Solutions Solutions A solution is a homogeneous mixture

Solutions

Solutions A solution is a homogeneous mixture of 2 or more substances in a single phase. One constituent is usually regarded as the SOLVENT and the others as SOLUTES.

Parts of a Solution �SOLUTE – the part of a solution that is being dissolved (usually the lesser amount) �SOLVENT – the part of a solution that dissolves the solute (usually the greater amount) �Solute + Solvent = Solution Solvent Solute

Nature of Solutes in Solutions l Spread evenly throughout the solution l Cannot be separated by filtration l Can be separated by evaporation l Not visible, solution appears transparent l May give a color to the solution 4

Solutions Examples Gas in a Liquid in a Liquid Solids in Solids Non-Examples salad soil Air Soda Gasoline Sea Water Brass water

Water is the universal solvent �because more substances dissolve in water than in any other chemical. �This has to do with the polarity of each water molecule.

Molecular Polarity Nonpolar molecules: -- e– are shared equally e. g. , fats and oils Polar molecules: -- e– NOT shared equally e. g. , water H H–C–H H O

Water Molecules �Are polar because O is more electronegative than H �Gives O a partial negative charge. �Form strong intermolecular hydrogen bonds. �Water molecules are attracted to one another better than other molecules its size.

Hydrogen bonding animation Hydrogen bonding occurs because of polarity One water molecule bonds to another. 9

Surface Tension �Because of the hydrogen bonds, water molecules are attracted to each other. �Liquid water acts like it has a skin. �Water forms round drops.

Properties of Water Hydrogen bonding causes: �High surface tension �Low vapor pressure �High specific heat capacity �High heat of vaporization �High boiling point

Properties of Water

What is, or is not, soluble in H 20? Like Dissolves Like �“Polar solvents dissolve ionic compounds and polar molecules �Water is polar therefore it can dissolve �Na. Cl �Copper (II) sulfate �Na. OH �Nonpolar solvents dissolve nonpolar compounds �Oil is nonpolar, which is why oil and water separate

Animations of the Solvation (Animation of a Solute Dissolving) While you watch each video clip, record your observations on your notes. Animation of Salt Dissolving in Water Animation of Sugar Dissolving in Water

When Ionic Solids Dissolve Animation H O H H H O H

Aqueous Solutions How do we know ions are present in aqueous solutions? The solutions can electricity conduct They are called ELECTROLYTES HCl, Mg. Cl 2, and Na. Cl are strong electrolytes. They dissociate completely (or nearly so) into ions.

Electrolyte vs. Non-Electrolyte Salt (Ionic Solids) Broke apart into ions Was able to light the light bulb an electrolyte Can Conduct an Electric Current Sugar (Molecular Solids) Both Water is the solvent. Forms a solution Broke apart into whole molecules Did not light the light bulb a non-electrolyte Can’t Conduct an Electric Current An electrolyte is a substance when dissolved in water can conduct an electric current. A non-electrolyte is a substance when dissolved in water can’t conduct an electric current.

Rate of Solution = How Fast Exploration 1) To an empty 250 m. L beaker, add approximately 100 m. L of warm-hot water from a hot plate. 2) To an empty 250 m. L beaker, add approximately 100 m. L of ice water. Be sure to leave the ice behind! 3) Add a sugar cube to each of the 250 m. L beakers. Observe what happens. 4) Record your observations on your notes. 5) List other ways that you believe that you could make a solute dissolve more quickly.

Electrolytes in the Body Carry messages to and from the brain as electrical signals Maintain cellular function with the correct concentrations electrolytes Make your own 50 -70 g sugar One liter of warm water Pinch of salt 200 ml of sugar free fruit squash Mix, cool and drink

Rate of Solution What are ways that you make a solute dissolve faster? 1) Increase the temperature. 2) Crush or use smaller size solute particles. 3) Stir the solutions.

Solubility = How Much Type of Solute Temperature Pressure Solid Solute Solubility generally increases as temperature increases. Pressure has no effect on the solubility of a solid. Gaseous Solute Solubility generally decreases as temperature increases. Solubility generally increases as pressure increases.

Types of Solutions There are three ways to classify a solution. 1) Unsaturated Solutions 2) Saturated Solutions 3) Supersaturated Solutions

Types of Solutions Type of Solution Description Picture Relation to Solubility Curve Unsaturated A solution in which more solute can dissolve Below the Line Saturated A solution in which contains the maximum amount of solute On the Line Supersaturated A solution in which contains more than the maximum amount of solute Above the Line

Supersaturated �The solution is holding more solute than it should be able to. This is achieved by heating the solution and then cooling it slowly. �Examples: rock candy, southern style sweet tea, chemical heat packs �Supersaturated solutions are unstable. The supersaturation is only temporary

Solubility UNSATURATED SOLUTION more solute dissolves SATURATED SOLUTION no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form increasing concentration

Supersaturated

Solubility Curves Solubility indicates the amount of solute that will dissolve in a given amount of solvent at a specific temperature. For this curve, �X-Axis � Temperature �Y-Axis � How Much Solute Dissolves in 100 g of Water �Various Lines � Each line represents a different solute.

Solubility Curves Supersaturated Saturated CO 2 Unsaturated

Using an available solubility curve, classify as unsaturated, or supersaturated. 80 g Na. NO 3 @ 30 o. C unsaturated per 100 g H 2 O 45 g KCl @ 60 o. C saturated 30 g KCl. O 3 @ 30 o. C supersaturated 70 g Pb(NO 3)2 @ 60 o. C unsaturated

Describe each situation below. (A) Per 100 g H 2 O, 100 g Na. NO 3 @ 50 o. C. unsaturated; all solute dissolves; clear solution. (B) Cool solution (A) very slowly to 10 o. C. supersaturated; extra solute remains in solution; still clear (C) Quench solution (A) in an ice bath to 10 o. C. saturated; extra solute (20 g) can’t remain in solution and becomes visible

How to use a solubility graph? A. IDENTIFYING A SUBSTANCE ( given the solubility in g/100 cm 3 of water and the temperature) • Look for the intersection of the solubility and temperature.

