﻿ Chapter Review - Chemical Composition

# Chemical CompositionChapter Review

Key Terms

· atomic mass unit (amu) (8.2)

· average atomic mass (8.2)

· mole (mol) (8.3)

· conceptual problem solving (8.4)

· molar mass (8.5)

· mass percent (8.6)

· empirical formula (8.7)

· molecular formula (8.7)

For Review

· Objects do not need to have identical masses to be counted by weighing. All we need to know is the average mass of the objects.

· To count the atoms in a sample of a given element by weighing, we must know the mass of the sample and the average mass for that element.

· Samples in which the ratio of the masses is the same as the ratio of the masses of the individual atoms always contain the same number of atoms.

· One mole of anything contains units of that substance.

· A sample of an element with a mass equal to that element’s average atomic mass (expressed in grams) contains mole of atoms.

· The molar mass of any compound is the mass in grams of mole of the compound.

· The molar mass of a compound is the sum of the masses of the component atoms.

·

·

· Percent composition consists of the mass percent of each element in a compound:

· The empirical formula of a compound is the simplest whole-number ratio of the atoms present in the compound.

· The empirical formula can be found from the percent composition of the compound.

· The molecular formula is the exact formula of the molecules present in a substance.

· The molecular formula is always a whole-number multiple of the empirical formula.

· The following diagram shows these different ways of expressing the same information.

Active Learning Questions

These questions are designed to be considered by groups of students in class. Often these questions work well for introducing a particular topic in class.

· 1.

In chemistry, what is meant by the term mole? What is the importance of the mole concept?

· 2.

What is the difference between the empirical and molecular formulas of a compound? Can they ever be the same? Explain.

· 3.

A substance is A by mass. Calculate the percent B (by mass) for .

· 4.

Give the formula for calcium phosphate and then answer the following questions:

a. Calculate the percent composition of each of the elements in this compound.

b. If you knew that there was g of phosphorus in your sample, how many grams of calcium phosphate would you have? How many moles of calcium phosphate would this be? How many formula units of calcium phosphate?

· 5.

How would you find the number of “chalk molecules” it takes to write your name on the board? Explain what you would need to do, and provide a sample calculation.

· 6.

A -mol sample of a substance composed of diatomic molecules has a mass of g. Identify this molecule.

· 7.

How many molecules of water are there in a -g sample of water? How many hydrogen atoms are there in this sample?

· 8.

What is the mass (in grams) of one molecule of ammonia?

· 9.

Consider separate -g samples of each of the following: , , , , . Arrange these samples from largest mass of nitrogen to smallest mass of nitrogen and prove/explain your order.

· 10.

A molecule has a mass of g. Provide two possible chemical formulas for such a molecule.

· 11.

Differentiate between the terms atomic mass and molar mass.

· 12.

Consider Figure 4.19 in the text. Why is it that the formulas for ionic compounds are always empirical formulas?

· 13.

Why do we need to count atoms by weighing them?

· 14.

The following claim is made in your text: mole of marbles is enough to cover the entire earth to a depth of miles. Provide mathematical support for this claim. Is it reasonably accurate?

· 15.

Estimate the length of time it would take you to count to Avogadro’s number. Provide mathematical support.

· 16.

Suppose Avogadro’s number was instead of . How, if at all, would this affect the relative masses on the periodic table? How, if at all, would this affect the absolute masses of the elements?

· 17.

Estimate the number of atoms in your body and provide mathematical support. Because it is an estimate, it need not be exact, although you should choose your number wisely.

· 18.

Consider separate equal mass samples of magnesium, zinc, and silver. Rank them from greatest to least number of atoms and support your answer.

· 19.

You have a -g sample of silver metal. You are given g of another metal and told that this sample contains twice the number of atoms as the sample of silver metal. Identify this metal.

· 20.

How would you find the number of “ink molecules” it takes to write your name on a piece of paper with your pen? Explain what you would need to do, and provide a sample calculation.

· 21.

