Chromel is an alloy composed of nickel, iron, and chromium. A 0.6429-g sample wa

Question

Chromel is an alloy composed of nickel, iron, and chromium. A 0.6429-g sample was dissolved and diluted to 250.0 mL. When a 50.00-mL aliquot of 0.05173 M EDTA was mixed with an equal volume of the diluted sample, all three ions were chelated, and a 5.35-mL back-titration with 0.06139 M copper(II) was required. The chromium in a second 50.0-mL aliquot was masked through the addition of hexamethylenetetramine; titration of the Fe and and Ni required 36.11 mL of 0.05173 M EDTA. Iron and chromium were masked with pyrophosphate in a third 50.0-mL aliquot, and the nickel was titrated with 26.83 mL of the EDTA solution. Calculate the percentages of nickel, chromium, and iron in the alloy.

Percentage of nickel = %

Percentage of iron = %

Percentage of chromium = %

Explanation / Answer

NT EDTA=50e-3*0.05173=2.5865e-3

Nedta back=5.35e-3*0.06139=3.284e-4

n(Fe+Ni+Cr)=2.5865e-3-3.284-4=0.002258

n(Fe+Ni)=36.1e-3*0.05173=0.001867

n(Ni)=26.86e-3*0.05173=0.001389

Replacing

nFe=4.8e-4

nCr=3.9e-4

Dilution factor 5

Multiply (5) and MW

mNi=58.69*1.388e-3*5=0.407309 g

mFe=55.845*4.8e-4*5=0.134028 g

mCr=51.99*3.9e-4*5=0.101381 g

Divide mT

%Ni=63.37

%Fe=20.85

%Cr=15.77

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