Chapter 04. Reactions in Aqueous Solution

Chapter 04 Reactions in Aqueous Solution

Composition Matter Homogeneous mixture Contains One visible distinct phase Uniform properties throughout Two or more substances that are mixed together Substances that have not reacted chemically with each other Can be separated by physical methods Also known as solutions https://upload.wikimedia.org/wikipedia/commons/a/ad/glass_of_milk_on_tablecloth.jpg 2

Solutions Solvent Substance present in greatest abundance Solutes All other substances Aqueous solution When water is the solvent Amount of the solute to dissolve in a solvent called solubility 2011 Pearson Education, Inc. 3

Aqueous Solutions Substances can dissolve in water by different ways: Ionic Compounds dissolve by dissociation Breaking down of a compound into its components Molecular compounds interact with water, but most do NOT dissociate Some molecular substances react with water when they dissolve 2011 Pearson Education, Inc. Cengage Learning. All Rights Reserved 4

Aqueous Solutions Substances can dissolve in water by different ways: Ionic Compounds dissolve by dissociation Breaking down of a compound into its components Molecular compounds interact with water, but most do NOT dissociate Some molecular substances react with water when they dissolve Polar bond 2011 Pearson Education, Inc. Cengage Learning. All Rights Reserved 5

Aqueous Solutions Classification of substances dissolved in water: Electrolyte - a substance that dissociates into ions when dissolved in water Nonelectrolyte - does not dissociate into ions when dissolved in water 2011 Pearson Education, Inc. 6

Electrolytes and Nonelectrolytes Strong bases Strong electrolyte - dissociates completely in water Weak electrolyte - dissociates partially in water Nonelectrolyte - does NOT dissociate in water 2011 Pearson Education, Inc. 7

Electrolytes and Nonelectrolytes Strong electrolyte - dissociates completely in water Weak electrolyte - dissociates partially in water Nonelectrolyte - does NOT dissociate in water 2011 Pearson Education, Inc. 8

Electrolytes Ion concentration determines the amount of electricity conducted 2011 Pearson Education, Inc. Cengage Learning. All Rights Reserved 9

How do you determine if an ionic compound will dissolve in water? 10

Solubility of Ionic Compounds Not all ionic compounds dissolve in water Solubility rules help you decide what combination of ions will dissolve 2011 Pearson Education, Inc. 11

Types of Chemical Reactions 1. Exchange Reactions 12

Exchange Reactions Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means to transpose Ions in the reactant compounds exchange, or transpose, ions, as seen in the equation below AgNO 3 (aq) + KCl(aq) AgCl(s) + KNO 3 (aq) 13

Types of Chemical Reactions 1. Exchange Reactions 2. Precipitation Reactions Occurs when an insoluble ionic solid, precipitate, is produced 14

Precipitation Reactions 1. Mix two solutions containing soluble salts 2. A salt falls out of solution, like snow out of the sky 3. Precipitate is produced 2011 Pearson Education, Inc. 15

Steps in Completing and Balancing Precipitation Reactions 1) Determine which ions are present from the reactant s chemical formula CoCl 2 (aq) and NaOH(aq) 2) Write formulas for the products: Cation from one reactant, anion from the other Use charges to write proper subscripts CoCl 2 (aq) + NaOH(aq) Co(OH) 2 + NaCl 3) Classify state of the products CoCl 2 (aq) + NaOH(aq) Co(OH) 2 (s) + NaCl(aq) 4) Balance the equation CoCl 2 (aq) + 2NaOH(aq) Co(OH) 2 (s) + 2NaCl(aq) 16

EXAMPLE WRITING EQUATIONS FOR PRECIPITATION REACTIONS Write an equation for the precipitation reaction that occurs (if any) when solutions of sodium carbonate and copper(ii) chloride are mixed? 1. Write the formulas of the two compounds being mixed as reactants in a chemical equation. 2. Below the equation, write the formulas of the potentially insoluble products that could form from the reactants. Obtain these by combining the cation from one reactant with the anion from the other. Make sure to write correct (charge-neutral) formulas for these ionic compounds. SOLUTION Na 2 CO 3 (aq) + CuCl 2 (aq) Potentially Insoluble Products NaCl CuCO 3 17

