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3.39 Cinnamic alcohol is used mainly in perfumery, particularly in soaps and cosmetics. Its molecular formula is CH100. (a) Calculate the percent composition by mass of c, h, and o in cinnamic alcohol. (b) How many molecules of cinnamic alcohol are contained in a sample of mass 0.469 g?
Accepted Answer
Here's how to calculate the percent composition and the number of molecules in cinnamic alcohol:
(a) Percent Composition by Mass
1. Find the molar mass:
C: 12.01 g/mol
9 = 108.09 g/mol
H: 1.01 g/mol
10 = 10.10 g/mol
O: 16.00 g/mol
1 = 16.00 g/mol
Total Molar Mass = 108.09 + 10.10 + 16.00 = 134.19 g/mol
2. Calculate the percent composition for each element:
% C = (108.09 g/mol / 134.19 g/mol)
100% = 80.56%
% H = (10.10 g/mol / 134.19 g/mol)
100% = 7.55%
% O = (16.00 g/mol / 134.19 g/mol)
100% = 11.91%
(b) Number of Molecules
1. Convert grams to moles:
Moles = mass (g) / molar mass (g/mol)
Moles = 0.469 g / 134.19 g/mol = 0.00350 mol
2. Use Avogadro's number to find the number of molecules:
Number of molecules = moles
Avogadro's number (6.022 x 10^23 molecules/mol)
Number of molecules = 0.00350 mol
6.022 x 10^23 molecules/mol = 2.11 x 10^21 molecules
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