Which of the following statements is wrong? a)An acidified solution of...
Statement b) In acidic solution, dichromate ions are converted to chromate ions
In acidic solution, dichromate ions (Cr2O7^2-) do not get converted to chromate ions (CrO4^2-). This statement is wrong.
Explanation:
1. Acidified solution of K2Cr2O7 liberates iodine from iodides:
- Potassium dichromate (K2Cr2O7) is a strong oxidizing agent. When it is added to an acidified solution containing iodide ions (I^-), it oxidizes iodide ions to iodine (I2).
- The reaction can be represented as: K2Cr2O7 + 6H+ + 6I^- → Cr^3+ + 3I2 + 2K+ + 3H2O
- The liberated iodine can be detected by its characteristic purple color.
2. Ammonium dichromate on heating undergoes exothermic decomposition to give Cr2O3:
- Ammonium dichromate (NH4)2Cr2O7 is a complex compound that decomposes when heated. The decomposition reaction is highly exothermic, releasing heat and producing solid chromium(III) oxide (Cr2O3), nitrogen gas (N2), and water vapor (H2O).
- The reaction can be represented as: (NH4)2Cr2O7 → Cr2O3 + N2 + 4H2O
- This reaction is commonly known as the "volcano" or "ammonium dichromate" reaction due to the visual effect it produces, resembling a volcanic eruption.
3. Potassium dichromate is used as a titrant for Fe2+ ions:
- Potassium dichromate (K2Cr2O7) is commonly used as a primary standard in redox titrations.
- It is used as a titrant (a solution of known concentration) to determine the concentration of a reducing agent, such as Fe2+ ions (ferrous ions).
- In the titration, the orange-colored dichromate ions (Cr2O7^2-) are reduced to green-colored chromium(III) ions (Cr^3+), while the Fe2+ ions are oxidized to Fe3+ ions.
- The end point of the titration is usually indicated by a color change from orange to green, which signifies the complete reaction between the dichromate ions and the Fe2+ ions.
In summary, the correct statement is that potassium dichromate is used as a titrant for Fe2+ ions. The other statements are also true, except for statement b) which is wrong.