EXAMPLE WRITING EQUATIONS FOR PRECIPITATION REACTIONS Continued 3. Use the solubility rules to determine whether any of the potential new products are indeed insoluble. NaCl is soluble (compounds containing Cl are usually soluble, and Na + is not an exception). CuCO 3 is insoluble (compounds containing CO 3 2 are usually insoluble, and Cu 2+ is not an exception). 4. If all of the potentially insoluble products are soluble, there will be no precipitate. Write NO REACTION next to the arrow. Because this example has an insoluble product, you proceed to the next step. 18

EXAMPLE WRITING EQUATIONS FOR PRECIPITATION REACTIONS Continued 5. If one or both of the potentially insoluble products are insoluble, write their formula(s) as the product(s) of the reaction, using (s) to indicate solid. Follow any soluble products with (aq) to indicate aqueous. 6. Balance the equation. Remember to adjust only coefficients, not subscripts. SKILLBUILDER Na 2 CO 3 (aq) + CuCl 2 (aq) CuCO 3 (s) + NaCl(aq) Na 2 CO 3 (aq) + CuCl 2 (aq) CuCO 3 (s) + 2 NaCl(aq) Write an equation for the precipitation reaction that occurs (if any) when solutions of potassium hydroxide and nickel(ii) bromide are mixed. Answer: 19

Ways to Write Precipitation Reactions 1) Formula (or Molecular) equation Lists the reactants and products without indicating the ionic nature of the compounds AgNO 3 (aq) + KCl(aq) AgCl(s) + KNO 3 (aq) 20

Ways to Write Precipitation Reactions 1) Formula (or Molecular) equation 2) Complete ionic equation Reflects the species that are found in the reaction mixture All strong electrolytes are dissociated into their ions (i.e. strong acids, strong bases) Ag + (aq) + NO 3 (aq) + K + (aq) + Cl (aq) AgCl(s) + K + (aq) + NO 3 (aq) 21

Ways to Write Precipitation Reactions 1) Formula (or Molecular) equation 2) Complete ionic equation 3) Net ionic equation Cross out anything in the complete ionic equation that appears the same on both sides of the equation Crossed out ions are called spectator ions Remaining ions are the reactants that form the product Ag + (aq) + NO 3 (aq) + K + (aq) + Cl (aq) AgCl(s) + K + (aq) + NO 3 (aq) 22

Writing Net Ionic Equations 1. Write a balanced molecular equation AgNO 3 (aq) + KCl(aq) AgCl(s) + KNO 3 (aq) 2. Dissociate all strong electrolytes (complete ionic equation) Ag + (aq) + NO 3 (aq) + K + (aq) + Cl (aq) AgCl(s) + K + (aq) + NO 3 (aq) 3. Cross out anything that remains unchanged from the left side to the right side of the equation Ag + (aq) + NO 3 (aq) + K + (aq) + Cl (aq) AgCl(s) + K + (aq) + NO 3 (aq) 4. Write the net ionic equation with the species that remain Ag + (aq) + Cl (aq) AgCl(s) 23

EXAMPLE WRITING COMPLETE IONIC AND NET IONIC EQUATIONS Consider this precipitation reaction occurring in aqueous solution. Pb(NO 3 ) 2 (aq) + 2 LiCl(aq) PbCl 2 (s) + 2 LiNO 3 (aq) Write a complete ionic equation and a net ionic equation for the reaction. Write the complete ionic equation by separating aqueous ionic compounds into their constituent ions. The PbCl 2 (s) remains as one unit. SOLUTION Complete ionic equation Pb 2+ (aq) + 2 NO 3 (aq) + 2 Li + (aq) + 2 Cl (aq) PbCl 2 (s) + 2 Li + (aq) + 2 NO 3 (aq) Write the net ionic equation by eliminating the spectator ions, those that do not change during the reaction. Net ionic equation Pb 2+ (aq) + 2 Cl (aq) PbCl 2 (s) 24

EXAMPLE WRITING COMPLETE IONIC AND NET IONIC EQUATIONS SKILLBUILDER Writing Complete Ionic and Net Ionic Equations Consider this reaction occurring in aqueous solution. 2 HBr(aq) + Ca(OH) 2 (aq) 2 H 2 O(l) + CaBr 2 (aq) Write a complete ionic equation and a net ionic equation for the reaction. Answers: Complete ionic equation: Net ionic equation: 25

