Mixtures and Solubility Chapter 12, sections 1 and 2 p

Solute vs Solvent  The solute is the substance dissolved into the solvent.  Solutions can be solid, liquid, or gas  Definition of solution: Homogeneous mixture of two or more substances in a single phase.  Solutions have particles that range from 0.01 to 1 nm in diameter

Solutions can be solid, liquid, or gas  Solid examples:  sugar in water (solid solute and liquid solvent);  Hg in Ag and Sn (dental amalgam – liquid solute in solid solvent)  metal alloys (solid solute and solid solvent );  brass (Zn + Cu),  sterling silver (Ag + Cu), or  different karats of gold  (24K is pure Au which is too soft to use in jewelry, but 14K contains even mixtures of Au, Ag, Cu which increases strength and hardness)

Solutions can be solid, liquid, or gas  Liquid examples:  sugar in water (solid solute and liquid solvent);  Alcohol in water (liquid solute and solvent)  Hg in Ag and Sn (dental amalgam – liquid solute in solid solvent)  Carbon dioxide in water (gas solute in liquid solvent)  Gas examples:  Oxygen in nitrogen (gas solute in gas solvent)  Carbon dioxide in water (gas solute in liquid solvent)

Liquid solutes  Rule of Thumb: “Like Dissolves Like”  This means that polar solutes will only dissolve in polar solvents (like water) and nonpolar solutes will only dissolve in nonpolar solvents (like toluene).  miscible - two liquids that can be dissolved in each other Ex: ethanol and water  immiscible - two liquids that cannot be dissolved in each other Ex: oil and vinegar

Gas solutes  gases can dissolve in liquids to form solutions  Ex: soda has dissolved CO 2 gas  Henry’s law - at a given temp, gas solubility (amount of gas dissolved) is directly related to pressure pressure = gas dissolved

Solubility and Temperature  Solid and liquid solutes dissolve faster when the temperature is hotter (direct relationship)  Ex. Sugar in sweet tea – add sugar when heating the tea for get it evenly dissolved.  Gas solutes dissolve faster when the temperature is colder (inverse relationship)  Ex. Carbonation in soda – stays carbonated longer when in the refrigerator, gets flat at room temperature or hot temperatures.

Mixtures can be physically separated Homogeneous looks even throughout Heterogeneous looks uneven throughout Solutions small particles stay dissolved Colloids large particles stay dissolved Suspensions large particles settle out

Types of Solutions  Colloid: particles are intermediate in size between solutions and suspensions.  Particles between 1 and 1000 nm in diameter  Ex. Muddy water after filtering out soil  Ex. Emulsion, foam, gel, aerosol  Paint, mud, gelatin, milk, mayonnaise, shaving cream, whipped cream, smoke, exhaust, fog, mist, clouds, aerosol spray, cheese, butter  Suspension: particles of solute are so large that they settle out of solution unless constantly agitated.  Particles over 1000 nm in diameter, can be filtered out  Ex. muddy water

The Tyndall effect  Distinguishes colloids and suspensions from true solutions  Light beamed into a colloid or suspension will scatter and be visible inside the mixture  An example of this effect is while driving in the fog: using the high beams will not help to make the road more visible because the bright light will be scattered by the dense fog particles. Low beams shine below the fog and illuminate the road without scattering and blinding anyone.

Solubility  Definition: Amount of solute that can be dissolved in a specific volume of solvent under certain conditions  Increase solubility by increasing:  Volume of solvent  Temperature  The solubility of a substance remains constant when the system reaches equilibrium

Saturation  Saturated - maximum amount of solute has dissolved  Unsaturated - more solute can still be dissolved  Supersaturation - more than the maximum amount of solute is dissolved  Usually must be heated or under pressure to create a supersaturated solution  Solutions are unstable - if more solute is added, crystals will form

Factors affecting Dissolving Rate 1. Temperature of the solvent  Faster movement causes more collisions between particles - solute is quickly surrounded and dissolves faster 2. Particle Size of the solute  Smaller solute is easier to dissolve - more surface area is exposed to the solvent 3. Stirring of the solution  Stirring increases collisions - exposes solute molecules to more solvent

Solubility Curves  Units of Solubility:  X grams of solute per 100 grams of solvent  Represents the amount of solute that will dissolve at different temperatures  Different for each solute/solvent

Chapter 12, section 3: concentration of solutions  Concentration is the measure of the amount of solute in a given amount of solvent or solution.  Dilute vs concentrated = less solute vs more solute.

Molarity  Molarity is measured in M, and it is found by dividing moles of solute by liters of solution  Liters of solution is not only liters of solvent, but the total solution, which includes the volume of the solute.  Equation: molarity (M) = amount of solute (mol) volume of solution (L) Units: M or mol/L

Write these down, then do the practice on p.421  Page 420: Sample problem  You have 350 mL of solution that contains 90.0 g of sodium chloride, NaCl. What is the molarity of that solution? a. Change mL to L (move the decimal 3 times to the left) b. Change grams to moles (divide by molar mass of NaCl) c. Divide moles by liters  Page 421  To produce 40.0 g of silver chromate, you will need at least 23.4 g of potassium chromate in a solution as a reactant. All you have on hand is 5 L of a 6 M K 2 CrO 4 solution. What volume of the solution is needed to give you the 23.4 g K 2 CrO 4 needed for the solution?  Cross out the first sentence. Convert 23.4 g K 2 CrO 4 to moles.  Plug into the formula M = mol/L solve for L  Is L less than the 5 L that you have?

5 Different units of concentration Parts per million: Parts per billion: Molarity (M) Molality (m):Percent by weight: