Chapter 15 - Solutions

Characteristics of solutions Solution – homogeneous mixture Solution – homogeneous mixture a) parts of a solution i) solute – substance being dissolved ii) solvent – substance doing dissolving both can be either solid, liquid, or gas

Solutions do not have to be solids in liquids gas in liquid liquid in liquid solid in liquid soda vinegar salt solution examplesolutionsolutesolvent CO 2 Water/syrup saltwater aceticacid water

Solubility Defn – ability of a solute to dissolve in a solvent Defn – ability of a solute to dissolve in a solvent Represented by a ___________________ Represented by a ___________________ Soluble – can be dissolved in solvent Soluble – can be dissolved in solvent Insoluble – cannot be dissolved in solvent Insoluble – cannot be dissolved in solvent numerical value ex: the solubility of NaCl in water is 35.9 g/100 g H 2 O at 20°C

“like dissolves like” Polar (or ionic) solutes dissolve in polar solvents Polar (or ionic) solutes dissolve in polar solvents Nonpolar solutes dissolve in nonpolar solvents Nonpolar solutes dissolve in nonpolar solvents

“like dissolves like” combo combo Polar solute in polar solvent example sugar in water ionic solute in polar solvent NaCl in water Gasoline in oil nonpolar solute in nonpolar solvent Note that water and oil do not mix. They are insoluble.

Water does not dissolve in carbon tetrachloride Water does not dissolve in carbon tetrachloride (CCl 4 ), but it does dissolve in milk (CCl 4 ), but it does dissolve in milk Benzene (C 6 H 6 ) does not dissolve in water but it Benzene (C 6 H 6 ) does not dissolve in water but it does dissolve in CCl 4. does dissolve in CCl 4. Glucose (C 6 H 12 O 6 ) does not dissolve in benzene Glucose (C 6 H 12 O 6 ) does not dissolve in benzene but it does dissolve in milk. but it does dissolve in milk. water C6H6C6H6C6H6C6H6 CCl 4 milk glucose polar nonpolar nonpolar polar polar

Factors Affecting Rate of Dissolving How can you dissolve something faster??? How can you dissolve something faster??? a) increase temp of solvent this accelerates particles creating more particle collisions

Factors Affecting Rate of Solvation b) agitate the solution (stir/shake) more particle collisions between solute and solvent more particle collisions between solute and solvent c) Increase surface area of solute breaking into smaller pieces allows more solute to be in contact w/ solvent

Factors that affect solubility Temperature (dissolved in liquids) Temperature (dissolved in liquids) –For solids, an increase in T, ______________ solubility. Ex: more sugar dissolves in hot tea than in ice tea –For gases, an increase in T, ______________ solubility. Ex: hot Coke goes flat faster than cold Coke increases decreases

Factors that affect solubility Pressure Pressure –An increase in pressure results in an ______________ in solubility. Ex: soda cans are pressurized to keep the CO 2 dissolved. Once opened, the pressure is decreases, and soda tend to get flat increase

Solubility rules for ionic compounds Soluble or insoluble? (gases in liquids) Soluble or insoluble? (gases in liquids) KCl _____________ PbSO 4 _____________ NaNO 3 ___________ CaBr 2 _____________ CaCO 3 ___________ Fe(OH) 3 ___________ soluble solublesoluble insolubleinsoluble insoluble

Solubility Terms how much solute can be put into solvent? how much solute can be put into solvent? Depends on amount and temperature

Unsaturated Solution Defn – less than max amt of solute dissolved at given temp Defn – less than max amt of solute dissolved at given temp if I put sugar into water and all sugar is dissolved, solution is unsaturated

Saturated Solution Defn – contains max amt of solute dissolved at given temp Defn – contains max amt of solute dissolved at given temp if I put sugar into water and not dissolves (you can see the sugar), the solution is saturated

Supersaturated Solution Defn – contains more solute dissolved than expected at given temp (exceeds max amount) Defn – contains more solute dissolved than expected at given temp (exceeds max amount) a saturated solution made at high temp cools slowly. Slow cooling allows excess solute to remain dissolved in solution at lower temperature very unstable

Solubility Curve (generic) Curve represents max amount solute allowed Temperature Solubility (g solute/ 100 g H 2 O) Unsaturated (below line) Saturated (line and above)

