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CHAPTER 9 Water and Solutions 9.3 Properties of Solutions

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2 Which acid will dissolve the limestone fastest? Reaction rates

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3 9.3 Properties of Solutions Which acid will dissolve the limestone fastest? Acid with the higher concentration Higher concentration generally means a faster reaction rate Reaction rates

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4 9.3 Properties of Solutions Higher temperature generally means a faster reaction rate Reaction rates

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5 9.3 Properties of Solutions Reaction rates Higher concentration Higher temperature Faster reaction rate

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6 9.3 Properties of Solutions hydration: the process of molecules with any charge separation to collect water molecules around them. Not chemically bonded

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7 9.3 Properties of Solutions The heat comes from calcium chloride dissolving In an exothermic process, energy is released

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8 9.3 Properties of Solutions In an endothermic process, energy is absorbed The cooling effect comes from ammonium nitrate absorbing heat as it dissolves

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9 9.3 Properties of Solutions heat of solution: the energy absorbed or released when a solution dissolves in a particular solvent. Energy released Energy absorbed

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Properties of Solutions From Chapter 3.2 first law of thermodynamics: energy can neither be created nor destroyed.

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Properties of Solutions The energy inside an isolated system is constant. From Chapter 3.2 first law of thermodynamics: energy can neither be created nor destroyed.

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Properties of Solutions The energy inside an isolated system is constant. The energy lost by a system must be gained by the surroundings or another system. From Chapter 3.2 first law of thermodynamics: energy can neither be created nor destroyed.

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Properties of Solutions Calorimetry A coffee cup calorimeter is an isolated system

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Properties of Solutions Calorimetry A coffee cup calorimeter is an isolated system Calori-metry heatmeasure thermometer Remember: Heat and temperature are related

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Properties of Solutions The energy inside the system is constant

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Properties of Solutions What changes is the enthalpy enthalpy: the energy potential of a chemical reaction measured in joule per mole (J/mole) or kilojoules per mole (kJ/mole). NH 4 NO 3 (s) + H 2 O(l) NH 4 + (aq) + NO 3 – (aq)H = kJ/mole HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l)H = –56 kJ/mole

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Properties of Solutions meanschange Enthalpy Endothermic reaction Exothermic reaction Positive value Negative value NH 4 NO 3 (s) + H 2 O(l) NH 4 + (aq) + NO 3 – (aq)H = kJ/mole HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l)H = –56 kJ/mole

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Properties of Solutions The energy inside the system is constant Heat released by the reaction = Heat gained by the solution HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l)H = –56 kJ/mole

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Properties of Solutions H reaction = –56 kJ/mole H solution = +56 kJ/mole Opposite signs! Heat released by the reaction = Heat gained by the solution HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l)H = –56 kJ/mole

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Properties of Solutions If we can calculate H solution, we can determine H reaction q solution = (grams of solution) x (specific heat of solution) x ΔT q solution = –q reaction ΔH reaction = q reaction / moles

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Properties of Solutions q solution = (grams of solution) x (specific heat of solution) x ΔT q solution = –q reaction ΔH reaction = q reaction / moles Seen in Chapter 3.2

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Properties of Solutions q solution = (grams of solution) x (specific heat of solution) x ΔT q solution = –q reaction ΔH reaction = q reaction / moles thermometer

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Properties of Solutions When a student mixes 40.0 mL of 1.0 M NaOH and 40.0 mL of 1.0 M HCl in a coffee cup calorimeter, the final temperature of the mixture rises from 22.0 o C to 27 o C. Calculate the enthalpy change for the reaction of hydrochloric acid (HCl) with sodium hydroxide (NaOH). Assume that the coffee cup calorimeter loses negligible heat, that the density of the solution is that of pure water (1.0 g/mL), and that the specific heat of the solution is the same as that of pure water.

