# Practice Homework 16: Mass ⇔ Moles ⇔ Particles

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Practice Homework 16: Mass  Moles  Particles
 This assignment is for practice only. It is not due.  Remember: write your conversion factors for both MM (molar mass) and Avogadro’s Number when
doing these problems.  Go to Questions 7, 8, 9, 10, and 11 for “twist” problems.
1) Calculate the number of carbon atoms in a 20.00-gram sample of carbon. The molar mass of carbon is 12.01 g/mol.
2) A sample of lead contains 4.750 × 1022 atoms of lead. Determine the mass (in grams) of the lead in the sample. The molar mass of lead is 207.2 g/mol.
3) A sample of zinc(II) chloride, ZnCl2, contains 3.204 × 1025 form of ZnCl2. Determine the mass (in grams) of zinc(II) chloride in the sample. The molar mass of zinc(II) chloride is 136.29 g/mol.
4) A sample of phosphorus triiodide contains 5.28 × 1022 molecules of phosphorus triiodide. Calculate the mass (in grams) of phosphorus triiodide in the sample. The molar mass of PI3 is 411.7 g/mol.
5) A 0.400-gram sample of acetylsalicylic acid (also called “aspirin”, C9H8O4, 180.16 g/mol) is dissolved in 2.00 L of water. How many molecules of C9H8O4 are present in the liquid? (Note: The volume of water, 2.00 L, is not needed in this calculation. But, in two weeks, it will be!
6) A sample of magnesium sulfate (espom salts, MgSO4, 120.37 g/mol) is found to have a mass of 0.24 grams. Calculate the number of magnesium sulfate formula units in the sample.
7) Calculate the volume (in mL) of bromine liquid, Br2(l), that contains 2.394 × 1023 molecules of Br2(l). The molar mass of bromine liquid is 159.8 g/mol. The density of bromine liquid is 3.1 g/mL. Treat molar mass, density, and Avogadro’s Number like exact numbers in this question.
Hint: Write all three conversion factors: the MM conversion factor, the Av# conversion factor, and the density conversion factor.
Note: The solution for this problem is included in this answer key.
8) Octane liquid, C8H18, is a component of gasoline. Calculate the number of octane molecules in a 212.4-liter sample of octane. The molar mass of octane is 114.23 g/mol. The density of octane is 0.703 g/mL. Again, you must use the original value of density in this calculation.
9) A sample of sucrose (table sugar), C12H22O11, has a mass of 12.00 grams. The molar mass of sucrose is 342.30 g/mol. Calculate the number of carbon atoms in the sample. The solution for this problem is included in this answer key.
10) Seratonin is a biological chemical that is believed to have a role in regulating sleeping patterns. Its chemical formula is C10H12N2O, and its molar mass is 176.22 g/mol. A sample of seratonin contains 2.99 × 1019 nitrogen atoms. Calculate the mass (in mg) of seratonin in the sample.
11)* Challenge Problem: A sample of carbon tetrachloride, an organic liquid, has a molar mass of 153.82 g/mol. A sample of carbon tetrachloride contains 4.02 × 1017 atoms of chlorine. Calculate the volume of carbon tetrachloride in nanoliters. Don’t worry: this would be an extra credit type question. The density of carbon tetrachloride is 1.59 g/mL.
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Remember: You can always write answers in scientific notation form with no penalty (as long as the values are written correctly in scientific notation form.)

1) 1.003 × 1024 C atoms

2) 163.4 g Pb (atoms)

OR 1.634 × 102 g Pb (atoms)

3) 7.251 × 103 g ZnCl2 (form)

OR 7.251 × 103 g ZnCl2 (form)

4) 35.9 g PI3 (molec)

OR 3.59 × 101 g PI3 (molec)

5) 1.34 × 1021 C9H8O4 molec

6) 1.2 × 1021 MgSO4 form

Question 7 Solution 159.8 g Br2 = 1 mol Br2

1 mol Br2 = 6.022 × 1023 Br2 molec

3.1 g Br2 = 1 mL Br2

2.394 × 1023 Br2 molec

1 mol Br2

159.8 g Br2 1 mL Br2

( 1 ) (6.022 × 1023 Br2 molec) ( 1 mol Br2 ) (3.1 g Br2) =

20.49 mL Br2

8) 7.872 × 1026 C8H18 molec

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Question 9 Solution 342.30 g C12H22O11 = 1 mol C12H22O11

1 C12H22O11 molec = 12 C atoms

12.00 g C12H22O11

1 mol C12H22O11

6.022 × 1023 C12H22O11 molec

12 C atoms

23

9) (

1

) (342.30 g C H O ) (

1 mol C H O

) (1 C H O molec) = 2.553 × 10 C atoms

12 22 11

12 22 11

12 22 11

10) 4.37 mg C10H12N2O 11) 16.2 mL CCl4

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