* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 4 Aqueous Reactions and Solution Stoichiometry
Marcus theory wikipedia , lookup
Biochemistry wikipedia , lookup
Physical organic chemistry wikipedia , lookup
Size-exclusion chromatography wikipedia , lookup
History of electrochemistry wikipedia , lookup
Rate equation wikipedia , lookup
Relativistic quantum mechanics wikipedia , lookup
Hydrogen-bond catalysis wikipedia , lookup
Hypervalent molecule wikipedia , lookup
Click chemistry wikipedia , lookup
Transition state theory wikipedia , lookup
Solvent models wikipedia , lookup
Spinodal decomposition wikipedia , lookup
Nucleophilic acyl substitution wikipedia , lookup
Chemical reaction wikipedia , lookup
Crystallization wikipedia , lookup
Thermometric titration wikipedia , lookup
Stoichiometry wikipedia , lookup
Chemical equilibrium wikipedia , lookup
Double layer forces wikipedia , lookup
Liquid–liquid extraction wikipedia , lookup
Electrolysis of water wikipedia , lookup
Metalloprotein wikipedia , lookup
Lewis acid catalysis wikipedia , lookup
Equilibrium chemistry wikipedia , lookup
Acid strength wikipedia , lookup
Electrochemistry wikipedia , lookup
Acid dissociation constant wikipedia , lookup
Stability constants of complexes wikipedia , lookup
Debye–Hückel equation wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Ionic compound wikipedia , lookup
Acid–base reaction wikipedia , lookup
Chemistry, The Central Science, 11th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Chapter 4 Aqueous Reactions and Solution Stoichiometry Solution Chemistry and the Hydrosphere Temperature and Salinity (halinity) in the Oceans Solution Terms • Solutions are homogeneous mixtures of two or more substances. • Solvent – the substance present in a solution in the greatest proportion (in number of moles). • Solute - the substance dissolved in the solvent. Aqueous Solution (aq) – a solution where water is the solvent. Ionic Dissociation • When an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and solvates them. • This process is called dissociation or ionization. NaCl(s) - Na+(aq) + Cl-(aq) Ionic Dissociation • An electrolyte is a substances that dissociates into ions when dissolved in water. • Since it is in water (solvent) these are referred to as aqueous solutions Aqueous Solutions Water is the dissolving medium Partial Charges on the water molecule 104.5o Aqueous Solutions Water is the dissolving medium Partial Charges on the water molecule red= area of negative charge blue= area of positive charge Some Properties of Water • Water is “bent” or V-shaped. • Water is a molecular compound. • Water is a polar (separaton of partial charge) molecule. • Hydration occurs when ionic compounds dissolve in water. Hydration of a solute Ion (Mg2+) Electrolytes Dissolved sugars would be examples of nonelectrolytes • An electrolyte is a substances that dissociates into ions (charged species) when dissolved in water. • A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so. Electrolytes and Nonelectrolytes Soluble ionic compounds tend to be electrolytes. Electrolytes and Nonelectrolytes Molecular compounds tend to be nonelectrolytes, except for acids and bases. H3COH (methanol) (aq) Electrolytes • A strong electrolyte dissociates completely when dissolved in water. • A weak electrolyte only dissociates partially when dissolved in water. Electrolytes Strong - conduct current efficiently Examples: Aqueous solutions of NaCl, HNO3, HCl Electrolytes Weak - conduct only a small current (vinegar, tap water) Non Electrolyte A solution in which no ionization occurs. There is no conduction of electrical current. Examples: Aqueous solutions of sugar, ethelyne glycol Strong Electrolytes Are… • Strong acids • Strong bases Strong Electrolytes Are… • Strong acids • Strong bases • Soluble ionic salts Solubility Guide 4.20 Using the solubility guide line (Table 4.1), predict the solubility of the following. a) Ni(OH)2 b) PbBr2 c) Ba(NO3)2 d) AlPO4 e) AgCl