Chapter 4: Types of Chemical Rxns AP Chemistry Zumdahl Text 2011 AP Chemistry Zumdahl Text 2011

4.1 - Water, the Common Solvent  Virtually all of the chemistry occurs in substances dissolved in water (aqueous). These substances make life possible.  Water is essential for sustaining the reactions that keep us alive. It is one of the most important substances on Earth!  Medical tests such as analyses of blood and body fluids, tests for cholesterol, and iron all occur in aqueous environments.  Environmental tests such as groundwater quality to examine amounts of chloroform and nitrates.  Virtually all of the chemistry occurs in substances dissolved in water (aqueous). These substances make life possible.  Water is essential for sustaining the reactions that keep us alive. It is one of the most important substances on Earth!  Medical tests such as analyses of blood and body fluids, tests for cholesterol, and iron all occur in aqueous environments.  Environmental tests such as groundwater quality to examine amounts of chloroform and nitrates.

Water the Common Solvent  In an aqueous solution there occurs to components:  Solute - the dissolved substance  Solvent - the dissolving medium usually the most abundant (water most common)  Examples - Soda (carbon dioxide - solute, water - solvent)  Water has the ability to dissolve many different substances.  How does this happen? What properties of water give it the ability to perform this disappearing act?  In an aqueous solution there occurs to components:  Solute - the dissolved substance  Solvent - the dissolving medium usually the most abundant (water most common)  Examples - Soda (carbon dioxide - solute, water - solvent)  Water has the ability to dissolve many different substances.  How does this happen? What properties of water give it the ability to perform this disappearing act?

Polarity  Because of the electronegativity of the atoms contained in a water molecule each of the atoms is able to pull the electrons closer to its orbital. This gives the atom an overall positive or negative charge. We call this polarity.  The delta, , in the picture to the right indicates a slight positive or slight negative charge.  Because of the electronegativity of the atoms contained in a water molecule each of the atoms is able to pull the electrons closer to its orbital. This gives the atom an overall positive or negative charge. We call this polarity.  The delta, , in the picture to the right indicates a slight positive or slight negative charge.

Hydration  Substances are able to dissolve because opposite charges attract. The positive side of the water molecule are attracted to the anion (negative end) and the negative side of the water molecule are attracted to the cation (positive end) of a substance.  When salts dissolve they break up into their anions and cations. For example salt, NaCl, dissolved in water becomes Na + (cation) and Cl - (anion).  Substances are able to dissolve because opposite charges attract. The positive side of the water molecule are attracted to the anion (negative end) and the negative side of the water molecule are attracted to the cation (positive end) of a substance.  When salts dissolve they break up into their anions and cations. For example salt, NaCl, dissolved in water becomes Na + (cation) and Cl - (anion).

Solubility  Solubility of ionic substances in water vary greatly.  The differences in solubility depend on the attractions of the ions for each other and the attraction of the ions for the water molecules.  Water also dissolves nonionic substances, ethanol is very soluble in water (wine, beer, and mixed drinks).  Substances that are nonpolar don’t typically dissolve in water.  Remember “Like dissolves like!” Polar or ionic compounds are typically more soluble in water.  Solubility of ionic substances in water vary greatly.  The differences in solubility depend on the attractions of the ions for each other and the attraction of the ions for the water molecules.  Water also dissolves nonionic substances, ethanol is very soluble in water (wine, beer, and mixed drinks).  Substances that are nonpolar don’t typically dissolve in water.  Remember “Like dissolves like!” Polar or ionic compounds are typically more soluble in water.

