Reactions In Solutions

Student can express solution concentrations in Mass %, Mole Fraction, Molarity, and Molality, and interconvert between them.

6 lessons

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Expressing Concentration

Introduce Mass Percent and Mole Fraction.

When we mix a solute into a solvent, we need to express exactly how much is in there. Mass percent (w/w %) is the simplest way:

$\text{Mass percent} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100$

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Molarity (M)

Define Molarity and dilution formula, with Problem 1.7.

Volume-Based Concentration

Molarity (M) is the most widely used unit in the chemistry lab. It is defined as the number of moles of solute dissolved in $1\text{ liter}$ of solution.

$\text{Molarity (M)} = \frac{\text{Moles of solute}}{\text{Volume of solution in liters}}$

Crucial Concept: Because liquids expand and contract with heat, volume changes with temperature. Therefore, Molarity is temperature-dependent.

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Molality (m)

Define Molality and density conversion, with Problem 1.8.

Mass-Based Concentration

Molality (m) is defined as the number of moles of solute present in $1\text{ kg}$ of solvent.

$\text{Molality (m)} = \frac{\text{Moles of solute}}{\text{Mass of solvent in kg}}$

Crucial Concept: Since mass does not change with heat, molality is unaffected by temperature, making it highly reliable for experiments across varying temperatures.

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Temperature Dependence

Test conceptual understanding of temperature effects on concentration.

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Which of the following concentration units is temperature dependent?

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Calculate Required Mass for Molarity

Exercise 1.5: Mass of sodium acetate required.

Calculate Required Mass for Molarity

Adaptation of Exercise 1.5: Calculate the mass of sodium acetate ( $CH_3COONa$ ) required to make $500\text{ mL}$ of a $0.375\text{ M}$ aqueous solution. The molar mass of sodium acetate is $82.0245\text{ g/mol}$ . Follow the steps to solve.

Given values (with units)*

Identify the known variables and ensure units are standard (like Liters).

Formulas to use*

State the algebraic formulas governing this relationship.

Substitution*

Plug the given numbers into the formulas.

Calculation steps*

Show the intermediate calculation for moles, then for mass.

Final Answer*

State your final numerical answer with units and correct significant figures.

Reasonableness / Sanity Check

Quickly estimate to ensure the number makes logical sense.

← previousStoichiometry And Limiting Reagents next →Review: Basic Concepts Of Chemistry

content

Expressing Concentration

Introduce Mass Percent and Mole Fraction.

When we mix a solute into a solvent, we need to express exactly how much is in there. Mass percent (w/w %) is the simplest way:

$\text{Mass percent} = \frac{\text{Mass of solute}}{\text{Mass of solution}} \times 100$

1 / 3

content

Molarity (M)

Define Molarity and dilution formula, with Problem 1.7.

Volume-Based Concentration

Molarity (M) is the most widely used unit in the chemistry lab. It is defined as the number of moles of solute dissolved in $1\text{ liter}$ of solution.

$\text{Molarity (M)} = \frac{\text{Moles of solute}}{\text{Volume of solution in liters}}$

Crucial Concept: Because liquids expand and contract with heat, volume changes with temperature. Therefore, Molarity is temperature-dependent.

1 / 5

content

Molality (m)

Define Molality and density conversion, with Problem 1.8.

Mass-Based Concentration

Molality (m) is defined as the number of moles of solute present in $1\text{ kg}$ of solvent.

$\text{Molality (m)} = \frac{\text{Moles of solute}}{\text{Mass of solvent in kg}}$

Crucial Concept: Since mass does not change with heat, molality is unaffected by temperature, making it highly reliable for experiments across varying temperatures.

1 / 5

feedback

Calculate Required Mass for Molarity

Exercise 1.5: Mass of sodium acetate required.

Calculate Required Mass for Molarity

Given values (with units)*

Identify the known variables and ensure units are standard (like Liters).

Formulas to use*

State the algebraic formulas governing this relationship.

Substitution*

Plug the given numbers into the formulas.

Calculation steps*

Show the intermediate calculation for moles, then for mass.

Final Answer*

State your final numerical answer with units and correct significant figures.

Reasonableness / Sanity Check

Quickly estimate to ensure the number makes logical sense.