Chemistry: Mixtures

Mixtures

• A mixture is a combination of two or more substances that do not combine chemically, but remain the same individual substances and can be separated by physical means.
• There are two types of mixtures: heterogeneous and homogeneous.

Heterogeneous Mixture

• A heterogeneous mixture is a mixture in which the composition is not uniform throughout the mixture.
• It consists of visibly different substances or phases (solid, liquid, gas).
• Examples: sand in water, oil and water.

Homogeneous Mixture

• A homogeneous mixture is a mixture in which the composition is uniform throughout the mixture.
• It has a uniform appearance and maintains one phase (solid, liquid, gas).
• Examples: salt water, sugar syrup.
• All solutions are mixtures, but not all mixtures are solutions.

Solution

• A solution is a homogeneous mixture of two or more substances whose particle size ranges between 0.1nm to 1nm.
• Examples: soda water, sugar syrup, salt solution.

Components of Solution

• Solute: the substance which is being dissolved.
• Solvent: the component of a solution in which the solute is being dissolved.
• Solute is the minor component in a solution, dissolved in the solvent.

Types of Solutions

• Gaseous solutions: air = Oxygen + Nitrogen.
• Liquid solutions: drinks = mix + water.
• Solid solutions: alloys = steel, brass, etc.

Properties of Solution

• It is a homogeneous mixture.
• Its particles are too tiny and have a diameter of less than 1 nm.
• The particles are not visible to the naked eye.
• Particles don’t scatter a beam of light passing through it and hence the path of the light is not visible.
• Solutes are inseparable from the mixture and do not sediment.
• A solution is stable.
• The components of a mixture cannot be separated using filtration.

Concentration

• The amount of solute dissolved in a solvent at a given temperature.
• Dilute solution: has a low concentration of solute dissolved.
• Concentrated solution: has a high concentration of solute dissolved.

Saturation

• Unsaturated: has less than the maximum concentration of solute dissolved.
• Saturated: has the maximum concentration of solute dissolved (can see solid in the bottom of the solution).
• Supersaturated: contains more dissolved solute than normally possible (usually requires an increase in temperature followed by cooling).

Solubility

• The amount of solute that dissolves in a certain amount of a solvent at a given temperature and pressure to produce a saturated solution.

Factors Affecting Solubility of Solids

• Temperature: increased temperature causes solids to dissolve faster.
• Particle Size: smaller particles dissolve faster because they have more surface area.
• Vibration (agitation): shaking or agitation causes solids to dissolve faster.

Solubility Curves

• Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.
• A point on the line is a saturated solution.
• Above the line is supersaturated.
• Below the line is unsaturated.

Mole

• According to the International System of Units (SI), a mole is defined as exactly 6.02214076 × 10²³ particles, which may be atoms, molecules, ions, or electrons.
• Example: 1 mole H2O = 6.022 × 10²³ H2O (water) molecules.

Mass and Mole

• The mass of one mole of a substance is equal to that substance's molecular weight.
• Example: Mass of water: 18.01528 g/mol.

Molarity (m)

• The number of moles of solute per liter of solution.
• M = moles of solute / liters of solution.

Dilutions and Molarity

• Use the formula: Molarity1 x Volume1 = Molarity2 x Volume2.
• Example: How many liters of 2.5 M HCl are required to make 1.5 L of 1.0 M HCl?

Molality (M)

• The number of moles of solute per kilogram of solvent.
• M = moles of solute / kilograms of solvent.

Normality

• The number of mole equivalents per liter of solution.
• Normality = number of mole equivalents / 1 L of solution.
• Equivalent weight or Mole equivalent = Molar mass / Valence factor.

Percent Solution

• v/v (volume per volume): 100 ml, 99 ml water + 1 ml HCl = 1% HCl v/v.
• w/v (weight per volume): 100 ml water, 2 gm NaCl = 2 % NaCl w/v.