Stainless steel is an alloy composed of between 11 and 30% chromium by mass. It

Question

Stainless steel is an alloy composed of between 11 and 30% chromium by mass. It may also contain other elements, such as nickel or manganese. The alloy is rust resistant. A stainless steel alloy is to be analyzed for its chromium content. A 6.80 g sample of the steel is used to produce 250.0 mL of a solution containing Cr2O72. A 10.0-mL portion of this solution is added to BaCl2(aq). When the pH of the solution is properly adjusted, 0.145 g BaCrO4(s) precipitates.

Part A

What is the percent Cr, by mass, in the steel sample?

Explanation / Answer

Moles of BaCrO4 = mass/molecular weight

= (0.145g) / ( 253.37 g/mol)

= 0.0005723 mol

Moles of Cr = Moles of BaCrO4 = 0.0005723 mol

Mass of Cr = Moles x molecular weight

= 0.0005723 mol x 51.9961 g/mol

= 0.02976 g

Mass of Cr in sample = 0.02976 g x (250 mL / 10 mL)

= 0.7439 g

Mass% of Cr = 0.7439 x 100 / 6.80

= 10.94 %

= 11%

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