Temporary hardness of water is due to the presence of bicarbonates of calcium and magnesium. Boiling precipitates:
A. MgCl₂
B. CaCl₂
C. CaSO₄
D. CaCO₃
Answer: Option D
Solution (By JKSSB Mock Tests)
On boiling, soluble calcium bicarbonate decomposes: Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂. The precipitate is calcium carbonate (limestone/chalk). Magnesium bicarbonate similarly forms MgCO₃ or Mg(OH)₂. This removes Ca²⁺ and Mg²⁺ ions, softening the water. Permanent hardness (CaSO₄, CaCl₂) doesn't precipitate on boiling and needs chemical treatment.
Explanation:
The ion M³⁺ has lost 3 electrons, so the neutral atom M has 10 + 3 = 13 electrons. Thus, the atomic number is 13. The mass number is protons + neutrons = 13 + 14 = 27. The element is Aluminum, and the specific isotope is Aluminum-27.
Explanation:
Baking powder contains sodium bicarbonate (NaHCO₃) and a weak solid acid such as tartaric acid or cream of tartar (potassium hydrogen tartrate). When moistened, they react to produce CO₂, making dough rise. Baking soda alone requires an acidic ingredient (yogurt, lemon). The acid in baking powder ensures reliable leavening. Sodium chloride and calcium carbonate do not serve this purpose.
Explanation:
Sodium and potassium are highly reactive alkali metals that react vigorously with oxygen and moisture in the air, potentially catching fire. To prevent accidental fires, they are stored immersed in kerosene oil. Magnesium and calcium do not require such extreme storage conditions.
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