4.2 The Nature of Aqueous Solutions: Strong and Weak Electrolytes  A solution is a homogeneous mixture. It is the same throughout but its composition may vary.  One way to characterize a solution is electrical conductivity.  Strong Electrolytes - good conductors  Weak Electrolytes - slight conductors  Nonelectrolytes - not a conductor  A solution is a homogeneous mixture. It is the same throughout but its composition may vary.  One way to characterize a solution is electrical conductivity.  Strong Electrolytes - good conductors  Weak Electrolytes - slight conductors  Nonelectrolytes - not a conductor

Strong Electrolytes  Completely ionized in water.  Examples of strong electrolytes are:  Soluble salts  Strong acids - Arrhenius Acids - strong electrolytes. He proposed that an acid is a substance that produces a H + ions as it dissolves in water.  Ex: HCl  H + (aq) + Cl - (aq)  Strong bases - contain a hydroxide ion. When dissolved in water they create the cation and the hydroxide ion.  Completely ionized in water.  Examples of strong electrolytes are:  Soluble salts  Strong acids - Arrhenius Acids - strong electrolytes. He proposed that an acid is a substance that produces a H + ions as it dissolves in water.  Ex: HCl  H + (aq) + Cl - (aq)  Strong bases - contain a hydroxide ion. When dissolved in water they create the cation and the hydroxide ion.

Check Your Understanding  Propose a hydration reaction for the following:  KOH  H 2 SO 4  KCl  Propose a hydration reaction for the following:  KOH  H 2 SO 4  KCl

4.3 The Composition of Solutions  Stoichiometry and Concentration  Molarity - moles of solute per volume of solution in liters:  M = molarity = moles of solute liters of solution  Stoichiometry and Concentration  Molarity - moles of solute per volume of solution in liters:  M = molarity = moles of solute liters of solution

Molarity I  Calculate the molarity of a solution prepared by dissolving 11.5 g of solid NaOH in enough to make 1.50L of solution.  Step 1 - convert grams to moles NaOH  Step 2 - Molarity is mol solute/L of solution.  Calculate the molarity of a solution prepared by dissolving 11.5 g of solid NaOH in enough to make 1.50L of solution.  Step 1 - convert grams to moles NaOH  Step 2 - Molarity is mol solute/L of solution.

Check Your Understanding: Molarity II  Calculate the molarity of a solution prepared by dissolving 1.56 g of gaseous HCl in enough water to make 26.8 mL of solution.

Concentration of Ions II  Calculate the number of moles of Cl - ions in 1.75 L of 1.0 x M ZnCl 2.  Step 1 - Need a balanced equation for dissolving ions? (Think hydration)  Molarity of Cl - ion in the solution?  2 x (1.0 x M) =  How many moles of Cl - ?  1.75 L solution x 2.0 x M Cl - =  Calculate the number of moles of Cl - ions in 1.75 L of 1.0 x M ZnCl 2.  Step 1 - Need a balanced equation for dissolving ions? (Think hydration)  Molarity of Cl - ion in the solution?  2 x (1.0 x M) =  How many moles of Cl - ?  1.75 L solution x 2.0 x M Cl - =

Concentration of Ions I  Give the concentration of each type of ion in the following solutions:  0.50 M Co(NO 3 ) 2  1 M Fe(ClO 4 ) 3  Always write the balanced equation for dissolving the ions.  What is the molarity of each ion?  Give the concentration of each type of ion in the following solutions:  0.50 M Co(NO 3 ) 2  1 M Fe(ClO 4 ) 3  Always write the balanced equation for dissolving the ions.  What is the molarity of each ion?

Dilution  Use the equation M 1 V 1 = M 2 V 2.  M 1 V 1 = mol solute before dilution  M 2 V 2 = mol of solute after dilution  Use the equation M 1 V 1 = M 2 V 2.  M 1 V 1 = mol solute before dilution  M 2 V 2 = mol of solute after dilution

Homework for Wednesday, 11/2/11  Read pgs in textbook.  Be ready for a quiz on Wednesday similar to homework problems.  4.23, 4.25  , , 35a, c  Post questions regarding the reading or homework on school rack.  In media center Mon - Wed (2:30 - 3:30 for assistance)  Read pgs in textbook.  Be ready for a quiz on Wednesday similar to homework problems.  4.23, 4.25  , , 35a, c  Post questions regarding the reading or homework on school rack.  In media center Mon - Wed (2:30 - 3:30 for assistance)