CBSE 2009] HCl + H2O $ H3O+ + Cl- The molecules of water associated with a crystalline HNO3 + H2O $ H3O + NO + - substance are called ‘water of crystallisation.’ 3 CuSO 4 $ 5H 2 O $ CuSO 4 + 5H 2 O 83. What is bleaching powder chemically? Give a reaction When hydrated copper sulphate is heated its colour for its preparation. State one of its use. changes from blue to dirty white and water droplets Ans : [CBSE 2011] are formed. If we add little quantity of water to anhydrous CuSO4, we get blue colour again. It is those Bleaching powder is chemically CaOCl2, calcium Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 16 Chap 2 : Acid Bases and Salts www.cbse.online presence of molecules water of crystallisation which chemical equation for its formation. List its two uses. was lost on heating. Ans : [CBSE 2018] Activity: To study the effect of heat on hydrated The salt is NaHCO3, sodium hydrogen carbonate. crystalline salts. NH 3 (g) + CO 2 (g) + NaCl (g) + H 2 O (l) $ NaHCO 3 (s) + NH 4 Cl i. Take 2 g of CuSO 4 $ 5H 2 O in a test tube. Uses: ii. Observe the initial colour of the salt. a. It is used as an antacid. iii. Heat the test tube at top of burner carefully as b. It is used in soda-acid fire extinguishers. shown in the diagram. iv. Record your observations. No salt has pH = 14. NaHCO3 has pH = 8.4. v. Cool the crystals and add few drops of water. vi. Record your observations again. 92. (a) Why does aqueous solution of an acid conduct Observations: Blue colour of CuSO 4 $ 5H 2 O is changed electricity? to dirty white anhydrous CuSO4 and water droplets (b) How does the concentration of H3O+ ions change were formed. On adding water, blue colour of salt was when a solution of an acid is diluted? restored. (c) Which one has a higher pH, a concentrated or a Conclusion: CuSO 4 $ 5H 2 O is a hydrated salt which dilute solution of hydrochloric acid? loses water of crystallisation, which on heating (d) What would to be the gas evolved on adding becomes dirty white and regains its colour when it dilute to hydrochloric acid to comes in contact with water. (i) Solid sodium carbonate placed in a test tube? Chemical reactions involved: (ii) Zinc metal in a test tube? Heat Ans : [CBSE 2018(C)] CuSO 4 $ 5H 2 O (S) CuSO 4 (s) + 5H 2 O (l) (Blue) (Dirty white) a. It contains ions which carry current. CuSO 4 (s) + 5H 2 O (l) Heat CuSO 4 $ 5H 2 O b. H3O+ ions will decrease when it is 7 diluted. (Blue) c. Dilute solution has higher pH than concentrated. 88. Write the chemical formulae of washing soda and d. (i) CO2 gas will be formed: baiting soda. Which one of these two is an ingredient Na2CO3 + 2HCl $ 2NaCl + H2O + CO2 of antacids? How does it provide relief in stomachache? (ii) Hydrogen gas will be formed: Ans : [CBSE 2000] Zn + 2HCl $ ZnCl2 + H2 Na 2 CO 3 $ 10H 2 O is washing soda, NaHCO3 is baking 93. pH has a great importance in our daily life. Explain soda. NaHCO3 is an ingredient of antacid. It neutralises by giving three examples. hyper acidity in stomach and gives relief. Ans : [CBSE Sample Paper 2018] 89. What is baking powder? How does it make the cake a. pH of our stomach is 2.0 and it is needed for the soft and spongy? digestion of proteins in our body. Ans : [CBSE 2008] b. Blood has pH = 7.36 to 7.42 which must be maintained for proper health. Baking powder is made up of NaHCO3 and tartaric c. pH of soil is determined and suitable chemicals acid. NaHCO3, on heating gives CO2 which makes the are added so as to make it suitable for growth of cake soft and spongy. crops. 94. Answer the following questions: THREE MARKS QUESTIONS a. State the colour of phenolphthalein in soap solution. b. Name the by-product of chlor-alkali process which 90. 2 mL of sodium hydroxide solution is added to a few is used for the manufacture of bleaching powder. pieces of granulated zinc metal taken in a test tube. c. Name one indicator which specifies the various When the contents are warmed, a gas evolves which is levels of H+ ion concentration. bubbled through a soap solution before testing. Write Ans : [CBSE 2016] the equation for the chemical reaction involved and a. Phenolphthalein will turn pink in soap solution. the test to detect the gas. Name the gas which will b. Chlorine is the by-product of chlor-alkali process be evolved when the same metal reacts with dilute which is used in the manufacture of bleaching solution of a strong acid. powder. Ans : [CBSE 2018] c. Universal indicator specifies the various levels of Zn (s) + 2NaOH Worm Na ZnO + H 2 H+ ion concentration. 