ACID AND BASE – Harmful or Helpful for Daily Life

                                                                   

Acid and Base

Some Naturally occurring Acid

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

  • Acid and Base Indicators – Indicate the presence of an acid or base in a solution.
  • 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.
  • Olfactory indicators – Show odour changes in acidic or basic media. e.g. onion and clove.

Acid and Base Indicators:

S. No                  Name of the IndicatorColour Change with AcidColour Change with Base
ABlue litmus solutionTo redNo Change
BRed litmus solutionNo ChangeTo Blue
CTurmericNo ChangeTo red
DMethyl orangeTo redTo yellow
EPhenolphthalein (Colorless)No ChangeTo Pink
  • Dilute Acid: Contains only a small amount of acid and a large amount of water.

Concentrated Acid: A concentrated acid contains a large amount of acid and a small amount of water.

  • Chemical Properties of Acids and Bases
  • Acid + Metal—->  Salt + Hydrogen

     2HCl + Zn  —–>  ZnCl2 + H2

     2HNO3 + Zn ——->  Zn (NO3)2 + H2

     H2SO4  +  Zn  ————> ZnSO4  + H2

     2CH3 COOH + Zn  ———–>  (CH3 COO)2   Zn+ H₂

  • Pop test:  When a burning 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.  
  • Base  +   Metal    ——————> Salt  +  Hydrogen

NaOH  +  Zn      ——————->    Na2ZnO2                    +          H2

                                                  Sodium Zincate

  • Action of Acids with metal Carbonates and metal bicarbonates
  • Metal Carbonate + Acid   —————–> Salt + Carbon dioxide + Water

Na2 CO3(S) + 2HCl(aq)  —–>2NaCl(aq) + H2O(l) + CO2(g)

  • Metal bicarbonate + Acid Salt + Carbon dioxide + Water

NaHCO3 + HCl—–> NaCl + CO2 + H2O

  • Lime water Test: On passing the CO2 gas evolved through lime water,

Ca(OH)2(aq)   + CO2(g) ——–>CaCO3(S)  + H2O(l)

Lime water                                     White precipitate                                        

     On passing excess CO2 the following reaction takes place

     CaCO3(S)  +  H2O(l)  +   CO2   ———-> Ca(HCO3)2(aq)

                                                                          Soluble in water

  • Neutralization Reactions
  • Base + Acid —————>Salt  + water

NaOH(aq)  +  HCl(aq)   ———–>NaCl(aq)  +  H2O(l)

Neutralization reaction takes place when the effect of a base is nullified by an acid and vice versa to give salt and water.

Reactions of metal oxides with acids

  • Metal Oxide  + Acid ———>   Salt  + Water

CuO                       +                      HCl                 —————>       CuCl2                +        H2O

   Copper oxide                 Hydrochloric acid                  Copper Chloride             Water        

     Reaction of Non-Metallic Oxide with Base

  • Non-metallic oxide  +  Base  ————->   Salt   +  Water

     Ca(OH)2    +   CO2     ————->  CaCO3    +   H2O

     NOTE: Non-metallic are said to be acidic in nature because on reacting with a base they produce salt  and water.

  • All acidic solutions conduct electricity

     Glowing of bulb indicates that there is a flow of electric current through the solution.

  • 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+) hydroniumion.

             H+   +  H2O      H3O+

                    Bases provide (OH–) ions is the presence of water

             NaOH(S)   Na+(aq)  + OH–(aq)

             KOH(S)    K+(aq)  +  OH–(aq)

             Mg(OH)2(S)    Mg2+(aq)  +  2OH–(aq)

  • Alkalis

All bases do not 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

  • 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.
  • 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.
  • 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.NoPH ValueColor  of the pH PaperNature of Solution   H+ion Conc.   OH– ion Conc.
1.0Dark red OrangeHighly acidicVery highVery low
2.4Or yellow GreenAcidicHighLow
3.7GreenNeutralEqualEqual
4.10Bluish green or blueAlkalineLowHigh
5.14Dark blue or violethighly basicVery lowVery high

Strong Acids give rise to more H+ ions.

e.g. HCl, H2SO4 and HNO3

Weak Acids give rise to less H+ ions

e.g. CH3COOH, H2 CO3 (Carbonic acid)

Strong Bases – Strong bases give rise to more OH–ions.

e.g. NaOH, KOH, Ca(OH)2

Weak Bases : give rise to less OH– ions.

e.g. NH4OH

  • More about Salts

Salts and their derivation

S.No.Name of SaltFormulaDerived fromDerived from
1.Potassium SulphateK2SO4KOHH2SO4
2.Sodium SulphateNa2So4NaOHH2SO4
3.Sodium ChlorideNaClNaOHHCl
4.Ammonium ChlorideNH4ClNH4OHHCl

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Importance of pH in our daily life

  • 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 neutralizes the excess acid and we get relief.
  • pH of Acid Rain: When pH of rainwater 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.
  • 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 then farmers add suitable fertilizers to it.

Our body functions between the range of 7.0 to 7.8 living organisms can survive only in the narrow range of pH change.

  • Tooth decay and pH: Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth. Using toothpaste which is generally basic can neutralize the excess acid and prevent tooth decay.
  • 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.
  • Neutral Salts: Strong Acid + Strong base pH value is 7

     e.g. NaCl, CaSO4

  • Acidic Salts: Strong Acid + weak base pH value is less than 7

     e.g., NH4Cl, NH4, NO3

  • Basic Salts: Strong base+ weak acid pH value is more than 7

     e.g. CaCO3, CH3, COONa

     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 colored large crystals. This mined like coal.
  • Common Salt is an important raw material for manymaterials of daily use such as.

     Sodium hydroxide,     Washing Soda,     Bleaching Power.

    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)

Salt -NaCl

Bleaching Power

Preparation     Ca(OH)2   +  Cl2     ————> CaOCl2   +   H2O

                       Calcium    chlorine                    bleaching    Water

Hydroxide                                   Power

Uses in textile, factories and laundry, used as disinfectant

Baking Soda

Common name – Sodium Hydrogen Carbonate Preparation

            NaCl      +      H2O      +   CO2    +    NH3    ————> NH4Cl    +     NaHCO3

  Sodium Chloride      water        Carbon    Ammounia         Sodium hydrogen carbonate

                                                   Dioxide

On heating NaHCO3 produces :

                        NaHCO3  ———->  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

Washing Soda

Preparation :  Recrystallization of Sodium carbonate

                        Na2CO3   +   10H2O ———> Na2Co3. 10H2O

Uses :

  • Used in glass, soap and paper industry
    • Cleaning agent for domestic purposes
    • Removal of hardness of water
    • Manufacturer of borax

Water of crystallization :  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.
  • gypsum also contains water of crystallization.
  • 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 .½H2O  +  1 ½ H2O   ———> CaSO4. 2H2O

  • Uses of plaster of Paris: Making toys, decorative material and smooth surfaces.

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