Important Salts — Set 2
Chemistry · महत्वपूर्ण लवण · Questions 11–20 of 40
Which salt is used to remove the permanent hardness of water?
Correct Answer: C. Washing Soda
• **Washing Soda (Na₂CO₃)** = reacts with dissolved Ca²⁺ and Mg²⁺ ions, forming insoluble precipitates. • **Softening mechanism** — carbonate ions precipitate hardness-causing ions, making water suitable for detergents. • 💡 Wrong-option analysis: Epsom Salt: contains Mg²⁺, adds to hardness; Baking Soda: only removes temporary hardness; Bleaching Powder: disinfectant, not for water softening.
Which salt is primarily responsible for the salinity of seawater?
Correct Answer: A. Sodium Chloride
• **Sodium Chloride** = comprises ~85% of dissolved salts in seawater, making oceans characteristically saline. • **Ocean composition** — derived from weathering of rocks and volcanic activity over geological timescales. • 💡 Wrong-option analysis: Calcium Chloride: minor dissolved salt in seawater; Magnesium Chloride: present but in much lower concentration; Potassium Chloride: trace element in ocean water.
What happens when baking soda is heated during the cooking process?
Correct Answer: D. Carbon dioxide is released
• **Carbon dioxide (CO₂)** = thermal decomposition of NaHCO₃ produces CO₂, water vapor, and sodium carbonate. • **Leavening effect** — CO₂ gas bubbles expand during baking, creating light and airy baked products. • 💡 Wrong-option analysis: Sodium metal: requires extreme temperatures and special conditions, not cooking heat; Hydrogen gas: no mechanism for hydrogen release from baking soda; Oxygen is released: baking soda doesn't decompose to release elemental oxygen.
Which salt is used as a supplement in common table salt to prevent goiter?
Correct Answer: D. Potassium Iodide
• **Potassium Iodide (KI)** = provides iodine essential for thyroid hormone synthesis and metabolism. • **Goiter prevention** — iodized salt ensures adequate iodine intake, preventing thyroid enlargement in iodine-deficient areas. • 💡 Wrong-option analysis: Magnesium Iodide: unstable compound, easily oxidized; Sodium Fluoride: for dental health, not thyroid function; Calcium Iodate: better chemical stability but potassium iodide is standard.
Which salt is produced when Copper oxide reacts with dilute Hydrochloric acid?
Correct Answer: A. Copper Chloride
• **Copper Chloride (CuCl₂)** = oxide anion accepts protons from HCl, forming salt and water. • **Acid-base neutralization** — metallic oxide reacts according to: CuO + 2HCl → CuCl₂ + H₂O. • 💡 Wrong-option analysis: Copper Carbonate: would form if copper oxide reacted with carbonic acid; Copper Nitrate: requires nitric acid, not hydrochloric; Copper Sulfate: product of reaction with sulfuric acid.
The salt 'Epsom Salt', used for medicinal baths and as a fertilizer, is chemically?
Correct Answer: C. Magnesium Sulfate
• **Magnesium Sulfate (MgSO₄)** = heptahydrate form contains 7 molecules of water of crystallization. • **Therapeutic properties** — provides magnesium for muscle relaxation and sulfate for detoxification in baths. • 💡 Wrong-option analysis: Sodium Sulfate: Glauber's salt, used as a laxative; Copper Sulfate: toxic, blue vitriol used as fungicide; Calcium Sulfate: gypsum, used in plaster and construction.
Which salt is used for making soda-acid fire extinguishers?
Correct Answer: B. Sodium Bicarbonate
• **Sodium Bicarbonate (NaHCO₃)** = reacts with H₂SO₄ to produce massive volumes of CO₂ gas. • **Smothering mechanism** — CO₂ cloud displaces oxygen around fire, extinguishing flames rapidly. • 💡 Wrong-option analysis: Calcium Bicarbonate: unstable in solution, decomposes spontaneously; Potassium Carbonate: reacts too violently with acid; Sodium Carbonate: produces less CO₂ per unit mass than bicarbonate.
What is the common name of the salt Calcium Oxychloride?
Correct Answer: D. Bleaching Powder
• **Bleaching Powder (CaOCl₂)** = formed by passing chlorine gas over slaked lime (Ca(OH)₂). • **Disinfectant action** — releases hypochlorous acid, a powerful oxidizing agent that kills bacteria and viruses. • 💡 Wrong-option analysis: Plaster of Paris: gypsum product used for bone casts; Baking Powder: leavening agent with no bleaching properties; Washing Soda: Na₂CO₃, used for softening water.
Which salt is used in the manufacture of fireworks to produce a green color?
Correct Answer: B. Barium Salt
• **Barium salts (Ba²⁺)** = emit bright green light when heated due to electron transitions. • **Color emission** — specific wavelength (~520 nm) corresponds to green visible to human eye. • 💡 Wrong-option analysis: Strontium Salt: produces red light in fireworks; Copper Salt: produces blue color; Sodium Salt: produces yellow-orange flames.
Which of the following is a 'Double Salt'?
Correct Answer: A. Potash Alum
• **Potash Alum (KAl(SO₄)₂·12H₂O)** = double salt containing K⁺ and Al³⁺ cations in fixed molar ratio. • **Crystal structure** — crystallizes as single compound but dissociates into component ions in solution. • 💡 Wrong-option analysis: Sodium Chloride: simple binary salt with one cation-anion pair; Calcium Sulfate: also binary salt; Potassium Nitrate: simple salt without dual cations.