Chapter 10

The circle graph at the right gives the percent composition for a blue solid. What is the empirical formula for this solid?

Determine the empirical formula for a compound that contains 35.98% aluminum and 64.02% sulfur.

Propane is a hydrocarbon, a compound composed only of carbon and hydrogen. It is 81.82% carbon and 18.18% hydrogen. What is the empirical formula?

Challenge Aspirin is the world’s most-often used medication. The chemical analysis of aspirin indicates that the molecule is 60.00% carbon, 4.44% hydrogen, and 35.56% oxygen. Determine the empirical formula for aspirin.

A compound was found to contain 49.98 g of carbon and 10.47 g of hydrogen. The molar mass of the compound is 58.12 g/mol. Determine the molecular formula.

A colorless liquid composed of 46.68% nitrogen and 53.32% oxygen has a molar mass of 60.01 g/mol. What is the molecular formula?

When an oxide of potassium is decomposed, 19.55 g of K and 4.00 g of O are obtained. What is the empirical formula for the compound?

Assess A classmate tells you that experimental data shows a compound’s molecular formula to be 2.5 times its empirical formula. Is he correct? Explain.

Calculate Analysis of a compound composed of iron and oxygen yields 174.86 g of Fe and 75.14 g of O. What is the empirical formula for this compound?

Calculate An oxide of aluminum contains 0.545 g of Al and 0.485 g of O. Find the empirical formula for the oxide.

Explain how percent composition data for a compound are related to the masses of the elements in the compound.

Explain how you can find the mole ratio in a chemical compound.

Apply The molar mass of a compound is twice that of its empirical formula. How are the compound’s molecular and empirical formulas related?

Analyze Hematite (Fe \(\mathrm{O}_{3}\) ) and magnetite \(\left(\mathrm{Fe}_{3} \mathrm{O}_{4}\right)\) are two ores used as sources of iron. Which ore provides the greater percent of iron per kilogram?

Challenge An 11.75-g sample of a common hydrate of cobalt(II) chloride is heated. After heating, 0.0712 mol of anhydrous cobalt chloride remains. What is the formula and the name of this hydrate?

Name the compound that has the formula \(\operatorname{Sr} \mathrm{Cl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}\)

Describe the experimental procedure for determining the formula of a hydrate. Explain the reason for each step.

Apply A hydrate contains 0.050 mol of \(\mathrm{H}_{2} \mathrm{O}\) to every 0.00998 mol of ionic compound. Write a generalized formula of the hydrate.

Arrange these hydrates in order of increasing percent water content: \(\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}, \mathrm{Ba}(\mathrm{OH})_{2} \cdot 8 \mathrm{H}_{2} \mathrm{O},\) and \(\mathrm{CoCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) .

What is the numerical value of Avogadro’s number?

How many atoms of potassium does 1 mol of potassium contain?

Compare a mole of Ag-108 and a mole of Pt-195 using atoms, protons, electrons, and neutrons.

Why is the mole an important unit to chemists?

Currency Examine the information in Table 10.2 and explain how rolls used to count pennies and dimes are similar to moles.

Explain how Avogadro’s number is used as a conversion factor.

Determine the number of representative particles in each substance a. 0.250 mol of silver b. \(8.56 \times 10^{-3}\) mol of sodium chloride c. 35.3 mol of carbon dioxide d. 0.425 mol of nitrogen \(\left(\mathrm{N}_{2}\right)\)

Determine the number of representative particles in each substance. a. 4.45 \(\mathrm{mol}\) of \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\) b. 0.250 \(\mathrm{mol}\) of \(\mathrm{KNO}_{3}\) c. 2.24 \(\mathrm{mol}\) of \(\mathrm{H}_{2}\) d. 9.56 \(\mathrm{mol}\) of \(\mathrm{Zn}\)

How many molecules are contained in each compound? a. 1.35 mol of carbon disulfide (CS_{2} ) b. 0.254 mol of diarsenic trioxide \(\left(\mathrm{As}_{2} \mathrm{O}_{3}\right)\) c. 1.25 mol of water d. 150.0 mol of \(\mathrm{HCl}\)

