1. Collision Theory Reactions occur when molecules collide together The collision theory says that: 1.atoms, ions, and molecules must collide in order to react. 2.Reacting substances must collide with the correct orientation 3.Reacting substances must collide with sufficient energy to form the activated complex The activated complex (or transition state) is a temporary, unstable arrangement of atoms that may form products or may break apart to reform the reactants.

2. Solutions A solution is a homogeneous mixture of two or more substances, whether solids, liquids, or gases, that has a uniform composition throughout and always has a single phase. In other words, looking at a solution, you cannot distinguish one substance from another after they have been mixed. Solute – the substance that is dissolved Solvent – the substance that does the dissolving Solutions can be mixtures of gas, liquid or solid, and in any combination.

3. Solubility When a substance dissolves in a solvent, it is said to be soluble. When a substance does not dissolve in a solvent, it is said to be insoluble. Ex: Sugar is soluble in water Table salt is soluble in water. Sand is insoluble in water. Solubility is the measurement of how well a substance can be dissolved into a solvent.

4. Solvation When a solute is placed in a solvent, solvent particles surround the solute. The attractive forces between the solvent and the solute begin to pull apart the solute, particle by particle. Each individual particle is then surrounded by solvent particles Solvation – the process of surrounding solute particles with solvent particles to form a solution. Ex: Dropping a cube of sugar into a glass of water “Like dissolves like” is a generalized rule for determining whether or not solvation will take place. The important consideration here is the type of bonding and polarity of the particles involved.

5. Factors That Affect Solvation Remember, solvation can only occur when solute particles contact solvent particles AND only when bonding forces of the molecules are compatible. –Nonpolar dissolves nonpolar –Polar dissolves polar and ionic Increasing the ability for solute particles to contact solvent increases the rate of solvation. This can be done by: Agitating the mixture (ie, shaking and stirring) Increasing the surface area Increasing the temperature of the solvent.

6. Identify the following mixtures as either soluble or insoluble. In the case of soluble, identify which is the solute and which is the solvent 1.Nitrogen and oxygen in the air. 2.Carbon dioxide and water (carbonated water) 3.Salt (NaCl) and water. 4.Sugar and water. 5.Sand and water. 6.Oil and water. 7.Alcohol and water. 8.Mercury and silver in dental amalgam 9.Salt and sand 10.Carbon and iron in steel

7. Factors That Affect Solubility Every solute has a characteristic solubility in a particular solvent under specific conditions. Changes in temperature increase the solubility of most (but not all) substances. Temperature vs Solubility graphs can be made to see how much of a substance dissolves into a set amount of solvent at different temperatures.

8. Factors That Affect Solubility Pressure plays an important role in the solubility of gaseous solutes. Henry’s Law states that as pressure increases, the solubility of the gas increases. Henry’s Law: S 1 = S 2 P 1 P 2 Ex: If 0.85g of a CO 2 at 4.0atm dissolves in 1.0L of water at 25 o C, how much will dissolve in 1.0L of water at 1.0atm and the same temperature?

9. Solution Concentration Concentration is the measurement of how much solute can be dissolved into a specific amount of solvent or solution. Concentrated solution – solution that contains a large amount of solute Dilute solution – a solution that contains a small amount of solute Ways to express concentration –Percent by mass –Mass of solute/mass of solution –Percent by volume –Volume of solute / volume of solution –Molarity –Moles of solute / Liter of solution –Molality –Moles of solute / kilogram of solvent –Mole Fraction –Moles of solute / (moles of solute + moles of solvent) –Part per million (ppm) –Milligrams solute / kilograms of solvent –Part per billion (ppb) –Micrograms solute / kilograms solvent –Part per trillion (ppt) –Nanograms solute / kilogram solvent

10. Molarity Molarity (M) is the calculation of choice for concentrations in chemistry. It is defined as the number of moles of solute dissolved in the total liter volume of solution made. This is easily related back to stoichiometry through grams and moles calculations.

11. Saturated Solutions A Saturated solution is obtained when a solvent (liquid) can dissolve no more of a solute (usually a solid) at a particular temperature. Supersaturation is the state of a solution that has a higher concentration of solute than would normally be obtained in a saturated solution. Supersaturation can be obtained because many solutes have a higher solubility at high temperatures. If a hot saturated solution is cooled slowly, sometimes the excess solute does not come out of solution. This is an unstable situation and the introduction of a small solid particle (seed crystal) will encourage the release of excess solute.

12. Dilution and Concentration Often in a laboratory environment, we begin with concentrated solutions (stock solutions) that must be diluted to a more useable, lower concentration. This is done by taking a known amount of the concentrated solution and adding enough pure solvent to reach the desired concentration. We can calculate the amounts to use by the equation: M 1 V 1 = M 2 V 2 Ex: What volume, of 2.00M calcium chloride (CaCl 2 ) stock solution would you use to make 0.50L of 0.300M CaCl 2 solution?