True or false? The atom with the largest subscript in a formula is the atom with the largest percent by mass in the compound.

If true, explain why with an example. If false, explain why and provide a counterexample. In either case, provide mathematical support.

· 22.

Which of the following compounds have the same empirical formulas?

· 23.

The percent by mass of nitrogen is for a species containing only nitrogen and oxygen. Which of the following could be this species?

· 24.

Calculate the molar mass of the following substances.

· 25.

Give the empirical formula for each of the compounds represented below.

Questions and Problems*: 8.1 Counting by Weighing

Questions and Problems with answers below also have full solutions in the Student Solutions Guide.

Problems

directs you to the Chemistry in Focus feature in the chapter

· 1.

Merchants usually sell small nuts, washers, and bolts by weight (like jelly beans!) rather than by individually counting the items. Suppose a particular type of washer weighs g on the average. What would such washers weigh? How many washers would there be in g of washers?

· 2.

The “Chemistry in Focus” segment Plastic That Talks and Listens! discusses polyvinylidene difluoride (PVDF). What is the empirical formula of PVDF? Note: An empirical formula is the simplest whole-number ratio of atoms in a compound. This is discussed more fully in Sections 8.7 and 8.8 of your text.

Questions and Problems*: 8.2 Atomic Masses: Counting Atoms by Weighing

Questions and Problems with answers below also have full solutions in the Student Solutions Guide.

Questions

· 3.

Define the amu. What is one amu equivalent to in grams?

· 4.

What do we mean by the average atomic mass of an element? What is “averaged” to arrive at this number?

Problems

· 5.

Using the average atomic masses for each of the following elements (see the table inside the cover of this book), calculate the mass (in amu) of each of the following samples.

a. carbon atoms

b. million potassium atoms

c. lithium atoms

d. atom of magnesium

e. iodine atoms

· 6.

Using the average atomic masses for each of the following elements (see the table inside the front cover of this book), calculate the number of atoms present in each of the following samples.

a. amu of calcium

b. amu of tungsten

c. amu of manganese

d. amu of iodine

· 7.

What is the average atomic mass (in amu) of iron atoms? What would iron atoms weigh? How many iron atoms are present in a sample of iron that has a mass of amu?

· 8.

The atomic mass of copper is amu. What would be the mass of copper atoms? How many copper atoms are contained in a sample of copper that has a mass of amu?

Questions and Problems*: 8.3 The Mole

Questions and Problems with answers below also have full solutions in the Student Solutions Guide.

Questions

· 9.

There are iron atoms present in g of iron.

· 10.

There are zinc atoms present in g of zinc.

Problems

· 11.

Suppose you have a sample of sodium weighing g. How many atoms of sodium are present in the sample? What mass of potassium would you need to have the same number of potassium atoms as there are sodium atoms in the sample of sodium?

· 12.

Consider a sample of silver weighing g. How many atoms of silver are present in the sample? What mass of copper would you need for the copper sample to contain the same number of atoms as the silver sample?

· 13.

What mass of hydrogen contains the same number of atoms as g of nitrogen?

· 14.

What mass of cobalt contains the same number of atoms as g of fluorine?

· 15.

If an average sodium atom has a mass of g, what is the mass of a magnesium atom in grams?

· 16.

If an average fluorine atom has a mass of g, what is the average mass of a chlorine atom in grams?

· 17.

Which has the smaller mass, mole of He atoms or moles of atoms?

· 18.

Which weighs less, mole of xenon atoms or moles of carbon atoms?

· 19.

Use the average atomic masses given inside the front cover of this book to calculate the number of moles of the element present in each of the following samples.

a. g of neon

b. g of nickel

c. mg of silver

d. of uranium ( is a standard abbreviation meaning “micro”)

e. g of iodine

· 20.

Use the average atomic masses given inside the front cover of this book to calculate the number of moles of the element present in each of the following samples.

a. g of sulfur

c. mg of chlorine

d. g of lithium

e. g of copper

f. mg of strontium

· 21.

