Which of the following is used for softening hard water?
A. Plaster of Paris
B. Bleaching powder
C. Baking soda
D. Washing soda
Answer: Option D
Solution (By JKSSB Mock Tests)
Washing soda (sodium carbonate, Na₂CO₃) is used to remove permanent hardness of water. It reacts with soluble calcium and magnesium chlorides/sulfates to form insoluble carbonates, which can be filtered out. Baking soda, bleaching powder, and plaster of Paris do not have this water-softening capability.
Explanation:
Calgon is the trade name for sodium hexametaphosphate (Na6P6O18). It is used to soften hard water because the hexametaphosphate ion binds (chelates) with calcium and magnesium ions in the water, forming a soluble complex. This prevents the metal ions from interfering with soap lathering.
Explanation:
Salt is soluble in water, sand is not. Add water, stir to dissolve salt, filter to separate sand. Then evaporate the filtrate to recover salt. Sublimation separates sublimable solids (NH₄Cl, naphthalene). Magnetic for magnetic materials. Fractional distillation for liquid mixtures. This is a standard separation technique.
Explanation:
Bakelite is a thermosetting plastic, heat resistant and electrical insulator. Polythene and PVC are thermoplastics; they soften on heating. Teflon is non-stick.
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