Question

Which of the following statements is/are incorrect?

• A. Rust is $Fe_2O_3. xH_2O$
• B. Zn - Cu cell is called Daniell cell
• C. Saline water slows down rusting
• D. Pure metals undergo corrosion faster than impure metals

Answer 1

Answer: (C), (D)

C, D

Answer 2

The question asks to identify the incorrect statement(s). Let's evaluate each option:

• A) Rust is $Fe_2O_3. xH_2O$: Rust is indeed hydrated ferric oxide, with the general formula $Fe_2O_3.xH_2O$. This statement is correct.
• B) Zn - Cu cell is called Daniell cell: A Daniell cell is a type of galvanic cell that uses zinc and copper electrodes, with zinc acting as the anode and copper as the cathode. This statement is correct.
• C) Saline water slows down rusting: Rusting is an electrochemical process. The presence of dissolved salts (electrolytes) in water increases its electrical conductivity. This increased conductivity facilitates the flow of ions and electrons, thereby accelerating the rusting process, not slowing it down. This statement is incorrect.
• D) Pure metals undergo corrosion faster than impure metals: Impurities in metals often create localized differences in electrode potentials, leading to the formation of tiny electrochemical cells on the metal surface. These cells accelerate the corrosion process. Pure metals, lacking such significant potential differences, generally corrode slower than impure metals. This statement is incorrect.

Therefore, statements (C) and (D) are incorrect.