F ACTORS A FFECTING S OLVATION 14.3: Pgs

S TEP 1 OF L AB 1. Obtain a CLEAN test tube!!! 2. Place 2.2 grams of Na 2 SO 4 into a test tube and add 10mL of water. 3. Dissolve the solid: Heat the test tube in a bunsen burner until you hear a “pop”. Remove the test tube from the bunsen burner and stir the contents with a stirring rod. Continue this process until the solid dissolves. 4. Place the test tube into the test tube rack when the solid is dissolved. 5. Place 2 ice cubes into a beaker and fill the beaker with water (You will use this later) 6. Sit back in your seat.

S OLUTION F ORMATION What did you do to make the solid dissolve faster?

S OLUTION F ORMATION Factors Affecting Solubility Rate: 1. Agitation  stirring increases the rate at which a solute dissolves Only affects the rate, NOT the amount! 2. Temperature  hot solvents dissolved solutes faster than cold solvents 3. Particle Size  fine powders dissolve more rapidly than large particles Think about sugar cubes vs. table sugar! 4. Pressure  refers to gases only!

S OLUBILITY Saturated Solutions : contain the maximum amount of solute for a given amount of solvent Solubility is the amount of solute that dissolves in a given quantity of a solvent at a given temperature to produce a saturated solution (i.e. NaCl = 36.2g per 100 mL H 2 O) Unsaturated solutions contain less than the maximum

S OLUBILITY

S TEP 2 OF THE L AB 1 person from your team must place your test tube into the beaker of ice water and then return to your seat.

D YNAMIC E QUILIBRIUM In saturated solutions, the rate of new particles dissolving vs. dissolved particles recrystalizing is EQUAL!

S OLUBILITY Supersaturated solutions Contains more solute than is allowed at a given temperature.

S OLUBILITY OF G ASES Gases have greater solubility in cold water then hot water  why? Gas solubility increases as the partial pressure above the solution increases – why?

S OLUBILITY OF G ASES Sodas are bottled at HIGH pressures! When the bottle is opened, the CO 2 escapes because the partial pressure of CO 2 above the liquid decreases

S OLUBILITY OF G ASES Henry’s Law At a given temperature, the solubility of a gas (S) is directly proportional to the pressure (P) of the gas above the liquid

P RACTICE P ROBLEM : If the solubility of a gas in water is 0.77g per 100mL of water at 3.5atm of pressure, what is its solubility (in g per 100mL of water) at 1.0atm of pressure. (Assume the temperature remains constant.)

L AST STEP OF THE LAB GENTLY remove the test tube from the cold water. Add a small amount of Na 2 SO 4 and observe. Clean up the lab: All solution/compounds can be rinsed down the drain. Sit back in your seat.

W HAT HAPPENED ? How should we label the solution before we added the crystal? Supersaturated solution Contains more solute than is allowed at a given temperature. Supersaturated solutions are unstable. If a small crystal of the solute is added to a supersaturated solution, the excess immediately crystallizes out. How should we label the solution after the crystal was added? unsaturated

Y ESTERDAY WE COVERED … 4 factors that will increase the rate of dissolution Today we will cover… How temperature not only increases the rate of dissolution, temperature also affects the amount that can dissolve.

F ACTORS A FFECTING S OLUBILITY Solubility is VERY temperature dependent! Ex: 36.2g of NaCl dissolves in 100g H 2 O at 25 o C, HOWEVER 39.2g NaCl can dissolve in 100g H 2 O at 100 o C! For most substances, solubility increases as temperature of the solvent increases

S OLUBILITY C URVES What substance has the highest solubility at 50 o C? (exclude KI) What has the lowest at 50 o C?

P ROBLEM : I dissolved 5.2g of a substance into 16g of water. What is the solubility of this substance in units of g / 100g of water?

S OLUBILITY C URVE L AB Not all substances are stable enough to create a supersaturated solution. Most substances can only form a saturated solution. We will complete this as a class. Each pair of students will be assigned a specific amount of salt to use and we will collaborate our data to create a lab report.