Solutions, Acids, and Bases Chapter 8 Solutions, Acids, and Bases

8.1 Formation of Solutions

Dissolving Recall that a solution is a homogeneous mixture of two or more substances Every solution has two components: Solute Substance whose particles are dissolved in a solution Solvent Substance in which the solute dissolves Ex. Seawater – water is solvent, salt is solute

Dissolving Solutes and solvents can take the form of solid, liquid, or gas Solution takes state of solvent Substances can dissolve in water in three ways Dissociation Dispersion Ionization

Dissociation of Ionic Compounds For a solute to dissolve in water The solute and solvent particles must attract to one another The solute particles are attracted and the solvent particles are attracted to one another So, before a solution can form, those attractions must be overcome Process in which an ionic compound seperates into ions as it dissolves is called dissociation

Dispersion of Molecular Compounds The water in your saliva dissolves the sugar and flavoring in candy throughout your mouth Sugar dissolves in water by dispersion, or breaking into small pieces that spread throughout the water Both sugar and water are polar, therefore attract When enough water molcules have surrounded the sugar molecule, sugar molecule breaks free and is pulled into solution

Ionization of Molecular Compounds HCl – molecular compound where hydrogen and chloride share an electron When HCl gas dissolves in water, the H molecule is transferred to water H30+ and Cl- are produced When a neutral molecule gain or lose electrons it is known as ionization This is a chemical change Unlike dispersion and dissociation

Properties of Liquid Solutions Three physical properties of a solution that can differ from those of its solute and solvent are: Conductivity Freezing point Boiling point

Conductivity Solid sodium chloride is a poor conductor When it dissociates in water, the sodium and chloride ions are able to move freely They will then conduct electricity

Freezing Point and Boiling Point MgCl2 is what is sometimes spread on icy roads When it dissolves in melting ice, it dissociates into Mg2+ and Cl- These ions are able to interfer with freezing process Salted roads have a freezing point of -15°C

Freezing Point and Boiling Point Solute can also raise boiling point ex. Coolant used in most car radiators Adding ethylene glycol to water raises the boiling point Solution helps prevent the engine from overheating Also prevents the the liquid from freezing in the winter

Heat of Solution During the formation of a solution, energy is either released or absorbed Can be described as either exothermic or endothermic Dissolving sodium hydroxide in water is exothermic, releases heat How it Works box explains how cold packs are used

Heat of Solution In order for a solution to form, all attractions must be broken That requires energy Formation of solutions, releases energy The difference between these energies is called the heat of solution

Factors Affecting Rates of Dissolving Reates of dissolving depend on the frequency and energy of collisions Formation of solutions, collisions occur between solute and solvent particles Factors that affect the rate of dissoling include: Surface area Stirring temperature

Factors Affecting Rates of Dissolving The greater the surface area of a solid solute, the more requent the collision are between the solute and the solvent particles Increase surface area by breaking into smaller pieces Stirring Moves dissolved particles away from surface Allows more collisions between solute and solvent

Factors Affecting Rates of Dissolving Increasing temperature is another way to speed up dissolving Increase in temperature causes the particles to move faster Both the number of collisions and the energy of these collisions increases Goes into solution more quickly

8.2 Solubility and Concentration

Solubility Solubility Solutions are described as: The max amount of a solute that dissolves in a given amount of solvent at a constant temperature Usually expressed in grams of solute in 100g of solvent Solutions are described as: Saturated Unsaturated Supersaturated

Solubility Saturated Sugar is very soluble in water At 20 degrees C you can dissolve 203.9 grams of sugar in 100g of water What will happen if you try to dissolve more than that? The extra sugar will not go into solution The solution is already saturated One that contains as much solute as the solvent can hold at a given temperature

Solubility Unsaturated A solution that has less than the max amount of solute that can be dissolved many beverages are unsaturated

Solubility Supersaturated If you heat a solvent above the average temperature it can dissolve more solute If you then carefully cool the solvent back to the average without jarring it, you may be able to keep the extra solute in the solution Supersaturated solution One that contains more solute than it can normally hold at a given temperature Very unstable If a tiny particle falls into a supersaturated solution, the extra solute may rapidly fall out

Factors Affecting Solubility Have you ever tried to wash oil or grease off your hands? Will not come off in just water, but in soapy water it will wash off Not soluble in water, but in soapy water it is Three factors that affect solubility: Polarity of the solvent Temperature pressure

Factors Affecting Solubility Polar and Nonpolar Solvents Oil molecules are nonpolar, water is polar Common guideline for predicting solubility is ‘like dissolves like’ More likely to dissolve if solute and solvent are both polar or both nonpolar Soap molecules have a polar and non polar end Makes it easy to dissolve oil

Factors Affecting Solubility Temperature In general the solubility of a solute increases when you increase the temperature of the solvent When water temp increases, bubbles start to come out of the water These are gas bubbles that are dissolved in water Unlike most solids, gases usually become less soluble as the temperature of solvent increases

Factors Affecting Solubility Pressure Incresing the pressure on a gas increases its solubility in a liquid Pressure of carbon dioxide in a 12 oz can of soda at room temp can by two to three times atmospheric pressure