Exam Based Notes - Acids, Bases And Salts - Class 10 Science

 Exam Based Notes - Class 10 Science 

Acids, Bases And Salts 

     ACIDS

✓ Properties 

• Sour in tast
• converts blue litmus paper into red colour
• Produce H+ ions in water.
• pH valve Below 7 (0-7)
• Ex: HCl, H2SO4, HNO3, CH3COOH

✓ The gas liberated when an acid reacts with a metal is hydrogen

✓ Reaction between acids and bases to form salt and water is called neutralisation reaction. 

Base + Acid → Salt + water.

Ex : NaOH + HCl → NaCl + H2O. 

✓ When an acid reacts with metallic carbonate , carbon dioxide gas is liberated. When carbon dioxide gas is passed through lime water(Ca(OH)2, calcium carbonate is produced as a white precipitate.

The chemical equation is :

Ca(OH)2 + CO2→ CaCO3 + H2O

But when the same gas is passed through lime water in excess, precipitate is not visible because of formation of calcium hydrogen carbonate. As calcium hydrogen carbonate is soluble in water, thus, the milky colour of solution mixture disappears

✓ While diluting an acid, the acid should be added to water not water to acid. Because adding water to a concentrated acid releases a large amount of heat, which can cause an explosion and acid burns on the skin, clothing, and other body parts.

✓ As the pH value of a neutral solution decrease then acidic property increases and number of H+ ions increases. Ex: pH values of  solutions 4 more acid ( produce more H+ ions), 6 is less acidic ( produce less H+ ions).

✓ Ions responsible for acidic and basic natures of the substances is H+ / H3O+ / Hydrogen / Hydronium

✓ Concentrated acid diluted by adding the acid slowly to the water with constant stirring. 

✓ When concentrated sulphuric acid is added to a test tube containing solid sodium chloride the HCl gas will be released. H+ and Cl-  ions formed when this gas is passed into water and salt(Nacl) and water are formed when this gas is passed into an aqueous basic solution obtained in the chlor-alkali process.

✓ Aqueous solution of acid shows acidic nature but the solution of alcohol does not show this nature because  acid releases H+ in aqueous solution but  Alcohol does not release H+ ions in aqueous solution.

✓ Stinging hairs of nettle leaves inject methanoic acid to the skin causes burning. To get relief from this burning, solution of baking soda is applied as it is a mild base ( neutralises the action of acid )

✓ Acid completely dissociates into ions is called strong acid (Acid that gives rise to more +H ions is said to be strong acid). Ex: HCl, H2SO4, HNO3. They  forms more H+ ions in water. 

✓ Acid incompletely dissociates into ions is called weak acid. Ex: CH3COOH, Lactic acid. They forms less H+ ions in water. 

✓ Acid with more concentration of H+ /H3O+ ions per unit volume is called concentrated acid.

✓ Acid with less concentration of H+ /H3O+ ions per unit volume is called diluted acid.

✓ Agricultural scientists have suggested to add a certain amount of lime powder to an agricultural field. Reason for Plants require a specific pH range for their healthy growth. Soil of his land is acidic. Lime powder is a base. So adding lime powder to the soil, decreases the acidic property / soil is neutralised. 

 Farmer treat the soil of his field with slaked lime when the soil is acidic nature 

✓ Causes of Tooth Decay 

Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. So the pH in the mouth decreases and the tooth enamel gets corroded.

Prevention: Using toothpastes which are generally basic, for cleaning the teeth.

✓ When pH of rain water is less than 5.6, it is called acid rain. 

✓ Some naturally occurring acids:

• Vinegar - Acetic acid
• Sour milk (Curd) - Lactic acid
• Orange - Citric acid
• Lemon - Tamarind
• Tartaric acid - Ant sting
• Tomato - Oxalic acid
• Nettle sting - Citric acid
• Methanoic acid - Methanoic acid

    BASES: 

✓ Properties 

•  Bitter in taste
•  Turns red litmus to blue 
•  Produce OH- ons
•  pH value above 7 (7-14)
• Ex: NaoH, KOH, Mg(OH)2

✓ As the pH value of a neutral solution increases then basic property increases and number of OH− ions increases

✓ Base is the substance that converts red litmus paper into blue colour 

✓ The pH value of a solution that turns red litmus paper into blue colour is 8 to 14 

✓ Ions responsible for d basic natures of the substances is OH− Hydroxyl / Hydroxide

    SALTS:

✓ Acid and base combination

  Strong acid + Weak Base = Acidic salt

  Weak Acid + Strong Base = Basis salt

  Strong Acid + Strong Base = Neutral salt

  Weak Acid + Weak Base = Neutral salt

✓ Aqueous solution of sodium chloride is called brine solution. when this solution is subjected to electrolysis products will obtained are  H2 / Hydrogen gas (at cathode), Cl2/ Chlorine gas(at anode) and NaOH / Sodium hydroxide.

Use of NaOH:

• Degreasing metals 
• Soaps & detergents 
• Paper making 
• Artificial fibres.

Use of Chlorine:

• As disinfectant in water purification  
• in swimming pools 
• In the manufacture of PVC / CFC / As insecticide. 

Use of hydrogen:

• as fuels 
• in the preparation of Margarine 
• in the manufacture of Ammonia for fertilizers.

✓ There is no change in the colour of red litmus and blue litmus paper when introduced into an aqueous solution of sodium chloride Because it is a neutral solution. After passing direct current through the same solution, red litmus changes to blue colour. Because Sodium Hydroxide is responsible for this change. 

✓ Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.  Ex: CuSO4.5H2O, Na2CO3.10H2O,  

Bleaching Powder:

Molecular formula : CaOCl2

chemical name : Calcium oxy chloride

Preparation:

Ca (OH)2 + Cl2 → CaOCl2 + H2O

Uses:

• for bleaching cotton and linen in the textile industry.
• for bleaching wood pulp in paper factories 
• for bleaching washed clothes in laundry.
• as an oxidising agent in many chemical industries
• to make drinking water free from germs

washing soda:

Molecular formula : Na2CO3

uses of washing soda. 

• In glass, soap and paper industries. 
• In the manufacture of sodium compounds such as borax. 
• As a cleaning agent for domestic purposes. 
• For removing permanent hardness of water.

Baking soda:

Chemical name : Sodium hydrogen carbonate / Sodium bicarbonate 

Molecular formula : NaHCO3 

Plaster of Paris:

Common Name: Plaster of paris

Chemical Name: Calcium sulphate hemihydrate.

Chemical formula : CaSO4.1/2H2O

Plaster of Paris is used in :

• Supporting fractured bones
• Making toys
• Decorative materials
• Making smooth surfaces. 

✓ Plaster of Paris should be stored in a moisture-proof container. Because Plaster of Paris in contact with moisture (water) changes to solid hard mass, gypsum. Therefore, it gets wasted. Hence it should be stored in moisture proof container.