Temperature (°C) g solute/100 g H 2 O

What trend do you notice about the compound above? The higher the temp, higher the solubility What is the solubility at 70°C? 60 g/100 g H 2 O At 90°C, if 60 g is dissolved, is it saturated or unsaturated? unsaturated

At 90°C, if 100 g is dissolved, is it saturated or unsaturated? saturated At 40°C, how many grams of solute can be dissolved in 300 g H 2 O? 50 x 3 = 150 g

Solution Concentration Problems How concentrated a solution is…… How concentrated a solution is…… a) Percent by mass b) Molarity

Percent by mass Formula Formula

Percent By Mass Ex prob: If 3.6 g NaCl is dissolved in 100 g H 2 O, what is the percent by mass? Ex prob: If 3.6 g NaCl is dissolved in 100 g H 2 O, what is the percent by mass? 3.6 g 3.6 g g X 100 = 3.5 % NaCl

Molarity Formula mol solute Formula mol solute L solution L solution unitmol = M (capital M) unitmol = M (capital M) L

Molarity Ex prob #1 Molarity Ex prob #1 A solution has a volume of 250 mL and has 0.70 mol NaCl. What is the molarity? A solution has a volume of 250 mL and has 0.70 mol NaCl. What is the molarity? 2.8 mol/L or 2.8 M L = 0.70 mol

Molarity ex prob #2 What is the molarity of a solution made of 47.3 g NaOH in 500 mL water? What is the molarity of a solution made of 47.3 g NaOH in 500 mL water? step 1: convert grams to moles 47.3 g NaOH 40 g NaOH 1 mol NaOH = mol NaOH

Molarity ex prob #2 Step 2: divide moles by volume (L) 2.37 mol/L NaOH or 2.37 M NaOH L = mol

Molarity ex prob #3 How many moles of solute are present in 1.5 L of 2.4 M NaCl? How many moles of solute are present in 1.5 L of 2.4 M NaCl? # moles = volume x molarity 1.5 L L 2.4 mol NaCl x = 3.6 mol NaCl

Dilutions Dilute – solution with a low solute amount for a given volume Dilute – solution with a low solute amount for a given volume Concentrated – solution with a high amount of solute for a given volume Concentrated – solution with a high amount of solute for a given volume

Dilutions How do you make a dilute solution? How do you make a dilute solution? water down a more concentrated solution

Dilutions We use the following formula to determine how to make a dilution We use the following formula to determine how to make a dilution Formula Formula M 1 V 1 = M 2 V 2 M 1 is more concentrated than M 2 M = molarity V = volume

Ex #1 If you dilute 20 mL of a 3.5 M solution and make a 100 mL solution, what is the molarity of the new solution? If you dilute 20 mL of a 3.5 M solution and make a 100 mL solution, what is the molarity of the new solution? M1=M1= V1=V1= M2=M2= V2=V2= 3.5 M? 20 mL 100 mL (3.5 M) (20 mL) = M 2 (100 mL) M 2 = 0.7 M

Ex #2 You have a 6.0 M stock solution. If you want to make a dilution so that you have 1000 mL of a 1.0 M solution, what volume of stock solution is required? You have a 6.0 M stock solution. If you want to make a dilution so that you have 1000 mL of a 1.0 M solution, what volume of stock solution is required? M1=M1= V1=V1= M2=M2= V2=V2= 6.0 M1.0 M ? 1000 mL (6.0 M) V 1 = (1.0 M)(1000 mL) V 1 = mL

Ex #2 How much water is needed? How much water is needed? Want to make 1000 mL……so must add water to mL 1000 mL – mL = mL H 2 O

Colligative Properties of Solutions Solutes affect the physical properties of their solvents Solutes affect the physical properties of their solvents Colligative Properties – properties that depend only on the amount of solute present, not the identity Colligative Properties – properties that depend only on the amount of solute present, not the identity –includes boiling point elevation, freezing point depression

Coligative Properties Examples What happens to……… What happens to……… –freezing point of water when salt is added to icy roads? lowers the freezing point of water, so ice melts –boiling point of water when salt is added to hot water for making pasta? raises the boiling point of water, so it boils hotter

General effect of solutes on solvents Solutes __________ the freezing point of Solutes __________ the freezing point of solvents and ___________ the boiling point of solvents lowers raises