Study sheet: Aqueous Solutions and Concentrations

📋 Course Outline

1. Solution Composition and Notation
2. Mass Concentration and Solubility
3. Mass Concentration and Density
4. Preparing Aqueous Solutions
5. Concentration by Calibration

📖 1. Solution Composition and Notation

🔑 Key Concepts & Definitions

• Solution : A homogeneous mixture obtained by dissolving one or more solutes in a solvent.

★ Must-know

📌 The solute is the dissolved chemical species and is often minor or unique, whereas the solvent is the chemical species that is major in the solution.

Further detail

• A solution is aqueous when water is the solvent, and the dissolved species are then written with the state symbol (aq).

• An aqueous potassium permanganate solution contains the aqueous species K+ (aq) and MnO4− (aq).

💡 Memory Hook

Solute is dissolved and usually minor; solvent is the major component.

📖 2. Mass Concentration and Solubility

🔑 Key Concepts & Definitions

• Mass concentration : The mass of solute dissolved per litre of solution.
• Saturated solution : When the solute mass concentration is maximal and no more solute dissolves in the solvent.
• Solubility : The maximum mass concentration of a solute in a solvent, denoted s.

★ Must-know

📐 Formula — Mass concentration satisfies $C_m=\frac{m}{V}$, where m is the dissolved solute mass and V is the solution volume; equivalently, $m=C_m\times V$.

Further detail

• A solution containing 5.0 g of saccharose in 0.20 L has a mass concentration of 25 g·L−1 and is not saturated because this is below its solubility of 2.0 × 10^3 g·L−1 in water at 25 °C.

• The concentration units obey 1 × 10−3 g·L−1 = 1 mg·L−1, 1 × 10−6 g·L−1 = 1 µg·L−1, and 1 × 10−9 g·L−1 = 1 ng·L−1.

💡 Memory Hook

More dissolved solute per volume → higher mass concentration, until saturation.

📖 3. Mass Concentration and Density

🔑 Key Concepts & Definitions

• Mass density : The ratio of the mass of the solution to its volume.

★ Must-know

📐 Formula — The mass density satisfies $\rho=\frac{m_{\mathrm{solution}}}{V}$, whereas the solute mass concentration satisfies $C_m=\frac{m_{\mathrm{solute}}}{V}$.

Further detail

📌 The mass of a solution is different from the mass of the solute dissolved in that solution, so mass density and solute mass concentration are different quantities.

💡 Memory Hook

Solution mass belongs to density; solute mass belongs to mass concentration.

📖 4. Preparing Aqueous Solutions

🔑 Key Concepts & Definitions

• Dilution factor : The dilution factor is defined by $F=\frac{V_f}{V_0}=\frac{C_{m0}}{C_{m1}}$; for the stated diluted solution, F = 2.3.

★ Must-know

• Preparing a solution by dissolution consists of putting a specified mass of solute into solution to obtain a specified mass concentration, using a volumetric flask with the required final volume.

• Dilution consists of adding solvent to a mother solution to prepare a daughter solution with a lower solute mass concentration.

📐 Formula — During dilution, the dissolved solute mass is conserved, so $C_{m0}\times V_0=C_{m1}\times V_f$.

Further detail

📐 Formula — The mother-solution volume to sample is $V_0=\frac{C_{m1}\times V_f}{C_{m0}}$.

• A volumetric pipette is selected to transfer the exact mother-solution volume V0, and the solution is completed with solvent in a volumetric flask of volume Vf while accounting for measurement precision.

💡 Memory Hook

Dissolve a solute or dilute a mother solution to obtain the daughter solution.

📖 5. Concentration by Calibration

🔑 Key Concepts & Definitions

• Standard solution : A solution whose solute mass concentration is known; a set of standard solutions has different known concentrations.

★ Must-know

• Calibration determines an interval for an unknown solute mass concentration by comparing the unknown solution with standard solutions.

Further detail

• For a colored solution, the unknown color is compared with the colors of standard solutions having the same hue, which form a scale of shades linked to solute mass concentrations.

• The concentration of an unknown solution can also be compared with standards by measuring a characteristic quantity such as absorbance.

💡 Memory Hook

A colored scale of standard solutions frames the unknown concentration.

📊 Synthesis Tables

Mass Density Versus Mass Concentration

Quantity	Mass used	Relation
Mass density	Mass of the solution	$\rho=m_{\mathrm{solution}}/V$
Solute mass concentration	Mass of dissolved solute	$C_m=m_{\mathrm{solute}}/V$