MIDTERM Ri CHEM 2200 Summer 2014 Version The FDA decided to test a common nutrit

Question

MIDTERM Ri CHEM 2200 Summer 2014 Version The FDA decided to test a common nutritional contaminant in low quality iron salts. Ten tablets of the supplement wet (to sample which was dissolved in dilute nitric acid, A lead. and dried at 105 C. The mass of the final precipitate was determined be 2 Don to of Pb(Noah lin parti per b. Bats Calculate the absolute urpertainty of th tration of PbINO, in the original sampie. ses of each compound have a relative uncertainty Assume all molar ratios are exa and the molar

Explanation / Answer

The question is not visible, i am solving the part which i am able to understand hence please try to understand the solution

Pb + HNO3 = Pb(NO3)2 + NO + H2O

Now, Pb(NO3)2 + H2SO4 ---> PbSO4.7H20

Hence number of moles of PbSO4.7H20 is equal to the mass present pf Pb in the sample

Number of moles of PbSO4.7H2O = 2.446 * 10^(-3)/429 = 5.73 * 10^(-6) moles

Hence moles of Pb present in the sample = 5.73 * 10^(-6) moles

mass of lead present in the sample = 5.73 * 10^(-6) * 207.2 = 1.187 * 10^(-3) gm

Mass percent = 1.187 * 10^(-3)/7.396 - 1.604 * 10^*(-4)

Hence it is present in the conc of 160 ppm

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