CHEM ---> mole calculation

2008-03-02 6:05 am

Lead(Pb)is an element in group 4 of the Periodic Table.

(a)An oxide of lead,X,contains 90.6% of lead by mass.Calculate the empirical
formula of X.

(b)X is known to be a mixed oxide composed of PbO and PbO2.Based
on your answer in (a) ,deduce the mole ratio of PbO to PbO2 in X

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回答 (1)

Audrey Hepburn

2008-03-02 6:19 am

✔ 最佳答案

a. Assume there is 100 gof X.
Mass of lead = 100 X90.6% = 90.6 g
Molar mass of lead =207.0 gmol-1
No. of mole of lead =Mass / molar mass = 90.6 / 207.0 = 0.438 mol
Mass of oxygen = 100 –90.6 = 9.4 g
Molar mass of oxygen= 16.0 gmol-1
No. of mole of oxygen= Mass / molar msas = 9.4 / 16.0 = 0.588 mol
Molar ratio of leadto oxygen in X = 0.438 : 0.588 = 3 : 4
So, the empiricalformula of X is Pb3O4.

b. To be the molar ratioof Pb and O be 3 : 4
So, no. of Pb and Oshould be in the ratio of 3 : 4
Therefore, in onemixture, there should be 2PbO and 1PbO2 for 3Pb and 4O.
So, the mole ratio ofPbO to PbO2 = 2 : 1

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