Find the concentration of tin(II) chloride

Question

Problem

What is the concentration of a tin(ll) chloride solution prepared from a sample of tin ore?

Experimental Design

The potassium dichromate solution is first standardized by titration with a sample of an acidified mol/L solution of the primary standard, iron(II) ammonium sulfate-6-water. The concentration of Cr₂O₇^2-_(aq) was found to be 0.0080 mol/L. The standardized dichromate solution is then titrated against a 10.00 mL sample of the acidified tin(II) chloride solution. 

Evidence 

	TITRATION OF TIN (II) SOLUTION	(volume of K2Cr2O7(aq) required to react with 10.00 ml of Sn2+(aq))
Trial	1	2	3	4
Final buret reading(ml)	11.8	22.9	33.9	45.0
Initial buret reading (ml)	0.3	11.8	22.9	33.9

 Find the concentration of the Sn²⁺_(aq) in mol/L: (give your answer to 4 decimal places)

Answer 1

The balance equation for the redox equation would be:

3Sn²⁺ + Cr₂O₇^2- + 14H⁺ ==> 3Sn⁴⁺ + 2Cr³⁺ + 7H₂O

Using the data for Trial 1:

volume Cr₂O₇^2- = 11.8 ml - 0.3 ml = 11.5 mls

moles Cr₂O₇^2- used = 11.5 ml x 1 L/1000 mls x 0.008 mols/L = 9.2x10^-5 mols

moles Sn²⁺ present = 9.2x10^-5 mols Cr₂O₇^2- x 3 mols Sn²⁺ / mol Cr₂O₇^2- = 2.76x10^-4 mols Sn²⁺ in 10.00 ml

Concentration of Sn²⁺ = 2.76x10^-4 mols / 0.0100 L = 0.02760 M

Repeat the above calculations for trials 2, 3 and 4, and then take the average of all four values to get your final answer.