Chapter 2: Acids, Bases and Salts

Chapter→2
ACIDS BASE AND SALTS

ACIDS:-  

*  These are the substances which have sour taste

• They turn blue litmus solution  red
• They give H⁺ ions in aqueous solution

Type  of acids are as follows →

1. Strong Acid :  Hcl , H₂SO₄
2. Weak Acid : CH₃COOH, HCOOH
3. Concentrated Acid : which have more amount of acid and less amount of water.
4. Dilute Acid : which have more amount of water and less amount of acid

BASES:-    

* These are the substances which have bitter taste and soapy in touch .

• They turn red litmus solution blue
• They give OH^- ions in aqueous solution.

Type of bases are as follows :-

1. Strong Bases :-  NaOH, KOH
2. WEAK BASES :- NH₄OH
3. ALKALI :- These are the bases which are soluble in water (like NaOH,KOH)

SALTS :-  A salts is a substance produced from the reaction of an acid and a base.

FOR EXAMPLE,  NaCl, KCl.

INDICATORS :- The substances that change their colour/ smell when they are added to acidic or alkaline solutions.

Types of Indicators.

1. Natural Indicators :- Litmus , turmeric
2. Synthetic Indicators :-  Phenolphthalein, Mythyl
3. Olfactory Indicators:- Onion, vanilla essence.

CHEMICAL PROPERTIES OF ACID AND BASES.

(i)  Reaction of Metal with :-     

(a)  ACIDS 

Acid   +  Metal      →           Salt +    Hydrogen  gas                      

For Example,

2Hcl           +          Zn       →             ZnCl₂      +    H₂

(Hydrochloric acid) (zinc)       (zinc chloride ) (hydrogen)

(b)  Bases  Base + metal     →   salt + hydrogen gas

For example,

2NsoH         +          Zn    →       Na₃ZnO₂        +        H₂ ↑ 

(sodium hydroxide )  ( zinc)  ( sodium zincate)  ( hydrogen gas )

 Hydrogen gas released can be tested by bringing burning candle near gas bubbles , it burst with pop sound.

(ii)    REACTION OF METAL CARBONATES / Metal Hydrogen carbonates with 

(a)  Acids :- 

(b) Acid   +   metal carbonate/ metal hydrogen carbonate   →  salt + carbon dioxide + water.

  For example :-

1. 2 Hcl + Na₂CO₃        →          2NaCl +  CO₂    +   H₂O
2. HCl +  NaHCO₃         →         NaCl +  CO₂  +H₂O
3. Ca(OH)₂   +   CO₂     →         CaCO₃ +  H₂O

                ( Line Water)                   ( White precipitate )

On passing CO₂  Through lime water , lime water turns milky and in this way CO₂ can be tested.

And when excess CO₂ is passed , milkiness disappers and the following reaction take place.

Passing carbon dioxide gas through calcium hydroxide.

CaCo₃    +    CO₂     +     H₂O    →    Ca (HCO3)

(iii)     Reaction of acids and bases with each other  

Acid     +       base        →       Salt   +    H₂O

Neutralisation Reaction :-   The reaction between an aid and a base to give a salt and water is known as neutralization reaction.

  For Example :-    

HCl (aq)   + NaOH (aq)    →  NaCl(aq) + H₂O(l)

(iV)  Reaction of Metallic Oxides with Acids  :-

Metallic oxide +  acid     →     salt   +  water

 Metallic oxides are basic in nature

For Example :- 

CaO  + 2HCl    →   CaCl₂   +    H₂O

(v) Reaction of Non- metallic Oxide with base :-

Non- metallic oxide + base    →        salt   +    H₂O 

Non- metallic oxide are acidic in nature.

For Example :-

CO₂   +   Ca(OH)₂    →   CaCO₃  +    H₂O

Common Things in All Acids and Bases:-

All acids have H⁺ ios in common

All bases have OH^- ions in common

 Acids produce H⁺ ions which  ar responsible for their acidic properties.

Acids solution in water conducts electricity.

An Acid or a Base in water solution:-

• Acids produce H⁺Ions in presence of water.
• H⁺ ions cannot exist alone , they exist as H₃O⁺ ions.

H⁺   +   H₂O  →    H₃O⁺

HCl  +  H₂O   →  H₃O⁺ +  Cl^-

Bases when dissolved in water gives  Oh^-  ions.

For Example:- 

 

→ Bases soluble in water are called alkali.

 → It is recommended that the acid / base should be added to water and not water. Is added to acid/ base, the heat generated may cause the mixture to splash out and cause burns and the glass

conatiner may also break due to exessing  heating.

  → Mixing an acid or base with water results in decrease of concentration of ions per unit volume. Such a process is called dilution.

