Chapter 11 Matter and Change 11.1 Describing Chemical Reactions

Chapter 11 Matter and Change 11.1 Describing Chemical Reactions
11.2 Types of Chemical Reactions 11.3 Reactions in Aqueous Solution

11-1 The Nature of Chemical Reactions
A chemical reaction is a process in which one or more substances is converted into new substances with different chemical and physical properties. The substance or substances entering the reaction are called reactants. The substance or substances made in the reaction are products. Atoms and compounds undergo reactions to become more stable by obtaining a more stable electron configuration

Ca(H2PO4)2 + CaSO4 + HF  Ca10F2(PO4)6 + H2SO4
11-1 Chemical Equations Chemical equations give information in two major areas. First, they tell us what substances are reacting (those being used up) and what substances are products (those being made). Second, the coefficients of a balanced equation tell us in what ratio the substances react or are produced. Word equations just give the names of reactants and products Formula equations contain the chemical symbols and formulas The reactants are on the left side of a chemical equation and the products are on the right side. However, you might ask, "On the left and right side of what?“ Answer - the arrow. 2 H2 + O2  2 H2O Be aware that there can be one, two, three, or more substances on either side of the arrow, as in this more complex equation: Ca(H2PO4)2 + CaSO4 + HF  Ca10F2(PO4)6 + H2SO4 Typically the arrow is replaced with "produces" or "yields" when the equation is said out loud.

Iron + oxygen → iron(III) oxide
Introduction to Chemical Equations Word Equations In a word equation, write the names of the reactants to the left of the arrow, separated by plus signs. Write the names of the products to the right of the arrow, also separated by plus signs. Notice that no plus sign is needed on the product side of the equation on the previous slide because iron(III) oxide is the only product. Iron + oxygen → iron(III) oxide

Hydrogen peroxide → water + oxygen
Introduction to Chemical Equations Word Equations The production of a new substance, a gas, is evidence of a chemical change. Two new substances are produced in this reaction, oxygen gas and liquid water. You could describe this reaction by saying “hydrogen peroxide decomposes to form water and oxygen gas.” Hydrogen peroxide → water + oxygen

The burning of methane is a chemical reaction.
Introduction to Chemical Equations Word Equations The burning of methane is a chemical reaction. Burning a substance typically requires oxygen, so methane and oxygen are the reactants. The products are water and carbon dioxide. Methane + oxygen → carbon dioxide + water

Introduction to Chemical Equations
A chemical equation is a representation of a chemical reaction; the formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right). Here is a chemical equation for rusting: Fe + O2 → Fe2O3

Equations that show just the formulas of the reactants and products are called skeleton equations. A skeleton equation is a chemical equation that does not indicate the relative amounts of the reactants and products. The first step in writing a complete chemical equation is to write the skeleton equation. Fe + O2 → Fe2O3

To write a skeleton equation, write the chemical formulas for the reactants to the left of the yields sign (arrow) and the formulas for the products to the right. Fe + O2 → Fe2O3

To add more information to the equation, you can indicate the physical states of substances by putting a symbol after each formula. Use (s) for a solid, (l) for a liquid, (g) for a gas, and (aq) for a substance in an aqueous solution (a substance dissolved in water). Fe(s) + O2(g) → Fe2O3(s)

In many chemical reactions, a catalyst is added to the reaction mixture. A catalyst is a substance that speeds up the reaction but is not used up in the reaction. A catalyst is neither a reactant nor a product, so its formula is written above the arrow in a chemical equation. H2O2(aq) H2O(l) + O2(g) MnO2

Symbols Used in Chemical Equations
Interpret Data Symbols Used in Chemical Equations Symbol Explanation + Separates two reactants or two products → “Yields,” separates reactants from products Use in place of → for reversible reactions (s), (l), (g) Designates a reactant or product in the solid state, liquid state, or gaseous state; placed after the formula (aq) Designates an aqueous solution; the substance is dissolved in water; placed after the formula Indicates that heat is supplied to the reaction A formula written above or below the yields sign indicates its use as a catalyst (in this example, platinum). Δ heat Pt

Balancing Chemical Equations
To write a balanced chemical equation, first write the skeleton equation. Then use coefficients to balance the equation so that it obeys the law of conservation of mass. In every balanced equation, each side of the equation has the same number of atoms of each element.