Using Solubility Curves 1) How much KNO 3 would dissolve in 100 g of water at 50 o. C? 84 g 2) How much NH 4 Cl would dissolve in 200 g of water at 70 o. C? 120 g 3) At what temperature would 22 g of KCl be able to dissolve in 50 g of water? 68 o. C 4) Which is more soluble (has a higher solubility) at 40 o. C? � � NH 3 KCl. O 3

Learning Check : What substance has a solubility of 90 g/100 cm 3 in water at a temperature of 25ºC ?

Learning Check : What substance has a solubility of 200 g/100 cm 3 of water at a temperature of 90ºC ?

Look for the temperature or solubility • Locate the solubility curve needed and see for a given temperature, which solubility it lines up with and visa versa.

Learning Check: What is the solubility of potassium nitrate at 80ºC ?

• What is the solubility of potassium nitrate at 80ºC ?

Learning Check : At what temperature will sodium nitrate have a solubility of 95 g/100 cm 3 ?

Learning Check: At what temperature will sodium nitrate have a solubility of 95 g/100 cm 3 ?

Learning Check: At what temperature will potassium iodide have a solubility of 230 g/100 cm 3 ?

Learning Check: At what temperature will potassium iodide have a solubility of 130 g/100 cm 3 ?

Using Solubility Curves: What is the solubility of sodium chloride at 25ºC in 100 cm 3 of water ? From the solubility graph we see that sodium chlorides solubility is 36 g.

SOLUBLE OR INSOLUBLE? �Soluble: �able to be dissolved �Insoluble: �does not dissolve in solution (or water) �Precipitate: �an insoluble solid formed when two solutions are mixed

Soluble compounds contain… Insoluble compounds contain… For these compounds, common exceptions are INSOLUBLE. For these compounds, common exceptions are SOLUBLE.

Double Replacement reactions AB + CD AD + CB Na. Cl + Ag. NO 3 Na. NO 3 + Ag. Cl

Concentration of Solute The amount of solute in a solution is given by its concentration. Molarity (M) = moles solute liters of solution

PROBLEM: Dissolve 5. 00 g of Ni. Cl 2 • 6 H 2 O in enough water to make 250 m. L of solution. Calculate the Molarity. Known Mass=5 g Volume = 0. 250 L Unknown Molarity of Ni. Cl 2 • 6 H 2 O ? Analysis molar mass = 237. 7 g M= n/ V; Step 1: Calculate moles of Ni. Cl 2 • 6 H 2 O Step 2: Calculate Molarity [Ni. Cl 2 • 6 H 2 O ] = 0. 0841 M

MOLARITY PROBLEM What mass of oxalic acid, H 2 C 2 O 4, is required to make 250. m. L of a 0. 0500 M solution? Known Volume = 0. 250 L M = 0. 0500 moles/L Unknown g of H 2 C 2 O 4, ? Analysis molar mass = 90. 00 g M= mol/ V; Step 1: Calculate moles of H 2 C 2 O 4 (0. 0500 mol/L) x (0. 250 L) = 0. 0125 moles Step 2: Convert moles to grams 0. 0125 mol H 2 C 2 O 4 x (90. 00 g/mol) = 1. 13 g H 2 C 2 O 4 1 mol H 2 C 2 O 4

Learning Check How many grams of Na. OH are required to prepare 400. m. L of 3. 0 M Na. OH solution? 1) 12 g 2) 48 g 3) 300 g

Making Molar Solutions …from liquids (More accurately, from stock solutions)

Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution. Dilution Add Solvent Moles of solute before dilution (i) = Moles of solute after dilution (f) Mi V i = M f. V f 4. 5

remove sample moles of solute initial solution mix Making a Dilute Solution same number of moles of solute in a larger volume diluted solution Timberlake, Chemistry 7 th Edition, page 344

Dilution �Preparation of a desired solution by adding water to a concentrate. �Moles of solute remain the same.

Dilution Practice Problem �What volume of 15. 8 M HNO 3 is required to make 250 m. L of a 6. 0 M solution? Known Molarity 1 = 15. 8 mol/L of HNO 3 Volume 2 = 250 m. L Molarity 2 = 6. 0 mol/L of HNO 3 Unknown Volume of HNO 3? Equation M 1 V 1 = M 2 V 2 Solution : V 1 = (6. 0 mol/L x 0. 250 L) / 15. 8 M = 0. 095 L

Dilution Practice Problem If we have 1 L of 3 M HCl, what is M if we dilute acid to 6 L? Known Molarity 1 = 3 mol/L Volume 1 = 1 L of HCl Volume 2 = 6 L of HCl Unknown Molarity of HCl? Equation M 1 V 1 = M 2 V 2 ; Solution : M 2 = (3 mol/L x 1 L) / (6 L) = 0. 5 M

Dilution Practice Problem What volume of 0. 5 M HCl can be prepared from 1 L of 12 M HCl? Known Volume 1 = 1 L of HCl Molarity 1 = 12 mol/L of HCl Molarity 2 = 0. 5 mol/L of HCl Unknown Volume of HCl? Solution : V 2 = (12 mol/L x 1 L) / (0. 5 L) = 24 L Equation M 1 V 1 = M 2 V 2