In: Chemistry
2Cu2+ + 4KI → 2CuI + I2 + 4K+ (rxn 1)
I2 + 2Na2S2O3 → 2NaI +
Na2S4O6 (rxn 2)
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 14.45 mL of Na2S2O3 had been added. What is the molar concentration of Cu2+ in the unknown solution?
2Cu2+ + 4KI → 2CuI + I2 + 4K+ (rxn 1)
I2 + 2Na2S2O3 → 2NaI +
Na2S4O6 (rxn 2)
Calculating moles of thiosulphate =molarity *volume
= 0.20 mol per L*0.01445 L per mole
=0.00289moles
Calculating moles of I2=0.00289 mole of Na2S2O3*1mole I2/2 mole Na2S2O3
=0.001445 mole of I2
Calculating moles of Cu^2+=0.001445 mole of I2*2 mole of Cu^2+/1 mole of I2
=0.00289 mole of Cu2+
Molarity of the Cu2+=Moles/Volume in L
=0.00289 mole/0.010 L
=0.289 Molar