Types of Chemical Reactions 1. Exchange Reactions 2. Precipitation Reactions 3. Acid Base Reactions Reaction that produces hydrogen ions during a chemical reaction Brønsted -Lowry acid donates protons (H + ) Brønsted -Lowry base accepts protons (H + ) 26

Acid Base: Strong or Weak? Acid Strong acids completely dissociate in water Weak acids only partially dissociate Base Strong bases dissociate to metal cations and hydroxide anions in water Weak bases only partially react to produce hydroxide anions 27

Acid-Base Reactions Acid-Base Reactions Called neutralization reactions A proton is donated to the base When the base is a metal hydroxide the products are water and a salt (an ionic compound) 2011 Pearson Education, Inc. 28

Acid-Base Reactions Molecular equation HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l) Ionic equation H + (aq) + Cl (aq) + Na + (aq) + OH (aq) Na + (aq) + Cl (aq) + H 2 O(l) Net ionic equation H + (aq) + OH (aq) H 2 O(l) 29

EXAMPLE WRITING EQUATIONS FOR ACID BASE REACTIONS Write a molecular and a net ionic equation for the reaction between aqueous HNO 3 and aqueous Ca(OH) 2. You must recognize these substances as an acid and a base. Write the skeletal reaction following the general pattern of acid plus base goes to water plus salt. SOLUTION Next, balance the equation. Write the net ionic equation by eliminating those ions that remain the same on both sides of the equation 2 HNO 3 (aq) + Ca(OH) 2 (aq) 2 H 2 O(l) + Ca(NO 3 ) 2 (aq) 2 H + (aq) + 2 OH (aq) 2 H 2 O(l) or simply H + (aq) + OH (aq) H 2 O(l) 30

EXAMPLE WRITING EQUATIONS FOR ACID BASE REACTIONS continued SKILLBUILDER Writing Equations for Acid Base Reactions Write a molecular and a net ionic equation for the reaction that occurs between aqueous H 2 SO 4 and aqueous KOH. Answers: Molecular equation: Net ionic equation: 31

Types of Chemical Reactions 1. Exchange Reactions 2. Precipitation Reactions 3. Acid Base Reactions 4. Gas-Forming Reactions Produces a product in the gas phase Na 2 S(aq) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + H 2 S(g) 32

Gas-Forming Reactions If a metathesis reaction results in the products carbonic acid (H 2 CO 3 ), sulfurous acid (H 2 SO 3 ), or hydrogen sulfide (H 2 S), a gas will be formed H 2 CO 3 decompose to form gases H 2 CO 3 (aq) ---> H 2 O (l) + CO 2 (g) H 2 SO 3 decompose to form gases H 2 SO 3 (aq) ---> H 2 O (l) + SO 2 (g) H 2 S is a gas Remember to look for the three products listed above when predicting the products of metathesis reactions 33

Gas-Forming Reactions Carbonate (CO 3 2- ) or bicarbonate (HCO 3- ) reacts with an acid to produce a salt, carbon dioxide, and water CaCO 3 (s) + 2 HCl(aq) CaCl 2 (aq) + CO 2 (g) + H 2 O(l) NaHCO 3 (aq) + Hr(aq) NaBr(aq) + CO 2 (g) + H 2 O(l) 34

EXAMPLE WRITING EQUATIONS FOR GAS EVOLUTION REACTIONS Write a molecular equation for the gas evolution reaction that occurs when you mix aqueous nitric acid and aqueous sodium carbonate. Begin by writing a skeletal equation that includes the reactants and products that form when the cation of each reactant combines with the anion of the other. SOLUTION You must recognize that H 2 CO 3 (aq) decomposes into H 2 O(l) and CO 2 (g) and write the corresponding equation. Finally, balance the equation. HNO 3 (aq) + Na 2 CO 3 (aq) H 2 O(l) + CO 2 (g) + NaNO 3 (aq) 2 HNO 3 (aq) + Na 2 CO 3 (aq) H 2 O(l) + CO 2 (g) + 2 NaNO 3 (aq) 35

EXAMPLE WRITING EQUATIONS FOR GAS EVOLUTION REACTIONS continued SKILLBUILDER Writing Equations for Gas Evolution Reactions Write a molecular equation for the gas evolution reaction that occurs when you mix aqueous hydrobromic acid and aqueous potassium sulfite. Answer: SKILLBUILDER PLUS Write a net ionic equation for the previous reaction. Answer: 36