Use the average atomic masses given inside the front cover of this book to calculate the mass in grams of each of the following samples.

a. mole of lithium

b. moles of aluminum

d. moles of chromium

e. moles of iron

f. mole of magnesium

· 22.

Use the average atomic masses given inside the front cover of this book to calculate the mass in grams of each of the following samples.

a. mole of calcium

b. mmol of boron

c. moles of aluminum

d. moles of barium

e. moles of phosphorus

f. mole of arsenic

· 23.

Using the average atomic masses given inside the front cover of this book, calculate the number of atoms present in each of the following samples.

a. g of silver,

b. mole of copper,

c. g of copper,

d. kg of magnesium,

e. oz of calcium,

f. g of calcium,

g. moles of calcium,

· 24.

Using the average atomic masses given inside the front cover of this book, calculate the indicated quantities.

a. the mass in grams of iron atoms

b. the mass in amu of iron atoms

c. the number of moles of iron atoms in g of iron

d. the mass in grams of moles of iron

e. the number of iron atoms in g of iron

f. the number of iron atoms in moles of iron

Questions and Problems*: 8.5 Molar Mass

Questions and Problems with answers below also have full solutions in the Student Solutions Guide.

Questions

· 25.

The of a substance is the mass (in grams) of mole of the substance.

· 26.

Describe in your own words how the molar mass of the compound below may be calculated.

Problems

· 27.

Give the name and calculate the molar mass for each of the following substances.

a.

b.

c.

d.

e.

f.

· 28.

Give the name and calculate the molar mass for each of the following substances.

a.

b.

c.

d.

e.

f.

· 29.

Write the formula and calculate the molar mass for each of the following substances.

a. barium chloride

b. aluminum nitrate

c. iron(II) chloride

d. sulfur dioxide

e. calcium acetate

· 30.

Write the formula and calculate the molar mass for each of the following substances.

a. carbon dioxide

b. aluminum phosphate

c. iron(III) carbonate

e. strontium chloride

· 31.

Calculate the number of moles of the indicated substance present in each of the following samples.

a. mg of nitrogen dioxide

b. g of copper(II) nitrate

c. g of carbon disulfide

d. g of aluminum sulfate

f. g of calcium carbonate

· 32.

Calculate the number of moles of the indicated substance present in each of the following samples.

a. g of aluminum oxide

b. kg of potassium bromide

c. mg of germanium

d. of uranium

e. g of sodium acetate

f. g of sulfur trioxide

· 33.

Calculate the number of moles of the indicated substance in each of the following samples.

a. g of

b. mg of

c. kg of

d. g of

e. g of

f. g of

· 34.

Calculate the number of moles of the indicated substance present in each of the following samples.

a. g of lithium carbonate

b. kg of calcium chloride

c. mg of strontium chloride

d. g of calcium sulfate

e. mg of nitrogen(IV) oxide

f. g of mercury(I) chloride

· 35.

Calculate the mass in grams of each of the following samples.

a. moles of aluminum chloride

b. moles of sodium hydrogen carbonate

c. millimoles of hydrogen bromide

d. moles of uranium

e. mole of carbon dioxide

f. moles of iron

· 36.

Calculate the mass in grams of each of the following samples.

a. moles of sulfur trioxide

c. mole of chloroform,

d. moles of trichloroethane,

e. mole of lithium hydroxide

f. moles of copper(I) chloride

· 37.

Calculate the mass in grams of each of the following samples.

a. mole of ethyl alcohol,

b. moles of carbon dioxide

c. moles of gold(III) chloride

d. moles of sodium nitrate

e. mole of iron

· 38.

Calculate the mass in grams of each of the following samples.

a. mole of benzene,

b. moles of calcium hydride

c. moles of hydrogen peroxide,

d. mmol of glucose,

e. moles of tin

f. mole of strontium fluoride

· 39.

Calculate the number of molecules present in each of the following samples.

a. mmol of phosphine,

b. g of phosphine,

e. a sample of benzene, , which contains a total of moles of carbon

· 40.

