Class 10 Chapter 02 Acid Bases and Salts NCERT Activity Explanation

NCERT Activity Chapter 02 Acid Bases and Salt Class 10 Chemistry

Activity 2.1

Indicator	Acid	Base
Red litmus	No Change	Blue
Blue Litmus	Red	No change
Phenolphthalein	Colourless	Pink
Methyl Orange	Pink	Yellow

Indictors are substance which change colour in acidic or basic media.

Activity 2.2

• There are some substances whose odour changes in in acidic or basic media.
• These are called olfactory indicators. Like onion vanilla, onion and clove. These changes smell in basic solution.

Activity 2.3

• Take about 5 mL of dilute sulphuric acid in a test tube and add few pieces of zinc granules to it.
• => You will observe bubbles of hydrogen gas on the surface of zinc granules.
• Zn + H2SO4 --> ZnSO4 + H2
• => Pass the Hydrogen gas through the soap solution.
• Bubbles formed in the soap solution as Hydrogen gas it does not get dissolved in it.
• Take a burning candle near a gas filled bubble. Candle burn with pop sound.
• The metal combines with the acid and forms a compound called a salt.

Activity 2.4

• Place a few pieces of granulated zinc metal in a test tube.
• And add 2 mL of sodium hydroxide solution and warm the contents of the test tube.
• There is a release of Hydrogen gas.
• NaOH + Zn → Na₂ZnO₂ (Sodium zincate) +  H₂

 Activity 2.5

• Take about 0.5 g of sodium carbonate (Na2CO3) in test tube A
• Take about 0.5 g of sodium hydrogen carbonate(NaHCO3) in test tube B. 
• Add about 2 mL of dilute HCl to both the test tubes.

You will observe gas evolved

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)

• Pass the gas produced in each case through lime water (calcium hydroxide solution) .
• => You will observe lime water turn milky due to formation of calcium carbonate.

On passing the carbon dioxide gas evolved through lime water,

Ca(OH) ₂ (aq) + CO₂ (g) → CaCO₃ ( s)+ H₂O(l)

On passing excess carbon dioxide through lime water milkiness disappear due to formation of

CaCO₃ + H₂O(l)+ CO₂ (g) → Ca(HCO)₃  

• 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.

Activity 2.6  Base + Acid → Salt + water

• Take about 2 mL of dilute NaOH solution in a test tube and add two drops of phenolphthalein solution.
• The colour of the solution changes to pink
• Add dilute HCl solution to the NaOH solution drop by drop
• The pink colour of solution disappears due to formation of Salt.

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

Acid and base when react cancel their properties and form neutral Salt. This reaction is called neutralization reaction.

• Now add a few drops of NaOH to the above mixture.
• The pink colour of phenolphthalein reappear as salt became basic.

Activity 2.7

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

• You will notice that the colour 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.

Cu O + H Cl  → Cu Cl₂ + H₂ O

Activity 2.8

Take solutions of glucose, alcohol, hydrochloric acid, sulphuric acid as electrolyte in voltaic cell one by one.

• The bulb will start glowing in the case of acids as acid contain H⁺(aq)
• In glucose and alcohol solutions bulb does not glow as they cannot ionize to release ions.
• Glowing of the bulb indicates that there is a flow of electric current through the solution. The electric current is carried through the solution by ions.

Activity 2.9

Take about 1g solid NaCl in a clean and dry test tube and Add some concentrated sulphuric acid to the test tube.

• We observe hydrogen chloride gas coming out of the delivery tube
• Test the gas evolved successively with dry and wet blue litmus paper.
• Wet the blue litmus paper change colour to red.
• This happen because acid release H+ Ion in aqueous solution.

Explanation :  2NaCl+H2SO4(conc.)→Na2SO4+2HCl

• Explanation: Dry HCl does not contain any hydrogen ions (H+) in it , so it does not show acidic behaviour so HCl gas does not change the colour of the dry of the dry blue litmus paper.
• When HCl gas it tested with wet blue litmus paper then HCl gas first dissolves in water to form HCl acid solution.
• HCl(g)   − dissolve in water→ HCl(aq)
• HCl(aq) → H⁺(aq) + Cl⁻(aq)
• HCl solution forms hydrogen ions which can turn blue litmus paper to red.
• Or, HCl+H₂O→H₃O⁺  +  Cl⁻
• Bases generate hydroxide (OH^–) ions in water. Bases which are soluble in water are called alkalis.
• NaOH(s) +  H₂O→ Na⁺ (aq) + OH^-

Activity 2.10
Add few drops of concentrated H2SO4 to test tube containing water and swirl the beaker slowly.

• Touch the base of the beaker to feel a change in temperature.
• =>It is an exothermic process

Repeat the above Activity with sodium hydroxide pellets you will get same observation.

• The acid must always be added slowly to water with constant stirring as it is exothermic process.
• Precaution :  If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns.
•  Increasing volume of water during mixing an acid or base with water results in decrease in the concentration of ions (H₃O⁺  / OH^–) per unit volume of solution. Such a process is called dilution and the acid or the base is said to be diluted.

 Activity 2.11

Test the pH values of acidic and basic solution using pH Paper

• Acid- pH 1 to 6 (acidic nature decreases),
• Neutral water pH 7
• Base – pH 8 to 14 (Basic nature increases)

Activity 2.12 Ph in daily life

• The ideal soil pH for the growth of plants is 6.0 to 7.0 (slightly acidic to neutral) range.
• Acidity of soil neutralise by adding calcium hydroxide

Activity 2.13. Naming of salt

• Salts having the same positive or negative radicals are said to belong to a family.
• NaCl and Na₂SO₄ belong to the family of sodium salts.
• NaCl and KCl belong to the family of chloride salts.
• Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate belong to the family of Sulphate salts
• Sodium nitrate and Potassium nitrate belong to the family of Nitrte salts
• Sodium carbonate, Zinc carbonate, Iron carbonate belong to the family of carbonate salts        

Activity 2.14

• Among the following salts, which salts are acidic, basic or neutral?
• Acidic salts: Aluminium chloride, zinc sulphate, copper sulphate, ammonium chloride.
• Basic salts: Sodium acetate, sodium carbonate.
• Neutral salts: Sodium chloride, potassium nitrate, sodium sulphate.
• Copper sulphate crystals CuSO4. 5H₂O  is blue in colour which seem to be dry but contain water of crystallisation.

Test: When we heat the Copper sulphate crystals , water is removed and the salt turns white.

If you moisten the crystals again with water, Copper sulphate crystals reappear blue in colour

Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt. E.g. Na2CO3.10H2O is not really wet.

CuSO4. 5H2O (Blue) ---Heat--> CuSO4 (white) + 5H2O

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Key terms class, 10, chapter, acid, bases, salts, ncert, activity,acids