January 2011 Chemistry Regents #75-77

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Questions

Base your answers to questions 75 to 77 on the information below.

Litharge, PbO, is an ore that can be roasted (heated) in the presence of carbon monoxide, CO, to produce elemental lead. The reaction that takes place during this roasting processis represented by the balanced equation below.

PbO(s) + CO(g) ==> Pb(ℓ) + CO2(g)

75 Write the balanced equation for the reduction half-reaction that occurs during this roasting process. [1]

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Pb2+ + 2e- ==> Pb

76 Determine the oxidation number of carbon in carbon monoxide. [1]

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+2

C+2 O -2

77 Calculate the percent composition by mass of oxygen in litharge (gram-formula mass = 223.2 grams per mole). Your response must include both a numerical setup and the calculated result. [2]

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SET UP

(16.0/223.2) x 100%

Answer

7.17%

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