Types of Chemical Reactions 1. Exchange Reactions 2. Precipitation Reactions 3. Acid Base Reactions 4. Gas-Forming Reactions 5. Oxidation Reduction Reactions Involves a transfer of electrons between two species 37

Oxidation-Reduction Reactions Redox reactions Loss of electrons is oxidation Gain of electrons is reduction One cannot occur without the other 2011 Pearson Education, Inc. 38

Oxidation-Reduction Reactions Oxidation State Number of electrons that an atom can gain, lose, or share when forming a bond Assigned to each element in a neutral compound or charged entity 39

Rules to Assign Oxidation Numbers 1. Elements in their elemental form have an oxidation number of zero 2. The oxidation number of a monatomic ion is the same as its charge 3. The sum of the oxidation numbers in a neutral compound is zero 4. The sum of the oxidation numbers in a polyatomic ion is the charge on the ion 40

Rules to Assign Oxidation Numbers 5. Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. Oxygen has an oxidation number of 2, except in the peroxide ion, in which it has an oxidation number of 1 Hydrogen is 1 when bonded to a metal, +1 when bonded to a nonmetal Fluorine always has an oxidation number of 1 The other halogens have an oxidation number of 1 when they are negative; they can have positive oxidation numbers, most notably in oxyanions 41

EXAMPLE ASSIGNING OXIDATION STATES Assign an oxidation state to each atom in each species. (a) Br 2 (b) K + (c) LiF (d) CO 2 (e) SO 4 2 Since Br 2 is a free element, the oxidation state of both Br atoms is 0. Since K + is a monoatomic ion, the oxidation state of the K + ion is +1. The oxidation state of Li is +1. The oxidation state of F is 1. Since this is a neutral compound, the sum of the oxidation states is 0. SOLUTION (a) Br 2 Br Br 0 0 (b) K + K + +1 (c)lif Li F +1 1 sum: +1 1 = 0 42

EXAMPLE ASSIGNING OXIDATION STATES continue The oxidation state of oxygen is 2. You deduce the oxidation state of carbon from the rule which states that the sum of the oxidation states of all the atoms must be 0. Since there are two oxygen atoms, you multiply the oxidation state of O by 2 when calculating the sum. The oxidation state of oxygen is 2. The oxidation state of S is expected to be 2. However, if that were the case, the sum of the oxidation states would not equal the charge of the ion. Since O is higher on the list, it takes priority, and you calculate the oxidation state of sulfur by setting the sum of all of the oxidation states equal to 2 (the charge of the ion). (d) CO 2 (C ox state) + 2(O ox state) = 0 (C ox state) + 2( 2) = 0 (C ox state) 4 = 0 C ox state = + 4 C O 2 +4 2 sum: +4 + 2( 2) = 0 (e)so 4 2 (S ox state) + 4(O ox state) = 2 (S ox state) + 4( 2) = 2 (S ox state) 8 = 2 S ox state = 2 + 8 S ox state = +6 S O 4 2 +6 2 sum: +6 + 4( 2) = 2 43

Oxidation-Reduction Reactions In displacement reactions, ions oxidize an element In this reaction, silver ions oxidize copper metal: Molecular equation: Net ionic equation: 2 Ag + (aq) + Cu(s) Cu 2+ (aq) + 2 Ag(s) 2011 Pearson Education, Inc. The reverse reaction does NOT occur. Why not? 44

Activity Series The reverse reaction does NOT occur. Why not? 2 Ag + (aq) + Cu(s) Cu 2+ (aq) + 2 Ag(s) Activity Series List of metals in order of decreasing ease of oxidation Elements higher on the activity series are more reactive More likely to exist as ions Used to predict which metals will displace other metals in aqueous solutions 2011 Pearson Education, Inc. 45

Activity Series Activity Series Elements above hydrogen will react with acids to produce hydrogen gas The metal is oxidized to a cation 2011 Pearson Education, Inc. 46

