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11 X – Science
CHAPTER – 2
ACIDS, BASES AND SALTS
q Acids Bases
- Sour in taste – Bitter in taste
- Change the blue litmus to red – Change red litmus to blue
- eg. HydrochloricAcid HCl eg. Sodium hydroxide NaOH
- SulphuricAcid H 2 SO 4 Potassium hydroxide KOH
- Nitric Acid HNO 3 Calcium hydroxide Ca(OH) 2
- Acetic Acid CH 3 COOH – Ammonium hydroxide NH 4 OH q 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.
12 X – Science q Acid – Base Indicators S. No. Name of the Colour Change Colour Change Indicator 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 →^ ZnCl 2 + H 2 2HNO 3 + Zn →^ Zn (NO 3 ) 2 + H 2 H 2 SO 4 + Zn →^ ZnSO 4 + H 2 2CH 3 COOH + Zn →^ (CH 3 COO) 2 Zn + H 2 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 →^ Na 2 ZnO 2 + H 2 Sodium Zincate Note – Such reactions are not possible with all the metals.
14 X – Science 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 + H 2 O →^ H 3 O+^ + Cl– H 3 O+^ – Hydronium ion.
- H+ion cannot exist alone. It exists as H+(aq) or (H 3 O+) hydronium ion. H+^ + H 2 O →^ H 3 O+
- Bases provide (OH–) ions in the presence of water
NaOH(s) H O 2 → Na+(aq) + OH– (aq)
KOH(s) H O 2 → K+(aq) + OH–(aq)
Mg(OH)2(s) H O 2 → Mg2+(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 NH 4 OH : 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.
15 X – Science When an acid or a base is mixed with water they become dilute. This results in the decrease in the concentration of H 3 O+ 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 Colour of the Nature of H+ion O H –^ i o n No. Value pH Paper Solution Conc. Conc.
- 0 Dark red Highly acidic very high very low
- 4 Orange or yellow Acidic high low
- 7: Green Neutral Equal Equal
- 10 Bluish green or blue Alkaline low high
- 14 Dark blue or voilet highly basic very low very high
- strong Acids give rise to more H+ions. eg. HCl, H 2 SO 4 and HNO 3.
- Weak Acids give rise to less H+^ ions eg. CH 3 COOH, H 2 CO 3 (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. NH 4 OH
17 X – Science Neutral Salts : Strong Acid + Strong base pH value is 7 eg. NaCl, CaSO 4 Acidic Salts : Strong Acid + weak base pH value is less than 7 eq. NH 4 Cl, NH 4 NO 3 Basic Salts : Strong base + weak acid pH value is more than 7 eg. CaCO 3 , CH 3 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) + 2H 2 O( l ) →^ 2NaOH(aq) + Cl2(g) + H2(g)
18 X – Science q Bleaching Power Preparation →^ Ca(OH) 2 + Cl 2 →^ CaOCl 2 + H 2 O calcium hydroxide chlorine bleaching water power uses in textile, factories and laundry, used as disinfectant q Baking Soda
- Common name – Sodium Hydrogen Carbonate Preparation NaCl + H 2 O + CO 2 + NH 3 →^ NH 4 Cl + NaHCO 3 Sodium Water Carbon Ammonia Sodium hydrogen chloride dioxide carbonate On heating NaHCO 3 produces : NaHCO 3 Heat^ → Na 2 CO 3 + H 2 O + CO 2 CO 2 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 NaHCO 3 + H+^ →^ CO 2 + H 2 O + Sodium Salt of acid q Washing Soda Preparation : Recrystallisation of sodium carbonate Na 2 CO 3 + 10H 2 O (^) Heat^ → Na 2 CO 3. 10H 2 O Uses
- Used in glass, soap and paper industry
- Cleaning agent for domestic purposes.
- Removal of hardness of water.
- Manufacturere of borax. q 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 – CuSO 4. 5H 2 O.
20 X – Science
- A testtube contains solution of NaOH and Phenolphthalein. Why the colour of the solution changes when HCl in added to it.
- Why metallic oxides are called as basic oxides and non-metallic oxides are calles acidic oxides?
- 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, 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)
- What is acid rain? What is its pH? How does it affect the aquatic life?
- What happens when a metal react with dilute hydrochloric acid? Write the reaction © NaOH + Zn →^ _________ + _________.
- 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 (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) _____ + Metal →^ Salt + _____ c) Metal carbonate / metal hydrogen carbonate + acid → (^) _______ + _______ + _______. d) NaOH (^) H O^2 → _______ + _______ e) Na 2 CO 3 + 10H 2 O →^ _______.