2 2 (Sodium zincate) Test: Bring a burning splinter near the gas. If it burns 95. a. Define a universal indicator. Mention its one use. with ‘pop’ sound, the gas liberated is hydrogen. b. Solution ‘A’ gives pink colour when a drop of Zn + H2SO4(dil) $ ZnSO4(aq) + H2 phenolphthalein indicator is added to it. Solution Hydrogen gas will be evolved by reaction of the same ‘B’ gives a red colour when a drop of methyl metal with dilute H2SO4, strong acid. orange is added to it. What type of solutions are ‘A’ and ‘B’ and which of these will have higher 91. The pH of a salt which is used to make tasty and pH? crispy pakoras is 14. Identify the salt and write a c. Name one salt whose solution has pH greater than Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 17 Chap 2 : Acid Bases and Salts www.cbse.online 7 and one salt with pH less than 7. CuSO 4 (s) + 5H 2 O (l) $ CuSO 4 $ 5H 2 O Ans : [CBSE 2016] Blue a. Universal indicator is mixture of indicators used b. Na2CO3.10H2O, washing soda (Sodium carbonate to find pH of solution. It is used to measure levels decahydrate) has 10 molecules of water of of H+ ion concentration. crystallisation. CaSO4.2H2O, gypsum, chemically b. ‘A’ is basic in nature, ‘B’ is acidic in nature. ‘A’ calcium sulphate dihydrate has 2 molecules of will have higher pH than ‘B’. It should be greater water of crystallisation. than 7. 100. You are provided with magnesium ribbon and sulphur c. Na2CO3 is the salt whose pH is more than, CuSO4 powder. Explain with the help of activity that metal is the salt whose pH is less than 7. oxides are basic and oxides of non-metals are acidic 96. a. Define pH scale. Draw a figure showing variation in nature. of pH with change in concentration of H+(aq) and Ans : [CBSE 2014] OH-(aq) ions. Bum magnesium ribbon with the help of tongs to b. Mention the pH of acidic, basic and neutral form white ash. Dissolve the ash in hot water. Add solutions respectively. red litmus which turns blue, showing that MgO is a Ans : [CBSE 2016] basic oxide. a. pH scale is a scale which is used for measuring 2Mg(s) + O2(g) $ 2MgO(s) hydrogen ion concentration in a solution. MgO(s) + H2O(Hot) $ Mg(OH)2(aq) Heat sulphur taken in a iron spatula and pass the gas through water. Add blue litmus into it. It will turn red showing SO2 is an acidic oxide. S + O2 $ SO2 SO2 + H2O $ H2SO3 (Sulphurous acid) b. pH < 7 is for acidic solution, pH > 7 basic solution, 101. List two differences between acids and bases on the pH = 7 for neutral solution. basis of chemical properties. 97. a. Define olfactory indicators. Name two substances Ans : [CBSE 2013] which can be used as olfactoiy indicators. b. Choose strong acids from the following: Acids Bases CH3COOH, H2SO4, H2CO3, HNO3 1. Acids turn blue litmus Bases turn red litmus Ans : [CBSE 2015] red. blue. a. Olfactory indicators: They give different smell in 2. Acids liberate CO2 Bases do not react acidic and basic medium e.g., onion, clove, vanilla. with metal carbonates with metal carbonates b. HNO3 and H2SO4 are strong acids among the given and hydrogen and hydrogen acids. carbonates. carbonates. 98. Explain the action of dilute hydrochloric acid on the following with suitable chemical equations: 102. A substance ‘X’ is used as antacid reacts with a. Magnesium ribbon, hydrochloric acid to produce a gas W which is used in b. Sodium hydroxide, fire extinguishers: c. Crushed egg shells. a. Name the substance X and ‘Y’. b. Write a balanced equation of the reaction between Ans : [CBSE 20151 X and hydrochloric acid. a. Mg(s) + 2HCl(dil) $ MgCl2(aq) + H2(g) Ans : [CBSE 2013] b. NaOH(aq) + HCl(dil) $ NaCl(aq) + H2O(l) c. CaCO 3 ^ s h + 2HCl ^dilh $ CaCl 2 ^gh + CO 2 ^gh + H 2 O ^ l h a. ‘X’ is NaHCO3 (Sodium hydrogen carbonate). ‘Y’ is CO2 gas, which is used in fire extinguishers. 99. a. The blue colour of crystals of a substance on b. NaHCO 3 (s) + HCl (aq) $ NaCl (aq) + H 2 O (l) + CO 2 (g) heating in a closed test tube gets changed but the colour was regained after sometime on cooling. 103. “Sodium hydrogen carbonate is a basic salt.” Justify Name that substance and write its chemical the statement. How is it converted into washing soda? formula. Explain the phenomenon involved. Explain. b. Write name and chemical formulae of two such Ans : [CBSE 2012] compounds whose one unit is associated with 10 NaHCO3 is a salt of NaOH which is a strong base and and 2 water molecules respectively. H2CO3 (Carbonic acid) which is a weak acid, therefore Ans : [CBSE 2015] it is a basic salt. It can be converted into washing soda a. Hydrated copper sulphate, CuSO4.5H2O is the by heating followed by crystallisation: Heat name and chemical formula of that substance. 2NaHCO 3 (s) Na 2 CO 3 (s) + CO 2 (g) + H 2 O (l) It loses water of crystallisation on heating and Na2 CO3 + 10H2 O $ Na 2 CO 3 $ 10H 2 O (washing soda) regains these molecules of water on exposure to the atmosphere: 104. Describe an activity with diagram to illustrate that CuSO 4 $ 5H 2 O Heat CuSO 4 + 5H 2 O the reaction of metal carbonates or metal bicarbonates Blue (Dirty while) Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 18 Chap 2 : Acid Bases and Salts www.cbse.online with acid produces carbon dioxide. Write the relevant b. D is strongly alkaline, equations of all the reactions that take place. Name c. ‘C’ is strongly acidic, any two forms in which calcium carbonate is found in d. A is weakly acidic, nature. e. ‘E’ is weakly basic. D