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Acid, Bases and Salts, , CHAPTER – 2, , ACIDS, BASES AND SALTS, q, , q, , Acids, – Sour in taste, , Bases, – Bitter in taste, , – Change the blue litmus to red, , – Change red litmus to blue, , – eg. HydrochloricAcid HCl, , eg. Sodium hydroxide NaOH, , – SulphuricAcid H2SO4, , Potassium hydroxide KOH, , – Nitric Acid HNO3, , Calcium hydroxide Ca(OH)2, , – Acetic Acid CH3 COOH, , – Ammonium hydroxide NH4OH, , Some Naturally occuring acids, Vinegar, , –, , Acetic Acid, , Orange, , –, , Citric Acid, , Lemon, , –, , Citric Acid, , Tamarind, , –, , Tartaric Acid, , Tomato, , –, , Oxalic Acid, , Sour milk (Curd), , –, , Lactic Acid, , Ant and Nettle sting, , –, , Methanoic Acid, , q, , Acid – Base Indicators – Indicate the presence of an acid or base in a, solution., , q, , Litmus solution – It is a natural indicator. It is a purple day extracted from, Lichens. Other examples are Red Cabbage and coloured petals of Petunia, and turmeric., , q, , Olfactory indicators – Show odour changes in acidic or basic media. eg., onion and clove., , www.tiwariacademy.com, , Page 1

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Acid, Bases and Salts, , q, , Acid – Base Indicators, S. No., , Name of the, Indicator, , Colour Change Colour Change, with Acid, with Base, , A., , Blue litmus solution, , To red, , No change, , B., , Red litmus solution, , No change, , To blue, , C., , Turmeric, , No change, , To red, , D., , Methyl orange, , To red, , To yellow, , E., , Phenolphthalein (colourless), , No change, , To pink, , q, , Dilute Acid : Contains only a small amounts of acid and a large amount of, water., , q, , Concentrated Acid : A concentrated acid contains a large amount of acid and, a small amount of water., , q, , Chemical Properties of Acids and Bases, Acid + Metal → Salt + Hydrogen, (Refer activity 2.3 on page No. 19 of NCERT Book), 2HCl + Zn → ZnCl2 + H2, 2HNO3 + Zn → Zn (NO3)2 + H2, H2SO4 + Zn → ZnSO4 + H2, 2CH3COOH + Zn → (CH3COO)2 Zn + H2, , q, , Pop test : When a buring candle is brought near a test tube containing, hydrogen gas it burns with a ‘Pop’ sound. This test is conducted for examining, the presence of hydrogen gas., , q, , Base + Metal → Salt + Hydrogen, NaOH + Zn → Na2ZnO2 + H2, Sodium Zincate, Note – Such reactions are not possible with all the metals., , www.tiwariacademy.com, , Page 2

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Acid, Bases and Salts, , Note : Non Metallic oxides are said to be acidic in nature because on reacting, with a base they produce Salt and Water., q, , All acidic solutions conduct electricity, Refer activity 2.3 on page 22 of NCERT Book, – Glowing of bulb indicates that there is a flow of electric current through the, solution., , q, , Acids or bases in a Water Solution, Acids produce H+ions in the presence of water, HCl + H2O → H3O+ + Cl–, H3O+ – Hydronium ion., –, , H+ion cannot exist alone. It exists as H+(aq) or (H3O+) hydronium ion., H+ + H2O → H3O+, , –, , Bases provide (OH–) ions in the presence of water, , H2O, +, –, NaOH(s) , → Na (aq) + OH (aq), H2O, +, –, KOH(s) , → K (aq) + OH (aq), H2O, 2+, –, Mg(OH)2(s) , → Mg (aq) + 2OH (aq), q, , Alkalis, All bases donot dissolve in water. An alkali is a base that dissolves in water., Common alkalis are, NaOH, , Sodium hydroxide, , KOH, , Potassium hydroxide, , Ca(OH)2, , Calcium hydroxide, , NH4OH : Ammonium hydroxide, Note : All alkalis are bases but all bases are not alkalis., q, , Precaution must be taken while mixing acid or base with water. The acid must, always be added to water with constant stirring as it is highly exothermic, reaction., , www.tiwariacademy.com, , Page 4