EXAMPLE IDENTIFYING REDOX REACTIONS Which of these are redox reactions? (a) 2 Mg(s) + O 2 (g) 2 MgO(s) (b) 2 HBr(aq) + Ca(OH) 2 (aq) 2 H 2 O(l) + CaBr 2 (aq) (c) Ca(s) + Cl 2 (g) CaCl 2 (s) (d) Zn(s) + Fe 2+ (aq) Zn 2+ (aq) + Fe(s) SOLUTION (a) Redox reaction; Mg reacts with elemental oxygen. (b) Not a redox reaction; it is an acid base reaction. (c) Redox reaction; a metal reacts with a nonmetal. (d) Redox reaction; Zn transfers two electrons to Fe 2+. 47

EXAMPLE IDENTIFYING REDOX REACTIONS continued SKILLBUILDER Identifying Redox Reactions Which of these are redox reactions? (a) 2 Li(s) + Cl 2 (g) 2 LiCl(s) (b) 2 Al(s) + 3 Sn 2+ (aq) 2 Al 3+ (aq) + 3 Sn(s) (c) Pb(NO 3 ) 2 (aq) + 2 LiCl(aq) PbCl 2 (s) + 2 LiNO 3 (aq) (d) C(s) + O 2 (g) CO 2 (g) Answers: 48

The quantity of solute in a solution can matter to a chemist CONCENTRATIONS OF SOLUTIONS 49

Concentration Terms Concentration Amount of solute dissolved in a given quantity of solvent or quantity of solution Molarity is one way to measure the concentration of a solution: Molarity (M) = moles of solute volume of solution in liters 50

Making a Solution of a Known Molarity 1. Weigh out a known mass (and, therefore, number of moles) of the solute 2. Add solute to a volumetric flask 3. Add solvent to the line on the neck of the flask moles 0.250 mol mol M 1.00 1. 00 Liter.250 L L M 2011 Pearson Education, Inc. 51

EXAMPLE CALCULATING MOLARITY Calculate the molarity of a solution made by putting 15.5 g NaCl into a beaker and adding water to make 1.50 L of NaCl solution. You are given the mass of sodium chloride (the solute) and the volume of solution. You are asked to find the molarity of the solution. GIVEN: 15.5 g NaCl 1.50 L solution FIND: molarity (M) To calculate molarity, substitute the correct values into the equation and calculate the answer. You must first convert the amount of NaCl from grams to moles using the molar mass of NaCl. SOLUTION 52

EXAMPLE CALCULATING MOLARITY SKILLBUILDER Calculating Molarity Calculate the molarity of a solution made by putting 55.8 g of NaNO 3 into a beaker and diluting to 2.50 L. Answer: 53

EXAMPLE USING MOLARITY IN CALCULATIONS How many liters of a 0.114 M NaOH solution contains 1.24 mol of NaOH? SORT You are given the molarity of an NaOH solution and the number of moles of NaOH. You are asked to find the volume of solution that contains the given number of moles. GIVEN: 0.114 M NaOH 1.24 mol NaOH FIND: L solution SOLUTION MAP STRATEGIZE The solution map begins with mol NaOH and shows the conversion to liters of solution using the molarity as a conversion factor. RELATIONSHIPS USED SOLUTION SOLVE Solve the problem by following the solution map. 54

EXAMPLE USING MOLARITY IN CALCULATIONS Continued SKILLBUILDER Using Molarity in Calculations How much of a 0.225 M KCl solution contains 55.8 g of KCl? Answer: 55

EXAMPLE CALCULATING ION CONCENTRATION Determine the molar concentrations of Na + and PO 4 3 in a 1.50 M Na 3 PO 4 solution. You are given the concentration of an ionic solution and asked to find the concentrations of the component ions. A formula unit of Na 3 PO 4 contains 3 Na + ions (as indicated by the subscript), so the concentration of Na + is three times the concentration of Na 3 PO 4. Since the same formula unit contains one PO 4 3 ion, the concentration of PO 4 3 is equal to the concentration of Na 3 PO 4. GIVEN: 1.50 M Na 3 PO 4 FIND: molarity (M) of Na + and PO 3 4 SOLUTION molarity of Na + = 3(1.50 M) = 4.50 M molarity of PO 3 4 = 1.50 M 56

EXAMPLE CALCULATING ION CONCENTRATION SKILLBUILDER Ion Concentration Determine the molar concentrations of Ca 2+ and Cl in a 0.75 M CaCl 2 solution. Answer: 57