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Properties of Solutions Break down the problem! When a student mixes 40.0 mL of 1.0 M NaOH and 40.0 mL of 1.0 M HCl in a coffee cup calorimeter, the final temperature of the mixture rises from 22.0 o C to 27 o C. Calculate the enthalpy change for the reaction of hydrochloric acid (HCl) with sodium hydroxide (NaOH). Assume that the coffee cup calorimeter loses negligible heat, that the density of the solution is that of pure water (1.0 g/mL), and that the specific heat of the solution is the same as that of pure water.

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Properties of Solutions When a student mixes 40.0 mL of 1.0 M NaOH and 40.0 mL of 1.0 M HCl in a coffee cup calorimeter, the final temperature of the mixture rises from 22.0 o C to 27 o C. Calculate the enthalpy change for the reaction of hydrochloric acid (HCl) with sodium hydroxide (NaOH). Assume that the coffee cup calorimeter loses negligible heat, that the density of the solution is that of pure water (1.0 g/mL), and that the specific heat of the solution is the same as that of pure water. Break down the problem! Given:40.0 mL of NaOH (1.0 M) mL of HCl (1.0 M) NaOH + HCl NaCl + H 2 O T initial = 22.0 o C and T final = 27 o C - Experimental setup

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Properties of Solutions When a student mixes 40.0 mL of 1.0 M NaOH and 40.0 mL of 1.0 M HCl in a coffee cup calorimeter, the final temperature of the mixture rises from 22.0 o C to 27 o C. Calculate the enthalpy change for the reaction of hydrochloric acid (HCl) with sodium hydroxide (NaOH). Assume that the coffee cup calorimeter loses negligible heat, that the density of the solution is that of pure water (1.0 g/mL), and that the specific heat of the solution is the same as that of pure water. Break down the problem! - Experimental setup - What is asked Asked:Amount of heat change ( H) for NaOH and HCl reaction

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Properties of Solutions When a student mixes 40.0 mL of 1.0 M NaOH and 40.0 mL of 1.0 M HCl in a coffee cup calorimeter, the final temperature of the mixture rises from 22.0 o C to 27 o C. Calculate the enthalpy change for the reaction of hydrochloric acid (HCl) with sodium hydroxide (NaOH). Assume that the coffee cup calorimeter loses negligible heat, that the density of the solution is that of pure water (1.0 g/mL), and that the specific heat of the solution is the same as that of pure water. Break down the problem! - Experimental setup - What is asked - Assumptions Given:Isolated system: H reaction = H solution Density (H 2 O) = 1.0 g/mL

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Properties of Solutions Relationships: Solve:First note that the temperature increased, so the reaction released energy to the solution. This means the reaction is exothermic and will have a negative H. Total volume of solution is 40.0 mL mL = 80.0 mL Total mass of solution is 80.0 g using the density water (1.0 g/mL).

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Properties of Solutions Relationships: Solve:First note that the temperature increased, so the reaction released energy to the solution. This means the reaction is exothermic and will have a negative H. Total volume of solution is 40.0 mL mL = 80.0 mL Total mass of solution is 80.0 g using the density water (1.0 g/mL). The positive sign indicates heat is absorbed. We reverse the sign as heat gained by the solution is lost by the reaction. Therefore q rxn = –1.67 kJ.

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Properties of Solutions Solve:q rxn = –1.67 kJ To find heat on a per mole basis, we use the molarity times the volume in liters to calculate moles; 1.0 M x L = moles of both reactants (where NaOH and HCl are in equimolar amounts).

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Properties of Solutions Solve:q rxn = –1.67 kJ To find heat on a per mole basis, we use the molarity times the volume in liters to calculate moles; 1.0 M x L = moles of both reactants (where NaOH and HCl are in equimolar amounts). Lastly, Since the temperature increased, heat was released form the reaction, making H negative. Answer: H = –41.8 kJ/mole

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Properties of Solutions What we have seen so far… Reaction rates increase with: increasing concentrations increasing temperatures

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Properties of Solutions What we have seen so far… Reaction rates increase with: increasing concentrations increasing temperatures Chemical reactions are accompanied by changes in enthalpy, ΔH

