"Determine the volume of a 0.925M K2Cr2O7 solution required to completely react with 5.28g of Cu."
My attempted method for solving was to convert the 5.28g of Cu to moles, find moles of K2Cr2O7 using the mole to mole ratio, and then use M=mol/L to solve for volume. Here is the chemical equation I came up with...
K2Cr2O7 + 2Cu -> Cu2Cr2O7^- + 2K^+
I'm not really sure what I'm doing wrong, but I think it may have something to do with the equation I came up with above.
Your approach is correct, but the chemical equation you have written is not balanced correctly. Allow me to explain the correct method step by step.
1. Start by balancing the chemical equation:
K2Cr2O7 + 3Cu -> Cu2Cr2O7 + 2K+
In this balanced equation, you can see that for every 1 mole of K2Cr2O7, you need 3 moles of Cu to react completely.
2. Convert the mass of Cu to moles:
The molar mass of Cu is 63.55 g/mol.
Moles of Cu = mass of Cu / molar mass of Cu
= 5.28 g / 63.55 g/mol
= 0.0831 mol Cu
So, you have 0.0831 moles of Cu.
3. Use the mole ratio from the balanced equation to find moles of K2Cr2O7:
From the balanced equation, we see that the mole ratio of Cu to K2Cr2O7 is 3:1.
Moles of K2Cr2O7 = Moles of Cu x (1 mole K2Cr2O7 / 3 moles Cu)
= 0.0831 mol Cu x (1 mol K2Cr2O7 / 3 mol Cu)
= 0.0277 mol K2Cr2O7
So, you would need 0.0277 moles of K2Cr2O7 to completely react with 5.28 g of Cu.
4. Use the molarity formula (M = moles/volume) to find the volume of the 0.925 M K2Cr2O7 solution:
Rearranging the equation, Volume = moles / Molarity
Volume = 0.0277 mol / 0.925 mol/L
= 0.03 L or 30 mL
Therefore, you would need 30 mL of the 0.925 M K2Cr2O7 solution to completely react with 5.28 g of Cu.