Mole conversion problems key provides detailed solutions for chemistry students tackling mole calculations. It includes step-by-step examples for converting grams to moles, moles to molecules, and grams to molecules for various compounds. This resource is essential for high school and college-level chemistry courses, particularly for students preparing for exams. The key covers molar masses for compounds like HCl, Fe2O3, and SO2, with calculations that illustrate the mole concept and Avogadro's number. Ideal for students seeking to enhance their understanding of stoichiometry and mole conversions.

Key Points

  • Includes solutions for converting grams to moles for HCl, Fe2O3, and Ca3(PO4)2.
  • Provides calculations for determining the number of molecules in given masses of C6H12O6 and SO2.
  • Covers mole conversion examples relevant for high school and college chemistry courses.
  • Demonstrates the use of molar mass and Avogadro's number in mole calculations.
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Date________________________Name_______________________________________ Per_________
Mole Conversion Problems
Complete the following practice problems for mole conversion. Show your work and units!
1. How many moles are in 72.9 g of HCl? Molar mass HCl = 36.46
௚
௠௢௟
72.9g
36.46
௚
௠௢௟
= 1.999 mol
2. How many moles are in 79.85 g Fe
2
O
3
? Molar mass = 159.7
௚
௠௢௟
79.85g
159.7
௚
௠௢௟
= 0.5 mol
3. How many molecules are in 720 g of C
6
H
12
O
6
? Molar mass = 180.18
௚
௠௢௟
720g 3.996 mol x (6.02 x 10
23
௣௔௥௧௜௖௟௘௦
௠௢௟
) = 2.406 x 10
24
particles
180.18
௚
௠௢௟
= 3.996 mol
4. How many grams are in 3.5 mol of Ca
3
(PO
4
)
2
? Molar mass = 310.18
௚
௠௢௟
310.18
௚
௠௢௟
x 3.5 mol = 1085.63 g
5. How many molecules are in 8550g of SO
2
? Molar mass = 64.07
௚
௠௢௟
8550g 133.45 mol x (6.02 x 10
23
௣௔௥௧௜௖௟௘௦
௠௢௟
) = 8.03 x 10
25
particles
64.07
௚
௠௢௟
= 133.45 mol
6. How many grams are in 3.01 × 10
24
molecules of (NH
4
)
2
SO
4
? Molar mass = 132.17
௚
௠௢௟
3.01× 10
24
particles 5 mol x 132.17
௚
௠௢௟
= 660.85 g
6.02 x 10
23
௣௔௥௧௜௖௟௘௦
௠௢௟
= 5 mol
7. How many molecules are in 85 g of AgNO
3
? Molar mass = 169.88
௚
௠௢௟
85g 0.5 mol x (6.02 x 10
23
௣௔௥௧௜௖௟௘௦
௠௢௟
) = 3.01 x 10
23
169.88
௚
௠௢௟
= 0.5 mol
8. How many grams are in 1.204 × 10
24
molecules of CH
3
COOH? Molar mass = 60.06
௚
௠௢௟
1.204 × 10
24
particles = 2.0 mol 2.0 mol x 60.06
௚
௠௢௟
= 120.12 g
6.02 x 10
23
௣௔௥௧௜௖௟௘௦
௠௢௟
Date________________________Name_______________________________________ Per_________
9. Convert 86.84 g of LiBr to moles: Molar mass = 86.84
௚
௠௢௟
86.84 g = 1.0 mol
86.84
௚
௠௢௟
10. Convert 8.045 g of H
2
CO
3
to moles: Molar mass = 62.03
௚
௠௢௟
8.045 g = 0.1297 mol
62.03
௚
௠௢௟
11. How many grams of lithium are there in 3.45 moles? Molar mass = 6.94
௚
௠௢௟
6.94
௚
௠௢௟
x 3.45 mol = 23.943 g
12. How many moles of nitrogen are there in 4.3 × 10
23
molecules?
4.3 × 10
23
particles = .714 mol
6.02 x 10
23
௣௔௥௧௜௖௟௘௦
௠௢௟
13. How many cadmium atoms are there in 6.57 × 10
3
moles?
6.57 × 10
3
moles x (6.02 x 10
23
௣௔௥௧௜௖௟௘௦
௠௢௟
) = 3.955 x 10
27
particles
14. How many grams of SO
2
are 4.5 × 10
24
molecules? Molar mass = 64.07
௚
௠௢௟
4.5 × 10
24
particles = 7.475 mol 7.475 mol x 64.07
௚
௠௢௟
= 478.93 g
6.02 x 10
23
௣௔௥௧௜௖௟௘௦
௠௢௟
15. How many copper atoms are in 5.6 mole of Cu
2
O
3
?
5.6 mol x (6.02 x 10
23
௣௔௥௧௜௖௟௘௦
௠௢௟
) = 3.37 x 10
24
particles
16. How many grams of sulfur are in 3.45 × 10
22
molecules of SO
2
? Molar mass Sulfur = 32.07
௚
௠௢௟
3.45 × 10
22
particles = 0.0573 mol 0.0573 mol x 32.07
௚
௠௢௟
= 1.838 g
6.02 x 10
23
௣௔௥௧௜௖௟௘௦
௠௢௟
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FAQs

