The Process of Dissolution The process of dissolving a solute in a solvent is a PHYSICAL CHANGE The intermolecular forces between the solvent and the solute are sufficient to overcome the intermolecular forces between solute particles –Remember the video of NaCl dissolving in water A TRUE SOLUTION IS A HOMOGENEOUS MIXTURE Suspensions of colloids (tiny particles) are not true solutions though they sometimes look like it. The TYNDALL EFFECT will distinguish between a true solution and a heterogeneous suspension True solution Heterogeneous mixture showing Tyndall effect

Factors that affect Dissolution Stirring: Continuous stirring or agitation will increase the rate of dissolving. Temperature: Increasing the temperature of the solvent will increase the rate of dissolving. Surface Area: Increasing the surface area of the solute will increase the rate of dissolving. How fast a solute can dissolve depends upon…. How fast a substance dissolves GOES UP when… Stirring or shaking is applied The substance is powdery vs. chunky (surface area) Temperature is increased

SOLUBILITY SOLUBILITY is defined by HOW MUCH solute dissolves, not how fast Reported as grams of solute in 100 grams of solvent at a given temperature REMEMBER: LIKE DISSOLVES LIKE Immiscible liquids Miscible liquids Non-polar in polar Polar in polar

UNSATURATED SATURATED SUPER SATURATED DEGREE OF SATURATION Solute completely dissolved and the solvent can hold more Some solute remains insoluble-solvent can’t dissolve more Unstable solution created by the dissolution of more solute than the solvent can theoretically dissolve

QUANTIFYING SOLUBILITY THE SOLUBILITY CURVE Super saturated saturated unsaturated If the solute is dissolved… Solubility g/100 g water Temperature o C

Using the Solubility Curve Solubility g/100 g water Temperature o C Read At 60 o C, the solution is saturated at 116 g/100 g water Read 80 g/100 g water will make a saturated solution at 17 o C Read A solution of 80 g/100 g water is unsaturated at 40 o C Read A solution of 120 g/100 g water is supersaturated at 40 o C

Other Features Gases display a “negative” solubility with temperature …in other words, as the solution temperature increases the solubility decreases Most solutes display a “positive” solubility with temperature…in other words, as the solution temperature increases the solubility increases

Henry’s Law-PRESSURE VS. SOLUBILITY FOR A GAS Henry’s Law states that the solubility of a gas is directly proportional to the partial pressure of that gas on the surface of the liquid INCREASE P above the liquid INCREASE solubility of the gas in the liquid TEMPERATURE VS. SOLUBILITY FOR A GAS Increased temperature causes an increase in kinetic energy There doesn’t need to be much energy input to cause gas SOLUTE intermolecular forces The higher kinetic energy causes more motion in molecules which break intermolecular forces of attraction (gas solute to solvent) and the gas can escape from solution. Why doesn’t this apply to most solids?

Ionization-occurs when an ionic compound dissociates during dissolution (dissolving) NaCl (s) Na + (aq) + Cl – (aq)100% HF (q) H + (aq) + F - (aq) 5-10% NaCl is a better CONDUCTOR of electricity than HF because it has a higher concentration of ions in solution Electrolytes-Solutions (or melts) of IONS that CONDUCT ELECTRICITY NaCl is a strong electrolyte HF is a weak electrolyte Is sugar an electrolyte? Is distilled (pure) water an electrolyte? Will tap water conduct electricity?

The word “colligative” refers to “counting” or “number of particles” Colligative properties are those properties that DEPEND on the NUMBER of dissolved particles When a sugar cube is dissolved in water, 1 particle (molecule) of sugar is dissolved for each one present in the cube –1 mole of sugar will give 1 mole of sugar molecules in solution –C 6 H 12 O 6 (s) C 6 H 12 O 6 (aq) When a NaCl crystal is dissolved in water, 2 particles (ions) are dissolved for each formula unit of NaCl in the crystal –1 mole of NaCl produces 2 moles of ions in solution –NaCl (s) Na+ (aq) + Cl- (aq) 2 moles of ions per mole of formula unit THE MORE PARTICLES IN SOLUTION (PER MASS OF SOLVENT) THE GREATER THE COLLIGATIVE AFFECT The boiling point (bp) of a liquid GOES UP The freezing point (fp) of a liquid GOES DOWN Colligative Properties 1) WHICH WILL GIVE THE BIGGEST INCREASE IN bp, 1 MOLE OF SUGAR OR 1 MOLE OF SALT IN 1000g OF WATER? 2) WHICH WILL GIVE THE BIGGESST DECREASE IN fp, 1 MOLE OF SALT IN 1 LITER OF WATER OR 1 MOLE OF SALT IN 500 g OF WATER