Chemistry Name __________________________

Hour _______

Chemistry

Approximate Timeline

Students are expected to keep up with class work when absent.

CHAPTER 6 – CHEMICAL COMPOSITION

Day Plans for the day Assignment(s) for the day

1 Begin Chapter 6

6.1 – Counting by weighing

o Atomic masses – counting by weighing

o The MOLE

atoms moles

grams moles

atoms grams

Assignment 6.0

Assignment 6.1a

2 o The MOLE

atoms moles

grams moles

atoms grams

Assignment 6.1b

3 Quiz 6.1 – Atoms & Moles

Discuss Experiment 22 – The Bean Lab

Assignment 6.1c

4 Perform Experiment 22 – The Bean Lab

Lab Report due in 2 days

Read section(s) 6.2

5 6.2 – Molar mass & % Composition Assignment 6.2

Read section(s) 6.3

6 Quiz 6.2 – Molar Mass & % Composition

6. 3 – Formulas of Compounds

o Empirical Formulas

o Calculation of Empirical Formulas

Assignment 6.3a

7 Discuss Empirical Formula Lab

8 Perform Empirical Formula Lab

Lab Report due in 2 days

9 6. 3 – Formulas of Compounds

o Calculation of Molecular Formulas

Assignment 6.3b

10 Quiz 6.3 – Formulas of Compounds Assignment 6.4

11 Grade & discuss Assignment 6.4

Review for chapter 6 test

12 Chapter 6 Test Read section(s) 7.1 – 7.2

Chemistry Name __________________________

Hour _______

Study Guides

Chapter 6 Quizzes

Quiz 6.1 Atoms & Moles 1. What two pieces of information are needed in order to “count by weighing”?

2. Define the term “mole”. (The chemistry mole, not some other version.)

3. How many carbon atoms are in exactly one mole of carbon?

4. What is the name given to the number of carbon atoms in exactly one mole of carbon?

5. Be able to convert between units of grams, moles, and atoms.

Quiz 6.2 Molar Mass & Percent Composition 6. Define the term “molar mass”.

7. How would you obtain the molar mass of a compound?

8. What is the basic equation used to calculate a percentage?

9. Be able to calculate the molar mass of a substance.

Quiz 6.3 Formulas of Compounds 1. Define the term “empirical formula” and give one example.

2. Define the term “molecular formula” and give one example.

3. Given the molecular formula of a compound, write its empirical formula.

4. Calculate the empirical formula of a compound.

5. Calculate the molecular formula of a compound.

Study Guide

Chapter 6 Test

At the completion of chapter 6 you should…

1. Know the definitions of the following terms.

a. Mole

b. Avogadro’s number

c. Molar mass

d. Mass percent

e. Empirical formula

f. Molecular formula

2. Counting by weighing

a. Know the two things needed to count by weighing.

b. Be able to perform the calculation.

3. The Mole

a. Define the term “mole”

b. Know the number of objects in one mole and the name given to this number.

c. Be able to perform calculations involving moles.

i. number of atoms to moles

ii. moles to number of atoms

iii. grams to moles

iv. moles to grams

v. atoms to grams

vi. grams to atoms

4. Molar Mass

a. Define the term “molar mass.”

b. Be able to calculate the molar mass of any chemical compound.

5. Percent Composition

a. Be able to calculate the percent composition of a compound.

6. Formulas of Compounds

a. Be able to find the empirical formula of a compound.

i. Starting with the molecular formula.

ii. Starting with grams of each element.

iii. Starting with percent composition of the compound.

b. Be able to find the molecular formula of a compound.

i. Starting with the empirical formula.

ii. Starting with grams of each element.

iii. Starting with percent composition of the compound.

Chemistry Name __________________________

Hour _______

Assignment 6.0 – Vocabulary

Define each of the following terms.

1. Mole

2. Avogadro’s number

3. Molar mass

4. Mass percent

5. Empirical formula

6. Molecular formula

Chemistry Name __________________________

Hour _______

Assignment 6.1a – Grams, Moles, & Molecules (1)

Perform the following conversions. You must use dimensional analysis. No work = No credit.

