Presentation on theme: "Chemistry II Aqueous Reactions and Solution Chemistry Chapter 4"— Presentation transcript:
1Chemistry II Aqueous Reactions and Solution Chemistry Chapter 4
2In this chapter we will consider chemical processes that occur in aqueous solutions: precipitation reactions, acid base reactions and oxidation – reduction reactions.
3We will then consider concentrations and how the concepts of stoichiometry can be applied to concentrations.
4Water has many properties that allow it to help support life Water has many properties that allow it to help support life. One of these properties is that it can dissolve a wide variety of materials. For this reason water is often referred to as what?
5Water has many properties that allow it to help support life Water has many properties that allow it to help support life. One of these properties is that it can dissolve a wide variety of materials. For this reason water is often referred to as what?The universal solvent
10A homogeneous mixture of two or more substances. Define solution:A homogeneous mixture of two or more substances.
11What is the difference between solvent and solute?
12What is the difference between solvent and solute? The substance that is present in greater quantity is usually called the solvent.The other substances in the solution are solutes. Solutes are dissolved in the solvent.
13Electrolytic Properties Pure water is not a good conductor of electricity. The presence of ions causes aqueous solutions to become good conductors. Ions carry the charge from one electrode to the next.
23What is a polar molecule What is a polar molecule. Explain the significance of this fact with respect to the dissociation of ionic solids.
24What is a polar molecule What is a polar molecule. Explain the significance of this fact with respect to the dissociation of ionic solids.
25What is a polar molecule What is a polar molecule. Explain the significance of this fact with respect to the dissociation of ionic solids.A polar molecule has one end that has a partial positive charge and a partial negative charge.
26Although water is an electrically neutral molecule, one end of the molecule is electron rich and carries a partial negative charge. The hydrogen side of the molecule has a partial positive charge.
27When ionic compounds dissolve the anions are surrounded by the water molecules so that the hydrogen side of the molecule surrounds the anion. The cations are surrounded by the oxygen side of the water molecule. This configuration stabilizes the ions in solution.
28How can we predict the charges of the ions present in solution?
29How can we predict the charges of the ions present in solution? Remember the formulas and charges of the common ions.i.e., Na2SO4 will separate into two Na+ ions and one SO42- ions.In solution for every one sodium sulfate three ions are formed.
31When a molecular compound dissolves in water, the solution usually consists of intact molecules dispersed throughout the solution. Usually molecular compounds are non-electrolytes. An exception to this rule is acids
37What are strong electrolytes? Those solutes that exist in solution completely or nearly completely as ions.Most ionic compounds and some acids and bases are strong electrolytes.
38What are weak electrolytes? Those solutes that exist in solution in the form of molecules but only partially disassociated into ions.
39Can you determine if a solute is a strong or weak electrolyte by how well it dissolves?
40Can you determine if a solute is a strong or weak electrolyte by how well it dissolves? No, for example acetic acid (vinegar) is very soluble in water, but only partially dissociates into ions.
41How can we indicate that an electrolyte is a weak electrolyte?
42How can we indicate that an electrolyte is a weak electrolyte? We can use double arrows to show that the reaction is significant in both directions.HC2H3O2(aq) ↔ H+(aq) + C2H3O2-(aq)* The state of equilibrium between molecules and ions varies from one weak electrolyte to another.
43How do chemists indicate the ionization of strong electrolytes?
44How do chemists indicate the ionization of strong electrolytes? With the use of a single arrow.HCl (aq) → H+(aq) Cl-(aq)The single arrow indicates that the ions have no tendency to recombine to molecules.
45In a the next few sections we will learn how to predict if a compound is a strong electrolyte, weak electrolyte or non-electrolyte. For now, in general, soluble ionic compounds are always strong electrolytes.
47How can we identify compounds are being ionic? Ionic compounds are composed of metals and nonmetalsNaClFeSO4Al(NO3)3NH4Br
48The diagram on the right represents an aqueous solution of one of the following compounds: MgCl2, KCl, or K2SO4. Which solution does the drawing best represent?
