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1) Do basic solutions also have H+ (aq) ions? If yes, then why, are these basic?, Ans. Basic solutions also have H+ (aq) ions. All aqueous, solutions have H+ (aq) ions as well as OH– ions. But the, concentration of OH– ions is much more than that of H+ (aq), ions and hence the solution is basic., 2) Under what soil condition do you think a farmer would treat, the soil of his fields with quicklime (calcium oxide) or slaked, lime (calcium hydroxide) or chalk (calcium carbonate)?, Ans. A farmer would treat the soil of his fields with quicklime, (calcium oxide), or slaked lime (calcium hydroxide) or chalk, (calcium carbonate) if the soil is too acidic having a low pH, value. All these materials are bases and hence react with, the excess acid present in the soil and reduce its acidity., 3) What is the common name of the compound CaOCl2 ?, Ans. Bleaching powder., 4) Name the substance which on treatment with chlorine, yields bleaching powder., Ans. Dry Slaked lime., 5) Name the sodium compound which is used for softening, hard water., Ans. Sodium carbonate (Washing soda)., 6) What will happen if a solution of sodium hydrogencarbonate, is heated? Give the equation of the reaction involved., Ans. When a solution of sodium hydrogencarbonate is, heated, it decomposes to form sodium carbonate with the, evolution of carbon dioxide gas., The equation of the reaction involved is:, 2 NaHCO3 ⎯⎯⎯→ Na2CO3 + CO2 + H2O
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7) Write an equation to show the reaction between Plaster of, Paris and water., Ans : Write from book., 8) A solution turns red litmus blue, its pH is likely to be:, (a) 1 (b) 4 (c) 5 (d) 10, Ans. (d) 10, 9) A solution reacts with crushed egg-shells to give a gas that, turns lime water milky. The solution contains:, (a) NaCl (b) HCl (c) LiCl (d) KCl, Ans : (b) HCl, 10) 10 mL of a solution of NaOH is found to be completely, neutralised by 8 mL of a given solution of HCl. If we take 20, mL of the same solution of NaOH, the amount of HCl, solution (the same solution as before) required to neutralise, it will be:, (a) 4 mL (b) 8 mL (c) 12 mL (d) 16 mL, Ans. (d) 16 mL, 11) Which one of the following types of medicines is used for, treating indigestion?, (a) Antibiotic (b) Analgesic (c) Antacid (d) Antiseptic, Ans. (c) Antacid, 12) Write word equations and then balanced equations for the, reactions taking place when: (a) dilute sulphuric acid reacts, with zinc granules (b) dilute hydrochloric acid reacts with, magnesium ribbon (c) dilute sulphuric acid reacts with, aluminium powder (d) dilute hydrochloric acid reacts with, iron filings, Ans :, (a) Sulphuric acid + Zinc ⎯⎯→ Zinc sulphate + Hydrogen, (b) Hydrochloric acid + Magnesium ⎯⎯→ Magnesium, chloride + Hydrogen.
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(c) Sulphuric acid + Aluminium ⎯⎯→ Aluminium sulphate +, Hydrogen, (d) Hydrochloric acid + Iron ⎯⎯→ Iron chloride + Hydrogen, 13) Compounds such as alcohol and glucose also contain, hydrogen but are not categorised as acids. Why? Describe, an activity to prove it., Ans. Only those compounds containing hydrogen are, considered to be acids which dissolve in water to produce, hydrogen ions, H+ (aq). The hydrogen containing, compounds such as alcohol and glucose are not, categorised as acids because they do not ionize to produce, hydrogen ions, H+ (aq), when dissolved in water., Activity : [ Notes already provided ], 14) Why does distilled water not conduct electricity whereas, rain water does?, Ans : Distilled water is a pure form of water and is devoid of, any ionic species. Therefore, it does not conduct electricity., Rain water, being an impure form of water, contains many, ionic species such as acids, salts etc, therefore it conducts, electricity., 15) Why do acids not show acidic behaviour in the absence of, water?, Ans. The acidic behaviour of acids is due to the presence of, hydrogen ions, H+ (aq) ions. The acids produce hydrogen, ions only on dissolving in water. In the absence of water,, acids do not produce hydrogen ions and hence do not show, acidic behaviour.
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16) Five solutions A, B, C, D and E when tested with universal, indicator showed pH as 4, 1, 11, 7 and 9 respectively., Which solution is, (a) Neutral, (b) strongly alkaline, (c) strongly acidic, (d) weakly acidic, (e) weakly alkaline?, Arrange the pH values in the increasing order of hydrogen, ion concentration., Ans :, (a) Neutral, → Solution D with pH 7, (b) Strongly alkaline → Solution C with pH 11, (c) Strongly acidic, → Solution B with pH 1, (d) Weakly acidic, → Solution A with pH 4, (e) Weakly alkaline, → Solution E with pH 9, The pH can be arranged in the increasing order of the, concentration of hydrogen ions as: 11 < 9 < 7 < 4 < 1, 17) Equal lengths of magnesium ribbons are taken in test-tubes, A and B. Hydrochloric acid (HCl) is added to test-tube A, while acetic acid (CH3COOH) is added to test-tube B. In, which test-tube will the fizzing occur more vigorously and, why?, Ans : The fizzing will occur strongly in test tube A, in which, hydrochloric acid (HCl) is added. This is because HCl is a, stronger acid than CH3COOH and therefore produces, hydrogen gas at a faster speed due to which fizzing occurs.
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18) Fresh milk has a pH of 6. How do you think the pH will, change as it turns into curd? Explain your answer., Ans. As the milk turns into curd, its pH will fall below 6, because curd is acidic in nature. The acids present in it, decrease the pH., 19) A milkman adds a very small amount of baking soda to, fresh milk. (a) Why does he shift the pH of the fresh milk, from 6 to slightly alkaline? (b) Why does this milk take a, longer time to set as curd?, Ans. (a) The milkman shifts the pH of the fresh milk from 6, to slightly alkaline because in alkaline condition, milk does, not set as curd easily., (b) Since this milk is slightly basic than usual milk, acids, produced to set the curd are neutralized by the base., Therefore, it takes a longer time for the curd to set., 20) Plaster of Paris should be stored in a moisture-proof, container. Explain why?, Ans : Plaster of Paris (POP) should be stored in a moistureproof container because Plaster of Paris, a powdery mass,, absorbs water (moisture) to form a hard solid known as, gypsum., 21) What is a neutralisation reaction? Give two examples., Ans : The reaction between an acid and a base to form salt, and water is called a neutralisation reaction., Acid + Base ⎯⎯→ Salt + Water, The examples of neutralisation reactions are as follows:, (i) 2NaOH (aq) + H2SO4 (aq) ⎯⎯→ Na2SO4 (aq) + 2H2O(l), (ii) Mg(OH)2 (aq) + 2HCl (aq) ⎯⎯→ MgCl2 (aq) + 2H2O (l)
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22) Give two important uses each of washing soda and baking, soda., Ans. (a) Uses of washing soda:, (i) It is used in glass, soap, and paper industries., (ii) Washing soda is used for removing permanent hardness, of water., (b) Uses of baking soda:, (i) It is used in soda-acid fire extinguishers., (ii) Baking soda is used in making baking powder (which is, used in making cakes, bread, etc.)
