Units & Concentration in Chemistry

Units & Concentration

• Molarity (M): The number of moles of solute dissolved in one liter of solution (water).
• Formula: M = moles of solute / liters of solution
• Used for substances that dissolve in water.
• Necessary units: grams and liters, convert if needed.

Molality (m)

• The number of moles of solute dissolved in one kilogram of solvent.
• Formula: m = moles of solute / kilograms of solvent
• Used for substances that dissolve in solvents other than water.

Normality (N)

• The number of gram equivalent weights of solute dissolved in one liter of solution; used for reactions involving acids, bases, or redox reactions.
• Formula: N = gram equivalent weight of solute / liters of solution

Strength (S)

• The weight in grams of a substance dissolved in a liter of solution.
• Formula: S = weight of solute (g) / volume of solution (L)

Standard Solution

• Solution with an exactly known concentration.
• Prepared by dissolving a known weight of substance in a definite volume of water.

Part Per Million (PPM)

• The weight of a substance in milligrams (mg) in one liter of solution.
• Formula: PPM = weight of substance (mg) / volume of solution (L)
  • Used in determining the concentration of substances like cholesterol, calcium, or urea.

Percentage

• Can be weight-percentage or volume-percentage. Weight percentage is the ratio by weight of one component (solute) to the total weight of the solution (solute + solvent), multiplied by 100
• Volume percentage is the ratio by volume of one component (solute) to the total volume of the solution (solute + solvent), multiplied by 100.
  • Used for general or commercial purposes.

Diluent Ratio

• The ratio of solute to solvent by volume
  • Used in determining concentration.

Dilution Law

• (Concentration) * (Volume) before dilution = (Concentration) * (Volume) after dilution.
  • For example: C1V1 = C2V2

Mole Fraction (X)

• The ratio of the number of moles of a constituent to the total number of moles of all constituents in a mixture.
• Formula: Xₙ = nₙ / (n₁ + n₂ + ... + nₙ) Where nₙ is the number of moles of constituent n, and the denominator sums the number of moles of all constituents in the mixture.

Activity (a)

• The relative effectiveness of a substance in a reaction. It corrects for changes in concentration that occur at high concentrations.
• Activity Coefficient (f): A value that compares activity to concentration.
• Activity is generally equal to or slightly lower than concentration at low concentrations and equal to or slightly higher than concentration at high concentrations. When concentration is low, a = concentration; as concentration increases beyond a specific point, activity is calculated using an activity coefficient (f).

Density of Solution (d)

• Mass of solution (kg)/Volume of solution (m³)

Test your understanding of molarity, molality, normality, and strength in solutions with this quiz. Learn how to calculate concentrations and the significance of standard solutions in chemical reactions. Challenge yourself with problems related to these essential chemistry concepts.