Hard water can be softened by adding washing soda because it:
A. Kills bacteria
B. Precipitates calcium and magnesium ions as carbonates
C. Increases pH
D. Removes chlorine
Answer: Option B
Solution (By JKExamLibrary)
Na₂CO₃ reacts with Ca²⁺/Mg²⁺ to form insoluble CaCO₃/MgCO₃, which are removed. This is permanent hardness removal. Boiling works for temporary hardness. Ion exchange is another method.
Explanation:
Calorific value is determined using a bomb calorimeter, where a known mass of fuel is burnt in excess oxygen in a sealed bomb, and the heat released is absorbed by a known mass of water. Temperature rise is measured. Corrections for cooling, wire, and acid formation are applied. Units: kJ/kg or kJ/mol. The bomb calorimeter works at constant volume.
Assertion (A): The first ionization energy of Nitrogen is higher than that of Oxygen. Reason (R): Nitrogen has a half-filled p-orbital which is exceptionally stable.
A.A is false but R is true.
B.Both A and R are true and R is the correct explanation of A.
C.A is true but R is false.
D.Both A and R are true but R is NOT the correct explanation of A.
Explanation:
Nitrogen (1s2 2s2 2p3) has a exactly half-filled p-subshell, which confers extra stability due to symmetry and exchange energy. Oxygen (1s2 2s2 2p4) has one paired electron in the p-orbital, leading to electron-electron repulsion, making it easier to remove. Thus, N has a higher IE than O. Both are true and R explains A.
Explanation:
Froth flotation separates sulfide ores from gangue based on their wetting properties. Sometimes, an ore contains multiple sulfides. A depressant (like NaCN) is added to selectively prevent one mineral (e.g., FeS2) from attaching to the froth, allowing only the desired mineral (e.g., PbS) to be separated.
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