Colligative Properties Colligative Properties Colligative Property a property

Colligative Properties Colligative Property: a property that depends only on the number of solute

Molality In order to work with colligative properties, we need to use a different

Molality Example What is the molality of a solution of 16. 8 grams of

Molality Practice What is the molality of a solution of 47. 3 grams of

Dissociation Factor Dissociation factor: How many particles a solute will break in to when

Dissociation Factor Examples What is the dissociation factor for each compound? 1. Determine if

Dissociation Factor Practice What is the dissociation factor for each compound? 1. Determine if

Dissociation Factor Practice What is the dissociation factor for each compound? 0. Write the

Freezing Point Depression What happens when something freezes (for example, water)? • Decrease in

Freezing Point Depression: adding a substance to a pure solvent lowers the freezing point

Freezing Point Depression Example What is the freezing point of 10. 2 grams of

Boiling Point Elevation Pure solvent Solution containing nonvolatile solute Solute particles also get in

Boiling Point Elevation: adding a substance to a pure solvent increases the boiling point

Boiling Point Elevation Example What is the boiling point of a solution containing 100.

Summary Freezing point depression: ΔTf = (m)(kf)(df) ¡ ¡ kf = 1. 86 o.

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Colligative Properties

Colligative Properties Colligative Property: a property that depends only on the number of solute particles, and not the type of particle Examples: 1. Freezing Point Depression (lowering) 2. Boiling Point Elevation (raising) 3. Vapor Pressure Lowering We will focus on Freezing Point.

Molality In order to work with colligative properties, we need to use a different type of concentration… Molality (m): the number of moles of solute per kilogram of solvent Units: m ex: 3. 0 m is “ 3 molal”

Molality Example What is the molality of a solution of 16. 8 grams of lithium sulfate dissolved in 0. 500 kg of water?

Molality Practice What is the molality of a solution of 47. 3 grams of potassium iodide dissolved in 0. 275 kg of water?

Dissociation Factor Dissociation factor: How many particles a solute will break in to when dissolved in a solution Dissociation Factor Covalent compounds: will not dissociate → df = 1 Ionic compounds: will dissociate into ions → df = # of ions per molecule

Dissociation Factor Examples What is the dissociation factor for each compound? 1. Determine if the compound is ionic or covalent 2. CIRCLE any polyatomic ions 3. Determine the dissociation factor 1. 2. 3. 4. 5. 6. 7. Al. PO 4 N 2 O 4 Ca. I 2 PCl 5 Pb(OH)4 Xe. F 4 Cu 2 CO 3

Dissociation Factor Practice What is the dissociation factor for each compound? 1. Determine if it is ionic or covalent 2. CIRCLE any polyatomic ions 3. Determine the dissociation factor 1. NH 4 Cl 2. CO 2 3. Ca 3(PO 4)2 4. Ca. Cl 2 5. Fe(NO 3)2 2 1 5 3 3 6. Na. OH 7. Na. Cl 8. Li 2 SO 4 9. Mg 3 P 2 10. Ca. C 2 O 4 2 2 3 5 2

Dissociation Factor Practice What is the dissociation factor for each compound? 0. Write the chemical formula! 1. Determine if it is ionic or covalent 2. CIRCLE any polyatomic ions 3. Determine the dissociation factor 1. manganese nitride 2. carbon tetrachloride 3. lead (IV) sulfide 4. strontium hydroxide 5. silver carbonate

Freezing Point Depression What happens when something freezes (for example, water)? • Decrease in energy slows molecules/atoms down • Intermolecular forces have more effect (atoms have less energy to fight them) • Frozen water (ice) molecules are in an orderly pattern. Adding Solute What happens when you add a solute? l The addition of another substance (a solute) disrupts and prevents water molecules from forming an orderly pattern.

Freezing Point Depression: adding a substance to a pure solvent lowers the freezing point To calculate the change in freezing point: ΔTf = (m)(kf)(df) molality constant Dissociation factor: how many particles the solute will break into in solution Dissociation Factor Covalent compounds: will not dissociate → d. f. = 1 Ionic compounds: will dissociate into ions → d. f. = # of ions per molecule

Freezing Point Depression Example What is the freezing point of 10. 2 grams of Na. Cl in 5. 1 kg of water? ΔTf = (m)(kf)(df) kf = 1. 86 o. C/m for water To find the new freezing point, SUBTRACT your answer from the normal freezing point

Boiling Point Elevation Pure solvent Solution containing nonvolatile solute Solute particles also get in the way of a solvent’s ability to boil, thereby increasing the boiling temperature.

Boiling Point Elevation: adding a substance to a pure solvent increases the boiling point To calculate the change in boiling point: ΔTb = (m)(kb)(df) molality constant Dissociation factor: how many particles the solute will break into in solution Dissociation Factor Covalent compounds: will not dissociate → d. f. = 1 Ionic compounds: will dissociate into ions → d. f. = # of ions per molecule

Boiling Point Elevation Example What is the boiling point of a solution containing 100. 0 g Mg. Cl 2 dissolved in 250. 0 g of water? ΔTb = (m)(kb)(df) kb = 0. 52 o. C/m for water To find the new boiling point, ADD your answer to the normal boiling point

Summary Freezing point depression: ΔTf = (m)(kf)(df) ¡ ¡ kf = 1. 86 o. C/m for water To find the new freezing point, SUBTRACT your answer from the normal freezing point Boiling point elevation: ΔTb = (m)(kb)(df) ¡ ¡ kb = 0. 52 o. C/m for water To find the new boiling point, ADD your answer to the normal boiling point