Carbon burns in the presence of oxygen to produce carbon dioxide.
Balancing Chemical Equations Carbon burns in the presence of oxygen to produce carbon dioxide. C(s) Carbon + O2(g) Oxygen CO2(g) Carbon dioxide Reactants 1 carbon atom, 2 oxygen atoms Product 1 carbon atom, 2 oxygen atoms This equation is balanced. You do not need to change the coefficients. They are all understood to be 1.

When hydrogen and oxygen are mixed, the product is water.
Balancing Chemical Equations When hydrogen and oxygen are mixed, the product is water. The formulas for all the reactants and the product are correct, but this equation is not balanced. As written, the equation does not obey the law of conservation of mass.

Balancing Chemical Equations When hydrogen and oxygen are mixed, the product is water. If you put the coefficient 2 in front of H2O, oxygen will be balanced. Now twice as many hydrogen atoms are in the product as are in the reactants.

Balancing Chemical Equations When hydrogen and oxygen are mixed, the product is water. To correct this equation, put the coefficient 2 in front of H2. The equation is now balanced.

Balancing Equations Coefficients are the numbers in front of the formulas. 2 H2 + O2  2 H2O Note the presence of a two in front of the hydrogen and also the water. These are called the coefficients. These numbers give two very important pieces of information about the equation. You must understand both in order to read and to use chemical equations successfully. First: the coefficients give the number of molecules (or atoms) involved in the reaction. In the example reaction, two molecules of hydrogen react with one molecule of oxygen and produce two molecules of water. Second: the coefficients give the number of moles of each substance involved in the reaction. In the example reaction, two moles of hydrogen react with one mole of oxygen and produce two moles of water.

Balancing Equations cont…
For mass to be conserved the number of atoms of each element on the reactant side must equal the number of atoms of each element on the product side What goes in must come out! Chemical equations do not come already balanced. This must be done before the equation can be used in a chemically meaningful way.

H2 + O2  H2O It is an unbalanced equation (sometimes also called a skeleton equation). This means that there are UNEQUAL numbers at least one atom on each side of the arrow. In the example equation, there are two atoms of hydrogen on each side, BUT there are two atoms of oxygen on the left side and only one on the right side. Remember this: A balanced equation MUST have EQUAL numbers of EACH type of atom on BOTH sides of the arrow. An equation is balanced by changing coefficients in a somewhat trial-and-error fashion. It is important to note that only the coefficients can be changed, NEVER change a subscript. The coefficient times the subscript gives the total number of atoms.

Two things you CANNOT do when balancing an equation. 1) You cannot change a subscript. You cannot change the oxygen's subscript in water from one to two, as in: H2 + O2  H2O2 True, this balances the equation, but you have changed the substances in it. H2O2 is a completely different substance from H2O. 2) You cannot place a coefficient in the middle of a formula. The coefficient goes at the beginning of a formula, not in the middle, as in: H2 + O2  H22O Water only comes as H2O and you can only use whole formula units of it. There is another thing you should avoid. Make sure that your final set of coefficients are all whole numbers with no common factors other than one. For example, this equation is balanced: 4 H2 + 2 O2  4 H2O However, all the coefficients have the common factor of two. Divide through to eliminate common factors like this..

Writing Complete Chemical Equations
Include the state symbols as subscripts in parentheses (s) solid, (l) liquid, (g) gas, (aq) aqueous (water) solution In most common reactions the reactants are gases, liquids, or aqueous solutions.

11-2 Types of Chemical Reactions
Single Replacement - one element replaces another element in a compound. There are two different possibilities: One cation replaces another. Written using generic symbols, it is: AX + Y  YX + A Cu + AgNO3  Ag + Cu(NO3)2 Fe + Cu(NO3)2  Fe(NO3)2 + Cu Ca + H2O  Ca(OH)2 + H2 Zn + HCl  ZnCl2 + H2 One anion replaces another. Written using generic symbols, it is: A + XY  XA + Y Cl2 + NaBr  NaCl + Br2 Br2 + KI  KBr + I2 In single replacement, one reactant is always an element. It does not matter if the element is written first or second on the reactant side. The other reactant will be a compound

11-2 Types of Chemical Reactions cont…
Double Replacement - During double replacement, the cations and anions of two different compounds switch places. In double replacement, both reactants are compounds, each with a cation part and an anion part. Diatomic elements do not count; they are included in the single replacement category. Written using generic symbols, it is: AB + XY  AY + XB A and X are the cations (postively-charged ions) in this example, with B and Y being the anions (negatively-charged ions). KOH + H2SO4  K2SO4 + H2O FeS + HCl  FeCl2 + H2S NaCl + H2SO4  Na2SO4 + HCl AgNO3 + NaCl  AgCl + NaNO3 These three are also examples of double replacement, but there is something special about them: CaCO3 + HCl  CaCl2 + CO2 + H2O K2SO3 + HNO3  KNO3 + SO2 + H2O NH4Cl + NaOH  NaCl + NH3 + H2O

