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Acids, Bases & Salts

General Science · Chemistry

Useful for: Railway RRB

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Overview

Acids release H⁺ ions, bases release OH⁻ ions, and they neutralise each other to form salt and water.

Key points

pH < 7 acidic, 7 neutral, > 7 basic.
Litmus: acids turn blue litmus red; bases turn red litmus blue.
Phenolphthalein turns pink in bases and stays colourless in acids.
Neutralisation: acid + base → salt + water.
Common acids: hydrochloric acid in the stomach, citric acid in lemon, acetic acid in vinegar, formic acid in ant stings.

Explanation

Baking soda: NaHCO₃; washing soda: Na₂CO₃·10H₂O; bleaching powder: CaOCl₂; plaster of Paris: CaSO₄·½H₂O.
Antacids (bases) relieve acidity.
Acid rain has pH below 5.6.
Toothpaste is basic to neutralise mouth acids.

Step by step

Identify the concept or law involved.
Recall the definition, unit or formula.
Check units and the direction of the effect before choosing.

Examples

Phenolphthalein in NaOH solution → pink.
An ant sting (formic acid) is soothed with baking soda.
Vinegar contains acetic acid.

Traps and advanced points

Trap: Mixing baking and washing soda.
Trap: Wrong litmus colours.
Trap: Calling pH 8 acidic.

Quick revision

pH 7 neutral.
Phenolphthalein pink in base.
Salt formulas table.

Practice MCQs

The SI unit of electrical resistance is what?
1. tesla
2. ampere
3. coulomb
4. ohm
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Answer: (d) ohm. The SI unit of electrical resistance is ohm.
Vitamin B3 deficiency causes what?
1. Night blindness
2. Scurvy
3. Beriberi
4. Pellagra
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Answer: (d) Pellagra. Vitamin B3 deficiency causes Pellagra.
Which Newton law is associated with action and reaction?
1. Second law
2. First law
3. Third law
4. Law of gravitation only
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Answer: (c) Third law. Third law is associated with action and reaction.
A convex lens is commonly used to correct which defect?
1. Myopia
2. Hypermetropia
3. Night blindness
4. Astigmatism only
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Answer: (b) Hypermetropia. A convex lens is commonly used to correct Hypermetropia.
Which option correctly answers this General Science check: atomic number equals the number of?
1. protons
2. oxygen
3. radiation
4. H₂O
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Answer: (a) protons. Atomic number is defined by proton count.
Which option correctly answers this General Science check: symbol Fe represents?
1. moisture
2. iron
3. ½mv²
4. liver
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Answer: (b) iron. Fe comes from Latin ferrum.
Which option correctly answers this General Science check: rusting of iron requires oxygen and?
1. negative charge
2. None of these
3. moisture
4. rate of reaction
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Answer: (c) moisture. Rusting is accelerated by water/moisture and electrolytes.
Which disease is caused by deficiency of vitamin K?
1. Beriberi
2. Rickets
3. Night blindness
4. Delayed blood clotting
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Answer: (d) Delayed blood clotting. Vitamin K is needed for clotting factors; deficiency causes bleeding tendency.
Lower pH means a solution is —
1. saltier
2. more acidic
3. more basic
4. neutral
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Answer: (b) more acidic. pH below 7 is acidic; lower is more acidic.
Bleaching powder is —
1. CaCO₃
2. CaOCl₂
3. NaCl
4. NaOH
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Answer: (b) CaOCl₂. Bleaching powder is calcium oxychloride.