10.0 mL of a Cu2+ solution of unknown concentration was placed in a 250 mL Erlenmeyer flask. An excess of KI solution was added. Indicator was added and the solution was diluted with H2O to a total volume of 75 mL. The solution was titrated with 0.20 M Na2S2O3. The equivalence point of the titration was reached when 16.20 mL of Na2S2O3 had been added. What is the molar concentration of Cu2+ in the unknown solution?
2Cu^2+ + 4I^- ==> 2CuI + I2
Then I2 + 2S2O3^2- ==> S4O6^2- + 2I^-
mols S2O3^2- = M x L = ?
Mols I2 = 1/2 that from the equation that 2 mol S2O3^2- = 1 mol I2.
mols Cu = 2x mols I2 from the first equation = ?
Then M Cu^2+ solution is mols Cu/volume = mols Cu/0.010 L
175754
28190
To find the molar concentration of Cu2+ in the unknown solution, we can use the concept of stoichiometry and titration.
First, let's understand the reaction that is happening during the titration:
The reaction between Cu2+ and KI can be represented by the equation:
Cu2+ + 2I- -> CuI2
The reaction between Na2S2O3 and CuI2 can be represented by the equation:
2Na2S2O3 + CuI2 -> Na2I2 + CuS2O3 + Na2S4O6
Based on these reactions, we can see that each mole of Cu2+ reacts with two moles of Na2S2O3.
Given the volume of Na2S2O3 used (16.20 mL) and its molar concentration (0.20 M), we can calculate the number of moles of Na2S2O3:
moles of Na2S2O3 = volume (L) x molar concentration (mol/L)
= 0.01620 L x 0.20 mol/L
= 0.00324 mol
Since each mole of Cu2+ reacts with two moles of Na2S2O3, the number of moles of Cu2+ can be determined as:
moles of Cu2+ = moles of Na2S2O3 / 2
= 0.00324 mol / 2
= 0.00162 mol
Now, let's calculate the molar concentration of Cu2+ in the unknown solution:
molar concentration of Cu2+ = moles of Cu2+ / volume of solution (L)
= 0.00162 mol / (75 mL / 1000 mL/L)
= 0.0216 M
Therefore, the molar concentration of Cu2+ in the unknown solution is 0.0216 M.