f) CaCO3 g) (NH4)2CO3 Precipitation Reactions When one mixes ions that form compounds that are insoluble (as could be predicted by the solubility guidelines), a precipitate is formed. Metathesis (Exchange) Reactions • Metathesis comes from a Greek word that means “to transpose.” AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) Metathesis (Exchange) Reactions • It appears the ions in the reactant compounds exchange, or transpose, ions. AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) Solution Chemistry • It is helpful to pay attention to exactly what species are present in a reaction mixture (i.e., solid, liquid, gas, aqueous solution). • If we are to understand reactivity, we must be aware of exactly what is changing during the course of a reaction. Molecular Equation The molecular equation lists the reactants and products in their molecular form. The (aq) indicates that the ions are dissociated in aqueous solution. AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) Ionic Equation • In the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions. • This more accurately reflects the species that are found in the reaction mixture. Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq) AgCl (s) + K+ (aq) + NO3- (aq) Net Ionic Equation • To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. • The only things left in the equation are those things that change phase (i.e., chemically react (precipitate) during the course of the reaction. • Those things that didn’t change (and were deleted from the net ionic equation) are called spectator ions. Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) AgCl (s) + K+(aq) + NO3-(aq) Net Ionic Equation • To form the net ionic equation, cross out the spectator ions (that not change from the left side of the equation to the right). • The only things left in the equation are those things that change (i.e., chemically react) during the course of the reaction. Ag+(aq) + Cl (aq) AgCl (s) Writing Net Ionic Equations 1. Write a balanced molecular equation. 2. Dissociate all strong electrolytes. 3. Cross out anything that remains unchanged from the left side to the right side of the equation. 4. Write the net ionic equation with the species that remain. Writing Net Ionic Equations Molecular Equation Ionic Equation Net Ionic Equation AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq) AgCl (s) + K+ (aq) + NO3- (aq) Writing Net Ionic Equations Molecular Equation Ionic Equation Net Ionic Equation AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq) AgCl (s) + K+ (aq) + NO3- (aq) Ag+(aq) + Cl-(aq) AgCl (s) 1. 2. 3. 4. Write a balanced molecular equation. Dissociate all strong electrolytes. Cross out anything that remains unchanged from the left side to the right side of the equation. Write the net ionic equation with the species that remain. Write the net ionic equation for the reaction of MgSO4 with BaCl2. Acids • Arrhenius defined acids as substances that increase the concentration of H+ when dissolved in water. • Brønsted and Lowry defined acids as proton donors. Acid-Base Reactions • Bronsted-Lowry acids are proton (H+) donors. • Bronsted-Lowry bases are proton acceptors. • Free hydrogen ions don’t exist in water because they strongly associate with a water molecule to create a hydronium ion (H3O+) (a hydrated proton). Acid-Base Reactions • A neutralization reaction takes place when an acid reacts with a base and produces a solution of a salt and water. • A salt is made up of the cation characteristic of the base and the anion characteristic of the acid. • Example: HCl + NaOH ---> NaCl + H2O Acids There are only seven strong acids: • • • • • • • Hydrochloric (HCl) Hydrobromic (HBr) Hydroiodic (HI) Nitric (HNO3) Sulfuric (H2SO4) Chloric (HClO3) Perchloric (HClO4) Bases • Arrhenius defined bases as substances that increase the concentration of OH− when dissolved in water. • Brønsted and Lowry defined them as proton acceptors. Bases The strong bases are the soluble metal salts