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Chapter 3: Problem 23

Calculate the molecular mass or formula mass (in amu) of each of the following substances: (a) \(\mathrm{CH}_{4}\) (b) \(\mathrm{NO}_{2},(\mathrm{c}) \mathrm{SO}_{3},\) (d) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (e) NaI, (f) \(\mathrm{K}_{2} \mathrm{SO}_{4}\) \((\mathrm{g}) \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}\)

Short Answer

Expert verified
Here are the molecular or formula masses for each compound: (a) \(CH_{4}\): 16.05 amu; (b) \(NO_{2}\): 46.01 amu; (c) \(SO_{3}\): 80.07 amu; (d) \(C_{6}H_{6}\): 78.12 amu; (e) NaI: 149.9 amu; (f) \(K_{2}SO_{4}\): 174.27 amu; (g) \(Ca_{3}(PO_{4})_{2}\): 310.20 amu.

Step by step solution

01

Determine the atomic masses

This step involves determining the atomic masses of each of the atoms involved in your molecule or compound. You can find these values on the periodic table. For instance, the atomic masses for Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O), Sulfur (S), Sodium (Na), Potassium (K), Iodine (I), Calcium (Ca), Phosphorus (P) are approximately: 12.01 amu, 1.01 amu, 14.01 amu, 16.00 amu, 32.07 amu, 22.99 amu, 39.10 amu, 126.9 amu, 40.08 amu, and 30.97 amu, respectively.
02

Calculate the individual atomic masses

In the molecule or compound, multiply the atomic mass of each atom by the number of atoms of that type in the molecule or compound. For example, the molecular mass of \(CH_{4}\) is (1 * 12.01 amu [for Carbon]) + (4 * 1.01 amu [for Hydrogen]) = 16.05 amu
03

Calculate the molecular mass for the remaining substances

Repeat this calculation for each of the remaining substances: (b) \(NO_{2}\), (c) \(SO_{3}\), (d) \(C_{6}H_{6}\), (e) NaI, (f) \(K_{2}SO_{4}\), (g) \(Ca_{3}(PO_{4})_{2}\). The sum of the atomic masses for each molecule or compound gives the molecular or formula mass for that substance.

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Most popular questions from this chapter

Carbon dioxide \(\left(\mathrm{CO}_{2}\right)\) is the gas that is mainly responsible for global warming (the greenhouse effect). The burning of fossil fuels is a major cause of the increased concentration of \(\mathrm{CO}_{2}\) in the atmosphere. Carbon dioxide is also the end product of metabolism (see Example 3.13). Using glucose as an example of food, calculate the annual human production of \(\mathrm{CO}_{2}\) in grams, assuming that each person consumes \(5.0 \times 10^{2} \mathrm{~g}\) of glucose per day. The world's population is 6.5 billion, and there are 365 days in a year.

Describe how the knowledge of the percent composition by mass of an unknown compound can help us identify the compound.

Heating \(2.40 \mathrm{~g}\) of the oxide of metal \(\mathrm{X}\) (molar mass of \(X=55.9 \mathrm{~g} / \mathrm{mol}\) ) in carbon monoxide \((\mathrm{CO})\) yields the pure metal and carbon dioxide. The mass of the metal product is \(1.68 \mathrm{~g}\). From the data given, show that the simplest formula of the oxide is \(\mathrm{X}_{2} \mathrm{O}_{3}\) and write a balanced equation for the reaction.

A compound X contains 63.3 percent manganese (Mn) and 36.7 percent O by mass. When \(X\) is heated, oxygen gas is evolved and a new compound \(\mathrm{Y}\) containing 72.0 percent \(\mathrm{Mn}\) and 28.0 percent \(\mathrm{O}\) is formed. (a) Determine the empirical formulas of \(X\) and Y. (b) Write a balanced equation for the conversion of \(X\) to \(Y\).

What is the mass (in amu) of a carbon-12 atom? Why is the atomic mass of carbon listed as 12.01 amu in the table on the inside front cover of this book?
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