Chapters 12-13: Solutions Modern Chemistry

Solution Solution – a homogeneous mixture of a solute and a solvent. soluble - capable of being dissolved Solute – the chemical that is dissolved Solvent – the substance it is dissolved in Ex.) Salt in water Different types depend on state of solute/solvents: Solid-liquid Liquid-liquid Gas-liquid Liquid-gas Solid-solid Gas-gas

A substance that dissolves in water to give a solution that conducts electric current is called an electrolyte. Any soluble ionic compound, such as sodium chloride, NaCl, is an electrolyte.

Do all compounds dissolve as well as others? No Solubility - Maximum amount of solute that can dissolve in a given amount of solvent at a given temperature

Factors affecting solubility 1. “Like dissolves like” Polar solvents – dissolve ionic/polar solutes Nonpolar solvents – dissolve nonpolar solutes 2. Pressure No impact on solid-liquid solutions For gas-liquid solutions,  P  Solubility 3. Temperature Solid-liquid solutions, T Solubility Gas- liquid solutions, T Solubility

Speed of solution formation Impacted by: 1. surface area 2. agitation 3. temperature

Once a solution forms… Saturated solution – contains the maximum amount of solute Unsaturated solution – contains less than the maximum amount of solute Supersaturated solution – contains more than the maximum amount of solute

Heat of solution Energy change when a solution forms Exothermic – releases energy (hot) Endothermic – absorbs energy (cold)

Solutions calculations 1. Molarity 2. Dilutions 3. Molality

1. Molarity, M Moles solute Liters solution M = M 1 mol L = Molarity is a standard used to express the concentration of a solution Moles solute Liters solution M = M 1 mol L =

Example: You have 3.50 L of solution that contains 90.0 g of sodium chloride, NaCl. What is the molarity of that solution? You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl does this solution contain?

To produce 40. 0 g of silver chromate, you will need at least 23 To produce 40.0 g of silver chromate, you will need at least 23.4 g of potassium chromate in solution as a reactant. All you have on hand is 5 L of a 6.0 M K2CrO4 solution. What volume of the solution is needed to give you the 23.4 g K2CrO4 needed for the reaction?

2. Dilutions The dilution equation is used to accurately make weaker solutions from stronger stock solutions by adding water M1V1 = M2V2 Initial Molarity x initial volume = final Molarity x final volume Stock solution Weaker solution

Example If you have 5L of a 12M HCl solution and you want a 3.5M solution, how much water should you add? If you have 2L of a 8.5M HCl solution and you accidentally added 0.65L of distilled water, what is the new molarity?

3. Molality, m m 1 moles solute kg solvent = m 1 mol kg = Another standard for showing concentration of a solution m 1 moles solute kg solvent = m 1 mol kg =

Examples A solution was prepared by dissolving 17.1 g of sucrose (table sugar, C12H22O11) in 125 g of water. Find the molal concentration of this solution.

Examples cont. A solution of iodine, I2, in carbon tetrachloride, CCl4, is used when iodine is needed for certain chemical tests. How much iodine must be added to prepare a 0.480 m solution of iodine in CCl4 if 100.0 g of CCl4 is used?

Chapter 12 Review Page 426 #’s 2-5, 7-9, 11-12, 17, 19-22, 26-29

CHAPTER 13

Compounds in Aqueous Solutions Dissociation- soluble compounds separate into ions NaCl(s)  Na+(aq) + Cl-(aq) CaCl2(s)  Ca3(PO4)2 

How many moles are produced when you dissociate Al2(SO4)3 ? How many moles are produced when you dissolve 1 mole of sodium carbonate?

General Solubility Guidelines

Putting solutions together Basically, just double replacement reactions Must determine what precipitates out Use the solubility rules to predict Cd(NO3)2 (aq) + (NH4)2S (aq)  CdS + 2NH4NO3 (s) (aq) Which is the precipitate?

What precipitate forms when you mix lead nitrate and potassium iodide? Pb(NO3)2 (aq) + 2KI (aq)  2KNO3 + PbI2

Identify the precipitate that forms when aqueous solutions of zinc nitrate and ammonium sulfide are combined. Write the equation for the possible double- displacement reaction and include the states of matter.

Spectator ions – do not take part in a chemical reaction Net Ionic Equation – includes only the compounds that undergo a chemical change in the reaction Spectator ions – do not take part in a chemical reaction Hint: Watch for a phase change! Solubility Table pg. 437 Common ion chart pg. 858

Pb(NO3)2 (aq) + 2KI (aq)  2KNO3 (aq) + PbI2 (s) Pb2+(aq) + 2NO3-(aq) + 2K+(aq) + 2I-(aq) 2K+(aq) + 2NO3-(aq) PbI2 (s) Spectator ions Called complete ionic equation **To write net ionic equation, eliminate substances that undergo no change** Remember, ionic compounds, dissociate in solution Pb2+(aq) + 2I-(aq)  PbI2 (s) Net ionic equation

Write complete ionic and net ionic for: 1. Potassium sulfate and barium nitrate 2. Silver nitrate and sodium chloride

Net ionic equation Strontium nitrate and sodium sulfate

Solution types Electrolyte – conducts electricity Strong electrolytes vs. weak electrolytes HCl vs. HF Nonelectrolyte – does not conduct electricity

Colligative Properties Properties that depend on the concentration of solute particles Vapor Pressure Freezing Point Boiling Point

1. Vapor Pressure Lowering Add solute, vapor pressure goes down (so boiling point goes up) Non-volatile substance – is one that has little tendency to become a gas under existing conditions

2. Freezing Point Depression Add solute, freezing point goes down Kf= freezing point constant = -1.86℃ Tf = Kf x m Ex.) Determine the freezing point of a water solution of fructose, C6H12O6, made by dissolving 58.0g of fructose in 185g of water.

Ex2. ) Calculate the molality of a solution of 39 Ex2.) Calculate the molality of a solution of 39.2g of urea, H4N2CO, in 485g of pure acetic acid. Determine the freezing point of this solution.

A solution consists of 10.3g of glucose, C6H12O6, dissolved in 250g of water. What is the freezing point depression of the solution?

3. Boiling Point Elevation Add solute, boiling point goes up Kb = molal boiling point constant = 0.51℃ Tb = Kb x m Ex. A solution contains 50g of sucrose, C12H22O11, dissolved in 500g of water. What is the boiling point elevation?

Ex2. If the boiling point elevation of an aqueous solution containing a nonvolatile electrolyte is 1.02℃, what is the molality of the solution?

A solution contains 450.0g of sucrose C12H22O11, a nonelectrolyte, dissolved in 250.0g of acetic acid. What is the boiling point of the solution?

In World War II, soldiers in the Sahara Desert needed a supply of antifreeze to protect the radiators of their vehicles. The temperature in the Sahara almost never drops to 0°C, so why was the antifreeze necessary?

Chapter 13 Review Pg. 458 #’s 1-3, 5, 8, 9, 11, 12, 14, 19, 20, 21, 25, 26, 30