# Solutions – homogeneous mixtures that can be solids, liquids, or gases

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Solutions – homogeneous mixtures that can be solids, liquids, or gases
Solutions are made up of: 1) solute – material that is dissolved. (ex) salt 2) solvent – material that does the dissolving. (ex) water – most universal solvent

The composition of the solute and solvent will determine whether a solute will dissolve or not.
There are several factors which determine how fast the solute will dissolve: 1) Stirring (agitation) – the dissolving process occurs at the surface of the crystals that are being dissolved. Stirring speeds up the process because fresh solvent is continually brought into contact with the surface of the solute. Stirring only increases the rate, not the quantity that will be dissolved. Stirring will not make something dissolve that is not soluble.

2) Temperature – As temperature increases, so does the rate of dissolving. The solvent particles have higher kinetic energy with increases in temperature. The higher the energy, the more collisions there are with the solute. 3) Particle size – The smaller the particle size of the solute the faster the dissolving rate. The smaller the particle size, the larger the surface area which exposes more solute to be dissolved.

Solubility - The solubility of a substance is the amount of solute that dissolves in a given quantity of solvent at a particle temperature. - Miscible – 2 liquids are miscible if they dissolve in all proportions in each other. - Immiscible – liquids that are insoluble in each other.

Solution Discriptions
Saturated solutions – contains the maximum amount of solute that can dissolve in a given amount of solvent for a particular temperature. The solute and solvent are in equilibrium. Unsaturated solutions - A solution that can dissolve more solute at a given temperature.

Supersaturated – A solution that contains more solute than it can dissolve at a given temperature.
The crystallization of a supersaturated solution can be initiated if a very small crystal, called a seed crystal, of solute is added.

Factors Affecting Solubility
Temperature - The solubility of most solid substances increases as the temperature of the solvent increases. 2) Pressure – Changes in pressure have little effect on the solubility of solids and liquids, but strongly effect the solubility of gases. - Gas solubility increases as the partial pressure of the gas above the solution increases.

Carbonated beverages are a good example of this
Carbonated beverages are a good example of this. These drinks contain large amounts of CO2 dissolved in water. These drinks are bottled under high pressure, which forces the CO2 gas into solution. When the beverage is opened , the partial pressure of CO2 above the liquid decreases. Immediately bubbles of CO2 gas form in the liquid and escape from the open bottle. As a result, the concentration of dissolved CO2 decreases and if the container is left open, it becomes flat (loses the CO2).

Henry’s Law States that at a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid. In other words, as the pressure of the gas above the liquid increases, the solubility of the gas increases. S S2 _____ = _____ P P2

Molarity = moles solute/liter soln
One method of expressing the concentration of a solution. Concentration – a measure of the amount of solute that is dissolved in a given amount of solvent. Dilute solution – one that contains a small amount of solute. Concentrated solution – one that contains a large amount of solute.

Making Dilutions M1V1 = M2V2
Diluting a solution reduces the number of moles of solute per unit volume, but the total number of moles of solute remains the same. What you essentially have done has been to increased the volume of solvent. M1V1 = M2V2

Colligative Properties of Solutions
Colligative property – a property that depends upon the number of solute particles, and not their identity. 1) Vapor pressure – the pressure exerted by a vapor that is in dynamic equilibrium with its liquid in a closed system. A solution that contains a solute that is nonvolatile (not easily vaporized) always has a lower vapor pressure than the pure solvent.

This is true because the water molecules in solution reduces the number of solute particles that have enough energy to escape as a gas. 2) Freezing-Point Depression – The difference between the freezing point of a solution and the freezing point of the pure solvent. When a substance freezes the particles of a solid take on an orderly pattern. The presence of a solute in water disrupts the formation of this pattern. As a result, more kinetic energy must be withdrawn from a solution than from the pure solvent to cause the solution to solidify.

The freezing point of a solution is lower than the freezing point of the pure solvent.
The magnitude of the freezing-point depression is proportional to the number of solute particles dissolved in the solvent and does not depend upon their identity. 3) Boiling-Point Elevation – the difference in temperature between the boiling point of a solution and the boiling point of a pure solvent. Boiling point – the temperature at which the vapor pressure of the liquid phase equals atmospheric pressure.

Adding a nonvolatile solute to a liquid decreases the vapor pressure of the solvent. Because of the decrease in vapor pressure, additional KE must be added to raise the vapor pressure of the liquid phase of the solution to atmospheric pressure and initiate boiling. Thus the boiling point of a solution is higher than the boiling point of the pure solvent. The magnitude of the boiling-point elevation is proportional to the number of solute particles dissolved in the solvent.

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