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Understanding Moles and Avogadro Constant: Masses of Atoms and Molecules, Slides of Chemistry

Information on the concept of moles as a unit of measurement for amount of substance in the international system of units (si), with a focus on the avogadro constant. It includes examples of calculating the number of moles and atoms for various elements and compounds, such as carbon, glucose, iron, and hemoglobin.

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2021/2022

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Fall 2016 โ€“ CH 6A mole & Avogadro constant Instructor: J.T.
๏‚ท The mole is the unit of measurement in the International System of Units (SI) for
amount of substance.
๏‚ท It has the unit symbol โ€œmolโ€.
๏‚ท Same as: [A dozen (doz) is a grouping of twelve entities.]
Is analogous to saying:
A mole is a grouping of ๐Ÿ”. ๐ŸŽ๐Ÿ๐Ÿ ร—๐Ÿ๐ŸŽ๐Ÿ๐Ÿ‘ entities.
Where: the Avogadro constant is: NA = 6.022 141 79 (30) x 1023 mol-1
๏‚ท By definition: A mole of ๐ถ
6
12 has exactly 12 grams mass.
It means: 12 g of carbon-12 contains ๐Ÿ”. ๐ŸŽ๐Ÿ๐Ÿ ร—๐Ÿ๐ŸŽ๐Ÿ๐Ÿ‘ atoms of carbon-12
๏‚ท By definition:
One โ€œatomic mass unitโ€ = 1
12 mass of one atom of ๐ถ
6
12
Or: 1 atom of ๐ถ
6
12 weighs 12.000 amu, โ€œuโ€
1) What is the mass of 1 atom of carbon?
We know:
1 mole ๏‚บ 6.022 ร—1023 carbon atoms ๏‚บ 12 g of carbon-12
๐‘š๐‘Ž๐‘ ๐‘  ๐‘œ๐‘“ 1 ๐‘Ž๐‘ก๐‘œ๐‘š ๐‘๐‘Ž๐‘Ÿ๐‘๐‘œ๐‘› = 12 ๐‘”
6.022 ร—1023 = 1.993 ร—10โˆ’23 ๐‘”
Note about the mole: i.e. Glucose: ๐ถ6๐ป12๐‘‚6
๏‚ท 1 molecule of glucose contains 6 atoms of C, 12 atoms of H, and 6 atoms of O
๏‚ท 1 mole of glucose contains 6 moles of C atoms, 12 moles of H atoms, and 6 moles of O atoms.
๏‚ท 10 moles of glucose contains 60 moles of C, 120 moles of H, and 60 moles of O atoms.
๏‚ท NA molecules of glucose contains 6 x NA atoms of C, 12 x NA atoms of H, and 6 x NA atoms of O.
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Fall 2016 โ€“ CH 6A mole & Avogadro constant Instructor: J.T.

๏‚ท The mole is the unit of measurement in the International System of Units (SI) for amount of substance. ๏‚ท It has the unit symbol โ€œ molโ€.

๏‚ท Same as: [ A dozen ( doz) is a grouping of twelve entities.] Is analogous to saying: A mole is a grouping of ๐Ÿ”. ๐ŸŽ๐Ÿ๐Ÿ ร— ๐Ÿ๐ŸŽ๐Ÿ๐Ÿ‘^ entities.

Where: the Avogadro constant is: N A = 6.022 141 79 (30) x 10^23 mol-^1

๏‚ท By definition: A mole of 126 ๐ถ^ has exactly 12 grams mass.

It means: 12 g of carbon-12 contains ๐Ÿ”. ๐ŸŽ๐Ÿ๐Ÿ ร— ๐Ÿ๐ŸŽ๐Ÿ๐Ÿ‘^ atoms of carbon- 12

๏‚ท By definition: One โ€œatomic mass unitโ€ = 1 12 mass of one atom of^6 ๐ถ

12

Or: 1 atom of 126 ๐ถ^ weighs 12.000 amu, โ€œuโ€

1) What is the mass of 1 atom of carbon?