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Properties of Solutions Whats next… Reaction rates increase with: increasing concentrations increasing temperatures Chemical reactions are accompanied by changes in enthalpy, ΔH Solution vs. pure solvent

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Properties of Solutions Volumes of solute and solvent do not add up to the volume of solution 20 g salt 80 mL water 87 mL solution! Solution vs. pure solvent

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Properties of Solutions Volumes of solute and solvent do not add up to the volume of solution 20 g salt 80 mL water 87 mL solution! Salt dissociates into ions, which fit in between water molecules Solution vs. pure solvent

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Properties of Solutions The density of a solution increases as more solute is added Solution vs. pure solvent

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Properties of Solutions Reaction rates increase with: increasing concentrations increasing temperatures Chemical reactions are accompanied by changes in enthalpy, ΔH Solution vs. pure solvent density (solution) > density (pure solvent)

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Properties of Solutions Reaction rates increase with: increasing concentrations increasing temperatures Chemical reactions are accompanied by changes in enthalpy, ΔH Solution vs. pure solvent density (solution) > density (pure solvent) colligative properties Whats next…

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Properties of Solutions Why does ice melt when salt is sprinkled on it?

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Properties of Solutions Freezing point depression Why does ice melt when salt is sprinkled on it? Pure water freezes at 0 o C, but a water and salt solution freezes at a lower temperature.

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Properties of Solutions Freezing point depression The freezing point is lowered in the presence of salt Pure solvent Solid formation is not hindered Solution Solute particles get in the way of solid formation OrderEntropy more lessmore less

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Properties of Solutions colligative property: physical property of a solution that depends only on the number of dissolved solute particles not on the type (or nature) of the particle itself. Pure solvent Solid formation is not hindered Solution Solute particles get in the way of solid formation OrderEntropy more lessmore less Freezing point depression is a colligative property

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Properties of Solutions To calculate the freezing point of a solution: Do not get confused with molarity, M (moles solute / L of solution)

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Properties of Solutions Calculate the freezing point of a 1.8 m aqueous solution of antifreeze that contains ethylene glycol (C 2 H 6 O 2 ) as the solute.

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Properties of Solutions Calculate the freezing point of a 1.8 m aqueous solution of antifreeze that contains ethylene glycol (C 2 H 6 O 2 ) as the solute. Asked:The freezing point of a 1.8 m solution of ethylene glycol Given:Molality = 1.8 m; K f = 1.86 o C/m (for water the solvent) Relationships:

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Properties of Solutions Calculate the freezing point of a 1.8 m aqueous solution of antifreeze that contains ethylene glycol (C 2 H 6 O 2 ) as the solute. Asked:The freezing point of a 1.8 m solution of ethylene glycol Given:Molality = 1.8 m; K f = 1.86 o C/m (for water the solvent) Relationships: Solve:

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Properties of Solutions Calculate the freezing point of a 1.8 m aqueous solution of antifreeze that contains ethylene glycol (C 2 H 6 O 2 ) as the solute. Asked:The freezing point of a 1.8 m solution of ethylene glycol Given:Molality = 1.8 m; K f = 1.86 o C/m (for water the solvent) Relationships: Solve: Answer:The freezing point is lowered by 3.35 o C.

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Properties of Solutions Electrolyte solutions electrolyte: solute capable of conducting electricity when dissolved in an aqueous solution. Aqueous solutions containing dissolved ions are able to conduct electricity 1 mole of solute 2 moles of ions 1 mole of solute 3 moles of ions

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Properties of Solutions Electrolyte solutions Aqueous solutions containing dissolved ions are able to conduct electricity 1 mole of solute 2 moles of ions 1 mole of solute 3 moles of ions The greater the number of particles in solution, the greater the effects. colligative property: physical property of a solution that depends only on the number of dissolved solute particles not on the type (or nature) of the particle itself.

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Properties of Solutions Reaction rates increase with: increasing concentrations increasing temperatures Chemical reactions are accompanied by changes in enthalpy, ΔH Solution vs. pure solvent density (solution) > density (pure solvent) colligative properties: freezing point depression as an example

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