Aqueous Reactions and Solution Stoichiometry Chapter 4

Aqueous Reactions HCl(aq) + NaOH(aq)  H 2 O(l) + NaCl(aq) This is a reaction in which reactants are in solution Solution – homogeneous mixture composed of two parts: solute – the medium which is dissolved solvent – the medium which dissolves the solute.

Molarity (M) Unit of concentration, moles of solute per liter of solution. Solutions

Example: What is the molarity(M) of a solution which contains 17.51g of NaCl in 751mL of solution? F.W. (NaCl): 58.45g/mol Solution volume Solutions

Example: What is the molarity (M) of a solution which contains 17.51g of NaCl in 751mL of solution? Solutions

Solutions Molarity

M dilute V dilute = M concentrated V concentrated Solutions Dilution

Example: What volume of 6.00M NaOH is required to make 500mL of 0.100M NaOH? M concentrated = 6.00MM dilute = 0.100M V concentrated = ?V dilute = 500mL 0.100M(500mL) = 6.00M(V concentrated ) V concentrated = 8.33mL Solutions Dilution

Some compounds conduct electricity when dissolved in water – electrolytes Those compounds which do not conduct electricity when dissolved in water are called – nonelectrolytes Properties of Solutes Compounds in Water

Some compounds conduct electricity when dissolved in water – electrolytes Those compounds which do not conduct electricity when dissolved in water are called – nonelectrolytes Properties of Solutes Compounds in Water

The conductivity of the solution is due to the formation of ions when the compound dissolves in water These ions are not the result of a chemical reaction, they are the result of a dissociation of the molecule into ions that compose the solid. Properties of Solutes Ionic Compounds in Water (Electrolytes)

Properties of Solutes Ionic Compounds in Water

In this case no ions are formed, the molecules just disperse throughout the solvent. Properties of Solutes Molecular Compounds in Water (Nonelectrolytes)

There are exceptions to this, some molecules are strongly attracted to water and will react with it. Properties of Solutes Molecular Compounds in Water(Nonelectrolytes)

There are exceptions to this, some molecules are strongly attracted to water and will react with it. Properties of Solutes Molecular Compounds in Water (Nonelectrolytes)

Strong electrolytes – A substance which completely ionizes in water. For example: Properties of Solutes Strong and Weak Electrolytes

Weak electrolyte: A substance which partially ionizes when dissolved in water. For example: Notice that the arrow in this reaction has two heads, this indicates that two opposing reactions are occurring simultaneously. Properties of Solutes Strong and Weak Electrolytes

Since both reactions occur at the same time, this is called a chemical equilibrium Properties of Solutes Strong and Weak Electrolytes

Acid - substance which ionizes to form hydrogen cations (H + ) in solution Examples: Hydrochloric AcidHCl Nitric AcidHNO 3 Acetic AcidCH 3 CO 2 H Sulfuric AcidH 2 SO 4 Notice that sulfuric acid can provide two H + ’s – Diprotic acid, the other acids can provide only one H + – Monoprotic acid. Acids, Bases, and Salts

H 2 SO 4  H + + HSO 4 - HSO 4 -  H + + SO 4 2- Acids, Bases, and Salts Diprotic acid

Bases - substances which reacts with H + ions formed by acids. Examples: ammoniaNH 3 sodium hydroxideNaOH Acids, Bases, and Salts Bases

H + + OH -  H 2 O -Metal hydroxides (NaOH for example) provide OH - by disassociation. -Bases like ammonia make OH - by reacting with water (ionization) NH 3 + H 2 O  NH OH - Acids, Bases, and Salts Acid-Base Reactions

-The strength of acids and bases are concerned with the ionization (or dissociation) of the substance, not its chemical reactivity. Example: Hydrofluoric acid (HF) is a weak acid, but it is very chemically reactive. - this substance can’t be stored in glass bottles because it reacts with glass (silicon dioxide). Acids, Bases, and Salts Strong Acids

Common Strong Acids Hydrochloric AcidHCl Hydrobromic AcidHBr Hydroiodic acidHI Nitric AcidHNO 3 Perchloric AcidHClO 4 Chloric AcidHClO 3 Sulfuric AcidH 2 SO 4 Acids, Bases, and Salts Common Strong Acids and Bases

Common Strong Bases Lithium HydroxideLiOH Sodium HydroxideNaOH Potassium HydroxideKOH Rubidium HydroxideRbOH Cesium HydroxideCsOH Calcium HydroxideCa(OH) 2 Strontium HydroxideSr(OH) 2 Barium HydroxideBa(OH) 2 Acids, Bases, and Salts Common Strong Acids and Bases

-Reaction between an acid and a base. HCl(aq) + NaOH(aq)  H 2 O(l) + NaCl(aq) “The reaction between an acid and a metal hydroxide produces water and a salt” Salt – an ionic compound whose cation comes from a base and anion from an acid. Acids, Bases, and Salts Neutralization Reaction

HCl(aq) + NaOH(aq)  H 2 O(l) + NaCl(aq) - despite the appearance of the equation, the reaction actually takes place between the ions. Acids, Bases, and Salts Neutralization Reaction