49If you were to draw diagrams (such as that shown on exercise 4 If you were to draw diagrams (such as that shown on exercise 4.1) representing aqueous solutions of each of the following ionic compounds, how many anions would you show if the diagram contained six cations?(a) NiSO4, (b) Ca(NO3)2, (c) Na3PO4, (d) Al2(SO4)3
60What is solubility ?The amount of substance that can be dissolved in a given quantity of solvent.Any substance with a solubility less than mol/L is referred to as insoluble.
61Experimental observations have led to guidelines for predicting solubility (page 118 Table 4.1)
62Sample exercise 4.2Classify the following ionic compounds as soluble or insoluble in water:(a) sodium carbonate (Na2CO3),(b) lead sulfate (PbSO4).
63Classify the following compounds as soluble or insoluble in water: (a) cobalt(II) hydroxide,(b) barium nitrate,(c) ammonium phosphate.
64How can we predict whether a precipitate forms when we mix aqueous solutions of two strong electrolytes?1.) note the ions present in the reactants.
65How can we predict whether a precipitate forms when we mix aqueous solutions of two strong electrolytes?1.) note the ions present in the reactants.2.) Consider possible combinations of cations and anions.
66How can we predict whether a precipitate forms when we mix aqueous solutions of two strong electrolytes?3.) Use solubility guidelines to determine if any combinations are insoluble
67How can we predict whether a precipitate forms when we mix aqueous solutions of two strong electrolytes?For example, will a precipitate form when Mg(NO3)2 and NaOH are mixed?
68Precipitation reactions are a type of double replacement reactions Precipitation reactions are a type of double replacement reactions. They are also known as exchange or metathesis reactions.
75In writing chemical equations for reactions in aqueous solutions, it is often helpful to know if the dissolved substances are present mainly as molecules or as ions. For example:Molecular Equation-Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq)
83Note: if every ion in a complete ionic equation is a spectator ion, then no reaction occurs.
84The net ionic equation includes only the ions and molecules directly involved in the reaction.
85How can net ionic equations be used? They can be used to show similarities between large numbers of reactionsA net ionic equation shows that more than one set of reactions can lead to the same net reaction.
86What are the steps for writing net ionic equations?
87What are the steps for writing net ionic equations? 1.) Write a balanced molecular equation for the reaction.2.) Rewrite the equation to show the ions that form only strong electrolytes are written in ionic form.3.) Identify and cancel spectator ions.
88Sample Exercise 4.4Write the net ionic equation for the precipitation reaction that occurs when solutions of calcium chloride and sodium carbonate are mixed.
89Write the net ionic equation for the precipitation reaction that occurs when aqueous solutions of silver nitrate and potassium phosphate are mixed.
94What are acids?Acids are substances that ionize in aqueous solutions to form hydrogen ions, increasing the concentration of hydrogen ions in solution.Because hydrogen ions are just a proton, acids are known as proton donors.
95The number of hydrogen ions produced depends on the number of hydrogen atoms present. Acids like HCl and HNO3 yield one hydrogen ion per molecule. Some acids such as H2SO4 yield 2 hydrogen ions.
96What is the difference between a monoprotic an diprotic acid?
97What is the difference between a monoprotic an diprotic acid? Acids that yield one hydrogen ion are monoprotic such as HClHCl → H+(aq) + Cl-(aq)Acids that yield two hydrogen ions are diprotic i.e., H2SO4H2SO4 → 2H+(aq) + SO42-(aq)
100What are bases?Bases are substances that accept H+ ions thereby reducing the number of H+ ions in solution.Bases produce OH- ions when dissolved in water.When bases are dissolved in water they release OH- and create more OH- ions by bonding to all of the available H+ ions.
101What are bases? Some bases do not contain OH- NH3 is an example NH3 + H2O → NH4+ + OH-
106What are weak acids and bases? Acids and bases that are only partly ionized in solution.
107Table 4. 2 on page 122 lists the strong acids and bases Table 4.2 on page 122 lists the strong acids and bases. These should be committed to memory. What are the strong acids and bases.