of hydroxide ion: • • • • Alkali metals Calcium Strontium Barium Strong Acids and Bases • A strong acid or strong base is completely ionized in aqueous solution. • HCl, HBr, HI, HNO3, HClO3, HClO4 and H2SO4 are all strong acids. All other acids are assumed to be weak acids. • A weak acid or weak base only partially ionizes (dissociates) in aqueous solution. • Amphiprotic substances can behave as either a proton acceptor or a proton donor. Water is an example. Types of Acid/Base Equations • Molecular Equations have reactants and products written as undissociated (not ionized) molecules. HCl(aq) + NaOH(aq) ---> NaCl(aq) + H2O(l) • Overall Ionic Equations show all the species, both ionic and molecular present in aqueous solution for the reaction. H+ + Cl- + Na+ + OH- --> Na+ + Cl- + H2O Continued • Strong acids and strong bases are written as the corresponding ions in an overall ionic equation. • Net Ion Equations describe the actual chemical reaction occurring. H+ + OH- ----> H2O • The Na+ and Cl- ions are spectator ions in this reaction, because they are unchanged by the reaction (as is the solvent). Neutralization Reactions Generally, when solutions of an acid and a base are combined, the products are a salt and water. CH3COOH (aq) + NaOH (aq) CH3COONa (aq) + H2O (l) Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq) Na+ (aq) + Cl- (aq) + H2O (l) Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq) Na+ (aq) + Cl- (aq) + H2O (l) H+ (aq) + OH- (aq) H2O (l) Problem Write a balanced molecular equation and a net ionic equation for the following reactions: a. Solid magnesium hydroxide reacts with a solution of sulfuric acid. Gas-Forming Reactions • Some metathesis reactions do not give the product expected. • In this reaction, the expected product (H2CO3) decomposes to give a gaseous product (CO2). CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l) Gas-Forming Reactions When a carbonate or bicarbonate reacts with an acid, the products are a salt, carbon dioxide, and water. CaCO3 (s) + HCl (aq) NaHCO3 (aq) + HBr (aq) CaCl2 (aq) + CO2 (g) + H2O (l) NaBr (aq) + CO2 (g) + H2O (l) Gas-Forming Reactions Similarly, when a sulfite reacts with an acid, the products are a salt, sulfur dioxide, and water. SrSO3 (s) + 2 HI (aq) SrI2 (aq) + SO2 (g) + H2O (l) Gas-Forming Reactions • This reaction gives the predicted product, but you had better carry it out in the hood, or you will be very unpopular! • But just as in the previous examples, a gas is formed as a product of this reaction. Na2S (aq) + H2SO4 (aq) Na2SO4 (aq) + H2S (g) Write the products and net ionic equation for the following HNO3(aq) + Ca(OH)2(aq) → FeO(s) + HClO4(aq) → Write the products and net ionic equation for the reaction of solid Strontium carbonate with aqueous perchloric acid. Oxidation-Reduction Reactions • An oxidation occurs when an atom or ion loses electrons. • A reduction occurs when an atom or ion gains electrons. • One transfer cannot occur without the other also occurring. Oxidation-Reduction Half Reactions • When copper wire is immersed in a solution of silver nitrate it is oxidized. • Cu ---> Cu2+ + 2 e• Ag+ + e- ---> Ag • Silver ion is reduced, and the copper metal is oxidized. Oxidation-Reduction Reactions Fe2O3(s) + Al(s) Fe(l) + Al2O3(s) M Oxidized X Reduced Loses e- Gains e- Oxidation State Increases Reduction State Increases Reducing Agent Oxidizing Agent e- M+ X- Oxidation Numbers To determine if an oxidation-reduction reaction has occurred, we assign an oxidation number to each element in a neutral compound or charged entity. Rules for Assigning Oxidation States 1. The oxidation number of elements in a neutral molecule sum to zero or sum to charge of the ion in an ion. 2. Oxidation state of an atom in an element = 0 3. Oxidation state of monatomic ion = charge 4. Fluorine = 1 in all compounds 5. Hydrogen = +1, Oxygen = 2 in most compounds (except in peroxides where oxygen = 1) 6. Unless combined with O, or F the halogens are -1. Determining