NCERT SCIENCE CLASS 10-2021-ACIDS, BASES AND SALTS- CHAPTER 2 -NOTES AND STUDY MATERIAL-PART -1

ACIDS, BASES AND SALTS- CHAPTER 2 CLASS 10 CBSE 

NOTES AND STUDY MATERIAL-part-1

NCERT SCIENCE CLASS 10-ACIDS, BASES AND SALTS- CHAPTER 2 -NOTES AND STUDY MATERIAL-PART -1

In the previous classes, you have studied about the food which is sour and bitter in taste and has learnt that it is due to the acids and bases present in the food. So let us study some more about acids, bases and salts and their chemical properties.

Suppose someone in your family suffers from acidity, what do you suggest to reduce the acidity? If you have lemon juice, vinegar and baking soda solution, would you like to reduce acidity by any of these? You will be taking baking soda.

 

So acidity can be removed only by baking soda solution because it is a weak base and it can neutralize the effect of acid.

HOW CAN WE TEST ACIDS OR BASES?

With the help of certain substances which can tell whether the solution is acidic or basic in nature. Those substances are called indicators.

There are two types of indicators- natural indicators and synthetic indicators.

ACTIVITY-Let we take blue litmus paper and red litmus paper now. If you put blue litmus paper in a test tube containing acid what will happen? The colour will change to red. Now take  NaOH solution in water and dip it in a red litmus paper. What will be the change in the colour? The colour of red litmus paper changes to blue.

 Suppose you put this red litmus paper as well as the blue litmus paper in distilled water and observe the change in colour. Will there be a change? No, there won't be any change as you know. Because distilled water is neutral and it will neither change the colour of red litmus paper nor it will change the colour of blue litmus paper.

There are so many other natural indicators also like turmeric. You must have observed that if it falls on the clothes, it leaves a yellow coloured stain. On washing the clothes, what happens? The stain changes to pink colour. 

Soap solution is a basic solution and it changes into pink on coming in contact with turmeric solution. 

So turmeric is also a natural indicator and it changes bases to pink in colour and no change in colour in the acids.

 Some more natural indicators can be prepared from red cabbage leaves or coloured petals of certain plants like hydrangea geranium and petunia. So these indicators can be extracted from these plants. 

The second type of indicators are synthetic indicators and you might have heard about these. Phenolphthalein and methyl orange are commonly used indicators.

 ACTIVITY-Take three test tubes. In one test tube, put dilute HCl, in another test-tube put some sodium hydroxide solution and in the third test, you distilled water and put a drop of phenolphthalein in all these three test tubes and see the changes. 

What do you observe? In the case of dilute HCl, you find that there is no change in colour, in the case of dilute NaOH solution you will find a change in colour. It changes to a pink colour  In the case of distilled water, there is no change in colour because it is neutral 

.Methyl orange is another indicator. Methyl Orange is orange in colour and it turns red with acids and no colour change with base. 

Another important type of indicator is olfactory indicators.

OLFACTORY INDICATORS- these indicators will show different odour with acids and bases.

Examples are onion, vanilla and clove.

ACTIVITY-take some chopped onions and put it in a plastic bag and also put some thin strips of cloth inside the packet and then put it in the refrigerator for the whole night. Next day when you take it out and smell the clothes strips, it smells of onion. Put a drop of dilute HCl on one cloth strip and a drop of NaOH solution on the other cloth strip. 

Wash both the clothes strip with water and smell it. You will find that there is no odour of onion on the clothes strip having dilute NaOH on it whereas the other strip on which dilute HCl was poured it still smells of onion.

 So we can indicate whether the given sample is a base or an acid-based on the change in odour.

 Other examples are vanilla essence and clove oil.  You will find that the test tube in which dilute NaOH has been taken does not smell of vanilla. The test tube which contains dilute HCl still smells of vanilla.

CHEMICAL PROPERTIES OF ACIDS AND BASES

1. HOW DO ACIDS AND METALS REACT WITH METALS?

ACTIVITY- a test tube is taken in which zinc granules and sulphuric acid are taken and it is fitted with the help of a clamp stand. The test tube is fitted with a rubber stopper through which passes a delivery tube. The other end of the delivery tube is dipped in water which is contained in a glass trough containing soap solution. 

As soon as zinc granules are mixed with sulphuric acid, a chemical reaction occurs and some gas bubbles are seen rising up. These gas bubbles which rise up passes through the delivery tube and go out in the form of soap bubbles.

 Let us test which gas is this. This gas can be tested by bringing a burning candle in front of this soap bubble. It is observed that the gas burns with a pop sound. This gas produced is hydrogen gas.