1) 0.0038 moles N to grams

2) 908 moles H to grams

3) 6.006 moles of Li to atoms

4) 9.100 moles of Cr to atoms

5) 1.09 grams Cu to moles

6) 9.5 grams P to moles

7) 0.00600 grams Ca to atoms

8) 0.250 grams Cs to atoms

Chemistry Name __________________________

Hour _______

Assignment 6.1b – Grams, Moles, & Molecules (2)

Perform the following conversions. You must use dimensional analysis. No work = No credit.

1) 1.000 x 10

25 atoms Fe to grams

2) 9.29 x 1016

atoms Na to grams

3) 3.0 x 1023

atoms Ba to moles

4) 7.05 x 1024

atoms S to moles

5) 6.80 moles Zn to grams

6) 36.0 moles of Ba to atoms

7) 0.9300 grams of C to moles

8) 4500 grams K to moles

9) 2.07 moles Br to grams

10) 4.25 grams Cd to moles

Chemistry Name __________________________

Hour _______

Assignment 6.1c – Atoms & Moles (2 pages)

1) Suppose you work in a hardware store. The manager asks you to fill an order for an

important customer who is waiting impatiently. You need 1200 nuts and 1200 bolts.

Unfortunately the nuts and bolts are not boxed – they are loose in big buckets. How can

you earn a bonus from your boss and make the customer happy by filling the order in less

than two minutes?

2) Why is the average atomic mass of any element not a whole number (for example: carbon

is 12.01 amu not 12 amu)?

3) A mole of any substance contains Avogadro’s number of atoms.

A) Write an equivalence statement for this definition.

B) Write the possible conversion factors from this relationship.

C) To determine the following, tell which conversion factor you would need to use.

i) Moles Al from atoms Al

ii) Atoms Au from mole Au

4) Complete the following table. Show your work below the table. No work = No credit.

Mass of Sample Moles of Sample Atoms in Sample

0.250 mol Al

25.4 g Fe

2.13 x 1024

atoms Au

5) Which sample contains more atoms: 3.89 g of nickel or 6.61 g of silver? Show your

work. No work = No credit.

Chemistry Name __________________________

Hour _______

Assignment 6.2 – Molar Mass & Percent Composition (2 pages)

Solve each of the following problems. No work = No credit.

1) Determine the molar mass of each of the following:

A) NH3

B) H2O

C) H2SO4

D) Ca(NO3)2

2) Determine the mass of each of the following samples:

A) 3 moles NH3

B) 0.25 moles H2O

C) 5.0 moles H2SO4

D) 0.75 moles Ca(NO3)2

3) Complete the following table. Show your work below the table.

Moles Mass # of molecules

4.7 moles NH3

1.80 g H2O

5.21 x 1022

molecules CH4

4) Explain how you would find the mass percent of each element in water. (Don’t do the

math, just explain with words.)

5) Calculate the percentage composition of H2SO4.

Chemistry Name __________________________

Hour _______

Assignment 6.3a – Empirical Formula (2 pages)

Solve each of the following problems. Show all of your work. No work = No credit.

1) Find the empirical formula for a sample that contains 2.802 g N and 6.400 g O.

2) What is the empirical formula of a substance that is composed of 12.61 g of carbon, 1.41

g of hydrogen, and 16.80 g of oxygen?

3) Analysis of an unknown substance reveals that it contains 15.01 g C and 3.79 g H. What

is the empirical formula of the substance?

4) A 25.0 g sample of an orange compound contains 6.64 g of potassium, 8.84 g of

chromium, and 9.52 g of oxygen. Find the empirical formula.

5) Find the empirical formula of a compound composed of 27.08% tin and 72.92% bromine.

6) Determine the simplest formula of citric acid, which has the composition: 37.51% C,

4.20% H, 58.29% O.

7) Determine the simplest formula of tetraethyl lead, which has the composition: 29.71% C,

6.234% H, 64.07% Pb.

8) A scientist finds that a compound is 78.24% silver, 4.36% carbon, and 17.41% oxygen.

