Acids Bases And Salts | Class 10th CBSE Chemistry Revision Notes

Acids, Bases, And Salts:- All the chemical compounds can be classified on the basis of their chemical properties as acids bases and salts.

Check Revision Notes: Chemical Reactions and Equations

Acids

Acids are those chemical substances that have a sour taste and change blue litmus paper red. It also have a corrosive nature.

Some common acids used are Hydrochloric acid (HCl), Nitric acid (HNO3), Sulphuric acid(H2SO4)

Some naturally occurring acids are:

Natural SourceAcids
VinegarAcetic acid
OrangeCitric acid
TamarindTartaric acid
TomatoOxalic acid
CurdLactic acid
Ant stingMethanic or formic acid
Acids Bases And Salts

Chemical properties of Acids

  1. Reaction with metals: It react with metals to form salt and release hydrogen gas.

  Metal + Acid = Salt + Hydrogen gas

Ex: Zn + HCl = ZnCl2 + H2

  • Reaction with metal carbonate and metal hydrogen carbonate: Acid reacts with metal carbonate and metal bicarbonate to form a salt, hydrogen gas, and carbon dioxide gas.

Metal carbonate/ Metal hydrogen carbonate + Acid = salt + CO2 + H2O

Ex:

 Na2CO3 + HCl = NaCl + CO2 + H2O

  Na2HCO3 + HCl = NaCl + CO2 + H2O

The CO2 released in the above reaction, when passed through lime water [Ca(OH)2], it turns milky due to the formation of white precipitate CaCO3. But when excess CO2 is passed through lime water the milkiness gets disappeared.

   Ca(OH)2 + CO2 = CaCO3 + H2O

                       (white Ppt)

  CaCO3 + H2O + CO2 = Ca(HC03)2

  • Reaction with metal oxides: Acid reacts with metal oxides to form salt and water ( metal oxides are basis in nature)

   Metal oxide + water = salt + water

   Cuo + H2SO4 = CuSO4 + H2O

Bases

Bases are those chemical substances that are bitter in taste and turn red litmus paper to blue. Ex: sodium hydroxide, calcium hydroxide, etc.

Chemical properties of Bases

  1. Reaction with metals: Some of the bases react with metals to form salt and hydrogen gas.

  Metal + Base = Salt + hydrogen gas

Ex:     

   Zn  + NaOH = Na2ZnO2 + H2

                      (sodium Zincate)

  • Reaction with non-metal oxides: Bases react with non metal oxides which are acidic in nature to form salt and water.

   Base + Non- metal oxide = salt + water

Ex:

    Ca(OH)2 + CO2 = CaCO3 + H2O

Acids and Bases in Water Solution

 Acids and Bases in presence of water dissociate into ions. Acids in presence of water dissociate into H+ ions. as H+ ions cannot exist alone it combines with water to form hydronium ions (H3O+). 

Bases in presence of water dissociate into OH- ions or hydroxide ions. Ex:

  1.  HCl + H2O = H3O + Cl-  
  2. KOH + H20 = K + OH-

Acid and Base reaction                          

 Acids and bases react together to form salt and water.  This process is called a neutralization reaction.

  Acid + Base = Salt + Water

Ex: NaOH(aq) + HCl(aq) = NaCl (aq) + H₂O(l)

Dilution

The process of mixing of an acid and base with water is called dilution.  The process reduces the concentration of ions  per unit volume . Dilution process is highly exothermic , so care must be taken while diluting an acid or a base .

Indicators

Indicators are those substances that indicate the acidic or basic nature of a substance.

Indicators can be classified into following ways :-

Natural indicators

These indicators are obtained from nature , from plants .

Some natural indicators with characteristics colours

IndicatorsColour in acidic mediumColour in basic medium
LitmusRedBlue
Turmeric juiceYellowReddish brown
Red cabbage juiceRedGreen
Natural Indicators

Synthetic indicators

These are those indicators  which are prepared in laboratory. Ex: phenolphthalein and mythyl orange.

IndicatorsColour in acidic mediumColour in basic medium
phenolphthaleinColourlessPink
mythyl orangeRedYellow
indicators

Olfactory indicator

The indicators which change their odor to indicate the acidic or basic in nature are called an olfactory indicator. Ex: onion and vanilla etc.

Universal indicator

These are the mixer of several indicators which act as an indicator. It also changes its colour according to different ph values.

The Ph Scale

The “P” in Ph is a german word Potenza which means power.

Neutral substances have PH of exactly 7. Pure water is natural Substance.

 Acids have a PH value of less than 7 Whenever a solution has a PH of less acidic than 7 It will be solutions More acidic solutions have less PA value PH strong of 0,1,2,3 are usually considered to be acids. And the solutions are considered to be weak having 4,5,6 acids solutions lower the PH, the stronger the acid.

