Concentrations

What is concentration?

• how much solute is present in a given amount of solvent / solution

What is a solute?

substance dissolved in a solution

What is a solvent?

• substance that dissolves the solute

  • usually in greater quantity

What are some ways to express concentration?

Molarity (M) • Percent by mass or volume • Molality (m) • Parts per million (ppm)

What is the most common unit for concentration in chemistry?

Molarity (M)

•M = moles of solute / liters of solution

What is molality (m)?

• Moles of solute per kilogram of solvent

• m = mol of solute / kg of solvent

What is percent by mass?

% by mass = (mass of solute / mass of solution) × 100

What is percent by volume?

% by volume = (volume of solute / volume of solution) × 100

How is concentration affected by dilution?

• Concentration decreases when more solvent is added

• Amount of solute stays the same

What is the dilution formula?

• M₁V₁ = M₂V₂ • M₁ = initial molarity

How do you prepare a specific molar solution in the lab?

• Calculate moles of solute needed

• Convert to grams using molar mass

• Dissolve in less than final volume of solvent

• Dilute to desired final volume in a volumetric flask

What happens to the concentration when a solution is evaporated?

• Concentration increases

• Solvent volume decreases

  • but solute stays the same

Why is accurate concentration important in chemistry?

Affects:

• Rxn rates

• Chemical equilibrium

• Stoichiometry

• Ensures reliable + reproducible results