Final answer:
In the balanced redox reaction of Cr(OH)3 and MnO4− in a basic medium, 5 OH− (hydroxide) ions are introduced to neutralize the H+ ions and balance the equation.
Step-by-step explanation:
The question asks how many hydroxide ions will appear in the balanced equation:
Cr(OH)3 (s) + MnO4−(aq) → CrO42− (aq) + MnO2 (s) in a basic medium.
To balance this redox reaction in a basic solution, we first balance the atoms other than oxygen and hydrogen and then balance the oxygen using water molecules. After that, we balance the hydrogens by adding hydrogen ions (H+). In a basic medium, we add an equal number of hydroxide (OH−) ions to both sides of the equation to neutralize the hydrogen ions.
If we follow the instructions from step 8 of the reference information:
Combine H+ and OH− ions to form H2O on the same side.
Add OH− ions equal to the number of H+ ions to the other side.
Simplify the equation by removing any redundant ions and molecules.
In the provided equation, we will have +5 H+ ions on one side, based on the half-reaction for chromium:
H2O(l) + Cr(OH)3 (s) →→→ CrO42−(aq) +5H+ (aq) + 3e−
Following step 8, we will need to add 5 OH− ions to both sides to neutralize the 5 H+ ions, thus introducing a total of 5 hydroxide ions into the equation.