Acidified potassium manganate(VII) reacts with iron(II) ethanedioate, \(\mathrm{FeC_2O_4}\).
The reactions taking place are shown.
\(\mathrm{MnO_4^-+8H^++5e^-\rightarrow Mn^{2+}+4H_2O}\)
\(\mathrm{Fe^{2+}\rightarrow Fe^{3+}+e^-}\)
\(\mathrm{C_2O_4^{2-}\rightarrow2CO_2+2e^-}\)
How many moles of iron(II) ethanedioate react with one mole of potassium manganate(VII)?
Correct Answer: \( \boxed{\mathrm{B}} \)
One mole of \(\mathrm{MnO_4^-}\) gains 5 electrons.
Each mole of \(\mathrm{FeC_2O_4}\) produces:
Therefore, one mole of \(\mathrm{FeC_2O_4}\) releases:
\(\mathrm{1+2=3}\) electrons.
Moles of \(\mathrm{FeC_2O_4}\) required:
\(\mathrm{\dfrac{5}{3}=1.67\,mol}\)
Therefore, the correct answer is (B).
One commercially available heat pad contains iron, activated carbon and water. The heat pad is activated by air. This causes the pad to get hotter.
Which statement describes the chemical reaction occurring in the heat pad when it is exposed to air?
Correct Answer: \( \boxed{\mathrm{D}} \)
The heat pad works by the oxidation of iron when exposed to oxygen in air.
Oxidation is the loss of electrons, so iron loses electrons as it forms iron ions.
The oxidation of iron releases heat, making the process exothermic.
Therefore, the correct answer is (D).
In which substance is the average oxidation number of sulfur the highest?
Correct Answer: \( \boxed{\mathrm{D}} \)
Calculate the average oxidation number of sulfur in each compound:
The highest average oxidation number is \(+6\) in \(\mathrm{SO_2Cl_2}\).
Therefore, the correct answer is (D).
