Mole Conversions

Learn the models, terms, and applications of mole conversions.

Lesson 2 of 32 parts Practice Flashcards

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Concepts and Models

Objective: Explain the concepts and assumptions used in mole conversions.

The mole counts entities using the exact Avogadro constant 6.02214076×10^23 mol⁻¹; these exercises round it to 6.022×10^23. Mass and amount connect through m=nM; particles and amount connect through N=nN_A. State whether entities are atoms, molecules, or formula units. Convert units explicitly and retain intermediate digits. Moles are not grams: substances with different molar masses can have equal amounts but different masses.

Formulas

$n=m/M$
$N=nN_A$

Worked examples

Try itH2O has molar mass 18 g/mol. What mass contains 0.25 mol?Show answer

1. Use mass = amount × molar mass. 2. 0.25×18=4.5 g.

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Concepts and Models

Objective: Explain the concepts and assumptions used in mole conversions.

Formulas

$n=m/M$
$N=nN_A$

Worked examples

Try itH2O has molar mass 18 g/mol. What mass contains 0.25 mol?Show answer

1. Use mass = amount × molar mass. 2. 0.25×18=4.5 g.

Applications and Worked Problems

Objective: Apply mole conversions to calculations, evidence, and specified situations.

For the application problems, define the system and list the quantities supplied before choosing a relation. Use n=m/M; N=nN_A. The relation must match the stated conditions. Convert to compatible units before substitution, preserve intermediate precision, and report the requested quantity with its unit or sign. When comparing alternatives, check the defining condition rather than a superficial word match. The worked examples below show the setup and calculation separately.

Formulas

$n=m/M$
$N=nN_A$

Worked examples

Try itH2O has molar mass 18 g/mol. What mass contains 0.25 mol?Show answer

1. Use mass = amount × molar mass. 2. 0.25×18=4.5 g.

Try itA H2O sample has mass 4.5 g and molar mass 18 g/mol. How many moles are present?Show answer

1. Use n=m/M. 2. 4.5/18=0.25 mol.

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