Solutions and Concentration Fundamentals

The page introduces key concepts about solutions and their concentrations in chemistry. The fundamental solution and concentration formula is presented as:

Concentration (mol dm⁻³) = number of moles of solute (mol) / volume of solution (dm³)

Definition: A solute is a substance that dissolves in a solvent to form a solution, while a solvent is the substance that does the dissolving.

Example: When calculating the concentration of NaOH solution, if 250 cm³ contains 20g of sodium hydroxide $Mr = 40.0$:

1. Convert mass to moles: 20g ÷ 40.0 = 0.5 mol
2. Convert volume to dm³: 250 cm³ ÷ 1000 = 0.25 dm³
3. Calculate concentration: 0.5 mol ÷ 0.25 dm³ = 2.0 mol dm⁻³

Highlight: When performing calculations involving concentrations in mol dm⁻³:

• Always convert mass in grams to moles
• Convert cm³ to dm³ by dividing by 1000

Vocabulary:

• Dilute solution: Contains a low concentration of solute
• Concentrated solution: Contains a high concentration of solute
• mol dm⁻³: Moles per cubic decimeter, the standard unit for concentration

The page also demonstrates how to calculate the mass of NaOH needed to prepare 20 dm³ of 2 mol dm⁻³ solution, which requires understanding the relationship between concentration, volume, and mass. This is particularly useful for concentration of solution problems with answers and practical laboratory work.