Strongness  about  Acids or Bases 

Strength of acid and base can be determined by universal indicator.

concentrations of H⁺ ions in the solution.

pH scale :-  A scale for measuring hydrogen ion concentration in a solution called PH scale.

pH = 7                      →     Neutral Solution

pH Less than 7       →      Acidic  Solution

pH more than 7     →      Basic solution

pH of some common substances shown on a pH paper.

Importance of  pH in everyday life :-

1 ,  Plants and animals are Ph sensitive.

• Our body works within the pH range of  7- 7.8 .
• When pH of rain water is less than 5.6, it is called acid rain.
• When acid rain flows into the rivers ,it lower the pH of river water and makes the survival  of aquatic life difficult.

2, pH of the soil

• Plants require a specific pH range for their healthy growth.

3,  pH in our digestive system.

• Our stomach produce hydrogenchloric acid which helps in digestion without harming the stomach.
• During indigestion, stomach produces more acid and cause pain and irritation.
• To get rid of pain ,prople use mild bases called antacid to neutralize the excess acid. Magnesium hydroxide ( Milk of magnesia) is an antacid.

  4,  Ph changes as the cause of tooth decay.

• Tooth decay starts when pH of mouth is lower than 5.5
• Tooth enamel is made up of calcium phosphate ( hardest substance in body) .it does not dissolve in water but carodes when pHis low than 5.5
• Using basic toothpaste , tooth decay can be prevented    

5, self defence by animals and plants through chemical warfare.

• Bee sting leaves an acid which cause pain and irritation. Bakig soda (mild base) gives relief by rubbing it on stung area.
• Stinging hair of nettle leaves inject  methanoic  acid causing  buring or pain rubbing this with leaf of dock plant give relief.

About  salts

1. Strong acid  +  strong base  →     neutral salt :  pH = 7
2. Salt of strong   +  weak base  →    Acidic salt :    pH <7
3. Salt of strong base + weak acid → Basic salt  :  pH  >7

Chemical from common salt

1;  sodium hydroxide  ( NaOH)

  When electricity is passed through an aqueous solution of NaCl (called brine) it decomposes to form NaOH.

This process is called chlor- alkali process.

2NaCl  +   2H₂O      →        2NaOH + Cl₂    + H₂

 At cathode  :→     H₂    gas

 At anode :→    Cl₂ gas

Near cathode :→   NaOH solution is formed

Uses

1. Cl₂ :→   Water treatment , PVC , pesticides.
2. H₂ :→      Fuels,  margarine.
3. Hcl : →      Medicines, cleaning steels.
4.  NaOH :→   De- greasing metals, soaps and paper making.

(2) Bleaching powder  ( CaOCl₂)

   Bleaching powder is produced by the action of chlorine on dry slaked lime   ( Ca(OH)₂).

 Cl₂  +  Ca(OH)₂ →       CaOCl₂  +   H₂O

 USES :→   * Bleaching cotton and linen in textile industry

• Bleaching washed clothes in laundry .
• Oxidising in chemical industries.
•  Make drinking water free from germs

(3)   Baking Soda ( NaHCO₃)

 The chemical name of the compound is sodium hydrogen carbonate.

NaCl+H₂O+CO₂+NH₃   →   NH₄Cl  +  NaHCO₃

                                     (Ammonium Chloride) (Sodium hydrogen carbonate)

• IT is a mild non- corrosive base.
• When it is heated during cooking.

2 NaHCO₃  →    Na₂CO₃  +   H₂O  +  CO₂

USES:-

1. For making baking powder, which is a mixture of baking soda ( sodium hydrogen carbonate ) and tartaric acid. Following reaction takes place.

 NaHCO₃   +  H⁺  →       CO₂  +  H₂O + Sodium salt of acid

2. Sodium hydrogen carbonate is an ingredient in antacids.
3. Used in soda-acid , fire extinguisher

 (4)  Washing Soda  :-   ( Na₂ CO₃IOH₂O)

  Recrystallisation of sodium carbonate gives washing sod. It is a basic salt.

  Na₂CO₃ + IOH₂O     →    Na₂CO₃. IOH₂O

   USES;   

1. In glass , soap and paper industries.
2. Manufacture of borax
3. Cleaning agent for domestic purpose.
4. For removing permanent hardness of water.

 (5)  Plaster of paris : CaSO₄ .2H₂ O. 

On heating gypsum ( CaSo₄.2H₂O) at 373k, ut loses water molecules and becomes plaster of paris (POP) .

It is a white powder and on mixing with waater it changes to gypsum.

 Removing water of crystallization.

 WATER OF CRYSTALLISATION ;

It is a fixed number of water molecules present in one formula unit of a salt.

For Example; 

• CuSO₄.5H₂O   has 5 water molecules.
• Na₂CO₃.10H₂  has 10 water molecules.
•  CaSO₄.2H₂O  has 2 water molecules.