Grade-8 (Science ) :-Acid ,Base and Salt

 

Unit :-14         Acid ,Base and Salt

Acid : A substance which gives hydrogen ions (H⁺) when dissolved in water is called acid. For example :

hydrochloric acid

Sulphuric acid

Nitric acid

Carbonic acid

Types of acid :

They are 2 types :

1)Organic acid :The acid which are obtained from living being( i.e. plants and animals  )are called organic acid . .For example :Carbonic acid , Acetic acid, Citric acid  etc.

2.)Inorganic acid :The acid which are obtained from minerals are called inorganic acid . .For example : Hydrochloric acid

Sulphuric acid

Nitric acid

 Properties

Physical properties

i)It possess sour test .

ii)Strong acid are highly corrosive in nature so,they are not tested .

iii)Some acid are poisonous i.e. Hydrogen cyanide is most poisonous acid .

iv)Some acid are solid i.e. Citric acid and some are liquid i.e. Hydrochloric acid.

v)Acid change blue litmus paper into red ,methyl orange into pink, phenolphthalein  into colourless ,and red cabbage juice into red colour .

Chemical properties

i)When acid react with base gives salt and water .

 ii)When acid react with reactive metal i.e. Na,K, gives salt and hydrogen gas .

Uses of acid

i)Sulphuric acid is used in the manufacture of fertilizer i.e. ammonium sulphate ,paint, and storage battery .

ii)Hydrochloric acid is used for cleaning of metal items .

iii)Nitric acid is used in the manufacturing of fertilizer i.e. ammonium nitrate ,plastic etc.

iii)Carbonic acid used for making soft drinks i.e. soda water .

iv)Tartaric acid is used for making baking powder .

v)Boric acid is used as antiseptic medicine .

Some of the Organic acid or acid used in daily life and their sources :

Name of acid	Source of acid
i.Lactic acid ii. Acetic acid iii. Citric acid iv. Tartaric acid v. Ascorbic acid or vitamin C vi. Formic acid	Curd Vinegar Lemon/Orange/Tomato Grapes/Bhogate Amala Sting of insect i.e. bee,ant

 

Base :Metalic oxides or hydroxides which  are neutralized by acid to produce salt and water is called base .i.e.

i.Sodium oxide

ii. Potassium oxide

iii. Calcium oxide

iv. Magnesium  hydroxide

v. Potassium hydroxide

vi. Calcium hydroxide etc.

Alkali :-The bases which are water soluble are called alkali ,therefore all alkali are bases but all bases are not alkali because all bases are not water soluble .

Properties

Physical properties

i)Bases are bitter in test and soapy in touch .

ii)Bases have P^H value more than 7.

iii)They change red litmus paper into blue ,methyl orange into yellow, phenolphthalein into pink and red cabbage juice into green colour.

Chemical properties

i)When base react with acid gives salt and water .

ii)When alkali solution react with ammonium chloride ,salt ammonia and  water are obtained .

Uses of  bases

i) Sodium hydroxide is used to make soap and paper .

ii)Calcium hydroxide  is used  to make cement ,white washing bulding and plaster .

iii) Magnesium hydroxide  and Aluminum hydroxide are used for making reducing hyperacidity .

iv)Ammonium hydroxide is used for making chemical fertilizer .

Some bases and sources  used in our daily life

Name of base	Sources
i.Potassium hydroxide (Castic potash) ii. Aluminum hydroxide iii. Sodium hydroxide (Castic Soda )	Ash (Kharani)  Antacids i.e. Medicine for hyper acidity Soap

 

Salt: A  neutral substance which is formed as result of the reaction between acid and base is called salt .

Properties of salt

i)Salt are salty in taste but some salt are bitter or test less .

ii)Salt are generally neutral but some salt are acidic or basic .iii)Most of salt are water soluble .

Uses of salt :

i)Common salt i.e Sodium chloride is used in daily life .

ii)Calcium sulphate is used for plastering of fractured bone and making ceramics .

iii)Sodium carbonate  is used for making detergent and softening hard water .

iv) Copper sulphate is used for electroplating .

Indicator :-A chemical substance which can change  its colour when kept int acid  base and salt is called indicator .It is used to test the substances whether they are acid ,base or neutral .For example :

Universal indicator :A special types of indicator which is used  to measure the strength of acid and base, is called universal  indicator .It is prepared by mixing several organic indicator of different colour .It is found in the form of yellow litmus paper .

P^H Scale : A scale which is used to measure strength of acid and  base is called P^H  Scale ^.   Or 

A scale which shows the quantities of H⁺  present in acid and (OH)^-  ions present in base solution .The P^H  value of acid is inversely proportional to the strength of acid and directly proportional to the strength of base .In P^H scale the P^H value below 7 i.e. 1 to 6  represent acidity and above 7 i.e. 8 to 14 represent alkalinity where as 7 represent neutrality or salt .