 Bases have PH values of more than 7 and are basic in nature. More basic nature, higher will be its PH. Ph value of 8,3,10 is usually considered weak bases.  PH of 11, 12, 13, 12 is usually strong bases.

  1. If Ph > 7 solution is basic
  2. If Ph < 7 solution is acidic
  3. If Ph = 7 solution is neutral.
  • The strength of an acid or base depends on the ions. If the no. of H+ ions are more then the acid is stronger, whereas if OH- ions are more then the base is stronger.

Importance of Ph in everyday life

  • The human body works within the Ph range of 7.0 – 7.8. When the Ph of rainwater is less than 5.6, it is called acid rain. The acid rain affects the plants and animals both on land and water
  • HCl is present in our stomach which helps indigestion. Excess release of HCl leads to pain and irritation. In such a situation, antacids are used which neutralizes the effect of acid.
  • When Ph of our teeth is less than 5.5 then it leads to tooth decay. Brushing the teeth with toothpaste helps to prevent tooth decay. Toothpaste consists of a base that reduces the effect of acid in our stomach.
  • Some insects and plants use an acid like methanoic acid to protect themselves from enemies.

Salts

  • Salts are the result of a neutralization reaction between acid and base. Salts have a Ph value of 7.
  • When a strong acid reacts with a weak base then salt formed is acidic in nature and have a Ph value of less than 7
  • When a weak acid reacts with a strong base then salt formed is basic in nature and has a Ph value of more than 7.
  • Common salt(NaCl) is used as a raw material for various other materials which are used in daily life like baking soda, caustic soda.
  • Due to the drying up of the sea, large crystals of salt are formed, these are known as rock salt.
  1. Caustic soda (NaOH):

On passing electricity through aqueous solution of NaCl(brine solution), it decomposes to form NaOH, H2, Cl2. This process is called chlor-alkali because of the product formed NaOH and Cl2.

  NaCl + H2O + Electricity = NaOH +  H2 +  Cl2

  • Chlorine is released at anode and hydrogen gas is released at cathode and NaOH is released near cathode.
  • The products of this process is used in various industrial and household work.

Uses of Hydrogen gas

  • It is used in making margarine
  • It is used as a rocket fuel
  • It is used to make fetilisers like ammonia

Uses of chlorine gas

  • It is used to disinfect the drinking water
  • It is used in making pesticides, CFCs
  • It is used in making plastics like PVC

Uses of NaOH

  • It is used in making soaps and detergents
  • It is  used in making artificial fibres and paper
  • It is used in purifying bauxite ore.
  • Bleaching Powder (CaOCl2)

When CO2 is passed through dry slaked lime it results in formation of bleaching powder,

Ca(OH)2 + CO2 = CaOCl2 + H20

Uses of bleaching powder

  • It is used in bleaching cotton, linen and paper
  • It is used as an oxidizing agent
  • It is used to disinfect the drinking water
  • Baking soda (NaHCO3)

Baking soda is produced by passing ammonia and carbon dioxide through NaCl solution

 NaCl + H2O + CO2 + NH3 = NaHCO3 + NH4Cl

Uses of baking soda

  • It is used as soda-acid fire extinguisher
  • It is used as an antacid to neutralize the effect of acid
  • It is used in making baking powder which is used in baking
  • Washing soda (Na2CO3)

It is prepared in the following ways:-

Baking soda is produced by passing ammonia and carbon dioxide through NaCl solution

 NaCl + H2O + CO2 + NH3 = NaHCO3 + NH4Cl

Baking soda obtained above , is then heated to form anhydrous washing soda

 NaHCO3 + heat = Na2CO3 + CO2 + H2O

Then anhydrous washing soda is mixed with water to obtain the crystals of washing soda

  Na2CO3 + 10H2O = Na2CO3.10H2O

Uses of washing soda

  • It is used in paper , soap , glass industries
  • It is used in removing permanent hardness of water
  • It is used as a cleansing agent
  • It is used to make sodium compounds like borax.
  • Plaster of Paris (CaSO4.1/2H20)

It is obtained by heating gypsum CaSO4.2H2O at 373K. Gypsum loses its water of crystallization to form POP.

 CaSO4.2H2O + Heat = CaSO4.1/2H2O + 1 ½ H20

When gypsum is heated above 400K then it loses it water of crystallisation to form anhydrous plaster of Paris, which is a solid mass.

Uses of Plaster of Paris

  • It is used to set fractured bones
  • It is used in making statues, blackboard, chalk
  • It is used for making decorative material

Water of Crystallisation

A fixed no. of water molecule chemically attached to a salt in the form of crystals.

Ex: CuSO4.5H2O

The above example copper sulphate has a 5 molecules of water of crystallization. Anhydrous copper sulphate does not has any water of crystallization and it is used to test the presence of water .

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