HCl(aq) + NaOH(aq)  H 2 O(l) + NaCl(aq) Total Ionic Equation H + (aq) + Cl - (aq) + Na + (aq) + OH - (aq)  H 2 O(l) + Na + (aq) + Cl - (aq) Acids, Bases, and Salts Neutralization Reaction

HCl(aq) + NaOH(aq)  H 2 O(l) + NaCl(aq) Total Ionic Equation H + (aq) + Cl - (aq) + Na + (aq) + OH - (aq)  H 2 O(l) + Na + (aq) + Cl - (aq) Some of the ions appear unchanged in both the reactants and products – spectator ion Acids, Bases, and Salts Neutralization Reaction

HCl(aq) + NaOH(aq)  H 2 O(l) + NaCl(aq) Total Ionic Equation H + (aq) + Cl - (aq) + Na + (aq) + OH - (aq)  H 2 O(l) + Na + (aq) + Cl - (aq) Net Ionic Equation H + (aq) + OH - (aq)  H 2 O(l) Acids, Bases, and Salts Neutralization Reaction

AX + BY  AY + BX Three driving forces for the reaction: -Formation of an insoluble solid (precipitation reaction) -Formation of a weak electrolyte or nonelectrolyte -Formation of a gas that escapes from solution Metathesis Reactions

Precipitation Reaction Metathesis Reactions

-A reaction which forms a solid (precipitate) AgNO 3 (aq) + NaCl(aq)  AgCl(s) + NaNO 3 (aq) -AgCl is classified as an insoluble substance Solubility – amount of substance that can be dissolved in a specific amount of water (g/L or mg/L) - for this textbook, any substance with a solubility less than 0.01mol/L is considered insoluble. Metathesis Reactions Precipitation Reaction

Solubility Guidelines for Ionic Compounds Metathesis Reactions 1.Most nitrates (NO 3 - ) and acetates (CH 3 CO 2 - ) are soluble in water. 2.All chlorides are soluble except: Hg +, Ag +, Pb 2+, Cu + 3.All sulfates are soluble except: Sr 2+, Ba 2+, Pb 2+ 4.Carbonates (CO 3 2- ), Phosphates (PO 4 3- ), Borates (BO 3 3- ), Arsenates (AsO 4 3- ), and Arsenites (AsO 3 3- ) are insoluble. 5.Hydroxides (OH - ) of group Ia and Ba 2+ and Sr 2+ are soluble. 6.Most sulfides (S 2- ) are insoluble.

Reactions Which Form Weak and Non- electrolytes Metathesis Reactions -One example of this type of reaction is a neutralization reaction. Mg(OH) HCl  MgCl H 2 O -Insoluble metal oxide (base) and a strong acid. MgO(s) + 2 HCl(aq)  MgCl 2 (aq) + H 2 O(l)

Reactions Which Form Gases Metathesis Reactions -Carbonates and Hydrogen Carbonates decompose to give CO 2 -Carbonate and Acid 2 HCl(aq) + Na 2 CO 3 (aq)  2 NaCl(aq) + CO 2 (g) + H 2 O(l) -Hydrogen Carbonate and Acid HCl(aq) + NaHCO 3 (aq)  NaCl(aq) + CO 2 (g) + H 2 O(l)

Oxidation-Reduction Reactions -reaction where electrons are exchanged. 2 Na(s) + 2 H 2 O(l)  2 NaOH(aq) + H 2 (g) Na(s)  Na + (aq) + 1 e - oxidation – loss of electrons 2 H + (g) + 2 e -  H 2 (g) reduction – gain of electrons

Oxidation-Reduction Reactions - Oxidation of metals by acids to form salts Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) - Oxidation of metals salts Fe(s) + Ni 2+ (aq)  Fe 2+ (aq) + Ni(s) Notice that the Fe is oxidized to Fe 2+ and the Ni 2+ is reduced to Ni.

Oxidation-Reduction Reactions - Oxidation of metals by acids to form salts Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g) - Oxidation of metals salts Fe(s) + Ni 2+ (aq)  Fe 2+ (aq) + Ni(s) but, Fe 2+ (aq) + Ni(s)  no reaction

Oxidation-Reduction Reactions -Some metals are more easily oxidized than others. -The relative ability of an element to be oxidized is summarized in a table. Activity series - a list of metals arranged in decreasing ease of oxidation. -The higher the metal on the activity series, the more active that metal. -Any metal can be oxidized by the ions of elements below it. The Activity Series

Oxidation-Reduction Reactions The Activity Series

Solution Stoichiometry -We can now use molarity to determine stoichiometric quantities. Example How many grams of hydrogen gas are produced when 20.0 mL of 1.75M HCl is allowed to react with 15.0g of sodium metal? 2 HCl(aq) + 2 Na(s)  H 2 (g) + 2 NaCl(aq)

Solution Stoichiometry Titrations

Solution Stoichiometry Titrations How many milliliters of 0.155M HCl are needed to neutralize Completely 35.0 mL of M Ba(OH) 2 solution? 2 HCl(aq) + Ba(OH) 2 (aq)  BaCl 2 (aq) + 2 H 2 O(l)