108Table 4. 2 on page 122 lists the strong acids and bases Table 4.2 on page 122 lists the strong acids and bases. These should be committed to memory. What are the strong acids and bases.ACIDSHCl HClO3 HNO3HBr HClO4 H2SO4HI
109Table 4. 2 on page 122 lists the strong acids and bases Table 4.2 on page 122 lists the strong acids and bases. These should be committed to memory. What are the strong acids and bases.BasesThe alkali group hydroxidesAlkaline earth metals Ca, Sr and Ba hydroxides.
111Is a soluble ionic compound a strong electrolyte, weak electrolyte or a nonelectrolyte?
112Is a soluble ionic compound a strong electrolyte, weak electrolyte or a nonelectrolyte? All soluble ionic compounds are strong electrolytes.
113How can you tell if a soluble molecular compound is a strong electrolyte, weak electrolyte or nonelectrolyte?All strong acids and bases are strong electrolytesAll weak acids and bases are weak electrolytesAll other soluble molecular compounds are nonelectrolytes.
114The following diagrams represent aqueous solutions of three acids (HX, HY, and HZ) with water molecules omitted for clarity. Rank them from strongest to weakest.
115Classify each of the following dissolved substances as a strong electrolyte, weak electrolyte, or nonelectrolyte: CaCl2, HNO3, C2H5OH (ethanol), HCOOH (formic acid), KOH.
122What is the definition of a salt? Any ionic compound whose cation comes from a base and whose anion comes from an acid.
123What is the net ionic equation for all neutralization reactions?
124What is the net ionic equation for all neutralization reactions? H+(aq) + OH-(aq)→ H2O(l)
125What type of reaction is a neutralization reaction? A double replacement (also known as a metathesis reaction or exchange reaction)Mg(OH)2 + 2HCl → MgCl2 + 2H2O
126Sample exercise 4.7(a) Write a balanced molecular equation for the reaction between aqueous solutions of acetic acid (CH3COOH) and barium hydroxide, Ba(OH)2.(b) Write the net ionic equation for this reaction.
127(a) Write a balanced molecular equation for the reaction of carbonic acid (H2CO3) and potassium hydroxide (KOH).(b) Write the net ionic equation for this reaction.
129There are two bases besides OH- that react with H+ There are two bases besides OH- that react with H+. Two of these include the sulfide and carbonate ions.
130There are two bases besides OH- that react with H+ There are two bases besides OH- that react with H+. Two of these include the sulfide and carbonate ions.Both of these react with acids to form gases.2HCl + Na2S → H2S + 2NaClHCl + NaHCO3 → NaCl + H2CO3
131Read chemistry at work antacids. Both NaHCO3 ( Sodium carbonate) and Na2HCO3 (Sodium Bicarbonate) are used as acid neutralizers and antacids.Read chemistry at work antacids.
134What is corrosion?The conversion of a metal into a metal compound by a reaction between the metal and some substance in its environment.
135What is corrosion?When a metal corrodes it lose electrons and forms cationsCa HCl → CaCl H2I______________lCalcium is oxidized because it lost electrons
136What is corrosion?Ca HCl → CaCl H2l_______________lHydrogen is reduced because it gained electrons.
137What are oxidation – reduction (redox) reactions? Reactions in which electrons are transferred between reactants.
138When an atom becomes positively charged. When it has lost electrons What is oxidation?When an atom becomes positively charged.When it has lost electronsLoss of electrons by a substance is called oxidation.
139The term oxidation is used because the first reactions of this sort to be studied were reactions with oxygen.
140What is reduction? Gain of electrons from a substance. The oxidation of one substance is always accompanied by the reduction of another substance.
