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# Molecular Weights and Percent of Element by Mass

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1. Calculate the molecular weight of the following compounds:

Al2(SO4)3 ____________________ SbBr5 ____________________

Fe(NO3)3 ____________________ C9H11NO2 ____________________

2. Calculate the number of moles in 25 grams of each of the following compounds:

C9H11NO2 ____________________

Al2(SO4)3 ____________________

3. Calculate the number of grams of each in 1.25 mol of the following compounds:

Fe(NO3)3 ____________________

SbBr5 ____________________

4. Calculate the percent of each element present in the following compounds:

C9H11NO2 C = __________ H = __________ N = __________ O = __________

Fe(NO3)3 Fe = __________ N = __________ O = __________

5. Determine the empirical formula for the following compounds whose % compositions are given below:

49.41% C, 4.56% H, 32.87% Br, 13.16% O ____________________

36.76% Fe, 21.11% S, 42.13% O ____________________

https://brainmass.com/chemistry/stoichiometry/molecular-weights-and-percent-of-element-by-mass-15-problems-218074

#### Solution Preview

1. Calculate the molecular weight of the following compounds:
Al2(SO4)3 = 27*2 + (32 + 16*4)*3 = 342
SbBr5 = 121.8 + 80*5 = 521.8
Fe(NO3)3 = 56 + (14 + 16*3)*3 = 242
C9H11NO2 = 12*9 + 11 + 14 + 16*2 = 165

2. Calculate the number of moles in 25 grams of each of the ...

#### Solution Summary

Molecular weights and percent of elements by mass is determined.

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