Class VII

Acids,Bases and Salts

Content:

* Introduction

* Physical properties of Acids, Bases and Salts

*Chemical properties of Acids.

*Testing for Acids and Bases

*Neutralization reaction

*Application of neutralization in our daily life.

*Formation of soap

Video link of the chapter acids, bases and salts

Part 1 - https://youtu.be/s1mZxsC1Xp4

Part 2 - https://youtu.be/ASE3x_CIq6M

Part 3 - https://youtu.be/l_cZftfTugo

*Introduction

Every day we consume variety of foods which tastes bitter(kadwa), salty(namkeen), sour(khatha) and sweet(meetha).

Have you ever thought why they taste different? It is because they contain different components in them.

Food that tastes sour contains acids in it like lemon, curd, orange, tamarind(imli).

Classification of acids:

1. Organic acids:

* Acids which are obtained from living things such as plants and animals.

* They are weak acids.

*They do not cause skin burns.

Organic Acids Present in Food item

*Citric acid Lemons & oranges

*Lactic acid Milk

*Acetic acid Vinegar

*Tartaric acid tamarind, unripe mangoes, grapes

*Amino acids Proteins

*Carbonic acids Carbonated drinks

2. Mineral Acids:

* A mineral acid is an acid derived from one or more inorganic compounds .

* They are strong acids

* They can cause severe skin burns.

* Hydrochloric acid(HCl), Sulphuric acid(H2SO4), Nitric acid(HNO3) and Carbonic acid(H2CO3).

Properties of acids:

* Acids are sour in taste

* Acids turns blue litmus to red.

* All acids solution conducts electricity because when acids are dissolved in water, it breaks down into ions(charged particles) which conducts electricity.

* Acids are corrosive. They corrode the metals therefore, pickles are not stored in metal jar because pickles are acidic in nature and they corrode the metal and form poisonous salt.

Concentrated and dilute acids:

When hydrogen chloride gas is dissolved in less quantity of water, it forms concentrated hydrochloric acid.

When same amount of hydrogen chloride gas is dissolved in large quantity of water, then it form dilute hydrochloric acid.

Acid is concentrated or dilute depend upon the amount of water present in it.

Dilution of an acid is done to reduce the strength and effectivity of an acid.

Chemical properties of acids:

1. Reaction with metals: When metals reacts with acids they form salt and evolution of hydrogen takes place.

Mg(Magnesium) + 2HCl(hydrochloric acid) ------> MgCl2(Magnesium Chloride) + H2 Metal Salt Hydrogen

Zn(Zinc) + H2SO4(Sulphuric acid) -----------> ZnSO4(Zinc sulphate) + H2

Metal Acid Salt Hydrogen

When metals reacts with acids, metals displace the hydrogen atom/atoms from their acids and form salt.

Metals like sodium, potassium, calcium, iron, lead, aluminium are more reactive than hydrogen that's why they displace hydrogen from its acid to form salt.

Exception: But few metals like copper, silver and gold are less reactive than hydrogen, so they cannot displace hydrogen from their acids and hence no reaction takes place.

Cu(Copper) + HCl -----------> No reaction

*Reaction of acids with metal carbonates:

When dilute sulphuric acid react with metal carbonates like calcium carbonate or sodium carbonate, it form salt, water and release of carbon dioxide gas.

CaCO3 + 2HCl --------> CaCl2 + H20 + CO2

Calcium Acid Salt Water Carbon dioxide

Carbonate

Na2CO3 + H2SO4 ---------> Na2SO4 + H2O + CO2

Sodium Acid Salt Water Carbon dioxide

Carbonate

Base

*Food that tastes bitter(kadwa) and feel soapy to touch contains base like baking soda(Sodium hydrogen carbonate), Copper oxide(CuO), Sodium hydroxide(NaOH) etc.