Calculate the number of molecules present in each of the following samples.

a. moles of sulfur dioxide,

b. g of sulfur dioxide,

c. g of ammonia,

d. moles of ammonia,

e. mg of ethane,

· 41.

Calculate the number of moles of carbon atoms present in each of the following samples.

a. g of ethanol,

b. g of 1,4-dichlorobenzene,

c. g of carbon suboxide,

d. g of methylene chloride,

· 42.

Calculate the number of moles of sulfur atoms present in each of the following samples.

a. g of sodium sulfate

b. g of sodium sulfite

c. g of sodium sulfide

d. g of sodium thiosulfate,

Questions and Problems*: 8.6 Percent Composition of Compounds

Questions and Problems with answers below also have full solutions in the Student Solutions Guide.

Questions

· 43.

The mass fraction of an element present in a compound can be obtained by comparing the mass of the particular element present in mole of the compound to the mass of the compound.

· 44.

If the amount of a sample doubles, what happens to the percent composition of each element in the compound?

Problems

· 45.

Calculate the percent by mass of each element in the following compounds.

a.

b.

c.

d.

e.

f.

· 46.

Calculate the percent by mass of each element in the following compounds.

a.

b.

c.

d.

e.

f.

· 47.

Calculate the percent by mass of the element listed first in the formulas for each of the following compounds.

a. methane,

b. sodium nitrate,

c. carbon monoxide,

d. nitrogen dioxide,

e. 1-octanol,

f. calcium phosphate,

g. 3-phenylphenol,

h. aluminum acetate,

· 48.

Calculate the percent by mass of the element listed first in the formulas for each of the following compounds.

a. copper(II) bromide,

b. copper(I) bromide,

c. iron(II) chloride,

d. iron(III) chloride,

e. cobalt(II) iodide,

f. cobalt(III) iodide,

g. tin(II) oxide,

h. tin(IV) oxide,

· 49.

Calculate the percent by mass of the element listed first in the formulas for each of the following compounds.

b. ammonium nitrate,

c. caffeine,

d. chlorine dioxide,

e. cyclohexanol,

f. dextrose,

g. eicosane,

h. ethanol,

· 50.

What is the mass percent of oxygen in each of the following compounds?

a. carbon dioxide

b. sodium nitrate

c. iron(III) phosphate

d. ammonium carbonate

e. aluminum sulfate

· 51.

For each of the following samples of ionic substances, calculate the number of moles and mass of the positive ions present in each sample.

a. g of ammonium iodide,

b. moles of ammonium sulfide,

c. g of barium phosphide,

d. moles of calcium phosphate,

· 52.

For each of the following ionic substances, calculate the percentage of the overall molar mass of the compound that is represented by the negative ions in the substance.

a. ammonium sulfide

b. calcium chloride

c. barium oxide

d. nickel(II) sulfate

Questions and Problems*: 8.7 Formulas of Compounds

Questions and Problems with answers below also have full solutions in the Student Solutions Guide.

Questions

· 53.

What experimental evidence about a new compound must be known before its formula can be determined?

· 54.

Explain to a friend who has not yet taken a chemistry course what is meant by the empirical formula of a compound.

· 55.

Give the empirical formula that corresponds to each of the following molecular formulas.

a. sodium peroxide,

b. terephthalic acid,

c. phenobarbital,

d. 1,4-dichloro-2-butene,

· 56.

Which of the following pairs of compounds have the same empirical formula?

a. acetylene, , and benzene,

b. ethane, , and butane,

c. nitrogen dioxide, , and dinitrogen tetroxide,

d. diphenyl ether, , and phenol,

Questions and Problems*: 8.8 Calculation of Empirical Formulas

Questions and Problems with answers below also have full solutions in the Student Solutions Guide.

Problems

· 57.

A compound was analyzed and was found to contain the following percentages of the elements by mass: barium, ; oxygen, . Determine the empirical formula of the compound.