Diluting a Solution of Known Molarity Calculate new molarity using: M c V c = M d V d M molarity V volume c concentrated d dilute V M d V M 0.100 M 250 ml 1.00 M d c 25. 0 c 2011 Pearson Education, Inc. ml 58

EXAMPLE SOLUTION DILUTION To what volume should you dilute 0.100 L of a 15 M NaOH solution to obtain a 1.0 M NaOH solution? You are given the initial volume and concentration of an NaOH solution and a final concentration. You are asked to find the volume required to dilute the initial solution to the given final concentration. Solve the solution dilution equation for V 2 (the volume of the final solution) and substitute the required quantities to calculate V 2. You can make the solution by diluting 0.100 L of the stock solution to a total volume of 1.5 L (V 2 ). The resulting solution has a concentration of 1.0 M. GIVEN: FIND: V 2 SOLUTION V 1 = 0.100 L M 1 = 15 M M 2 = 1.0 M 59

EXAMPLE SOLUTION DILUTION SKILLBUILDER Solution Dilution How much 6.0 M NaNO 3 solution should you use to make 0.585 L of a 1.2 M NaNO 3 solution? Answer: 60

Molarities: Stoichiometric Calculations 2011 Pearson Education, Inc. 61

TITRATION 62

Titration Titration An analytical technique Used to calculate the concentration of a solute in a solution Indicator: A substance that changes color depending on the amount of acid present 2011 Pearson Education, Inc. 63

Titration Titration An analytical technique Equivalence point: amount of titrant added is enough to completely neutralize the analyte solution Endpoint: point at which an indicator changes color and a titration is stopped 2011 Pearson Education, Inc. 64

EXAMPLE The titration of 10.00 ml of an HCl solution of unknown concentration requires 12.54 ml of a 0.100 M NaOH solution to reach the equivalence point. What is the concentration of the unknown HCl solution? SORT You are given the volume of an unknown HCl solution and the volume of a known NaOH solution required to titrate the unknown solution. You are asked to find the concentration of the unknown solution. ACID BASE TITRATION GIVEN: 10.00 ml HCl solution 12.54 ml of a 0.100 M NaOH solution FIND: concentration of HCl solution (mol/l) 65

EXAMPLE continued ACID BASE TITRATION STRATEGIZE First write the balanced chemical equation for the reaction between the acid and the base. The solution map has two parts. In the first part, use the volume of NaOH required to reach the equivalence point to calculate the number of moles of HCl in the solution. The final conversion factor comes from the balanced neutralization equation. In the second part, use the number of moles of HCl and the volume of HCl solution to determine the molarity of the HCl solution. SOLUTION MAP HCl(aq) + NaOH(aq) H 2 O(l ) + NaCl(aq) RELATIONSHIPS USED 1 mol HCl : 1 mol NaOH (from balancedchemical equation) 66

EXAMPLE ACID BASE TITRATION Continued SOLVE Calculate the moles of HCl in the unknown solution by following the first part of the solution map. To find the concentration of the solution, divide the number of moles of HCl by the volume of the HCl solution in L. (Note that 10.00 ml is equivalent to 0.01000 L.) The unknown HCl solution therefore has a concentration of 0.125 M. SOLUTION 67

EXAMPLE ACID BASE TITRATION Continued SKILLBUILDER Acid Base Titration The titration of a 20.0-mL sample of an H 2 SO 4 solution of unknown concentration requires 22.87 ml of a 0.158 M KOH solution to reach the equivalence point. What is the concentration of the unknown H 2 SO 4 solution? Answer: 68

69

EXAMPLE WRITING EQUATIONS FOR NEUTRALIZATION REACTIONS Write a molecular equation for the reaction between aqueous HCl and aqueous Ca(OH) 2. SOLUTION First identify the acid and the base and write the skeletal reaction showing the production of water and the salt. The formulas for the ionic compounds in the equation must be charge neutral. Balance the equation. Notice that Ca(OH) 2 contains 2 mol of OH for every 1 mol of Ca(OH) 2 and therefore requires 2 mol of H+ to neutralize it. 70

EXAMPLE WRITING EQUATIONS FOR NEUTRALIZATION REACTIONS continued SKILLBUILDER Writing Equations for Neutralization Reactions Write a molecular equation for the reaction that occurs between aqueous H 3 PO 4 and aqueous NaOH. Hint: H 3 PO 4 is a triprotic acid, meaning that 1 mol of H 3 PO 4 requires 3 mol of OH to completely react with it. Answer: 71