* All the Metal oxide- CuO(Copper Oxide), MgO( Magnesium Oxide), Fe2O3(Iron Oxide)

Metal hydroxides - Mg(OH)2(Magnesium hydroxide), KOH(Potassium hydroxide) , NaOH (Sodium Hydroxide)

Metal Carbonates - CaCO3(Calcium Carbonate), Na2CO3(Sodium Carbonate), CuCO3(Copper carbonate)

Metal bicarbonates- NaHCO3 (Baking soda) are the examples of the bases.

*

Exception: Ammonium hydroxide(NH4OH) is the only base which does not have a metal atom in its molecule.

* All the bases which are soluble in water are called alkalis like NaOH, KOH, Ca(OH)2

* Bases which are not soluble in water are called bases only like CuO.

* Strong bases are corrosive and can burn the skin same as acids. For example: Sodium hydroxide, Potassium hydroxide.

* Weak bases are not corrosive and it do not burn skin like magnesium hydroxide, copper hydroxide and ammonium hydroxide.

Testing for Acids and Bases

It is not safe to taste every substance to check whether the substance is acidic or basic because strong acids and bases can cause skin burn.

Acid - Base indicators

Natural Indicators Acid Base

Litmus paper Blue litmus turns red Red litmus turns blue

Turmeric Remains yellow Yellow turns red

China rose petals Dark pink Green

Inorganic indicators

Methyl orange Red Yellow

Phenolphthalein Colourless Pink

Salts

*Neutralization reaction: The reaction of an acid with base,to form salt and water is called neutralization reaction.

Acid + Base ------> Salt + Water

HCl + NaOH ------> NaCl + H2O

H2SO4 + 2KOH -------> K2SO4 + 2H2O

During the reaction evolution of heat takes place and such reactions in which heat is evolved during the reaction are called Exothermic reaction.

Neutralization reaction is considered as exothermic reaction because heat is evolved during reaction.

* Salt can be neutral, acidic and basic depending upon the composition.

Strong acid + weak base -----> Acidic salt + water

Weak acid + strong base ------> Basic salt + water

Strong acid + strong base ------> Neutral salt + water

Properties of salt:

*Most of the salt are solids with high melting and boiling point.

*Salts are soluble in water

*Salt solutions(salt dissolved in water) are good conductor of electricity because salt dissociates into ion when dissolved in water and these ions(charged particles)conducts electricity.

Application of neutralization in everyday life

* Indigestion: Our stomach produce hydrochloric acid for digestion of food.Too much acid can cause stomach pain and indigestion.

Milk of magnesia which contains magnesium hydroxide is used as an antacid to neutralise excessive acidity in the stomach.

*Ant bite: When ant bites it, injects the formic acid into the skin. Baking soda or calamine solution(Zinc carbonate) is used to neutralize the acid and provides relief.

*Soil treatment: Excessive use of chemical fertilizers makes the soil acidic. Plants do not grow well in acidic solution. Calcium oxide(Quick lime) 0r Calcium hydroxide(Slaked lime) is added to neutralise the acid present in the soil.

*Factory Wastes: The wastes of many factories contain acids. If they are allowed to dump in water bodies, it make the water acidic which can hamper the growth and existence of the aquatic animals. The factory waste are therefore treated with calcium hydroxide to neutralize the acid before the water is disposed off.

Formation of soap

*Soap is the Sodium and potassium salt of fatty acids.

*Soap can be prepared by boiling vegetable oil or animal fat with caustic soda(NaOH).

* Experiment: Take 20 ml of castor oil or coconut oil in a beaker. Prepare sodium hydroxide solution by dissolving half a teaspoon of caustic soda in about 20 ml water. Mix the oil and sodium hydroxide solution. Heat the mixture and let it boil for 5 to 10 minutes. Stir continuously

Reaction

Oil + Sodium Hydroxide -----> Soap + glycerine

To separate the soap from mixture, add a teaspoon of salt to the beaker and stir on cooling solid soap separates out at the top of the solution.