If you pass 10.0mL of a 50.0mL solution of [Co(en)2Cl2]Cl that has been reduced with Zn through a cation exchange column, you will obtain a solution that has three H+ ions for every Co3+ ion that was originally present in the sample. These H+ ions are titrated with 0.10-M NaOH solution. It is found that 20.0mL of NaOH are required. How many moles of complex must have originally been present in the 50.0mL?
If you had 6.67E-4 moles in 10 mL you should have 5x that in 50 mL.
To determine the number of moles of complex that must have originally been present in the 50.0 mL solution, we need to use the concept of stoichiometry.
First, let's consider the reaction that occurs between the complex [Co(en)2Cl2]Cl and Zn:
[Co(en)2Cl2]Cl + Zn -> [Zn(en)2Cl2] + Co2+ + 2Cl-
This reaction converts the Co3+ ions from the complex into Co2+ ions. Since we are interested in the number of moles of complex, we need to find the number of moles of Co3+ ions in the original solution.
Given that 10.0 mL of the solution was passed through the cation exchange column and that the resulting solution has a 3:1 ratio of H+ ions to Co3+ ions, we can conclude that the original 50.0 mL solution contained 3 times as many moles of Co3+ ions as there are moles of H+ ions in the titrated solution.
The number of moles of H+ ions in the titrated solution can be determined from the volume and molarity of the NaOH used. Since 20.0 mL of 0.10 M NaOH are required, the number of moles of H+ ions can be calculated as follows:
moles of H+ ions = volume of NaOH (in liters) × molarity of NaOH
= 0.020 L × 0.10 mol/L
= 0.002 mol
Therefore, the original 50.0 mL solution contained 3 times as many moles of Co3+ ions as there are moles of H+ ions in the titrated solution, which means there are 3 × 0.002 mol = 0.006 mol of Co3+ ions in the original solution.
Since the stoichiometry of the reaction indicates that there is a 1:1 ratio between Co3+ ions and the [Co(en)2Cl2]Cl complex, the number of moles of complex in the original solution is also 0.006 mol.
Therefore, the original 50.0 mL solution contained 0.006 moles of the [Co(en)2Cl2]Cl complex.