Chapter 4 – Aqueous Systems Many chemical reactions occur in solution, when substances are dissolved in water. In this unit, we will explore the various properties of aqueous solutions and the types of chemical reactions that occur in them.

Aqueous Systems Formation of Aqueous Solutions o Solvation – When a solute becomes dissolved by a solvent (water). o Which type of substances does water dissolve?

Aqueous Systems Formation of Aqueous Solutions o Dissociation – Occurs when water breaks apart an ionic compound, or acid, into its ions. CaCl 2(s)  Ca +2 (aq) + 2Cl - (aq)

Aqueous Systems Formation of Aqueous Solutions o Dissociation – Write the dissociation reaction when aluminum bromide is dissolved in water.

Aqueous Systems Formation of Aqueous Solutions o Electrolytes o A solution that conducts electricity. o An electrolyte conducts electricity because of dissolved ions that are present in an aqueous solution. o The negatively charged ions can migrate across the solution and ‘pass’ the electron on.

Aqueous Systems Formation of Aqueous Solutions o Electrolytes o A strong electrolyte forms from the dissociation of a very soluble salt. o A weak electrolyte forms form a slightly soluble salt. o A nonelectrolyte is a solution that does not contain ions in solution. (sugar water or pure water)

Aqueous Systems Double Replacement Reactions – The cations of two ionic compounds switch anions. But one of the products has to be one of the following; 1.) insoluble in water 2.) a gas 3.) a water molecule

Aqueous Systems Double Replacement Reactions AgNO 3 (aq) + NaCl (aq)  NaNO 3 (aq) + AgCl (s) HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) HNO 3 (aq) + NaHCO 3 (aq)  NaNO 3 (aq) + H 2 O (l) + CO 2 (g)

Aqueous Systems Double Replacement Reactions – A solubility table must be used in order to determine whether or not an ionic compound will be soluble in water or not. NaCl (aq) + Pb(NO 3 ) 2 (aq) 

Aqueous Systems Double Replacement Reactions – What will happen when aqueous solutions of potassium chloride and sodium hydroxide are mixed? KCl (aq) + NaOH (aq) 

Aqueous Systems Na 2 SO 4 (aq) + Ba(NO 3 ) 2 (aq)  HNO 3 (aq) + KOH (aq)  Na 2 SO 4 (aq) + KCl (aq) 

Aqueous Systems Net Ionic Equations A chemical equation which only the ions that participate in the formation of the non- aqueous product are written. General Equation: Na 2 SO 4 (aq) + Ba(NO 3 ) 2 (aq  2NaNO 3 (aq) + BaSO 4 (s) Ionic Equation: 2Na +1 (aq) + SO 4 -2 (aq) + Ba +2 (aq) + 2NO 3 -1 (aq)  2Na +1 (aq) + 2 NO 3 -1 (aq) + BaSO 4 (s) Net Ionic Equation: Ba +2 (aq) + SO 4 -2 (aq)  BaSO 4 (s) 

Aqueous Systems Net Ionic Equations Ions that do not participate in the net ionic equation are called spectator ions. General Equation: Na 2 SO 4 (aq) + Ba(NO 3 ) 2 (aq  2NaNO 3 (aq) + BaSO 4 (s) Ionic Equation: 2Na +1 (aq) + SO 4 -2 (aq) + Ba +2 (aq) + 2NO 3 -1 (aq)  2Na +1 (aq) + 2NO 3 -1 (aq) + BaSO 4 (s) Net Ionic Equation: Ba +2 (aq) + SO 4 -2 (aq)  BaSO 4 (s) 

Aqueous Systems Writing Net Ionic Equations Write the net ionic for the chemical reaction between sodium dichromate and mercury (II) nitrate.

Aqueous Systems Single Replacement Reactions o Occur when an element reacts with with an ionic compound. o Single replacement reactions will only occur if the element is more reactive than its analog in the ionic compound. Na (s) + CaCl 2(aq)  F 2(g) + SrBr 2(aq) 

Aqueous Systems Single Replacement Reactions o How do we know if one metal is more reactive than another?

Aqueous Systems Single Replacement Reactions o How do we know if one nonmetal is more reactive than another? Look at the halogens on the periodic table. F 2 most reactive Cl 2 Br 2 I 2 At 2 least reactive

Aqueous Systems Single Replacement Reactions o Predict the products of the following chemical reactions; Cu (s) + Sn(NO 3 ) 4(aq)  Zn (s) + AlCl 3(aq)  MgI 2(aq) + Cl 2(g) 

Acids and Bases The concept of acidic and basic solutions is perhaps one of the most important topics in chemistry. Acids and bases affect the properties of foods, biochemical reactions, pharmaceuticals, and industrial materials.

Acids and Bases Properties of Acids Sour or tart taste. Corrosive (deteriorate). Electrolytes Electrolytes are able to conduct an electrical current because of the presence of ions in aqueous solutions.

Acids and Bases Properties of Acids (cont.) Will react with most metals to form hydrogen gas. Some acids are ‘stronger’ than others All acids contain a hydrogen that they can give away.

Acids and Bases Properties of Bases Bitter tasting Slippery Caustic – They will degrade biological tissue. Chemical burns from strong bases are nasty. Bases form the hydroxide ion (OH -1 ) in water.

Acids and Bases Arrhenius Acids Svante Arrhenius (1900) defined an acid. Acids are hydrogen containing compounds that yield a hydrogen ion (H + ) in water. An Arrhenius acid donate an H + ion.

