NCERT Revision Notes for Chapter 2 Acids, Bases and Salts Class 10 Science
CBSE NCERT Revision Notes1
Answer
→ The sour and bitter tastes of food are due to acids and bases are present in them.
→ Acids are sour in taste and change the colour of blue litmus to red.
→ Litmus solution is a purple dye, which is extracted from lichen. When the litmus solution is neither acidic nor basic, its colour is purple.
→ 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.
2
Answer
• The term ‘acid’ has been derived from the Latin word, 'acidus' which means sour.
• Acids have sour taste.
• They turn blue litmus solution red.
• They give H+ ions in aqueous solution.
Strong Acids: HCl, H2 SO4 , HNO3
Weak Acids: CH3COOH, Oxalic acid, Lactic acid
Concentrated Acids: More amount of acid + Less amount of water
Dilute Acids: More amount of water + Less amount of acid
3
Answer
• These are the substances which are bitter in taste and soapy in touch.
• They turn red litmus solution blue.
• They give OH- ions in aqueous solution.
Strong Bases: NaOH, KOH, Ca(OH)2
Weak Bases: NH4OH
Alkalies: These are bases which are soluble in water. Examples: NaOH, KOH, Ca(OH)2.
4
Answer
Indicators: Substances which change their colour/smell in different types of substances (like acids and bases).
Types of Indicators:
(i) Natural indicators
(ii) Synthetic indicators
(iii) Olfactory indicators
(i) Natural indicators: Found in nature in plants. Examples: Litmus, red cabbage leaves extract, flowers of hydrangea plant, turmeric.
(ii) Synthetic indicators: These are chemical substances. Examples: Methyl orange, phenolphthalein.
(iii) Olfactory indicators: These substances have different odour in acid and bases.
5
Answer
→ Reaction of Acids with Metals
• Acids react with metal to form metal salt and releases Hydrogen Gas.
Acid + Metal → Salt + Hydrogen Gas
• Example: Zinc granules react with dilute Hydrochloric acid in a test tube.
2HCl + Zn → ZnCl2 + H2
→ Reaction of Bases with Metals
• Bases react with metal to evolve hydrogen Gas. Also, note that all metals do not react with bases. The metal must be more reactive than the metals present in the base for the reaction to take place.
Base + Metal → Salt + Hydrogen gas
• Example: Zinc granules react with NaOH solution to form sodium zincate and evolve hydrogen gas.
2NaOH + Zn → Na2ZnO2 + H2
• Hydrogen gas released can be tested by bringing burning candle near gas bubbles, it burst with pop sound.
6
Answer
• Acids reacts with Metal Carbonates and Metal Hydrogencarbonates to form Salt, Carbon dioxide and water.
Metal carbonate/Metal hydrogen carbonate + Acid → Salt + Carbon dioxide + Water
• Examples: (i) 2HCl + Na2CO3 → 2NaCl + CO2 + H2O
(ii) HCl + NaHCO3 → NaCl + CO2 + H2O
• CO2 can be tested by passing it through lime water. It turns lime water milky.
Ca(OH)2 + CO2 → CaCO3 + H2O
• When excess CO2 is passed, milkiness disappears.
CaCO3 + CO2 + H2O → Ca(HCO)3
• Bases do not react with Metal Carbonates and Metal Hydrogencarbonates.
Base + Metal Carbonate/Metal Hydrogen Carbonate → No Reaction
7
Answer
• Acids and Bases react to form salt and water.
Acid + Base → Salt + H2O
• Neutralisation Reaction: Reaction of acid with a base is called as neutralization reaction.
Example: HCl + NaOH → NaCl + H2O
• Strong Acid + Weak Base → Acidic salt + H2O
• Weak Acid + Strong Base → Basic salt + H2O
• Strong Acid + Strong Base → Neutral salt + H2O
• Weak Acid + Weak Base → Neutral salt + H2O
Reaction of Metallic Oxides with Acids
→ Metallic oxides are basic in nature.
Example: CaO, MgO are basic oxides.
Metallic Oxide + Acid → Salt + H2O
CaO + 2HCl → CaCl2 + H2O
Reaction of Non-metallic Oxides with Bases
→ Non-metallic oxides are acidic in nature.
→ Non-metallic Oxide + Base → Salt + H2O
CO2 + Ca(OH)2 → CaCO3 + H2O
Reaction of Acid
(i) Acid + Metal Carbonate → Salt + CO2 + Water
(ii) Acid + Metal → Salt + H2
(iii) Acid + Metal Hydrogen Carbonate → Salt + CO2 + H2O
(iv) Acid + Metallic oxide → Salt +H2O
(v) Acid + Base → Salt + H2O
Reaction Of Base
(i) Base + Metal → Salt + H2
(ii) Base + Metal Carbonate → No Reaction
(iii) Base + Metal Hydrogen Carbonate → No Reaction
(iv) Base + Acid → Salt + H2O
(v) Base + Non Metallic oxide → Salt + H2O
8
Answer
→ All acids have H+ ions in common. All acids produce H+ ions
→ Acids produce H+ ions in solution which are responsible for their acidic properties.
→ All bases have OH- (hydroxyl ions) in common. All bases produce OH- ions
Acid or Base in Water Solution
→ Acids produce H+ ions in presence of water.
→ H+ ions cannot exist alone, they exist as H3O+ (hydronium ions).
H+ + H2O → H3O+
HCl + H2O → H3O+ + Cl-
→ Bases when dissolved in water gives OH − ions.
→ Bases soluble in water are called alkali.
→ While diluting acids, it is recommended that the acid should be added to water and not water to acid because the process of dissolving a acid or a base in water is highly exothermic.
9
Answer
→ Strength of acid or base can be estimated using universal indicator.
→ Universal indicator: It is a mixture of several indicators. It shows different colours at different concentrations of H+ ions in the solution.
→ pH Scale: A scale for measuring H+ ion concentration in a solution. p in pH stands for ‘potenz’ a German word which means power.
• If value of ph is equal to 7 → neutral solution.
• If value of pH is less than 7 → acidic solution.
• If value of pH more than 7 → basic solution.