· 58.

A compound was analyzed and was found to contain the following percentages of the elements by mass: nitrogen, ; chlorine, . Determine the empirical formula of the compound.

· 59.

A -g sample of a new compound has been analyzed and found to contain the following masses of elements: carbon, g; hydrogen, g; oxygen, g. Calculate the empirical formula of the compound.

· 60.

A compound was analyzed and was found to contain the following percentages of the elements by mass: boron, ; hydrogen, . Determine the empirical formula of the compound.

· 61.

If a -g sample of aluminum metal is heated in a chlorine gas atmosphere, the mass of aluminum chloride produced is g. Calculate the empirical formula of aluminum chloride.

· 62.

A compound was analyzed and was found to contain the following percentages of the elements by mass: tin, ; chlorine, . Determine the empirical formula of the compound.

· 63.

When g of zinc is heated in pure oxygen, the sample gains g of oxygen in forming the oxide. Calculate the empirical formula of zinc oxide.

· 64.

If cobalt metal is mixed with excess sulfur and heated strongly, a sulfide is produced that contains cobalt by mass. Calculate the empirical formula of the sulfide.

· 65.

If g of aluminum metal is heated in an atmosphere of fluorine gas, g of aluminum fluoride results. Determine the empirical formula of aluminum fluoride.

· 66.

If g of aluminum metal is heated in a stream of fluorine gas, it is found that g of fluorine will combine with the aluminum. Determine the empirical formula of the compound that results.

· 67.

A compound used in the nuclear industry has the following composition: uranium, ; fluorine, . Determine the empirical formula of the compound.

· 68.

A compound was analyzed and was found to contain the following percentages of the elements by mass: lithium, ; oxygen, . Determine the empirical formula of the compound.

· 69.

A compound has the following percentage composition by mass: copper, ; nitrogen, ; oxygen, . Determine the empirical formula of the compound.

· 70.

When lithium metal is heated strongly in an atmosphere of pure nitrogen, the product contains and on a mass basis. Determine the empirical formula of the compound.

· 71.

A compound has been analyzed and has been found to have the following composition: copper, ; phosphorus, ; oxygen, . Determine the empirical formula of the compound.

· 72.

Tetraphenylporphyrin is a synthetic compound that resembles naturally occurring porphyrins. Porphyrins are found in hemoglobin and cytochromes, which are important to biological functions in humans. Tetraphenylporphyrin is composed of only , , and atoms. Experiments show that tetraphenylporphyrin is and by mass. What is the empirical formula of tetraphenylporphyrin?

· 73.

When mg of lithium metal is reacted with fluorine gas , the resulting fluoride salt has a mass of mg. Calculate the empirical formula of lithium fluoride.

· 74.

Phosphorus and chlorine form two binary compounds, in which the percentages of phosphorus are and , respectively. Calculate the empirical formulas of the two binary phosphorus—chlorine compounds.

Questions and Problems*: 8.9 Calculation of Molecular Formulas

Questions and Problems with answers below also have full solutions in the Student Solutions Guide.

Questions

· 75.

How does the molecular formula of a compound differ from the empirical formula? Can a compound’s empirical and molecular formulas be the same? Explain.

· 76.

What are the molecular and empirical formulas for the following molecule? Explain your reasoning.

Problems

· 77.

A binary compound of boron and hydrogen has the following percentage composition: boron, hydrogen. If the molar mass of the compound is determined by experiment to be between and g, what are the empirical and molecular formulas of the compound?

· 78.

A compound with empirical formula was found by experiment to have a molar mass of approximately g. What is the molecular formula of the compound?

· 79.

A compound with the empirical formula was found to have a molar mass of approximately g. What is the molecular formula of the compound?

· 80.

A compound with empirical formula was found in a separate experiment to have a molar mass of approximately g. What is the molecular formula of the compound?

· 81.

A compound having an approximate molar mass of g has the following percentage composition by mass: carbon, ; hydrogen, ; oxygen, ; nitrogen, . Determine the empirical and molecular formulas of the compound.