Acids and Bases Arrhenius Acids HCl (s)  H + (aq) + Cl - (aq) H 2 SO 4(s)  H 2 O (l) 

Acids and Bases Arrhenius Acids Acids that have one hydrogen ion to donate are called monoprotic. Acids that have 2 hydrogen ions to donate are called diprotic. Acids that have 3 hydrogen ions to donate are called ____protic.

Acids and Bases Arrhenius Bases Compounds that produce the hydroxide ion(s) (OH -1 ) in water are called Arrhenius Bases. NaOH (s) 

Acids and Bases Arrhenius Acids and Bases Problem with the Arrhenius definition; Some bases can form OH- ions in solution but not have an OH- ion in the chemical formula. NH 3(g) + H 2 O (l)  NH 4 + (aq) + OH - (aq)

Acids and Bases Bronsted-Lowry Acids and Bases A better definition of an acid and a base Bronsted-Lowry Acid – A molecule that donates an H + to another molecule. Bronsted-Lowry Base – A molecule that accepts an H + from the B-L acid. Identify the Bronsted-Lowry acid and base; NH 3(g) + H 2 O (l)  NH 4 + (aq) + OH - (aq)

Acids and Bases Bronsted-Lowry Acids and Bases Conjugate Acid – becomes the H + donor in the reverse reaction. Conjugate Base – becomes the H + acceptor in the reverse reaction. Identify the BL acid, base, conjugate acid and conjugate base; HClO 2(aq) + H 2 O (l)  H 3 O +1 (aq) + ClO 2 - (aq)

Chapter 20 – Redox Reactions One of the earliest recognized chemical reactions were with oxygen. Some substances would combine with oxygen, and some would release oxygen. If a substance would gain oxygen, it was said that the substance was oxidized. If the substance lost oxygen, it was said that it was reduced. Since then, reduction-oxidation reactions (redox reactions) have been defined to explain why these substances lost or gained oxygen.

Redox Reactions Oxidation (Old School Definition); Any substance that gained oxygen in a chemical reaction. 4Fe (s) + 3O 2(g)  2Fe 2 O 3(s) We can say that the iron was oxidized.

Redox Reactions Reduction (Old School Definition); Any substance that loses oxygen in a chemical reaction. 2Fe 2 O 3(s) +3C (s)  4Fe (s) +3 CO 2(g) We can say that the iron (III) oxidized was reduced.

Redox Reactions Oxidation (New School Definition); Any substance that loses electrons in a chemical reaction. 3Mg (s) + N 2(g)  Mg 3 N 2(s) In this chemical reaction, Mg goes from zero charge as a reactant to a +2 charge as a product. Mg (s)  Mg +2 (aq) + 2e -

Redox Reactions Reduction (New School Definition); Any substance that gains electrons in a chemical reaction. 3Mg (s) + N 2(g)  Mg 3 N 2(s) In this chemical reaction, N goes from zero charge as a reactant to a -3 charge as a product. N 2(s) + 6e -  2N -3 (aq)

Redox Reactions Reduction-Oxidation (Redox) Reactions Redox reactions occur when one atom loses electrons, while another gains electrons. We can tell if electrons have been transferred by looking at the individual charge (oxidation number), of each atom.

Redox Reactions Rules for Assigning Oxidation Numbers 1.Monoatomic Ions have the same sign and charge of its ionic charge.

Redox Reactions Rules for Assigning Oxidation Numbers 2.The oxidation number for hydrogen in a compound is +1 except when it is part of a metal hydride.

Redox Reactions Rules for Assigning Oxidation Numbers 3.The oxidation number of oxygen in a compound is -2 unless it is part of a peroxide where it is -1. Oxygen can have a -1 charge if it is part of a compound where there is an element more electronegative than it.

Redox Reactions Rules for Assigning Oxidation Numbers 4.The oxidation of atoms in their elemental forms is zero.

Redox Reactions Rules for Assigning Oxidation Numbers 5.For neutral compounds, the sum of the oxidation numbers must equal zero.

Redox Reactions Rules for Assigning Oxidation Numbers 6.For polyatomic ions, the sum of the oxidation numbers must equal the charge of the polyatomic ion.

Redox Reactions Assigning Oxidation Numbers Assign an oxidation number for each element in the following compounds; 1.) SO 2

Redox Reactions Assigning Oxidation Numbers Assign an oxidation number for each element in the following compounds; 2.) CO 3 -2

Redox Reactions Assigning Oxidation Numbers Assign an oxidation number for each element in the following compounds; 3.) Na 2 SO 4

Redox Reactions Assigning Oxidation Numbers Assign an oxidation number for each element in the following compounds; 4.) (NH 4 ) 2 S

Redox Reactions Assigning Oxidation Numbers Assign an oxidation number for each element in the following compounds; 5.) Fe

Aqueous Solutions Calculating Solution Concentration Molarity (M): Molarity is defined as the number of moles of solute per liter of solution. Molarity (M) = moles of solute 1.0 L of H 2 O

Aqueous Solutions What is the molarity of a solution that was made by dissolving 5.0 grams of NaCl in 500. mL of water.

Aqueous Solutions How many moles of calcium chloride would be contained in 30.0 mL of a 1.5 M calcium chloride solution?

Aqueous Solutions Dilutions A solution can be diluted by adding water. Adding water will reduce the concentration of the solute by increasing the volume of the solution. C i V i = C f V f (initial # moles = final # moles)

Aqueous Solutions Dilutions Lets assume you want to make 2.0 L of a 1.0 M HCl solution. Your stock solution of HCl is 12 M. What volume of the stock solution must be used in order to make the diluted solution?

Aqueous Solutions Dilutions Describe how you would make mL of a 0.35 M KNO 3 solution from a 1.0 M stock solution of KNO 3.