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UPboard(Eng)Class 10th Science : Chapter 2 Acids, Bases, & Salts
CHAPTER 2: ACIDS, BASES, AND SALTS
Acids:
- Properties: Sour taste, turn blue litmus red, pH less than 7, react with metals to produce hydrogen gas.
- Examples: Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄).
- Reactions:
- With Metals: Acid + Metal → Salt + Hydrogen Gas
- (e.g., Zn + 2HCl → ZnCl₂ + H₂)
- With Carbonates: Acid + Carbonate → Salt + Water + Carbon Dioxide
- (e.g., 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂)
Bases:
- Properties: Bitter taste, slippery feel, turn red litmus blue, pH greater than 7.
- Examples: Sodium hydroxide (NaOH), Ammonium hydroxide (NH₄OH).
- Reactions:
- With Acids: Acid + Base → Salt + Water (This is called Neutralization Reaction)
- HCl + NaOH ---> NaCl + H2O
Salts:
- Formation: Result of neutralization reaction.
- Properties: Can be acidic, basic, or neutral depending on the nature of the acid and base.
- Examples: Sodium chloride (NaCl), Potassium nitrate (KNO₃).
pH Scale:
- A measure of acidity or basicity of aqueous solutions.
- Neutral pH is 7; acids have pH less than 7, bases have pH greater than 7.
Important Acids and Their Formulas:
- Hydrochloric Acid: HCl
- Sulfuric Acid: H₂SO₄
- Nitric Acid: HNO₃
- Acetic Acid: CH₃COOH (vinegar)
- Citric Acid: C₆H₈O₇ (found in citrus fruits)
- Formic Acid ,Methanoic Acid : Ant Sting
Bases and Their Formulas:
- Sodium Hydroxide: NaOH
- Potassium Hydroxide: KOH
- Calcium Hydroxide: Ca(OH)₂
- Ammonium Hydroxide: NH₄OH
- Magnesium Hydroxide: Mg(OH)₂
Acids in Daily Use Products:
- Vinegar: Acetic Acid (CH₃COOH) - used in cooking, cleaning.
- Lemon Juice: Citric Acid (C₆H₈O₇) - flavoring, cleaning.
- Soda Drinks: Carbonic Acid (H₂CO₃) - carbonation.
- Battery Acid: Sulfuric Acid (H₂SO₄) - in car batteries.
- Cleaning Agents: Hydrochloric Acid (HCl) - for removing rust and scale.
Milk - Lactic Acid
Tomato - Citric Acid, Malic Acid
Lemon - Citric Acid
Orange - Citric Acid
Carrot - Malic Acid
Apple - Malic Acid
Grape - Malic Acid, Tartaric Acid
Plum - Malic Acid
Apricot - Malic Acid
Banana - Tartaric Acid
Kiwi - Ascorbic Acid (Vitamin C)
Guava - Ascorbic Acid (Vitamin C)
Bell Pepper - Ascorbic Acid (Vitamin C)
Rhubarb - Oxalic Acid
Spinach - Oxalic Acid
Beet Greens - Oxalic Acid
Chard - Oxalic Acid
Kale - Oxalic Acid
Potato - Malic Acid
Sauerkraut - Lactic Acid
Indicators : Indicators are such natural or chemical compounds which are used to identify Acids and Bases. They show different colours in both mediums.
Natural Indicators:
Litmus:
Acid: Red
Base: Blue
Turmeric:
Acid: Yellow
Base: Red
Red Cabbage Juice:
Acid: Red
Base: Green to yellow
Hydrangea Flowers:
Acid: Blue
Base: Pink
Chemical Indicators:
Phenolphthalein:
Acid: Colorless
Base: Pink
Methyl Orange:
Acid: Red
Base: Yellow
Bromothymol Blue:
Acid: Yellow
Base: Blue
Importance in Daily Life:
- Acids in digestion (HCl in stomach), bases in cleaning agents (sodium bicarbonate), salts in food preservation (sodium chloride).
Common Salt (NaCl) -
The common salt is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing
soda, bleaching powder and many more.
Sodium hydroxide (NaOH) -
When electricity is passed through an aqueous solution of sodium
chloride (called brine), it decomposes to form sodium hydroxide. The
process is called the chlor-alkali process because of the products formed–
chlor for chlorine and alkali for sodium hydroxide.
2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)
Chlorine gas is given off at the anode, and hydrogen gas at the cathode.
Sodium hydroxide solution is formed near the cathode.
Bleaching Powder (CaOCl2) -
Bleaching powder is produced by
the action of chlorine on dry slaked lime [Ca(OH)2].
Ca(OH)2 + Cl2 → CaOCl2 + H2O
Use of Bleaching powder –
(i) for bleaching cotton and linen in the textile industry, for bleaching
wood pulp in paper factories and for bleaching washed clothes
in laundry;
(ii) as an oxidising agent in many chemical industries; and
(iii) to make drinking water free from germs.
Baking soda (NahCO3) -
The baking soda is commonly used in the kitchen for making tasty crispy pakoras, etc. Sometimes it is added for faster cooking.
The chemical name of the compound is sodium hydrogencarbonate (NaHCO3). It is
produced using sodium chloride as one of the raw materials.
NaCl + H2O + CO2 + NH3 -> NH4Cl + NaHCO3
Uses of Baking soda -
(i) For making baking powder, which is a mixture of baking soda (sodium hydrogencarbonate) and a mild edible acid such as
tartaric acid.
Washing soda (Na2CO3.10H2O) -
Sodium carbonate can be obtained by heating baking soda; recrystallisation of
sodium carbonate gives washing soda. It is also a basic salt.
Na2CO3 + 10 H2O -> Na2CO3.10H2O
Uses of washing soda -
(i) Sodium carbonate (washing soda) is used in glass, soap and
paper industries.
(ii) It is used in the manufacture of sodium compounds such as borax.
(iii) Sodium carbonate can be used as a cleaning agent for domestic
purposes.
(iv) It is used for removing permanent hardness of water.
Plaster of Paris
On heating Gypsum(CaSO4.2H2O) at 373 K, it loses water molecules and becomes
calcium sulphate hemihydrate (CaSO4.½H2O). This is called Plaster of Paris.
CaSO4.2H2O(gypsum)<--->CaSO4.½H2O (Plaster of Paris ) + H2O
Key Points:
- Water can act both as an acid and a base (amphoteric nature).
- The strength of acids or bases can be compared using their dissociation constants (Ka for acids, Kb for bases).