· 82.

A compound containing only sulfur and nitrogen is by mass. The molar mass is g/mol. What is the correct name for this compound?

· 83.

Use the periodic table shown in Fig. 4.9 to determine the atomic mass (per mole) or molar mass of each of the substances in column 1, and find that mass in column 2.

 Column 1 Column 2 (1) molybdenum (a) g (2) lanthanum (b) g (3) carbon tetrabromide (c) g (4) mercury(II) oxide (d) g (5) titanium(IV) oxide (e) g (6) manganese(II) chloride (f) g (7) phosphine, (g) g (8) tin(II) fluoride (h) g (9) lead(II) sulfide (i) g (10) copper(I) oxide (j) g

· 84.

Complete the following table.

 Mass of Sample Moles of Sample Atoms in Sample g mol atoms g mol atoms

· 85.

Complete the following table.

 Mass of Sample Moles of Sample Molecules in Sample Atoms in Sample g mol molecules mol molecules g

· 86.

Consider a hypothetical compound composed of elements , , and with the empirical formula . Given that the atomic masses of , , and are , , and , respectively, calculate the percentage composition by mass of the compound. If the molecular formula of the compound is found by molar mass determination to be actually , what is the percentage of each element present? Explain your results.

· 87.

A binary compound of magnesium and nitrogen is analyzed, and g of the compound is found to contain g of magnesium. When a second sample of this compound is treated with water and heated, the nitrogen is driven off as ammonia, leaving a compound that contains magnesium and oxygen by mass. Calculate the empirical formulas of the two magnesium compounds.

· 88.

When a -g sample of copper is heated in an atmosphere in which the amount of oxygen present is restricted, the sample gains g of oxygen in forming a reddish-brown oxide. However, when g of copper is heated in a stream of pure oxygen, the sample gains g of oxygen. Calculate the empirical formulas of the two oxides of copper.

· 89.

Hydrogen gas reacts with each of the halogen elements to form the hydrogen halides ( , , , ). Calculate the percent by mass of hydrogen in each of these compounds.

· 90.

Calculate the number of atoms of each element present in each of the following samples.

a. g of water

b. g of carbon dioxide

c. g of benzene,

d. moles of

· 91.

Calculate the mass in grams of each of the following samples.

a. nitrogen molecules

b. carbon dioxide molecules

c. moles of sodium chloride

d. moles of 1,2-dichloroethane,

· 92.

Calculate the mass of carbon in grams, the percent carbon by mass, and the number of individual carbon atoms present in each of the following samples.

a. g of carbon suboxide,

b. molecules of carbon monoxide

c. mole of phenol,

· 93.

Find the item in column 2 that best explains or completes the statement or question in column 1.

Column 1

o (1)

amu

o (2)

amu

o (3)

mass of the “average” atom of an element

o (4)

number of carbon atoms in g of carbon

o (5)

molecules

o (6)

total mass of all atoms in mole of a compound

o (7)

smallest whole-number ratio of atoms present in a molecule

o (8)

formula showing actual number of atoms present in a molecule

o (9)

product formed when any carbon-containing compound is burned in

o (10)

have the same empirical formulas, but different molecular formulas

Column 2

o (a)

o (b)

atomic mass

o (c)

mass of hydrogen atoms

o (d)

benzene, , and acetylene,

o (e)

carbon dioxide

o (f)

empirical formula

o (g)

g

o (h)

molecular formula

o (i)

molar mass

o (j)

mole

· 94.

You have a sample of copper and a sample of aluminum . You have an equal number of atoms in each sample. Which of the following statements concerning the masses of the samples is true?

a. The mass of the copper sample is more than twice as great as the mass of the aluminum sample.

b. The mass of the copper sample is more than the mass of the aluminum sample, but it is not more than twice as great.

c. The mass of the aluminum sample is more than twice as great as the mass of the copper sample.

d. The mass of the aluminum sample is more than the mass of the copper sample, but it is not more than twice as great.

e. The masses of the samples are equal.

