Final answer:
When 4.25 grams of copper are plated out in the reaction 3Cu²⁺ + 2Al → 3Cu + 2Al³⁺, 1.20 grams of aluminum would dissolve. This is calculated using stoichiometry and molar masses of copper and aluminum.
Step-by-step explanation:
The student is asked to calculate the mass of aluminum that would dissolve when a certain amount of copper is plated out in a redox reaction. To do this, we must use stoichiometry based on the balanced chemical equation given.
The balanced chemical equation is:
3Cu²⁺ + 2Al → 3Cu + 2Al³⁺
This equation indicates that 2 moles of aluminum will dissolve to form 2 moles of Al3+ for every 3 moles of Cu that is plated out. To find the mass of aluminum that dissolved, we need to use the molar mass of copper and aluminum to convert between grams and moles.
Using the molar mass of copper (63.55 g/mol), we convert the given 4.25 grams of copper to moles:
4.25 g Cu × (1 mol Cu / 63.55 g Cu) = 0.0669 mol Cu
From the balanced equation, we know that the mole ratio of Al to Cu is 2:3. So, we can calculate the moles of Al :
0.0669 mol Cu × (2 mol Al / 3 mol Cu) = 0.0446 mol Al
Finally, using the molar mass of aluminum (26.98 g/mol), we can find the mass of aluminum that dissolved:
0.0446 mol Al × (26.98 g Al / 1 mol Al) =
1.20 grams of Al
Therefore, when 4.25 grams of copper are plated out, 1.20 grams of aluminum would dissolve.