Class 10th Science Chapter 2 Acid Base Salt Part 1

Class 10th Science Chapter 2

Sour liquid-Acidic in nature,  Bitter liquid - Basic in nature

If you are having acidity among Lemon, Vinegar 

 , Baking soda , you should take Baking Soda coz its Basic in nature other 2 are acidic in nature. 

Acid turns Blue litmus paper into Red. Basic does opposite.

Litmus Paper is made by soaking the absorbing paper in litmus solution (dye extracted from lichen((fungi+alga) living together as 1. Lichen is a plant belonging to the division Thallophyta,))

When the litmus solution is neither acidic nor basic, its colour is purple. There are many other natural

materials like red cabbage leaves, turmeric, coloured petals of some flowers such as

Hydrangea , Petunia  and Geranium , which indicate the presence of acid or base in a solution. These are called acid-base indicators or sometimes simply indicators

Q U E S T I O N 

 1. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

Answer: Red Litmus paper will turn Blue for basic solution.

Activity 2.1

Note: some substances whose odour changes in acidic or basic media. These are called olfactory indicators.

Activity 2.2

1. Take some finely chopped onions in a plastic bag along with some strips of clean cloth. Tie up the bag tightly and leave overnight in the fridge. The cloth strips can now be used to test for acids and bases.
2. Take two of these cloth strips and check their odour.
3. Keep them on a clean surface and put a few drops of dilute HCl solution on one strip and a few drops of dilute NaOH solution on the other.

when sodium hydroxide NaOH solution is added to a close strip treated with onion extract then the onion smell cannot be detected.

Acidic solution hydrochloric acid HCl does not destroy the smell of onions this can be used as a test for acids and bases.
Vanilla extract has pleasant smell if a basic solution like sodium hydroxide solution is added to Vanilla extract then we cannot detect the smell of vanilla extract.

Acidic solution like hydrochloric acid HCl does not destroy the smell of Vanilla extract this can be can be used as test of acids and bases.

How Chemical reaction takes place?

Based on Atomic no. electron shell of element can be identified, it fills in sequence of

2,8,18,32,32,18,2 for eg. Na Sodium has atomic no. 11 shell configuration will be

2,8,1, so there will be 1 electron in outer most shell, for Cl atomic no. is 17 so electrons will fill the shell 2,8,7. means -1 electron for stable state.

Ca has atomic no. 20 electrons will fill 2,8,8,2 so it has extra 2 electrons which it can give to some other element & form compound. for eg. CaCl2

Sodium has 1+ electron in its outer valance cell & clorine needs 1 electron, so they make ionic bond & form Sodium Cloride salt.

2.1.2 How do Acids and Bases React with Metals?

Activity 2.3

CAUTION: This activity needs the teacher’s assistance.

1. Set the apparatus as shown in Fig. 2.1. 
2. Take about 5 mL of dilute sulphuric acid in a test tube and add a few pieces of zinc granules to it.
3. What do you observe on the surface of zinc granules?
4. Pass the gas being evolved through the soap solution.
5. Why are bubbles formed in the soap solution?
6. Take a burning candle near a gas filled bubble.
7. What do you observe?
8. Repeat this Activity with some more acids like HCl, HNO3 and CH3COOH.
9. Are the observations in all the cases the same or different?

3.Acid + Metal → Salt + Hydrogen gas

Zn + H2SO4 ———> ZnSO4 + H2

6. Burning of gas filled bubbles

How do Metal Carbonates and Metal

Hydrogencarbonates React with Acids?

Activity 2.4

Place a few pieces of granulated zinc metal in a test tube.

1. Add 2 mL of sodium hydroxide solution and warm the contents of the test tube.
2. Repeat the rest of the steps as in Activity 2.3 and record your

observations.

Zn(s) + 2NaOH(aq) ———-> Na2ZnO2(s) + H2(g)

               Sodium Hydroxide         Sodium Zincate

Observation: Bubbles come out from zinc granule which burns with a flame.

hydrogen is formed in the reaction. However, such reactions are not possible with all metals.

2.1.3 How do Metal Carbonates and Metal Hydrogen carbonates React with Acids?

Activity 2.5

1. Take two test tubes, label them as A and B.
2. Take about 0.5 g of sodium carbonate (Na2CO3) in test tube A and about0.5 g of sodium hydrogencarbonate (NaHCO3) in test tube B.
3. Add about 2 mL of dilute HCl to both the test tubes.
4. What do you observe?
5. Pass the gas produced in each case through lime water (calcium hydroxide solution) as shown in Fig. 2.2 and record your observations.

Observation:When we add acid to carbonates and hydrogen carbonates of metal, bubbles start appearing from the carbonates. When we pass this air to a quick lime solution, it turns the lime water milky.

Test Tube A: Na2CO3(s)+2HCl(aq)→2NaCl(aq)+H2O(l)+CO2(g)

Test Tube B: NaHCO3(s)+HCl(aq)→NaCl(aq)+H2O(l)+CO2(g)

On Passing the carbon dioxide gas evolved through lime water

Ca(OH)2(aq)+CO2(g)→CaCO3(s)+H2O(l)

Lime water                    white precipitate

On passing excess carbon dioxide the following reaction takes place:

CaCO3(s)+H2O(l)+CO2(g)→Ca(HCO3)2(aq)

                                                (Soluble in water)

Limestone, chalk and marble are different forms of calcium carbonate.

All metal carbonates and hydrogen carbonates react with acids to give a corresponding salt, carbon dioxide and water. Thus, the reaction can be summarised as –

Metal carbonate/Metal hydrogen carbonate + Acid → Salt + Carbon dioxide + Water

Acids and Bases Reaction

Activity 2.6

1. Take about 2 mL of dilute NaOH(Caustic Soda) solution in a test tube and add two drops of phenolphthalein solution.
2. What is the colour of the solution? Pink
3. Add dilute HCl solution to the above solution drop by drop. Is there any colour change for the reaction mixture? Pink Color disappears
4. Why did the colour of phenolphthalein change after the addition of an acid?  color change in phenolphthalein is a result of ionization, adding HCL nutralizes it & it goes back to its previous color.
5. Now add a few drops of NaOH to the above mixture. Does the pink colour of phenolphthalein reappear? Pink 
6. Why do you think this has happened? Solution will become basic & pink color will reappear.
   NaOH+HCL→  NaCL+H2O  

          Base + Acid → Salt + Water

2.1.5 Reaction of Metallic Oxides with Acids

Activity 2.7

Take a small amount of copper oxide in a beaker and add dilute hydrochloric acid slowly while stirring.

CuO+2HCl → CuCl2+H2O

Observation: Color of the solution becomes "blue-green" and the copper oxide dissolves. The blue-green colour of the solution is due to the formation of copper(II) chloride in the reaction. The general reaction between a metal oxide and an acid can be written as –

Metal oxide + Acid → Salt + Water

Non Metal Oxide

E.g.sulfur dioxide (SO₂); sulfor trioxide (SO₃); chlorine dioxide (ClO₂); nitrous oxide (N₂O); nitrogen dioxide (NO₂); phosphorus pentoxide (P₄O₁₀, a combination of two P₂O₅ molecules); and many others.

Non Metal Oxide + Base → Salt + Water

 SO2 (aq) + 2 NaOH (aq) → Na 2SO3 (aq) + H2O

Since this is similar to the reaction between a base and an acid, we can conclude that nonmetallic oxides are acidic in nature.(i.e. NaOH+HCl   NaCl(salt)+ H2O)

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