Solubility Chemistry

Learning Objectives TLW investigate factors that influence solubilities and rates of dissolution such as temperature, agitation, and surface area (TEKS 10.F)

SOLUBILITY… A. In order for there to be mixtures, one substance is usually dissolved into another B. Solubility is the amount of solute that will dissolve in a specific amount of solvent C. Factors that affect solubility or dissolving rate

Temperature a. Solubility of a salt or solid in a liquid increases with increasing temperature *dissolves faster at higher temperatures b. Solubility of a gas in a liquid increases with decreasing temperature * dissolves faster at lower temperatures

Molecular Motion a. Stirring or shaking a mixture speeds up the dissolving rates b. The more the molecules move; the faster the substance dissolves c. Adding sugar to tea = you always stir before you drink

Amount of Surface Area a.The more surface area that is exposed to the solvent the faster a solute will dissolve b. Little pieces dissolve faster than larger pieces

c. So…crushing a solute increases the dissolving rate * by increasing the surface area exposed to the solvent.

Volume Increasing the volume of the solvent can cause solutes to dissolve more/faster

Change the Solvent Different solvents have different properties which may increase their solubility.

More on Solubility of Gases a. As we saw previously, increasing a gas’ temperature will decrease solubility in liquid b.Gas solubility depends on pressure, as well as temperature. c.Solubility of a gas in a liquid increases ( ) with increasing ( ) pressure, because the pressure forces the gas molecules into solution (harder for the molecules to escape) d. For example -- carbon dioxide (a gas) is dissolved into water evenly when the can is closed. When opened gas is released and solubility decreases.

Water a. Water dissolves most solutes. As a result, it is called the universal solvent b. A water molecule has a positive end and a negative end making water a very good solvent c. 2/3 of Earth is water, 3/4 of your body is water

Saturation A. At some point most solutions become saturated with solute 1. Saturation is when the solvent cannot dissolve anymore solute 2. A saturated solution is in equilibrium * if more solute is added it will not dissolve and settles to the bottom

3. The same number of solute molecules are dissolving as are coming back out of solution. * this is equilibrium * this is known as the saturation point 4. The only way to tell if a solution is saturated is by seeing excess solutes

B. A solution that is able to dissolve more solute is called an unsaturated solution C. A solution that holds more dissolved solutes than it should is called a supersaturated solution * most solutions can dissolve more by heating up the solvent

unsaturated Saturated

Solubility Rules for Ionic Compounds See EOC/STAAR Reference Material for Water Solubility Information Common compounds formed with Group 1 elements and ammonium ions (NH 4+ ) are soluble –Otherwise carbonate, hydroxide, oxide, silicate, and phosphates are insoluble Compounds formed between Group 7 elements (except Fluorine) and most metals are soluble All nitrates (NO 3 - ) are soluble Acetate, chlorate, sulfate are soluble (unless sulfate is paired with Ba, Sr, Ca, Pb, or Hg) Sulfide compounds are soluble – only if they contain Ca, Ba, Sr, Mg, Na, K, or NH 4+

Summary 1. The amount of solute that will dissolve in a certain amount of solvent is called Solubility 2. When temperatures increase the solubility of a solid in a liquid will Increase

3. When temperatures decrease the solubility of a gas in a liquid will Increase 4. Stirring or shaking up a solution will do what to the dissolving rate Speed it up 5. The more surface area exposed causes the solute to dissolve faster

6. What is the universal solvent? Water 7. A solution that cannot dissolve anymore solute is called Saturated 8. When there is an equal amount of solvent and solute, the solution is at Equilibrium

9. A solution that can still dissolve more solute is Unsaturated 10. A solution holding more solute than it should is said to be supersaturated