Determine the number of moles in each substance. a. \(3.25 \times 10^{20}\) atoms of lead b. \(4.96 \times 10^{24}\) molecules of glucose c. \(1.56 \times 10^{23}\) formula units of sodium hydroxide d. \(1.25 \times 10^{25}\) copper (II) ions

Perform the following conversions. a. \(1.51 \times 10^{15}\) atoms of Si to mol of Si b. \(4.25 \times 10^{-2}\) mol of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) to molecules of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) c. \(8.95 \times 10^{25}\) molecules of \(\mathrm{CCl}_{4}\) to mol of \(\mathrm{CCl}_{4}\) d. 5.90 \(\mathrm{mol}\) of Ca to atoms of Ca

How many moles contain the given quantity? a. \(1.25 \times 10^{15}\) molecules of carbon dioxide b. \(3.59 \times 10^{21}\) formula units of sodium nitrate c. \(2.89 \times 10^{27}\) formula units of calcium carbonate

RDA of Selenium The recommended daily allowance \((\mathrm{RDA})\) of selenium in your diet is \(8.87 \times 10^{-4} \mathrm{mol}\) . How many atoms of selenium is this?

Jewelry A bracelet containing 0.200 mol metal atoms is 75% gold. How many particles of gold atoms are in the bracelet?

If you could count two atoms every second, how long would it take you to count a mole of atoms? Assume that you counted continually for 24 hours every day. How does the time you calculated compare with the age of Earth, which is estimated to be \(4.5 \times 10^{9}\) years old?

Chlorophyll The green color of leaves is due to the presence of chlorophyll, \(\mathrm{C}_{55} \mathrm{H}_{72} \mathrm{O}_{5} \mathrm{N}_{4} \mathrm{Mg}\) . A fresh leaf was found to have \(1.5 \times 10^{-5} \mathrm{mol}\) of chlorophyll per \(\mathrm{cm}^{2} .\) How many chlorophyll molecules are in 1 \(\mathrm{cm}^{2} ?\)

Explain the difference between atomic mass (amu) and molar mass (g).

Which contains more atoms, a mole of silver atoms or a mole of gold atoms? Explain your answer

Which has more mass, a mole of potassium or a mole of sodium? Explain your answer.

Explain how you would convert from number of atoms of a specific element to its mass.

Discuss the relationships that exist between the mole, molar mass, and Avogadro’s number.

Calculate the mass of each element. a. 5.22 mol of He b. 0.0455 mol of Ni c. 2.22 mol of Ti d. 0.00566 mol of Ge

Perform the following conversions. a. 3.50 mol of Li to g of Li b. 7.65 g of Co to mol of Co c. 5.62 g of Kr to mol of Kr d. 0.0550 mol of As to g of As

Determine the mass in grams of each element. a. \(1.33 \times 10^{22} \mathrm{mol}\) of \(\mathrm{Sb}\) b. \(4.75 \times 10^{14} \mathrm{mol}\) of \(\mathrm{Pt}\) c. \(1.22 \times 10^{23} \mathrm{mol}\) of Ag d. \(9.85 \times 10^{24} \mathrm{mol}\) of Cr

Calculate the number of atoms in each element. a. 25.8 g of Hg b. 0.0340 g of Zn c. 150 g of Ar d. 0.124 g of Mg

Arrange from least to most in moles: \(3.00 \times 10^{24}\) atoms Ne, 4.25 mole \(\mathrm{Ar}, 2.69 \times 10^{24}\) atoms \(\mathrm{Xe}, 65.96 \mathrm{g} \mathrm{Kr}\) .

Balance Precision A sensitive electronic balance can detect masses of \(1 \times 10^{-8}\) g. How many atoms of silver would be in a sample having this mass?

A sample of a compound contains 3.86 g of sulfur and 4.08 g of vanadium. How many atoms of sulfur and vanadium does the compound contain?

Which has more atoms, 10.0 g of C or 10.0 g of Ca? How many atoms does each have?

Which has more atoms, 10.0 mol of C or 10.0 mol of Ca? How many atoms does each have?

A mixture contains 0.250 mol of Fe and 1.20 g of C. What is the total number of atoms in the mixture?