· 95.

Calculate the number of grams of cobalt that contain the same number of atoms as g of iron.

· 96.

A compound was analyzed and found to contain the following percentages of elements by mass: carbon, ; hydrogen, .

a. Determine the empirical formula of the compound.

b. Which of the following could be a molar mass of the compound?

i. g/mol

ii. g/mol

iii. g/mol

iv. g/mol

v. g/mol

· 97.

Calculate the number of grams of lithium that contain the same number of atoms as kg of zirconium.

· 98.

Given that the molar mass of carbon tetrachloride, , is g, calculate the mass in grams of molecule of .

· 99.

Calculate the mass in grams of hydrogen present in g of each of the following compounds.

a. benzene,

b. calcium hydride,

c. ethyl alcohol,

d. serine,

· 100.

If you have equal mole samples of and , which of the following must be true?

a. The number of molecules in each sample is the same.

b. The number of atoms in each sample is the same.

c. The masses of the samples are the same.

d. molecules are present in each sample.

· 101.

A strikingly beautiful copper compound with the common name “blue vitriol” has the following elemental composition: , , , . Determine the empirical formula of the compound.

· 102.

A certain transition metal ion forms a compound with oxygen . The molar mass of the compound is g/mol. If the charge on the transition metal ion is , what is the identity of the transition metal, ?

a.

b.

c.

d.

e.

· 103.

The mass g is equivalent to .

· 104.

Although exact isotopic masses are known with great precision for most elements, we use the average mass of an element’s atoms in most chemical calculations. Explain.

· 105.

Using the average atomic masses given in Table 8.1, calculate the number of atoms present in each of the following samples.

a. amu of oxygen

b. amu of nitrogen

c. amu of aluminum

d. amu of hydrogen

e. amu of sodium

· 106.

If an average sodium atom weighs amu, how many sodium atoms are contained in amu of sodium? What will sodium atoms weigh?

· 107.

Using the average atomic masses given inside the front cover of this text, calculate how many moles of each element the following masses represent.

a. mg of chromium

b. g of strontium

c. g of boron

d. of californium

e. ton ( lb) of iron

f. g of barium

g. g of cobalt

· 108.

Using the average atomic masses given inside the front cover of this text, calculate the mass in grams of each of the following samples.

a. moles of potassium

b. mole of mercury

c. moles of manganese

d. moles of phosphorus

e. moles of iron

f. moles of lithium

g. mole of fluorine

· 109.

Using the average atomic masses given inside the front cover of this text, calculate the number of atoms present in each of the following samples.

a. g of gold

b. mole of platinum

c. g of platinum

d. lb of magnesium

e. mL of liquid mercury

f. moles of tungsten

g. g of tungsten

· 110.

Calculate the molar mass for each of the following substances.

a. ferrous sulfate

b. mercuric iodide

c. stannic oxide

d. cobaltous chloride

e. cupric nitrate

· 111.

Calculate the molar mass for each of the following substances.

b. caffeine,

c. eicosane,

d. cyclohexanol,

e. vinyl acetate,

f. dextrose,

· 112.

Calculate the number of moles of the indicated substance present in each of the following samples.

a. g of ammonium sulfide

b. g of calcium nitrate

c. g of dichlorine monoxide

d. lb of ferric chloride

e. kg of ferric chloride

· 113.

Calculate the number of moles of the indicated substance present in each of the following samples.

a. g of iron(II) sulfate

b. mg of mercury(II) iodide

c. of tin(IV) oxide

d. lb of cobalt(II) chloride

e. g of copper(II) nitrate

· 114.

If you have equal-mole samples of each of the following compounds, which compound contains the greatest number of oxygen atoms?

a. magnesium nitrate

b. dinitrogen pentoxide

c. iron(III) phosphate

d. barium oxide

e. potassium acetate

· 115.