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Acid, Bases and Salts, , When an acid or a base is mixed with water they become dilute. This results, in the decrease in the concentration of H3O+ or OH– per unit volume in acids, and bases respectively., q, , Strength of an Acid or Base, Strength of acids and bases depends on the no. of H+ions and OH–ions, produced respectively., With the help of a universal indicator we can find the strength of an acid or, base. This indicator is called PH scale., pH = Potenz in German means power., This scale measures from 0 (very acidic) to 14 (very alkaline) 7 Neutral, (water in Neutral)., pH paper : Is a paper which is used for measuring PH., Variation of PH, S., PH, No. Value, , Colour of the, pH Paper, , Nature of, Solution, , H+ion, Conc., , 1., , 0, , Dark red, , 2., , 4, , Orange or yellow, , Acidic, , high, , low, , 3., , 7:, , Green, , Neutral, , Equal, , Equal, , 4., , 10, , Bluish green or blue, , Alkaline, , low, , high, , 5., , 14, , Dark blue or voilet, , highly basic, , very low, , very high, , –, , Highly acidic very high, , O H –i o n, Conc., very low, , strong Acids give rise to more H+ions., eg. HCl, H2SO4 and HNO3., , –, , Weak Acids give rise to less H+ ions, eg. CH3 COOH, H2 CO3 (Carbonic acid), , –, , Strong Bases – Strong bases give rise to more OH– ions., eg. NaOH, KOH, Ca(OH)2, , –, , Weak Bases : give rise to less OH– ions., eg. NH4OH, , www.tiwariacademy.com, , Page 5

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Acid, Bases and Salts, , q, , More about Salts, Salts and their derivation, S. No. Name of Salt, , Formula, , Derived from Derived from, , 1., , Potassium Sulphate, , K2 SO4, , KOH, , H2SO4, , 2., , Sodium Sulphate, , Na2SO4, , NaOH, , H2SO4, , 3., , Sodium Chloride, , NaCl, , NaOH, , HCl, , 4., , Ammonium Chloride NH4Cl, , NH4OH, , HCl, , Note : NaCl and Na2 SO4 belong to the family of sodium salts as they have, the same radicals. Similarly NaCl and KCl belong to the family of chloride, salts., Importance of pH in our daily life, q, , Importance of pH in our digestive system – pH level of our body regulates, our digestive system. In case of indigestion our stomach produces acid in a, very large quantity because of which we feel pain and irritation in our stomach., To get relief from this pain antacids are used. These antacids neutralises the, excess acid and we get relief., , q, , pH of Acid Rain : When pH of rain water is less than 5.6 it is called Acid, Rain.When this acidic rain flows into rivers these also get acidic, which causes, a threat to the survival of aquatic life., , q, , pH of Soil : Plants require a specific range of pH for their healthy growth. If, pH of soil of any particular place is less or more than normal than the farmers, add suitable fertilizers to it., , q, , Our body functions between the range of 7.0 to 7.8 living organisms can, survive only in the narrow range of pH change., , q, , Tooth decay and pH : Bacteria present in the mouth produce acids by, degredation of sugar and food particles remaining in the mouth. Using toothpaste, which is generally basic can neutralise the excess acid and prevent tooth, decay., , q, , Bee sting or Nettle sting contains methanoic acid which causes pain and, irritation. When we use a weak base like baking soda on it we get relief., , www.tiwariacademy.com, , Page 6

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Acid, Bases and Salts, , Neutral Salts : Strong Acid + Strong base, pH value is 7, eg. NaCl, CaSO4, Acidic Salts : Strong Acid + weak base, pH value is less than 7, eq. NH4Cl, NH4 NO3, Basic Salts : Strong base + weak acid, pH value is more than 7, eg. CaCO3, CH3 COONa, q, , Chemicals from Common Salt, – Sodium chloride is called as common salt used in our food. It is derived, from seawater., – Rock Salt is the brown coloured large crystals. This s mined like coal., – Common Salt is an important raw material for many materials of daily use, such as., Sodium hydroxide, Washing Soda, Bleaching Power., , q, , Sodium Hydroxide, Preparation : Prepared by the method called chlor-alkali, Called chlor-alkali because we get chlorine and a base in this., 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g), , www.tiwariacademy.com, , Page 7

