Answered: a.) The percent composition of an…

Chemistry: The Molecular Science

5th Edition

ISBN:9781285199047

Author:John W. Moore, Conrad L. Stanitski

Publisher:John W. Moore, Conrad L. Stanitski

Chapter2: Chemical Compounds

Section: Chapter Questions

Problem 2.DCP

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Question

a.) The percent composition of an unknown compound is 48.71% C, 30.73% O, 11.96% N, and 8.60% H. What is its empirical formula? Show your work.

b.) We have an oxide of cobalt (the substance contains only Co and O) that is, by mass, 58.93% Co. What is its empirical formula?

Expert Solution

Step 1

According to the mole concept, in terms of mass, the amount of substance in moles is equal to the ratio of its mass to the molar mass.

Step 2

The empirical formula of the unknown compound is calculated as follows:

Element	Mass %	Molar mass	Molar ratio	Simplest molar ratio	Simplest whole number molar ratio
C	48.71	12	$\frac{48.71}{12} = 4.059$	$\frac{4.059}{0.854}$ =4.75	19
O	30.73	16	$\frac{30.73}{16} = 1.920$	$\frac{1.920}{0.854} = 2.25$	9
N	11.96	14	$\frac{11.96}{14} = 0.854$	$\frac{0.854}{0.854} = 1$	4
H	8.60	1	$\frac{8.60}{1} = 8.60$	$\frac{8.60}{0.854} = 10.07$	40

Thus, the empirical formula of the unknown sample is C₁₉H₄₀N₄O₉.

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