How do you convert grams to moles using molar mass?
To convert grams to moles, divide the mass of the substance by its molar mass. For example, if you have 72.9 grams of HCl, and the molar mass of HCl is 36.46 g/mol, you would calculate 72.9 g ÷ 36.46 g/mol, resulting in approximately 1.999 moles of HCl. This method applies to any substance as long as you know its molar mass.

What is the significance of Avogadro's number in mole conversions?
Avogadro's number, approximately 6.02 x 10^23, is crucial in mole conversions as it defines the number of particles in one mole of a substance. This constant allows chemists to relate the mass of a substance to the number of atoms, molecules, or ions it contains. For instance, if you calculate the number of molecules in 3.996 moles of glucose, you would multiply 3.996 moles by Avogadro's number to find the total number of molecules.

What are common mistakes in mole conversion problems?
Common mistakes in mole conversion problems include miscalculating the molar mass, forgetting to convert units properly, and mixing up grams with moles. Students often overlook the importance of unit cancellation, which can lead to incorrect answers. It's essential to carefully track units throughout the calculation process to ensure accuracy.

How can mole conversion problems help in understanding stoichiometry?
Mole conversion problems are foundational for understanding stoichiometry, which involves the relationships between reactants and products in chemical reactions. By mastering mole conversions, students can predict how much of a reactant is needed to produce a certain amount of product, or vice versa. This skill is vital for balancing chemical equations and performing quantitative analysis in chemistry.

What types of compounds are covered in the mole conversion problems key?
The mole conversion problems key covers a variety of compounds, including ionic compounds like Fe2O3 and molecular compounds like HCl and C6H12O6. Each example illustrates different aspects of mole conversions, such as calculating moles from grams and determining the number of molecules from moles. This diversity helps students apply the mole concept across different types of chemical substances.

What is the process for calculating grams from moles?
To calculate grams from moles, multiply the number of moles by the molar mass of the substance. For example, if you have 3.5 moles of Ca3(PO4)2 and the molar mass is 310.18 g/mol, you would calculate 3.5 moles x 310.18 g/mol, resulting in approximately 1085.63 grams. This process is essential for converting between the amount of substance and its mass.

How do you find the number of molecules from grams?
To find the number of molecules from grams, first convert grams to moles using the molar mass, then multiply the result by Avogadro's number. For instance, if you have 720 grams of glucose (C6H12O6), you would first calculate the moles by dividing 720 g by the molar mass of 180.18 g/mol, which gives you about 3.996 moles. Then, multiply 3.996 moles by Avogadro's number to find the total number of molecules.