Victoria Hon

Andrea Ma

Period 5

Solution– a homogenous mixture of two or more substances in a single phaseSoluble- capable of being dissolvedSolvent- dissolving medium in a solutionSolute- substance being dissolved

Solutions occur when two or more substances form a mixture that has the same composition and properties throughout.

Examples: Water, sterling silver, brass

Suspensions contain particles so large that they settle out unless the mixture is constantly stirred/agitated.

Examples: Sand in water, pulp in orange juice, mud in water

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Colloids contain particles that are intermediate in size, between those in solutions and suspensions.

The particles in a colloid are small enough to be suspended in the solvent by the constant movement of the surrounding molecules.

Though many colloids appear homogeneous because the individual particles cannot be seen, the particles are large enough to scatter light. When light is shone through a colloid, the particles are scattered, making the beam visible. In this way, a beam of light distinguishes a colloid from a solution.

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Figure 11.23: The Tyndall effect.

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Solutions Colloids Suspensions

Homogeneous Heterogeneous Heterogeneous

Particle size: 0.01-1.0 nm; can be

atoms, ions, molecules

Particle size: 1-1000 nm; can be

aggregates or large molecules

Particle size: over 1000 nm; cam be

aggregates or large particles

Do not separate on standing

Do not separate on standing

Particles settle out

Cannot be separated by

filtration

Cannot be separated by

filtration

Can be separated by filtration

Do not scatter light Scatter light (Tyndall effect)

May scatter light, not transparent

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The Dissolution of a Solid in a Liquid

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Figure 11.1: The formation of a liquid solution can be divided into three steps: (1) expanding the solute, (2)

expanding the solvent, and (3) combining the expanded solute and solvent to form the solution.

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Figure 11.2: The heat of solution (a) ?Hsoln has a negative sign (the process is exothermic) if step 3 releases more energy than that required

by steps 1 and 2. (b) ?Hsoln has a positive sign (the process is endothermic) if steps 1 and 2 require more energy than is released in step 3. (If the energy changes for steps 1 and 2 equal that for step 3,

then ?Hsoln is zero.)

An electrolyte is a substance that dissolves in water to give a solution that conducts electricity.

Examples: NaCl, HCl

A non-electrolyte is a substance that does not conduct an electric current when dissolved in water.

Examples: sucrose

Increasing the surface area of the solute: because the dissolution process occurs at the surface of the solute, it can be speeded up if the surface area is increased. (example: crushing sugar cubes increases the surface area, so it dissolves quickly)

Agitating the solution: stirring helps to disperse solute particles, bringing fresh solvent into contact with the solute surface (example: stirring sugar into iced tea)

Heating the solvent: as the temperature of the solvent increases, more collisions between the solvent molecules and the solute occur, helping to separate solute molecules from one another and to spread them throughout the solvent molecules, making dissolving faster. (example: sugar dissolves more quickly in warm water than in cold water)

When a solution contains the maximum amount of dissolved solute, it is called a saturated solution.

A solution that contains less solute than a saturated solution under the same conditions is called an unsaturated solution.

A supersaturated solution contains more dissolved solute than a saturated solution under the same conditions.

Figure 11.6: The solubilitiesof several solids as a function of temperature.

Figure 11.7: The solubilitiesof several gases in water as a function of temperature at a constant pressure of 1 atm of gas above the solution.

Immiscible- liquid solutes and solvents that are not soluble in each other

Miscible- liquids that dissolve freely in one another in any proportion

Solution equilibrium- physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates Effects of pressure on solubility: increases in pressure increase gas solubilities in liquid

Effects of temperature on solubility: as the temperature increases, the average kinetic energy of the molecules also increases, decreasing solubility

Effervescence- the rapid escape of a gas from a liquid in which it is dissolved

Henry’s Law: The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid.

Molarity- the number of moles of solute in one liter of solution

Molarity (M) = amount of solute (mol) volume of solution (L)

Molality- the concentration of a solution expressed in moles of solute per kilogram of Solvent

Molality (m) = moles of solute (mol) mass of solvent (kg)