Oxidation Numbers SO2 CrO42NH3 ClO3SF6 Cl2 Oxygen is -2 and Sulfur is +4 Displacement Reactions • In displacement reactions, ions in solution are displaced (or replaced) by oxidation of another element. Zn(s) + 2 HBr(aq) Fe(s) + Ni(NO3)2(aq) ZnBr2(aq) + H2(g) Fe(NO3)2(aq) + Ni(s) Displacement Reactions In this reaction, silver ions oxidize copper metal. Cu (s) + 2 Ag+ (aq) Cu2+ (aq) + 2 Ag (s) Displacement Reactions The reverse reaction, however, does not occur (under normal conditions). Cu2+ (aq) + 2 Ag (s) x Cu (s) + 2 Ag+ (aq) Activity Series For example, scrap iron is used to reduce Cu2+ in Berkeley Pit (mine) waters. That is any element on the list can be oxidized by the ions of the elements below it on the list. Try Sample Exercise 4.10 (p. 142). Activity Series Using the Activity Series, write a balanced chemical equation for the following reactions: a) zinc metal is added to a solution of Magnesium sulfate, b) aluminum metal is added to a solution of cobalt(II) sulfate. Balancing redox reactions by method of half-reactions. 1. 2. 3. 4. 5. 6. 7. 8. 9. Separate the reactions into oxidation and reduction processes Work with one (ox or red) first Balance number of non-oxygen, non-hydrogen atoms first. Then balance oxygen with water Then balance hydrogen with H+ Then balance charge with electrons. Then balance other half-reaction using steps 3 through 6. Balance numbers of electrons between both half reactions and then add together. If you need to change to a basic solution then add the same number of hydroxide ions (OH-) to each side as H+ ions in balanced equation. These rules for balancing redox reaction are on page 847 in the text but you can also find them on the course website. See “A Closer Look” and “Strategies in Chemistry”, p. 143. Balancing by Half-Reaction Method in Acid Solution 1. Write separate reduction, oxidation halfreactions. KMnO4 + Cu+ Cu2+ + Mn2+ Ox. rxn: • Red. Rxn • Cu+ Cu2+ Cu+ Cu2+ + eKMnO4 Mn2+ + K+ KMnO4 + 5e- Mn2+ + K+ Balance number of non-oxygen, non-hydrogen atoms first. 3. For each half-reaction, balance oxygen with water KMnO4 + 5e- Mn2+ + K+ + 4 H2O 4. Then balance hydrogen with H+ 8H+ + KMnO4 + 5e- Mn2+ + K+ + 4 H2O 5. Balance numbers of electrons between both half reactions and then add together. 5(Cu+ Cu2+ + e-) + (KMnO4 + 8 H+ + 5 e- Mn2+ + K+ + 4 H2O) 5 Cu+ + KMnO4 + 8 H+ + 5 e- 5 Cu2+ + 5 e- + Mn2+ + K+ + 4H2O Practice Balance the following equation in acid solution: Br-(aq) + MnO4-(aq) Br2( ) + Mn2+(aq) Br-(aq) + MnO4-(aq) → Br2(l) + Mn2+(aq) Balance the following oxidation-reduction reaction in acidic and then for basic solution. Ag(s) + CN- + O2(g) Ag(CN)2-(aq) + H2O(l) Ag(s) Ag(CN)2-(aq) Ag(s) + 2 CN- Ag(CN)2-(aq) Ag(s) + 2 CN- Ag(CN)2-(aq) + eO2(g) H2O(l) O2(g) 2 H2O(l) O2(g) + 4 H+ 2 H2O(l) O2(g) + 4 H+ + 4 e- 2 H2O(l) 4(Ag(s) + 2 CN- Ag(CN)2-(aq) + e-) O2(g) + 4 H+ + 4 e- 2 H2O(l) 4 Ag(s) + 8 CN- + O2(g) + 4 H+ 4 Ag(CN)2-(aq) + 2 H2O(l) To convert to basic solution (add hydroxide to each side): 4 Ag(s) + 8 CN- + O2(g) + 4 H+ + 4 OH- 4 Ag(CN)2-(aq) + 2 H2O(l)+ 4 OH4 Ag(s) + 8 CN- + O2(g) + 4 H2O(l) 4 Ag(CN)2-(aq) + 2 H2O(l) + 4 OH4 Ag(s) + 8 CN- + O2(g) + 2 H2O(l) 4 Ag(CN)2-(aq) + 4 OH- How much of a solute dissolves? Concentration – ratio of the quantity of solute to either the mass or volume of the solution or solvent in which the solute is dissolved. Consequently, there are many different concentration terms depending on: 1. What is used to identify the quantity of solute (e.g. moles, mass, volume, etc.) 2. Whether the denominator of the ratio is the solvent or solution. 