Which of the following is a method to remove permanent hardness of water?
A. Boiling
B. Adding washing soda
C. Filtration
D. Cooling
Answer: Option B
Solution (By JKExamLibrary)
Permanent hardness (due to CaSO₄ etc.) can be removed by adding Na₂CO₃, which precipitates CaCO₃. Boiling only removes temporary hardness. Ion exchange and calgon also work.
Explanation:
Highly reactive metals like sodium, potassium, calcium, and aluminum cannot be reduced by chemical reducing agents like carbon. They are extracted by the electrolysis of their molten chlorides or oxides. For example, sodium is extracted by the electrolysis of molten NaCl in the Down's cell.
Explanation:
The salt bridge (often KCl-agar) allows ion migration to maintain electrical neutrality in half-cells, completing the circuit. It prevents direct mixing of electrolytes.
Explanation:
Evaporation of water is a physical change—liquid water changes to water vapor, but the chemical composition (H₂O) remains unchanged. Souring of milk and curd formation involve lactic acid bacteria converting lactose to lactic acid (chemical change). Fermentation of grapes involves yeast converting sugars to ethanol and CO₂. Chemical changes produce new substances. Physical changes only alter the state or form.
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