We know: 1 mole ๏‚บ 6. 022 ร— 1023 carbon atoms ๏‚บ 12 g of carbon- 12

6. 022 ร— 1023

= 1. 993 ร— 10 โˆ’^23 ๐‘”

Note about the mole: i.e. Glucose: ๐ถ 6 ๐ป 12 ๐‘‚ 6

๏‚ท 1 molecule of glucose contains 6 atoms of C, 12 atoms of H, and 6 atoms of O ๏‚ท 1 mole of glucose contains 6 moles of C atoms, 12 moles of H atoms, and 6 moles of O atoms. ๏‚ท 10 moles of glucose contains 60 moles of C, 120 moles of H, and 60 moles of O atoms. ๏‚ท NA molecules of glucose contains 6 x NA atoms of C, 12 x NA atoms of H, and 6 x NA atoms of O.

Fall 2016 โ€“ CH 6A mole & Avogadro constant Instructor: J.T.

2) How many moles of Fe are in 5.6 g Fe? How many Fe atoms are contained in the sample?

By definition we know: 1 mole of Fe is 55.85 g per mole {see the periodic table}.

5.6 ๐‘” ร—

1 ๐‘š๐‘œ๐‘™ 55,85 ๐‘” = 0.10 ๐‘š๐‘œ๐‘™

0.10 ๐‘š๐‘œ๐‘™ ร—

6.022ร—10^23 ๐‘Ž๐‘ก๐‘œ๐‘š๐‘  1 ๐‘š๐‘œ๐‘™ = 6.04 ร— 10

3) What mass of sulfur contains the same number of moles as are in 10.0 g of Fe?

First: Find the number of moles of Fe.

๐‘š๐‘Ž๐‘ ๐‘  ๐‘š๐‘œ๐‘™๐‘Ž๐‘Ÿ ๐‘š๐‘Ž๐‘ ๐‘  =^

55.85 = 0.1791 ๐‘š๐‘œ๐‘™^ of Fe

mol of โ€œSโ€ = mol of โ€œFeโ€ = 0.1791 mol

๐‘š๐‘Ž๐‘ ๐‘  = ๐‘š๐‘œ๐‘™ ร— ๐‘š๐‘œ๐‘™๐‘Ž๐‘Ÿ ๐‘š๐‘Ž๐‘ ๐‘ 

๐‘š๐‘Ž๐‘ ๐‘  ๐‘œ๐‘“ ๐‘ ๐‘ข๐‘™๐‘“๐‘ข๐‘Ÿ = 0.1891 ร— 32.06 = 5.74 ๐‘” ๐‘ ๐‘ข๐‘™๐‘“๐‘ข๐‘Ÿ

4) Hemoglobin is the oxygen-carrying protein of most mammals. Each molecule of hemoglobin contains 4 atoms of iron. The molecular weight of hemoglobin is about 64000 g/mol. How many moles of iron are contained in 0.50 moles of hemoglobin? Calculate the number of iron atoms in 0.128 g of hemoglobin.

1 mole of hemoglobin contains 4 X (moles) of iron. 0.5 mole of hemoglobin contains 4 X (0.5 moles) of iron = 2.00 moles of iron.

= 2.00 โˆ’6^ ๐‘š๐‘œ๐‘™

2.00 ร— 10โˆ’6^ ๐‘š๐‘œ๐‘™ ๐ป๐‘’๐‘š๐‘œ๐‘”๐‘™๐‘œ๐‘๐‘–๐‘› ร—

= 8.00 ร— 10โˆ’6^ ๐‘š๐‘œ๐‘™๐‘’๐‘  ๐น๐‘’

8.00 ร— 10โˆ’6^ ๐‘š๐‘œ๐‘™ ร—

6.022ร—10^23 ๐‘Ž๐‘ก๐‘œ๐‘š๐‘  1 ๐‘š๐‘œ๐‘™ = 4.82 ร— 10