Solutions!

What is a solution? A homogeneous mixture!

Made up of a solute and solvent.

2 Parts of a Solution Solvent – Does the dissolving. Usually present in the larger amount.

Solute – Is dissolved. Usually present in the smaller amount.

Aqueous Solutions

Water is a good solvent because the molecules are polar.

The oxygen atoms have a partial negative charge.

The hydrogen atoms have a partial positive charge.

Hydration

The process of breaking the ions of salts apart.

Ions have charges and attract the opposite charges on the water molecules.

Hydration

H HOH

H OH

HO

H HO

HHO

HH

O

HH

OH

H

O

HH

O

Hydration NaCl Na+ + Cl-

Al(NO3)3 Al3+ + 3NO3-

MgCl2 Mg2+ + 2Cl-

Soluble Vs. Insoluble Soluble: when attraction between ions and water molecules stronger than the attraction between ions

Insoluble: when attraction between the ions is stronger than the attraction between the ions and water molecules

Electrolytes

Conducts an electric current when placed in aqueous solution or in molten state. (Soluble)

Non-electrolytes do not conduct an electric current in either state. (Insoluble)

Properties of Solutions Solubility – how much dissovles

Determined by a few factors.- Nature of solvent and

solute.- Agitation.- Surface area of solute.- Temperature.

Nature of Solvent and Solute “Like dissolves like.”

Water is polar. It has small charges.

It dissolves ionic and polar compounds.

Non-polar will not dissolve.

Agitation Shaking increases the interaction between water and the solute.

What do you do when you make Kool-Aid?

Surface Area More exposed surface area means the water molecules can interact more with the solute.

A powder dissolves better than a solid.

Solubility of Solids Increases with temp

Solubility of Gases - Decreases with

temp inc.

Concentration A quantitative measure of the amount of solute dissolved in a given quantity of solution

Can use a few terms to define concentration. Solubility Molarity Molality

Solubility The amount of a substance that dissolves in a given quantity of a solvent at a given temperature. (g solute/100g solvent)

Saturated vs. Unsaturated vs. Supersaturated

Solubility Saturated

Solvent can’t dissolve more solute

Unsaturated Solvent can dissolve more solute

Supersaturated Solvent dissolved more than expected

Molarity M = moles solute/liters of solution

Uses the symbol M

Example: 2 moles of glucose are dissolved to make 2 liters of solution.

M = 2 moles/2L = 1M

Sample Problem #1 A saline solution contains 0.90g of NaCl in exactly 100mL of solution. What is the molarity of the solution?

Sample Problem #2 How many moles are present in 250mL of 0.24M calcium chloride?

Molality Another term used to describe the concentration.

Uses the symbol m.

m = moles solute/kg solvent

Sample Problem #1 What is the resulting molality when 30g of NaCl is dissolved in 100g of water?

Dilutions Use a concentrated stock solution to make a more dilute solution.

M1V1 = M2V2

Dilutions We want 4.5L of a 1M HCl solution. How much 12M HCl should we use?

Colligative Properties Depend on the number of particles dissolved in a given mass of solvent.

Freezing point depression Boiling point elevation Vapor pressure lowering

Colligative Properties Freezing point depression and boiling point elevation both use a similar equation. ∆T = K(m)(i)

• K is a constant based on the solvent• m is the molality of the solution• i is the van’t Hoff factor, the number of particles a

solute creates in solution

Van’t Hoff Factor NaCl

Al2(CO3)3

MgCl2

Colligative Properties Which of the following will lower the freezing point of water the most?a. NaClb. Glucosec. CaI2

d. Al2(CO3)3

Types of Reactions

Precipitation reactions When aqueous solutions of ionic compounds are poured together a solid forms.

A solid that forms from mixed solutions is a precipitate

If you’re not a part of the solution, you’re part of the precipitate

Precipitation reactions

NaOH(aq) + FeCl3(aq) NaCl(aq) + Fe(OH)3(s)

is really Na+(aq)+OH-(aq) + Fe+3(aq) + Cl-(aq)

Na+ (aq) + Cl- (aq) +Fe(OH)3(s) So all that really happens is OH-(aq) + Fe+3 (aq) Fe(OH)3(s) Double replacement reaction

Precipitations Reactions

Only happen if one of the products is insoluble

Otherwise all the ions stay in solution- nothing has happened.

Need to memorize the rules for solubility

Solubility Rules

All nitrates are soluble Alkali metals ions and NH4+ ions are soluble

Halides are soluble except Ag+, Pb+2, and Hg2

+2

Most sulfates are soluble, except Pb+2, Ba+2, Hg+2,and Ca+2

Solubility Rules

Most hydroxides are insoluble except NaOH and KOH

Sulfides, carbonates, chromates, and phosphates are insoluble

Lower number rules supersede so Na2S is soluble

Precipitation reaction

We can predict the products Can only be certain by experimenting

AgNO3(aq) + KCl(aq)

Zn(NO3)2(aq) + BaCr2O7(aq)

Three Types of Equations

Molecular Equation- written as whole formulas, not the ions.

K2CrO4(aq) + Ba(NO3)2(aq) Complete Ionic equation show dissolved electrolytes as the ions.

2K+ + CrO4-2 + Ba+2 + 2 NO3

-

BaCrO4(s) + 2K+ + 2 NO3

-

Spectator ions are those that don’t react.

Three Type of Equations

Net Ionic equations show only those ions that react, not the spectator ions

Ba+2 + CrO4-2 BaCrO4(s)

Write the three types of equations for the reactions when these solutions are mixed.

iron (III) sulfate and potassium sulfide