3. Whether mass or volume is used as the unit in the denominator. Molarity • Two solutions can contain the same compounds but be quite different because the proportions of those compounds are different. • Molarity is one way to measure the concentration of a solution. Molarity (M) = moles of solute volume of solution in liters Concentration of Solutions • Molarity (M) = moles of solute per volume of solution in liters: M molarity 3 M HCl moles of solute liters of solution 6 moles of HCl 2 liters of solution Problem What is the molarity of nitrate ions in a 0.0525 M solution of aluminum nitrate? Other Common Units of Concentration • Molality (m): moles solute/kg solvent • ppm: parts per million; mg solute/kg solution • ppb: mg solute/kg solution • ppt: ng solute/kg solution • % by weight: (grams of solute/total g solution) x 100% • Mole fraction: mole solute/total moles in solution Average Concentrations of the 11 Major Constituents of Seawater. Ions g/kg mmol/kg mmol/L Na+ 10.781 468.96 480.57 K+ 0.399 10.21 10.46 Mg2+ 1.284 52.83 51.14 Ca2+ 0.4119 10.28 10.53 Sr2+ 0.00794 0.0906 0.0928 Cl- 19.353 545.88 559.40 SO42- 2.712 28.23 28.93 HCO3- 0.126 2.06 2.11 Br- 0.0673 0.844 0.865 B(OH)3 0.0257 0.416 0.426 F- 0.00130 0.068 0.070 Total 35.169 1119.87 1147.59 Mixing a Solution • To create a solution of a known molarity, one weighs out a known mass (and, therefore, number of moles) of the solute. • The solute is added to a volumetric flask, and solvent is added to the line on the neck of the flask. Problem What is the molarity of an aqueous solution prepared by adding 36.5 g of barium chloride (208.233g/mol) to enough water to make 750.0 mL of solution? Determining the Number of Moles of Solute # of moles of solute Molarity = # of liter of solution • # moles Solute = (Molarity)(# Liters of Solution) • n = M x volume (in Liters) Problem How many grams of aluminum nitrate (212.996 g/mol) are required to make 500.0 mL of a 0.0525 M aqueous solution? Dilution • One can also dilute a more concentrated solution by Using a pipet to deliver a volume of the solution to a new volumetric flask, and Adding solvent to the line on the neck of the new flask. Dilution The molarity of the new solution can be determined from the equation Mc Vc = Md Vd, where Mc and Md are the molarity of the concentrated and dilute solutions, respectively, and Vc and Vd are the volumes of the two solutions. Practice Hydrochloric acid is obtained in 12.0 M stock solution. What volume of stock solution is required to make 500.0 mL of a 0.145 M dilute solution? Using Molarities in Stoichiometric Calculations Problem What mass of barium sulfate (233.390g/mo) is produced when 100.0 mL of a 0.100 M solution of barium chloride is mixed with 100.0 mL of a 0.100 M solution of iron (III) sulfate? What mass of barium sulfate (233.390g/mo) is produced when 100.0 mL of a 0.100 M solution of barium chloride is mixed with 100.0 mL of a 0.100 M solution of iron (III) sulfate? Titration Titration is an analytical technique in which one can calculate the concentration of a solute in a solution. Titration Terms • A titration is a volumetric analytical method used to determine the concentration of an unknown solution by reacting it with a standard solution. • A standard solution is a solution of known concentration. • The equivalence point in a titration is reached when enough standard solution has been added to completely react with the unknown solution. • The end point in a titration is reached when an indicator changes color or a specific pH (acid/base) or potential (redox) is reached. Stoichiometry Calculations H2SO4 + 2 NaOH --> Na2SO4 + 2 H2O What is the concentration of sulfuric acid if 15.00ml of it reacts with 18.45 mL of a 0.0973 M NaOH solution? Titration Example H2SO4 + 2 NaOH ---> Na2SO4 + 2 H2O NaOH H2SO4 End Point H2SO4(aq) + 2 NaOH(aq) --> Na2SO4(aq) + 2 H2O(l) What is the concentration of sulfuric acid if 15.00 ml of it reacts with 18.45 mL of a standardized 0.0973 M NaOH solution? Prob. 114 The arsenic in a 1.22g sample of a pesticide was converted to AsO43- by chemical treatment. It was then titrated with Ag+ to form Ag3AsO4 as a precipitate. a) What is the oxidation state of arsenic in AsO43- ? b) If it took 25.0 mL of 0.102 M Ag+ to reach the end point for this titration, what is the mass percentage of arsenic in the pesticide. 25.0 mL of 0.102 M Ag+ to reach the end point