142What are oxidation numbers? The oxidation number of an atom in a substance is the actual charge of the atom if it is a monoatomic ionor it is the hypothetical charge assigned using a set of rules
143Rules for assigning oxidation numbers 1.) For an atom in the elemental form, the oxidation number is always zero.H2, Ca, O2
144Rules for assigning oxidation numbers 2.) For any monatomic ion, the oxidation number equals the charge on the ionK+ = 1+S2- = 2-
145Rules for assigning oxidation numbers 3.) non-metals usually have negative oxidation numbers.a.) oxygen is usually 2- w/ the exception of the peroxide ion (O2) which has the oxidation number 1-
146Rules for assigning oxidation numbers b.) hydrogen has an oxidation number of 1+ when bonded to a nonmetal [(HCl) H 1+ ; Cl 1-]and has a oxidation of 1- when bonded to a metal[ CaH2 – Ca 2+ , H 1-]
147Rules for assigning oxidation numbers The sum of the oxidation numbers of all atoms in a nuetral compound is zero.The sum of the oxidation numbers in a polyatomic ion equals the charge of the ion.
148Sample exercise 4.8 page 128Determine the oxidation number of sulfur in each of the following:(a) H2S,(b) S8,(c) SCl2,(d) Na2SO3,(e) SO42–.
149What is the oxidation state of the element in each of the following: (a) P2O5 (b) NaH (c) Cr2O7 2– (d) SnBr4 (e) BaO2
150Oxidation of metals by acids and salts Some common types of redox reactions are combustion reactions and reactions between metals and acids or salts.
151Oxidation of metals by acids and salts The common form of an acid reacting with a metal isA + BX → AX + BZn + 2HCl → Zn Br2 + H2
152What do we call these types of reactions and why are they classified as redox reactions? These reactions are called displacement or single replacement reactions. The ion in solution is displaced or replaced through the oxidation of an element.
153Use the reaction between magnesium and hydrochloric acid to show that oxidation and reduction have occurred.Mg(s) + 2HCl → MgCl2(aq) + H2l___oxidized__ll_____reduced_____l
154Write the net ionic equation for the reaction of magnesium and hydrochloric acid. Mg(s)+ 2H+(aq)+ 2Cl- → Mg2+(aq) + 2Cl- + H2(g)Cl- is a spectator ion.Mg(s)+ 2H+(aq) → Mg2+(aq) + H2(g)
155Metals can also be oxidized by aqueous solutions of various salts Metals can also be oxidized by aqueous solutions of various salts. Show the oxidation – reduction that occurs when iron reacts with nickel II nitrate
156Fe(s) + Ni(NO3)3(aq) → Fe(NO3)2(aq) + Ni(s) l______oxidized_____ll___________reduced______lNO3 is the spectator ion.Net ionic equationFe(s) + Ni 2+(aq) → Fe 2+ (aq) + Ni(s)l_____reduced______l
157Sample 4.9Write the balanced molecular and net ionic equations for the reaction of aluminum with hydrobromic acid.
158Write the balanced molecular and net ionic equations for the reaction between magnesium and cobalt(II) sulfate* What is oxidized and what is reduced in the reaction?
159The Activity SeriesDifferent metals vary in the ease with which they are oxidized.
160What is the activity series? The activity series is a list of metals arranged in order of decreasing ease of oxidation. The metals at the top of the table are the most easily oxidized.They react the most easily to form compounds.
161What are active metals?The metals at the top of the activity series are the most easily oxidized metals.
162Which are the noble metals? The metals are the bottom of the activity series. These metals are very stable and can be used to make coins and jewelry.
163How can the activity series be used to predict the outcome of reactions? Any metal on the list can be oxidized by the ions of the an element below it.Cu + HCl → No reactionCopper is not oxidized by hydrogen because hydrogen is not below copperCu + AgNO3 → Ag + Cu(NO3)2Copper is oxidized by silver because silver is below copper on the activity series.
164Sample Exercise 4.10Will an aqueous solution of iron(II) chloride oxidize magnesium metal? If so, write the balanced molecular and net ionic equations for the reaction.
165Which of the following metals will be oxidized by Pb(NO3)2: Zn, Cu, Fe?
181What are stock solutions? The concentrated solutions.