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Acid, Bases and Salts, , q, , Bleaching Power, Preparation → Ca(OH)2, , +, , calcium hydroxide, , Cl2 → CaOCl2, chlorine, , +, , bleaching, power, , H2O, water, , uses in textile, factories and laundry, used as disinfectant, q, , Baking Soda, – Common name – Sodium Hydrogen Carbonate, Preparation NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3, Sodium, chloride, , Water, , Carbon, dioxide, , Ammonia, , Sodium hydrogen, carbonate, , On heating NaHCO3 produces :, NaHCO3, , Heat →, , , Na2CO3 + H2O + CO2, , CO2 produced causes dough to rise and make cakes, pastries spongy., Uses :, , In household, ingredients of antacid, In making baking power, , On heating baking powder produces, NaHCO3 + H+ → CO2 + H2O + Sodium Salt of acid, q, , Washing Soda, Preparation : Recrystallisation of sodium carbonate, Na2CO3 + 10H2O, Uses, –, –, –, –, , q, , Heat →, , , Na2CO3. 10H2O, , Used in glass, soap and paper industry, Cleaning agent for domestic purposes., Removal of hardness of water., Manufacturere of borax., , Water of crystallisation : Fixed no. of water molecules present in one formula, unit of a salt., –, , On heating copper sulphate crystals water droplets appear, formula of, hydrated copper sulphate – CuSO4. 5H2O., , www.tiwariacademy.com, , Page 8

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Acid, Bases and Salts, , –, , gypsum also contains water of crystallisation., , –, , Formula of gypsum – CaSO4.2H2O, , –, , On heating gypsum at 373k it becomes CaSO4.½H2O is plaster of, paris., , –, , Plaster of Paris is used as plaster for fractured bones., , –, , When plaster of Paris is mixed with water it changes to gypsum., CaSO4.½ H2O + 1½ H2O → CaSO4.2H2O, , Uses of plaster of Paris : Making toys, decorative material and smooth surfaces., , EXERCISE, (Question Bank), Very Short answer type questions, , (1 mark), , 1., , Two solution have pH number 4 and 9 respectively which solution has more, H+ ion concentration?, , 2., , Why should cured and sour substances not be kept in brass and copper, vessel?, , 3., , What is the chemical name of bleaching powder?, , 4., , Write down the molecular formula for one strong and one weak acid., , 5., , Explain why plaster of Paris should be stored in a moisture proof container?, , 6., , Name the gas evolved when dil. sulphuric acid acts on sodium carbonate., , 7., , What is the use of common salt in soap industry?, , 8., , What do you observe when a buring candle is brought near the testube, containing hydrogen gas?, , 9., , Name the indicator used to measure pH values over the whole range., , 10., , Write the formula of washing powder., , Short Answer Type Questions, , (2 marks), , 1., , Write two physical properties of an acid, , 2., , Complete the reaction CaCO3 + H2O → name the products formed., , www.tiwariacademy.com, , Page 9

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Acid, Bases and Salts, , 3., , A testtube contains solution of NaOH and Phenolphthalein. Why the colour, of the solution changes when HCl in added to it., , 4., , Why metallic oxides are called as basic oxides and non-metallic oxides are, calles acidic oxides?, , 5., , In a beakey a solution of HCl is poured and an electric circuit containing bulb, is placed systemtically. What happens to the bulb and why?, What will happen if HCl is repplaced by NaOH?, , 6,, 7., , Identify the type of reaction, H X + M OH → MX + HOH, Why all bases are not alkalies but all alkalis are bases?, , Answer the following questions in detail, , (3 marks), , 1., , What is acid rain? What is its pH? How does it affect the aquatic life?, , 2., , What happens when a metal react with dilute hydrochloric acid? Write the, reaction, © NaOH + Zn → _________ + _________., , 3., , What happens when an acid or a base is added to the water? Why does the, beaker appear warm? Why should we always add acid or base to the water, and not water to the acid or base., , Answer the following question in detail, 1., , 2., , (5 marks), , (a), , Write down five products formed with the help of common salt on, industrial level., , (b), , Write down the chemical name of these compounds and one use of, each of them., , Fill in the blanks, a), Acid + ______ → Salt + Water.., b), c), , _____ + Metal → Salt + _____, Metal carbonate / metal hydrogen carbonate + acid, , → _______ + _______ + _______., , d), , NaOH, , e), , Na2CO3 + 10H2O → _______., , H2 O, , →, , _______ + _______, , www.tiwariacademy.com, , Page 10