Decomposition (analysis)-During decomposition, one compound splits apart into two (or more) pieces. These pieces can be elements or simpler compounds Written using generic symbols, it is usually shown as: AB  A + B HgO  Hg + O2 MgCl2  Mg + Cl2 CaCO3  CaO + CO2 FeS  Fe + S Na2CO3  Na2O + CO2 KClO3  KCl + O2 Ba(ClO3)2  BaCl2 + O2 H2O  H2 + O2 Notice how, in every case so far, there is only one substance on the left-hand (reactant) side. This is always the case in a decomposition reaction.

Direct Combination (synthesis)-Syntheses are, at this introductory level, almost always the reverse of a decomposition reaction. That means that two pieces join together to produce one, more complex compound. These pieces can be elements or simpler compounds. Complex simply means that the product compound has more atoms than the reactant molecules. Usually!! Written using generic symbols, it is usually shown as: A + B AB Mg + O2 MgO H2 + O2  H2O K + Cl2  KCl Fe + O2  Fe2O3 CaO + CO2  CaCO Na2O + CO2  Na2CO KCl + O2  KClO3 Notice how, in every case so far, there is only one substance on the right-hand (product) side. This is not always the case in a synthesis reaction. Sometimes there will be two products. Here's an example: CO2 + H2O  C6H12O6 + O2

Combustion, at its most general, can mean the reaction of oxygen gas (O2) with anything. However, we will understand combustion to mean the reaction of oxygen with any compound containing carbon and hydrogen. A common synonym for combustion is burn. Written using generic symbols, it is usually shown as: CxHy + O2  CO2 + H2O Balance these examples CH4 + O2  CO2 + H2O C2H6 + O2  CO2 + H2O C6H12O6 + O2  CO2 + H2O C2H5OH + O2  CO2 + H2O

Predicting Products Single Replacement - ZnS + O2 
(1) Decide if the reactant element (O2 in this case) is normally positive or negative. (It is a negative 2. Just use O, not O2.) (2) Identify the opposite charged (from step one) portion of the compound and its charge. (Zn has a charge of +2.) (3) Write a formula using information from step one & two.(ZnO since Zn = +2 and O = -2.) (4) Write the left over element as the second product. Write it as diatomic if it is. So the final answer looks like this: ZnS + O2  ZnO + S Double Replacement - Ca(OH)2 + HCl  (1) Identify the cations and anions in each compound: Ca(OH)2 has Ca2+ and OH¯ and HCl has H+ and Cl¯ All you have to do is identify each, you need not worry about amounts yet. (2) Pair up each cation with the anion from the OTHER compound: Ca2+ pairs with Cl¯and H+ pairs with OH¯ (Write two new (CORRECT!!) formulas using the pairs from step two. (3) CaCl2 since Ca is positive 2 and Cl is minus one and H2O since H is plus one and OH is negative one So the final answer looks like this: Ca(OH)2 + HCl  CaCl2 + H2O

Predicting Products cont…
Analysis (decomposition) - NaClO3  Figuring out what the products are in decomposition is harder (maybe you'll think it's easier!!) because you will have to recognize several categories of decomposition reactions. Here are your first three: 1) All binary compounds will break down into their elements. 2) All carbonates break down to the oxide and carbon dioxide. 3. Chlorates will break down to the binary salt and oxygen. (1)Identify the type of compound decomposing: NaClO3 is a chlorate Notice that you have to be able to "read" a formula and identifiy the parts (cation and anion) that make it up. (2) Apply the rule for that type: chlorates decompose to the binary salt and oxygen gas (3) Write two new (CORRECT!!) formulas using the rule from step two. NaCl since Na is positive 1 and Cl is minus one O2 since oxygen is a diatomic gas So the final answer looks like this: NaClO3  NaCl + O2

Synthesis (direct combination) –LiCl + O2  Since synthesis reactions are the reverse of decomposition, you might ask if the decomposition categories apply, just in reverse. The answer is yes! 1) Direct union of two elements will produce a binary compound. 2) Metallic oxides and carbon dioxide react to produce carbonates. 3. Binary salts and oxygen react to produce a chlorate. (1) Ask yourself what type of decomposition produces these products: LiCl + O2 are the products of a chlorate decomposing. Notice that you have to be able to "read" a formula and identifiy the parts (cation and anion) that make it up. (2) Write the reactant formula using the compounds from step one. Chlorate is always ClO3¯ Li is plus one So the final answer looks like this: LiCl + O2  LiClO3

Combustion-C7H6O + O2  (1) Identify the reaction as combustion: A carbon-hydrogen compound reacting with oxygen (2) Know that the combustion products are always CO2 and H2O So the final answer looks like this: C7H6O + O2  CO2 + H2O Now Balance!