EXAMPLE WRITING EQUATIONS FOR PRECIPITATION REACTIONS Write an equation for the precipitation reaction that occurs (if any) when solutions of lithium nitrate and sodium sulfate are mixed? 1. Write the formulas of the two compounds being mixed as reactants in a chemical equation. SOLUTION 2. Below the equation, write the formulas of the potentially insoluble products that could form from the reactants. Obtain these by combining the cation from one reactant with the anion from the other. Make sure to write correct (charge-neutral) formulas for these ionic compounds. Potentially Insoluble Products 72

EXAMPLE WRITING EQUATIONS FOR PRECIPITATION REACTIONS Continued 3. Use the solubility rules to determine whether any of the potential new products are indeed insoluble. 4. If all of the potentially insoluble products are soluble, there will be no precipitate. Write NO REACTION next to the arrow. 73

EXAMPLE WRITING EQUATIONS FOR PRECIPITATION REACTIONS Continued SKILLBUILDER Write an equation for the precipitation reaction that occurs (if any) when solutions of ammonium chloride and iron(iii) nitrate are mixed. Answer: 74

EXAMPLE PREDICTING AND WRITING EQUATIONS FOR PRECIPITATION REACTIONS Write an equation for the precipitation reaction (if any) that occurs when solutions of lead(ii) acetate and sodium sulfate are mixed. If no reaction occurs, write NO REACTION. 1. Write the formulas of the two compounds being mixed as reactants in a chemical equation. 2. Below the equation, write the formulas of the potentially insoluble products that could form from the reactants. Determine these by combining the cation from one reactant with the anion from the other. Make sure to adjust the subscripts so that all formulas are charge-neutral. SOLUTION Potentially Insoluble Products 75

EXAMPLE PREDICTING AND WRITING EQUATIONS FOR PRECIPITATION REACTIONS continued 3. Use the solubility rules to determine whether any of the potentially insoluble products are indeed insoluble. 4. If all of the potentially insoluble products are soluble, there will be no precipitate. Write NO REACTION next to the arrow. 5. If one or both of the potentially insoluble products are indeed insoluble, write their formula(s) as the product(s) of the reaction, using (s) to indicate solid. Follow any soluble products with (aq) to indicate aqueous. 76

EXAMPLE PREDICTING AND WRITING EQUATIONS FOR PRECIPITATION REACTIONS Continued 6. Balance the equation. SKILLBUILDER Predicting and Writing Equations for Precipitation Reactions Write an equation for the precipitation reaction (if any) that occurs when solutions of potassium sulfate and strontium nitrate are mixed. If no reaction occurs, write NO REACTION. Answer: 77

What dissolved species are present in a solution of KCN? a. H 2 O(l) b. K + (aq) and H 2 O(l) c. CN (aq) d. K + (aq) and CN (aq) 78

What dissolved species are present in a solution of NaClO 4? a. H 2 O(l) b. Na + (aq) and H 2 O(l) c. ClO 4 (aq) d. Na + (aq) and ClO 4 (aq) 79

Which solute will cause a light bulb in solution to glow most brightly, CH 3 OH, NaOH, or CH 3 COOH? a. CH 3 OH(aq) b. NaOH(aq) c. CH 3 COOH(aq) d. Cannot determine 80

Which ions, if any, are spectator ions in this reaction? AgNO 3 (aq) + NaCl(aq) AgCl(s) + NaNO 3 (aq) a. Ag + (aq) and Cl (aq) b. NO 3 (aq) and Cl (aq) c. Na + (aq) and NO 3 (aq) d. No spectator ions are involved. 81

Why isn t Al(OH) 3 classified as a strong base? a. Al(OH) 3 is not basic in water. b. Al(OH) 3 is insoluble in water. c. Al(OH) 3 is a strong acid in water, not basic. d. Al(OH) 3 is a weak acid in water, not basic. 82

By analogy to examples given in the text, predict what gas forms when Na 2 SO 3 (s) reacts with HCl(aq). a. SO 2 (g) b. H 2 (g) c. CO 2 (g) d. H 2 S(g) 83