What is the empirical formula of the compound?

Chemistry Name __________________________

Hour _______

Assignment 6.3b – Molecular Formula (2 pages)

Solve each of the following problems. Show all of your work. No work = No credit.

1) A compound with the empirical formula CH2O was found to have a molar mass between

89 and 91 grams. What is the molecular formula of the compound?

2) A compound containing 11.21 g of nitrogen and 25.60 g of oxygen was found to have a

molecular mass of 92.02 g. What is the molecular formula of the compound?

3) Another compound was tested and was found to contain 12.61 g C, 2.83 g H, and 5.60 g

O. The molar mass is 120.22 g/mol. What is the molecular formula of the compound?

4) The molar mass of a compound composed of carbon, hydrogen and chlorine is 98.96 g.

Analysis found the percentage composition to be 24.27% C, 4.08% H, and 71.65% Cl.

What is the molecular formula of the compound?

5) The percentage composition of a compound is 68.87% C, 15.06% H, and 16.07% N. The

molar mass of the compound is 87.19 g. What is the molecular formula of the compound?

Chemistry Name __________________________

Hour _______

Assignment 6.4 – Chapter Review

NO WORK = NO CREDIT. (8 pages)

1) A sample equal to the atomic mass of an element measured in grams contains ___ atoms.

2) In 24.02 grams of carbon, there are ___ carbon atoms.

3) Calculate the average mass in grams of 1 atom of oxygen.

4) Using the average atomic masses for each element, calculate the number of moles of each

element in samples with the following masses.

A) 41.5 grams of calcium

B) 1.42 x 1023

grams of palladium

C) 1.00 kg of iron

5) Using the average atomic masses for each element, calculate the mass in grams in each of

the following samples.

A) 0.521 mol of nickel

B) 72.5 mol of lead

C) 4.87 x 103 mol of aluminum

6) Calculate the molar mass for each of the following substances.

A) magnesium sulfate

B) copper(II) nitrate

C) phenol, C6H6O

Chemistry Name __________________________

Hour _______

7) Calculate the number of moles of the indicated substances in each of the following

samples.

A) 7.44 x 104 kg of lead(IV) oxide

B) 3.27 mg of trichloroethane, C2H3Cl3

C) 521 g of copper(I) chloride

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

A) 1.91 x 10-3

mol of benzene, C6H6

B) 4.56 x 105 mol of ethanol, C2H5OH

C) 2.27 mol of calcium nitrate

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

A) 6.37 g of carbon monoxide

B) 2.62 x 10-6

mol of water

C) 5.23 g of benzene, C6H6

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

A) sodium sulfite

B) sodium thiosulfate, Na2S2O3

Chemistry Name __________________________

Hour _______

C) potassium hydrogen phosphate, K2HPO4

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

A) terephthalic acid, C8H6 O4

B) 1,4-dichloro-2-butene, C4H6Cl2

12) A new compound has been prepared. A 0.4791 g sample was analyzed and was found to

contain the following masses of elements. Determine the empirical formula of the new

compound.

carbon, 0.1929 g

hydrogen, 0.01079 g

oxygen, 0.08566 g

chlorine, 0.1898 g

13) A compound has the following percentages by mass. Determine the empirical formula of

this compound.

barium, 58.84%

sulfur, 13.74%

oxygen, 27.43%

14) If cobalt metal is mixed with excess sulfur and heated strongly, a sulfide is produced that

contains 55.0% cobalt by mass. Calculate the empirical formula of the compound.

Chemistry Name __________________________

Hour _______

15) A compound with empirical formula CH2 was found to have a molar mass of

approximately 84 g. What is the molecular formula of the compound?

16) A compound having a molar mass of 168.15 grams has the following percentage

composition by mass. Find both the empirical and molecular formulas of the compound.

carbon, 42.87%

hydrogen, 3.598%

oxygen, 28.55%

nitrogen, 25.00%

17) A compound consists of 65.45% C, 5.492% H, and 29.06% O by mass and has a molar

mass of approximately 110 grams. Determine the empirical and molecular formulas of

the compound.