Acid Base Reactions Neutralization – Acid + Base  Salt + Water or HCl + NaOH  NaCl + H2O Here are acid base decomposition reactions: Ca(OH)2  CaO + H2O HNO3  N2O5 + H2O NaOH  Na2O + H2O H3PO4  P2O5 + H2O The first two substances are bases and the last two are acids. In each case, the acid or base breaks down into the oxide of the metal (in the case of bases) or the oxide of the nonmetal (in the case of acids) plus water. Here are acid base synthesis reactions: CaO + H2O  Ca(OH)2 N2O5 + H2O  HNO3 Na2O + H2O  NaOH P2O5 + H2O  H3PO4 The first two substances are metallic oxides and the last two are nonmetallic oxides. In each case, the oxide plus water will produce a base (in the case of the metallic oxide) or an acid (in the case of the nonmetallic oxide).

HOFBrINCl & Friends Memorize us!
The Seven Diatomic Substances (plus two friends) Hydrogen - H2 Oxygen - O2 Fluorine - F2 Bromine - Br2 Iodine - I2 Nitrogen - N2 Chlorine - Cl2 In addition to the above, phosphorous is P4 and sulfur is S8.

Chapter 11 Chemical Reactions 11.3 Reactions in Aqueous Solution
11.1 Describing Chemical Reactions 11.2 Types of Chemical Reactions 11.3 Reactions in Aqueous Solution Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

How did soda straws get into limestone caves?
CHEMISTRY & YOU How did soda straws get into limestone caves? These “soda straws” are really stalactites in a limestone cave. Soda straws grow on cave ceilings as thin-walled hollow tubes that result from chemical reactions involving water. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What does a net ionic equation show?
Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Your world is water based.
Net Ionic Equations Your world is water based. More than 70 percent of Earth’s surface is covered by water, and about 66 percent of the adult human body is water. It is not surprising, then, that many important chemical reactions take place in water—that is, in aqueous solution. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
Net Ionic Equations The reaction of aqueous solutions of silver nitrate and sodium chloride to form solid silver chloride and aqueous sodium nitrate is a double-replacement reaction. AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Net Ionic Equations The equation does not show that, like most ionic compounds, the reactants and one of the products dissociate, or separate, into cations and anions when they dissolve in water. AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 40

Net Ionic Equations When sodium chloride dissolves in water, it separates into sodium ions (Na+(aq)) and chloride ions (Cl–(aq)). AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 41

Net Ionic Equations When sodium chloride dissolves in water, it separates into sodium ions (Na+(aq)) and chloride ions (Cl–(aq)). When dissolved in water, silver nitrate dissociates into silver ions (Ag+(aq)). AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 42

Net Ionic Equations You can use these ions to write a complete ionic equation, an equation that shows dissolved ionic compounds as dissociated free ions. Ag+(aq) + NO3–(aq) + Na+(aq) + Cl–(aq) → AgCl(s) + Na+(aq) + NO3–(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 43

Net Ionic Equations Notice that the nitrate ion and the sodium ion appear unchanged on both sides of the equation. The equation can be simplified by eliminating these ions because they don’t participate in the reaction. Ag+(aq) + NO3–(aq) + Na+(aq) + Cl–(aq) → AgCl(s) + Na+(aq) + NO3–(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 44

