Name: aqueous reactions and ionic equations
Uploaded: 2020-09-03T13:38:26.000Z
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K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.6.1

Chemical Reactions in Aqueous Solutions

Many chemical reactions occur in aqueous solutions. These reactions fall into 3 main categories: precipitation, acid&#8211;base, and oxidation&#8211;reduction. 

In a typical precipitation reaction, dissolved cations and anions come together to form an insoluble ionic compound that precipitates from the solution. For example, the reaction between aqueous potassium chloride and aqueous silver nitrate leads to the precipitation of insoluble silver chloride. 

In an acid&#8211;base reaction, the acid and base neutralize each other, such as when a proton (H+ ion) from an acid and a OH&#8722; ion from a base react to form water. The counterions typically react to form a salt. For example, hydrogen bromide reacts with potassium hydroxide to give water and potassium bromide. 

In an oxidation&#8211;reduction, or redox, reaction, electrons are transferred from one reactant to another. For example, an atom of potassium loses one electron to an atom of chlorine when they combine to form potassium chloride. 

When a chemical reaction occurs in an aqueous solution, water-soluble molecular solids dissolve as intact molecules, whereas water-soluble ionic solids exist as separated ions. Ionic solids that are water-insoluble remain un

chemical reactions in aqueous solutions

Chemical substances interact in many different ways. Certain chemical reactions exhibit common patterns of reactivity. Due to the vast number of chemical reactions, it becomes necessary to classify them based on the observed patterns of interaction.

Water is a good solvent that can dissolve many substances. For this reason, many chemical reactions take place in water. Such reactions are called aqueous reactions. The three most common types of aqueous reactions are precipitation, acid-base, and oxidation-reduction.

<h4>Reactions in Aqueous Solutions </h4>

A precipitation reaction involves the exchange of ions between ionic compounds in aqueous solution to form an insoluble salt or a precipitate. In an acid-base reaction, an acid reacts with a base, and the two neutralize each other, producing salt and water. An oxidation&#8211;reduction reaction involves the transfer of electrons between reacting species. The reactant that loses electrons is said to be oxidized, and the reactant that gains electrons is said to be reduced.

<h4>Equations for Aqueous Reactions </h4>

When ions are involved, there are various ways of representing the reactions that take place in aqueous media, each with a different level of detail. To understand this, let us take an example of a precipitation reaction. The reaction is between aqueous solutions of ionic compounds, like BaCl2 and AgNO3. The products of the reaction are aqueous Ba(NO3)2 and solid AgCl. 

<img alt="Chemical reaction: BaCl&#8322;(aq) + 2AgNO&#8323;(aq) &#8594; Ba(NO&#8323;)&#8322;(aq) + 2AgCl(s). Equation, precipitation reaction." src="/files/core/CDNSource/lessons/1024/1024_Equations-01.png" style="height: 40px;" data-altupdatedat="1754904545000" data-alt="Chemical reaction equation: BaCl&#8322;(aq) + 2AgNO&#8323;(aq) &#8594; Ba(NO&#8323;)&#8322;(aq) + 2AgCl(s). Precipitation process." />

This balanced equation is called a molecular equation. Molecular equations provide stoichiometric information to make quantitative calculations and also helps identify the reagents used and the products formed. However, molecular equations do not provide the details of the reaction process in solution; that is, it does not indicate the different ionic species that are present in solution. 

Ionic compounds such as BaCl2, AgNO3, and Ba(NO3)2 are water-soluble. They dissolve by dissociating into their constituent ions, and their ions are homogeneously dispersed in solution. 

