concentration of the potassium dichromate solution

Question

25.0 mL of an acidic 0.100 mol/L tin (II) chloride solution required an average volume of 12.7 mL of potassium dichromate solution for complete reaction. What is the concentration of the potassium dichromate solution?

Answer 1

3SnCl₂ + K₂Cr₂O₇ + 14HCl → 3SnCl₄ + 2CrCl₃ + 2KCl + 7H₂O ... balanced equation

moles SnCl₂ present = 25.0 ml x 1 L / 1000 ml x 0.100 mol/L = 0.0025 mols SnCl₂

mols K₂Cr₂O₇ required = 0.0025 mol SnCl₂ x 1 mol K₂Cr₂O₇/3 mol SnCl₂ = 0.000833mols K₂Cr₂O₇ needed

[K₂Cr₂O₇] = 0.000833 mols / 12.7 mls x 1000 mls / L = 0.0656 mols / L = 0.0656 M