Net Ionic Equations An ion that appears on both sides of an equation and is not directly involved in the reaction is called a spectator ion. When you rewrite an equation leaving out the spectator ions, you have the net ionic equation. Ag+(aq) + NO3–(aq) + Na+(aq) + Cl–(aq) → AgCl(s) + Na+(aq) + NO3–(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Ag+(aq) + Cl–(aq) → AgCl(s)
Net Ionic Equations The net ionic equation is an equation for a reaction in solution that shows only those particles that are directly involved in the chemical change. Ag+(aq) + Cl–(aq) → AgCl(s) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Ag+(aq) + Cl–(aq) → AgCl(s)
Net Ionic Equations In writing balanced net ionic equations, you must make sure that the ionic charge is balanced. The net ionic charge on each side of the equation is zero and is therefore balanced. Ag+(aq) + Cl–(aq) → AgCl(s) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Pb(s) + AgNO3(aq) → Ag(s) + Pb(NO3)2(aq)
Net Ionic Equations Consider the skeleton equation for the reaction of lead with silver nitrate. Pb(s) + AgNO3(aq) → Ag(s) + Pb(NO3)2(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Net Ionic Equations Consider the skeleton equation for the reaction of lead with silver nitrate. Pb(s) + AgNO3(aq) → Ag(s) + Pb(NO3)2(aq) The nitrate ion is the spectator ion in this reaction. The net ionic equation is as follows: Pb(s) + Ag+(aq) → Ag(s) + Pb2+(aq) (unbalanced) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 49

Pb(s) + Ag+(aq) → Ag(s) + Pb2+(aq) (unbalanced)
Net Ionic Equations Why is this equation unbalanced? Notice that a single unit of positive charge is on the reactant side of the equation. Two units of positive charge are on the product side. Pb(s) + Ag+(aq) → Ag(s) + Pb2+(aq) (unbalanced) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Pb(s) + 2Ag+(aq) → 2Ag(s) + Pb2+(aq) (balanced)
Net Ionic Equations Placing the coefficient 2 in front of Ag+(aq) balances the charge. Pb(s) + 2Ag+(aq) → 2Ag(s) + Pb2+(aq) (balanced) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 51

Net Ionic Equations A net ionic equation shows only those particles involved in the reaction and is balanced with respect to both mass and charge. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Net Ionic Equations A net ionic equation shows only those particles involved in the reaction and is balanced with respect to both mass and charge. Of the five types of reactions identified in this chapter, both single- and double-replacement reactions can be written as net ionic equations. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 53

Writing and Balancing Net Ionic Equations
Sample Problem 11.8 Writing and Balancing Net Ionic Equations Aqueous solutions of iron(III) chloride and potassium hydroxide are mixed. A precipitate of iron(III) hydroxide forms. Identify the spectator ions and write a balanced net ionic equation for the reaction. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Analyze Identify the relevant concepts.
Sample Problem 11.8 Analyze Identify the relevant concepts. 1 Write the complete ionic equation. Eliminate aqueous ions that appear in both the reactants and products. Then balance the equation with respect to both mass and charge. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Solve Apply concepts to this problem.
Sample Problem 11.8 Solve Apply concepts to this problem. 2 Write the complete ionic equation for the reaction, showing soluble ionic compounds as individual ions. Fe3+(aq) + 3Cl–(aq) + 3K+(aq) + 3OH–(aq) → Fe(OH)3(s) + 3K+(aq) + 3Cl–(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Solve Apply concepts to this problem.
Sample Problem 11.8 Solve Apply concepts to this problem. 2 Eliminate aqueous ions that appear as both reactants and products. The spectator ions are K+ and Cl–. Fe3+(aq) + 3Cl–(aq) + 3K+(aq) + 3OH–(aq) → Fe(OH)3(s) + 3K+(aq) + 3Cl–(aq) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Fe3+(aq) + 3OH–(aq) → Fe(OH)3(s)
Sample Problem 11.8 Solve Apply concepts to this problem. 2 Balance the net ionic equation. Fe3+(aq) + 3OH–(aq) → Fe(OH)3(s) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What is the difference between complete ionic equations and net ionic equations?
Complete ionic equations show all ions present in solution during a reaction. Net ionic equations show only those ions that are directly involved in the reaction. Ions that do not participate, known as spectator ions, are not shown in a net ionic equation. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 60

Predicting the Formation of a Precipitate
How can you predict the formation of a precipitate in a double-replacement reaction? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

You have seen that mixing solutions of two ionic compounds can sometimes result in the formation of an insoluble salt called a precipitate. Some combinations of solutions produce precipitates, while others do not. Whether or not a precipitate forms depends upon the solubility of the new compounds that form. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Solubility Rules for Ionic Compounds
Interpret Data Solubility Rules for Ionic Compounds Compounds Solubility Exceptions Salts of alkali metals and ammonium Soluble Some lithium compounds Nitrate salts and chlorate salts Few exceptions Sulfate salts Compounds of Pb, Ag, Hg, Ba, Sr, and Ca Chloride salts Compounds of Ag and some compounds of Hg and Pb Carbonates, phosphates, chromates, sulfides, and hydroxides Most are insoluble Compounds of the alkali metals and of ammonia Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