Calculate the mass in grams of each of the following samples.

a. moles of ammonium carbonate

b. moles of sodium hydrogen carbonate

c. moles of carbon dioxide

d. mmol of silver nitrate

e. mole of chromium(III) chloride

· 116.

Calculate the number of molecules present in each of the following samples.

a. g of

b. moles of

c. g of

d. g of

e. mmol of

· 117.

Calculate the number of moles of hydrogen atoms present in each of the following samples.

a. g of ammonia

b. mole of water

c. mg of sulfuric acid

d. g of ammonium carbonate

· 118.

How many anions are there in g of calcium bromide?

· 119.

Calculate the percent by mass of the element mentioned first in the formulas for each of the following compounds.

a. sodium azide,

b. copper(II) sulfate,

c. gold(III) chloride,

d. silver nitrate,

e. rubidium sulfate,

f. sodium chlorate,

g. nitrogen triiodide,

h. cesium bromide,

· 120.

The percent by mass of nitrogen is for a species containing only nitrogen and oxygen. Which of the following could be this species?

a.

b.

c.

d.

e.

· 121.

A -g sample of a new compound has been analyzed and found to contain the following masses of elements: carbon, g; hydrogen, g; nitrogen, g; oxygen, g. Calculate the empirical formula of the compound.

· 122.

What mass of sodium hydroxide has the same number of oxygen atoms as g of ammonium carbonate?

· 123.

When g of calcium is heated in pure nitrogen gas, the sample gains g of nitrogen. Calculate the empirical formula of the calcium nitride formed.

· 124.

Topical hydrocortisone is often used to treat a variety of skin conditions, such as insect bites, eczema, and rashes. Each molecule of hydrocortisone contains atoms of carbon (plus other atoms). The mass percentage of carbon in hydrocortisone is . What is the molar mass of hydrocortisone?

· 125.

When g of metallic chromium is heated with elemental chlorine gas, g of a chromium chloride salt results. Calculate the empirical formula of the compound.

· 126.

When barium metal is heated in chlorine gas, a binary compound forms that consists of and by mass. Calculate the empirical formula of the compound.

ChemWork Problems

These multiconcept problems (and additional ones) are found interactively online with the same type of assistance a student would get from an instructor.

· 127.

Determine the molar mass for the following compounds to four significant figures.

 Compound Molar Mass (g/mol) Water iron(III) chloride potassium bromide ammonium nitrate sodium hydroxide

· 128.

Vitamin , cyanocobalamin, is essential for human nutrition. Its molecular formula is . A lack of this vitamin in the diet can lead to anemia. Cyanocobalamin is the form of the vitamin found in vitamin supplements.

a. What is the molar mass of cyanocobalamin to two decimal places?

b. How many moles of cyanocobalamin molecules are present in mg of cyanocobalamin?

c. What is the mass of mole of cyanocobalamin?

d. How many atoms of hydrogen are in mole of cyanocobalamin?

e. What is the mass of molecules of cyanocobalamin?

f. What is the mass (in grams) of one molecule of cyanocobalamin?

· 129.

Calculate the number of moles for each compound in the following table.

 Compound Mass Moles Magnesium phosphate g Calcium nitrate g Potassium chromate g Dinitrogen pentoxide g

· 130.

a. How many atoms of carbon are present in g of ?

b. How many atoms of carbon are present in g of ?

c. How many atoms of nitrogen are present in g of ?

· 131.

Consider samples of phosphine , water , hydrogen sulfide , and hydrogen fluoride , each with a mass of g. Rank the compounds from the least to the greatest number of hydrogen atoms contained in the samples.

· 132.

The chemical formula for aspirin is . What is the mass percent for each element in mole of aspirin? (Give your answer to four significant figures.)

 carbon hydrogen oxygen

· 133.

Arrange the following substances in order of increasing mass percent of nitrogen.

a.

b.

c.

d.

· 134.

A compound with molar mass g/mol has the following composition by mass:

Determine the empirical and molecular formulas of the compound.

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