Final answer:
To determine the moles of ClO2-(aq) needed to react with a KMnO4 solution, one must know the stoichiometry from the balanced chemical equation. Without this information, an exact calculation cannot be made.
Step-by-step explanation:
To determine how many moles of ClO2-(aq) are needed to react completely with a 20 mL of 0.20 M KMnO4 solution, you must first convert the volume of KMnO4 solution to liters since concentration is given in moles per liter (mol/L). Since 20 mL is equivalent to 0.020 liters, you can use the molarity to find the number of moles of KMnO4 present.
Number of moles of KMnO4 = Molarity × Volume in liters = 0.20 mol/L × 0.020 L = 0.004 moles KMnO4.
Referring to the balanced chemical equation that was mentioned (but not provided in the question), you can determine the stoichiometric relationship between KMnO4 and ClO2-. For example, if the balanced equation indicates that 1 mole of KMnO4 reacts with 5 moles of ClO2-, then you would need:
Number of moles of ClO2- needed = Stoichiometric ratio × Number of moles of KMnO4 = 5 moles ClO2-/mol KMnO4 × 0.004 moles KMnO4 = 0.020 moles ClO2-.
However, without the specifics of the balanced equation, we cannot calculate the exact number of moles of ClO2- needed.