<img alt="Chemical equation of barium chloride dissociation, BaCl&#8322;(aq)&#8594;Ba&#178;&#8314;(aq)+2Cl&#8315;(aq), formula." src="/files/core/CDNSource/lessons/1024/1024_Equations-02.png" style="height: 40px;" data-altupdatedat="1754904545000" data-alt="Chemical equation: BaCl2(aq) &#8594; Ba2+(aq) + 2Cl-(aq); illustrating ionic dissociation." />

<img alt="Chemical reaction equation: 2AgNO3(aq) &#8594; 2Ag+(aq) + 2NO3&#8722;(aq), illustrating ionization." src="/files/core/CDNSource/lessons/1024/1024_Equations-03.png" style="height: 40px;" data-altupdatedat="1754904545000" data-alt="Chemical equation of silver nitrate dissociation in aqueous solution, illustrating ion generation." />

<img alt="Chemical equilibrium equation: Ba(NO&#8323;)&#8322;(aq) &#8594; Ba&#178;&#8314;(aq) + 2NO&#8323;&#8315;(aq), ion dissociation process." src="/files/core/CDNSource/lessons/1024/1024_Equations-04.png" style="height: 40px;" data-altupdatedat="1754904545000" data-alt="Aqueous barium nitrate dissociation equation, chemical equilibrium, ionic dissociation." />

Since AgCl is an insoluble salt, it does not dissociate into ions and stays in solution as a solid. Considering the above factors, a more realistic representation of the reaction would be: 

<img alt="Chemical reaction equation, Ba&#178;&#8314;(aq) + 2Cl&#8315;(aq) + 2Ag&#8314;(aq) &#8594; Ba&#178;&#8314;(aq) + 2NO&#8323;&#8315;(aq) + 2AgCl(s) precipitate." src="/files/core/CDNSource/lessons/1024/1024_Equations-05.png" style="height: 62px;" data-altupdatedat="1754904545000" data-alt="Balancing chemical equations, Ba&#178;&#8314;(aq)+2Cl&#8315;(aq)+2Ag&#8314;(aq)&#8594;Ba&#178;&#8314;(aq)+2NO&#8323;&#8315;(aq)+2AgCl(s)." />

This is the complete ionic equation in which all dissolved ions are explicitly represented. 

This complete ionic equation indicates two chemical species that are present in identical form on both sides, Ba2+ (aq) and NO3&#8722; (aq). These are called spectator ions. The presence of these ions is required to maintain charge neutrality. Since they are neither chemically nor physically changed by the process, they may be eliminated from the equation. 

<img alt="Chemical equation illustrating a double displacement reaction; Ba&#178;&#8314;, NO&#8323;&#8315; ions, AgCl(s) formed." src="/files/core/CDNSource/lessons/1024/1024_Equations-06.png" style="height: 62px;" data-altupdatedat="1754904545000" data-alt="Precipitation reaction equation; Ba&#178;&#8314;(aq) + 2Cl&#8315;(aq) + 2Ag&#8314;(aq) &#8594; Ba&#178;&#8314;(aq) + 2AgCl(s); chemistry diagram." />

<img alt="Chemical equation for silver chloride formation, formula: 2Cl&#8315;(aq) + 2Ag&#8314;(aq) &#8594; 2AgCl(s)." src="/files/core/CDNSource/lessons/1024/1024_Equations-07.png" style="height: 40px;" data-altupdatedat="1754904545000" data-alt="Chemical reaction equation: 2Cl&#8315;(aq) + 2Ag&#8314;(aq) &#8594; 2AgCl(s), precipitation reaction diagram." />

This equation can be further simplified to give: 

<img alt="Chemical reaction equation: Cl&#8315;(aq) + Ag&#8314;(aq) &#8594; AgCl(s). Precipitation diagram, ionic reaction." src="/files/core/CDNSource/lessons/1024/1024_Equations-08.png" style="height: 40px;" data-altupdatedat="1754904545000" data-alt="Chemical reaction: Cl-(aq) + Ag+(aq) &#8594; AgCl(s), equation illustrating precipitation reaction." />

This is the net ionic equation. It indicates that solid silver chloride may be produced from dissolved chloride and silver ions, regardless of the source of these ions. 

This text is adapted from <a href="https://openstax.org/books/chemistry-2e/pages/4-1-writing-and-balancing-chemical-equations">OpenStax Chemistry 2e, Section 4.1: Writing and Balancing Chemical Equations. </a>

Chemical substances interact in many different ways. Certain chemical reactions exhibit common patterns of reactivity. Due to the vast number of chemical ...