182When solvent is added to dilute a stock solution the number of moles of solute before dilution is equal to the number of moles of solute after dilution.
183To prepare 250mL of a 0.100 M CuSO4 from a stock of 1M CuSO4… 1st determine the number of moles of CuSO4 we will need in the dilute solution.(.250 L) ( .10 mol/ 1L) = mol CuSO4
184To prepare 250mL of a 0.100 M CuSO4 from a stock of 1M CuSO4… Then determine the volume of stock solution neededL conc. Soln.= .025 mol CuSO4 ( 1L/ 1 mole CuSO4)= .025 L of 1 molar CuSO4 = 25 mLAdd 25 mL of 1 molar CuSO4 to a 250 mL volumetric flask and bring up to volume.
185To work the same problem quickly we can note Moles of solute in concentrated soln. = moles of solute in diluted soln. Mconc.Vconc= Mdil.Vdil( 1M) ( Vconc) = (.1M) ( 250 mL)Vconc = 25 mL
186Sample exercise 4.14How many milliliters of 3.0 M H2SO4 are needed to make mL of 0.10 M H2SO4?
187What volume of 2. 50 M lead(II) nitrate solution contains 0 What volume of 2.50 M lead(II) nitrate solution contains mol of Pb 2+ ?
188How many milliliters of 5 How many milliliters of 5.0 M K2Cr2O7 solution must be diluted to prepare 250 mL of 0.10 M solution?
189If 10.0 mL of a 10.0 M stock solution of NaOH is diluted to 250 mL, what is the concentration of the resulting stock solution?
190Solution Stoichiometery and Chemical Analysis Recall that the coefficients in a balanced equation give the relative number of moles of reactants and products.
191Sample exercise 4.15How many grams of Ca(OH)2 are needed to neutralize 25.0 mL of .10M HNO3
192How many grams of NaOH are needed to neutralize 20. 0 mL of 0 How many grams of NaOH are needed to neutralize 20.0 mL of M H2SO4 solution?
193How many liters of M HCl(aq) are needed to react completely with mol of Pb(NO3)2(aq), forming a precipitate of PbCl2(s)?
195What is a titration?A titration involves combining a sample of the solution with a reagent solution of known concentration called the standard solution.
196What is the equivalence point? The point at which stoichiometrically equivalent quantities are brought together.
197How does a chemist know when the equivalence point is reached? An indicator is used. The indicator will show pH changes when the color changes the acid has been nuetralized. The color change indicates the end point of the titration.
198Sample exercise 4.16The quantity of Cl– in a municipal water supply is determined by titrating the sample with Ag+. The reaction taking place during the titration isAg+(aq) + Cl-(aq) → AgCl(s)The end point in this type of titration is marked by a change in color of a special type of indicator. (a) How many grams of chloride ion are in a sample of the water if 20.2 mL of M Ag+ is needed to react with all the chloride in the sample? (b) If the sample has a mass of 10.0 g, what percent Cl– does it contain?
199A sample of an iron ore is dissolved in acid, and the iron is converted to Fe2+. The sample is then titrated with mL of M MnO4– solution. The oxidation-reduction reaction that occurs during titration is as follows:(a) How many moles of MnO4– were added to the solution? (b) How many moles of Fe2+ were in the sample? (c) How many grams of iron were in the sample? (d) If the sample had a mass of g, what is the percentage of iron in the sample?
200One commercial method used to peel potatoes is to soak them in a solution of NaOH for a short time, remove them from the NaOH, and spray off the peel. The concentration of NaOH is normally in the range of 3 to 6 M. The NaOH is analyzed periodically. In one such analysis, 45.7 mL of M H2SO4 is required to neutralize a 20.0-mL sample of NaOH solution. What is the concentration of the NaOH solution?
201What is the molarity of an NaOH solution if 48 What is the molarity of an NaOH solution if 48.0 mL is needed to neutralize 35.0 mL of M H2SO4?
202(b) How many milliliters of 0 (b) How many milliliters of 0.50 M Na2SO4 solution are needed to provide mol of this salt?