2Na+(aq) + CO32–(aq) + Ba2+(aq) + 2NO3–(aq) → ?
Predicting the Formation of a Precipitate Will a precipitate form when aqueous solutions of Na2CO3(aq) and Ba(NO3)2(aq) are mixed? 2Na+(aq) + CO32–(aq) + Ba2+(aq) + 2NO3–(aq) → ? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 65

Predicting the Formation of a Precipitate Will a precipitate form when aqueous solutions of Na2CO3(aq) and Ba(NO3)2(aq) are mixed? 2Na+(aq) + CO32–(aq) + Ba2+(aq) + 2NO3–(aq) → ? When these four ions are mixed, the cations could change partners. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 66

Predicting the Formation of a Precipitate Will a precipitate form when aqueous solutions of Na2CO3(aq) and Ba(NO3)2(aq) are mixed? 2Na+(aq) + CO32–(aq) + Ba2+(aq) + 2NO3–(aq) → ? The two new compounds that would form are NaNO3 and BaCO3. These are the only new combinations of cation and anion possible. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 67

Predicting the Formation of a Precipitate Will a precipitate form when aqueous solutions of Na2CO3(aq) and Ba(NO3)2(aq) are mixed? 2Na+(aq) + CO32–(aq) + Ba2+(aq) + 2NO3–(aq) → ? To find out if an exchange will occur, refer to the solubility rules for ionic compounds. Sodium nitrate will not form a precipitate because alkali metal salts and nitrate salts are soluble. Carbonates in general are insoluble. Barium carbonate will precipitate. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 68

Will a precipitate form when aqueous solutions of Na2CO3(aq) and Ba(NO3)2(aq) are mixed? 2Na+(aq) + CO32–(aq) + Ba2+(aq) + 2NO3–(aq) → ? In this reaction, Na+ and NO3– are spectator ions. The net ionic equation for this reaction is: Ba2+(aq) + CO32–(aq) → BaCO3(s) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 69

CHEMISTRY & YOU How did the soda straws, which are composed of calcium carbonate, get into the cave? Soda straws form when there is calcium carbonate dissolved in water that drips very slowly from the ceiling of the cave. Because calcium carbonate is not very soluble, it comes out of solution and forms “soda straws” made of calcium carbonate. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 71

Writing and Balancing Net Ionic Equations
Sample Problem 11.9 Writing and Balancing Net Ionic Equations Aqueous potassium carbonate reacts with aqueous strontium nitrate. Identify the precipitate formed and write the net ionic equation for the reaction. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Analyze Identify the relevant concepts.
Sample Problem 11.9 Analyze Identify the relevant concepts. 1 Write the reactants. Look at possible new pairings of cation and anion that give an insoluble substance. Eliminate the spectator ions. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Solve Apply concepts to this situation.
Sample Problem 11.9 Solve Apply concepts to this situation. 2 Write the reactants, showing each as dissociated free ions. 2K+(aq) + CO32–(aq) + Sr2+(aq) + 2NO3–(aq) → ? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Sample Problem 11.9 Solve Apply concepts to this situation. 2 Look at possible new pairings of cation and anion that give an insoluble substance. Use the solubility rules to identify the precipitate formed. Of the two possible combinations, KNO3 is soluble and SrCO3 is insoluble. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Sample Problem 11.9 Solve Apply concepts to this situation. 2 Eliminate the spectator ions and write the net ionic equation. CO32–(aq) + Sr2+(aq) → SrCO3(s) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

In a double-replacement reaction that forms a precipitate, are the spectator ions those that form a precipitate, or those that stay in solution? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

In a double-replacement reaction that forms a precipitate, are the spectator ions those that form a precipitate, or those that stay in solution? The spectator ions are those that stay in solution. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 78

Key Concepts A net ionic equation shows only those particles involved in the reaction and is balanced with respect to mass and charge. By using the general rules for solubility of ionic compounds, you can predict the formation of a precipitate. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Glossary Terms complete ionic equation: an equation that shows dissolved ionic compounds as dissociated free ions spectator ion: an ion that is not directly involved in a chemical reaction; an ion that does not change oxidation number or composition during a reaction net ionic equation: an equation for a reaction in solution showing only those particles that are directly involved in the chemical change Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

BIG IDEA Reactions Net ionic equations show only those particles involved in the reaction.

Chapter 11 Matter and Change 11.1 Describing Chemical Reactions

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