Which of the following represents a chemical change?
A. Melting of ice
B. Dissolving sugar in water
C. Rusting of iron
D. Sublimation of iodine
Answer: Option C
Solution (By JKExamLibrary)
Rusting is a chemical change because iron reacts with atmospheric oxygen and moisture to form hydrated iron(III) oxide. This new compound possesses entirely different chemical properties from the original iron. The process involves the formation of new chemical bonds and cannot be easily reversed by simple physical methods.
Explanation:
Boyle's law states that at constant temperature, the volume of a given mass of gas is inversely proportional to pressure: PV = constant. So P ∝ 1/V. Charles' law relates V and T at constant P. Gay-Lussac's law relates P and T at constant V. Boyle's law is used in syringes and scuba diving. Graph of P vs V is a hyperbola; P vs 1/V is a straight line.
Explanation:
Boiling converts soluble bicarbonates of Ca and Mg to insoluble carbonates: Ca(HCO₃)₂ (heat) → CaCO₃↓ + H₂O + CO₂, which can then be filtered. Permanent hardness (due to sulfates/chlorides) is not removed by boiling; requires washing soda, ion exchange, or calgon. Calcium sulfate addition would increase permanent hardness. Filtration removes solid particles, not dissolved ions.
Explanation:
In both electrolytic and galvanic cells, oxidation occurs at the anode (AN OX). The anode is positive in electrolytic cells, negative in galvanic. Reduction at cathode (RED CAT). Electroplating: object at cathode, dissolution at anode.
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