What do we conclude? Zinc reacts with sulphuric acid and forms hydrogen gas and zinc sulphate. Most of the metals  react with all the acids and form salt and hydrogen gas.

METAL + ACID → SALT + HYDROGEN

The same activity can be performed by taking a base and a metal and using the same type of apparatus. Sodium hydroxide and zinc react and sodium zincate and hydrogen are formed.

2 NaOH + Zn → Na2ZnO2 + H2

All metals do not react with the bases to produce salt and hydrogen.

2.HOW DO METAL CARBONATES AND METAL HYDROGEN CARBONATES REACT WITH ACIDS?

For this let us, first of all, discuss an activity to be performed in the lab.

ACTIVITY-  take a test tube and add sodium carbonate to it and then add dilute HCl by thistle funnel. Dilute HCl reacts with sodium carbonate and the gas formed rises up the delivery tube into the test tube which is filled with a solution of calcium hydroxide. (The solution of calcium hydroxide in water is called lime water) .

 When the gas is passed over lime water, you will find that milkiness appears. It is due to the formation of an insoluble substance called calcium carbonate.

When sodium carbonate reacts with dilute HCl, NaCl, carbon dioxide and water are formed.

Na2CO3 + 2 HCl → 2 NaCl + CO2 + H2O

CO2 + Ca(OH)2 → CaCO3 + H2O

 When carbon dioxide gas is passed through lime water for a long time, the milkiness disappears. It is due to the formation of a soluble compound, that is calcium bicarbonate.

CO2 + CaCO3  + H2O →  Ca(HCO3)2

If the same experiment is performed by taking sodium hydrogen carbonate  and dilute HCl is added with the help of the Thistle funnel, the gas evolves. It is again passed through the delivery tube into the lime water and in the same manner as in the previous activity lime water turns milky. 

So again carbon dioxide gas evolves and reacts with lime water and milkiness appears due to the formation of insoluble salt, that is calcium carbonate.

NaHCO3 + HCl → NaCl + CO2 + HCl

So we can see from this that both metal carbonates as well as metal hydrogen carbonates react with dilute HCl to produce carbon dioxide gas, a salt is formed and water is also formed

 METAL CARBONATE OR METAL HYDROGEN CARBONATE + ACID → SALT + CARBON DIOXIDE + WATER

3. HOW DO ACIDS AND BASES REACT WITH EACH OTHER?

Acid and base react and nullify the effect of each other and this type of reaction is called a neutralization reaction. It forms salt and water.

Base + Acid → Salt + Water

 What happens when NaOH reacts with HCl? NaCl and water are formed. So a neutralization reaction is a chemical reaction in which acid reacts with the base to form salt and water.

NaOH + HCl → NaCl + H2O

 If somebody suffers from acidity what remedy will you suggest? You will suggest a base to remove the acidity. The weak base used is baking soda solution which nullifies the effect of the acid produced in the stomach.

4. HOW DO METAL OXIDES REACT WITH ACIDS?

ACTIVITY- take a metallic oxide-cupric oxide which is black in colour in a test tube and add some amount of dilute HCl to it. The colour of the solution changes to blue-green due to the formation of a new substance cupric chloride.

CuO  +2 HCl  → CuCl2 + H2O

Bases also react with acids to form salt and water and in the same way, metallic oxides also react with acids to form salt and water. Here cupric chloride is the salt formed. So metallic oxides are basic in nature and therefore metallic oxides are also called basic oxides.

5. HOW DO NON-METAL OXIDES REACT WITH BASES?

Non-metallic oxide is the compound of a non-metal with oxygen.Example of carbon dioxide. 

We have already seen that when carbon dioxide gas is passed through lime water which is a base( that is calcium hydroxide solution in water) it turns milky due to the formation of insoluble salt that is calcium carbonate.  When acids react with bases what is formed? Salt and water.

CO2 + Ca(OH)2 → CaCO3 + H2O

Non-metallic oxides react with the base and form salt and water. So non-metallic oxides are behaving like acids. So they are acidic in nature. That is why non-metallic oxides are also called acidic oxides.

You can expect many questions related to activities from acids, bases and salts. Learn all the diagrams given in the NCERT textbook related to the topic.

Do you want to learn about the strength of acids and bases, pH and salts?

YOU CAN ALSO READ: PART 2 ACIDS, BASES AND SALTS

                                   : PART 3 ACIDS, BASES AND SALTS

                                       : PART 4 ACIDS, BASES AND SALTS

                                       : PART 5 ACIDS, BASES AND SALTS