What is the oxidation number of nitrogen in aluminum nitride, AlN? a. +1 b. 1 c. 2 d. 3 84

What is the oxidation number of nitrogen in nitric acid, HNO 3? a. +6 b. +5 c. +4 d. 1 85

Does a reaction occur when an aqueous solution of NiCl 2 (aq) is added to a test tube containing strips of metallic zinc? a. Yes b. No 86

Does a reaction occur when NiCl 2 (aq) is added to a test tube containing Zn(NO 3 ) 2 (aq)? a. Yes b. No 87

Which is more concentrated, a solution prepared by dissolving 21.0 g of NaF (0.500 mol) in enough water to make 500 ml of solution or a solution prepared by dissolving 10.5 g (0.250 mol) of NaF in enough water to make 100 ml of solution? a. 21.0 g of NaF dissolved in water to make 500 ml of solution b. 10.5 g of NaF dissolved in water to make 100 ml of solution 88

How is the molarity of a 0.50 M KBr solution changed when water is added to double its volume? a. The concentration (molarity) remains the same. b. The new concentration is 0.25 M. c. The new concentration is 1.00 M. d. The new concentration is 2.50 M. 89

A homogeneous mixture of two or more components is referred to as a. a solute. b. a solution. c. an electrolyte. d. a mess.

The solvent in a sample of soda pop is a. sugar. b. carbon dioxide. c. water. d. air.

The gaseous solute in a sample of soda pop is a. sugar. b. carbon dioxide. c. water. d. air.

Gatorade and other sports drinks conduct electricity because they contain a. water. b. sugar. c. air. d. electrolytes.

When Fe(NO 3 ) 2 dissolves in water, the particles in solution are a. Fe + and (NO 3 ) 2. b. Fe 2+ and 2 NO 3. c. Fe and 2 NO 3. d. Fe and N 2 and 3 O 2.

Which set includes only substances that produce electrolytes in water? a. NaBr, KCl, MgSO 4 b. C 6 H 12 O 6, CH 3 OH, C 6 H 6 c. HCl, NH 3, Cl 2, N 2 d. SiO 2, CaCO 3, H 2 SO 4

Which compound below is not soluble in water? a. NaBr b. KNO 3 c. MgSO 4 d. ZnS

Pb(NO 3 ) 2 + 2 KI PbI 2 + 2 KNO 3 The physical evidence that the above reaction occurs is a. an explosion. b. the formation of a gas. c. that the solution boils. d. the formation of a precipitate.

Which pair of compounds will produce a precipitate if solutions of appropriate concentrations are mixed together? a. H 2 SO 4 and NaOH b. HNO 3 and CaCl 2 c. Ba(NO 3 ) 2 and Na 3 PO 4 d. LiCl and SrI 2

When an acid reacts with a base, the result is a. cancellation. b. elimination. c. neutralization. d. adduct formation.

When nitric acid is neutralized by potassium hydroxide, the spectator ions are a. K + and NO 3. b. H + and OH. c. H + and NO 3. d. K + and OH.

Which compound below is not a strong acid? a. HC 2 H 3 O 2 b. H 2 SO 4 c. HNO 3 d. HBr

When an atom undergoes oxidation, it electrons. a. gains b. loses c. retains d. balances

When an atom undergoes reduction, it electrons. a. gains b. loses c. retains d. balances

When Zn(s) reacts with HCl(aq) to produce H 2 (g) and ZnCl 2 (aq), the zinc is because it electrons. a. reduced; gains b. reduced; loses c. oxidized; gains d. oxidized; loses

Al + H + Al 3+ + H 2 When the oxidation reduction reaction above is correctly balanced, the coefficients are a. 1, 2 1, 1. b. 1, 3 1, 2. c. 2, 3 2, 3. d. 2, 6 2, 3.

A solution is prepared by dissolving 35.0 g of NaCl in water to make 500 ml of solution. What is the molarity? a. 7.00 M b. 3.04 M c. 1.97 M d. 1.20 M

250.0 ml of 0.100 M AgNO 3 solution contains g of silver nitrate. a. 4.25 b. 8.50 c. 17.0 d. 34.0

To make 250.0 ml of 0.500 M KI solution, ml of 6.00 M KI must be used. a. 20.8 b. 41.7 c. 500.0 d. 3000.0