3. The complexometric (EDTA) analysis of iron in two ore samples was performed.

Question

3. The complexometric (EDTA) analysis of iron in two ore samples was performed. The ore samples were crushed and digested in 25 mL nitric acid/hydrogen peroxide using microwave heating. Separate 5 mL aliquots of the extractate were transferred to 25 mL volumetric flasks, buffered to pH 5, and Variamine blue b base (VB) indicator was added before the flasks were filled to the line and mixed well. The replicate trials produced from the aliquots are reported below after titration to the VB endpoint with 0.009732 M EDTA (previously standardized using primary standard calcium carbonate): Sample 1 - 0.1490 g ore, Trial 1 required 27.51 mL of EDTA Sample 1 - 0.1490 g ore, Trial 2 required 27.38 mL of EDTA Sample 1 - 0.1490 g ore, Trial 3 required 27.62 mL of EDTA Sample 2 - 0.1671 g ore, Trial 1 required 31.47 mL of EDTA Sample 2 - 0.1671 g ore, Trial 2 required 31.14 mL of EDTA Sample 2 - 0.1671 g ore, Trial 3 required 31.07 mL of EDTA Sample 2 - 0.1671 g ore, Trial 4 required 31.10 mL of EDTA A.) Calculate the percent iron in the ore samples. (AW Fe = 55.845)

Explanation / Answer

3. Estimation of Fe in ore

Sample 1

Trial 1 : moles of EDTA used = 0.009732 M x 27.51 ml = 0.27 mmol

Trial 2 : moles of EDTA used = 0.009732 M x 27.38 ml = 0.26 mmol

Trial 3 : moles of EDTA used = 0.009732 M x 27.62 ml = 0.27 mmol

Average moles of EDTA = 0.266 mmol

Fe content in 0.1490 g ore = 0.266 mmol x 25 x 55.845/5 = 0.074 g

percent Fe in ore sample 1 = 0.074 x 100/0.1490 = 49.66%

Sample 2

Trial 1 : moles of EDTA used = 0.009732 M x 31.47 ml = 0.306 mmol

Trial 2 : moles of EDTA used = 0.009732 M x 31.14 ml = 0.303 mmol

Trial 3 : moles of EDTA used = 0.009732 M x 31.07 ml = 0.302 mmol

Average moles of EDTA = 0.303 mmol

Fe content in 0.1671 g ore = 0.303 mmol x 25 x 55.845/5 = 0.085 g

percent Fe in ore sample 1 = 0.085 x 100/0.1671 = 50.87%

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