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Chemical Quantities and Aqueous Reactions

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KEY TERMS AND CONCEPTS

aqueous reactions and ionic equations

Aqueous reactions are chemical reactions that take place in water. Water is a good solvent, so it can dissolve many substances. Because of that, many chemical reactions happen in aqueous solution. In high school chemistry, these reactions are often grouped into three common patterns: precipitation, acid-base, and oxidation-reduction.

A precipitation reaction happens when ions in two aqueous ionic compounds exchange partners and form an insoluble salt, called a precipitate. In an acid-base reaction, an acid reacts with a base and they neutralize each other. This produces salt and water. An oxidation-reduction reaction involves electron transfer between reacting species. The species that loses electrons is oxidized, and the species that gains electrons is reduced.

Aqueous reactions can be written in more than one way, depending on how much detail is needed. A molecular equation shows the balanced reaction, the substances used, and the products formed. For example, aqueous BaCl2 and AgNO3 react to form aqueous Ba(NO3)2 and solid AgCl. Molecular equations are useful for stoichiometric calculations, but they do not show which ions are present in solution.

A more detailed form is the complete ionic equation. In this version, all dissolved ions are written separately. Water-soluble ionic compounds such as BaCl2, AgNO3, and Ba(NO3)2 dissociate into ions in water. AgCl is insoluble, so it stays as a solid and does not dissociate. The complete ionic equation shows the ions that actually exist in the aqueous mixture.

The complete ionic equation also shows spectator ions. These are ions that appear in the same form on both sides of the equation, such as Ba2+ and NO3− in this example. They help maintain charge neutrality, but they are not chemically or physically changed by the reaction. When these ions are removed, the result is the net ionic equation. This simplified equation shows that solid silver chloride can form from dissolved silver and chloride ions, no matter where those ions came from.

Aqueous Reactions and Ionic Equations

reaction stoichiometry

Using Balanced Equations to Predict Amounts

Balanced chemical equations show how much of each substance reacts and forms in a chemical change. The formulas identify the reactants and products, which helps classify the reaction. The coefficients show the relative numbers of each substance, which lets chemists measure the relationships between amounts consumed and produced. These quantitative relationships are called stoichiometry. The word comes from the Greek words stoicheion, meaning element, and metron, meaning measure. Stoichiometry...

limiting reactant

Limiting Reactant in Water Formation

Limiting reactants control how much product forms in a chemical reaction. In a balanced equation, the listed amounts of reactants and products are called stoichiometric amounts. In real reactions, the reactants are not always present in those exact proportions. The limiting reactant is the reactant that gets used up first. Once it is gone, the reaction stops making more product. The other reactant is called the excess reactant. Chemists often use extra amounts of one reactant to make sure the...

reaction yield

Calculating Percent Yield in Reactions

Percent yield shows how much product a chemical reaction actually makes compared with how much it should make. The expected amount is called the theoretical yield. It comes from the balanced chemical equation and the stoichiometry, or mole ratios, in that equation. The theoretical yield assumes that the limiting reactant is completely converted into the desired product. The product collected after a reaction is the actual yield. In many cases, the actual yield is lower than the theoretical...

general properties of solutions

Solvents, Solutes, and Solution Types

Solutions are common mixtures found in everyday life. Ocean water, air, and gasoline are all examples of solutions. These mixtures contain two or more types of atoms or molecules in varying amounts. A solution is a homogeneous mixture, which means its composition is uniform throughout. This is different from a heterogeneous mixture, which has a non-uniform composition. In a homogeneous mixture, the components are evenly spread out and thoroughly mixed. Every solution has a solvent and a...

solution concentration and dilution

Molarity and Dilution in Solutions

Molarity and dilution are key ideas for describing solution concentration. Concentration means the relative amount of one component in a solution. In many solutions, one component is present in much larger amount. That component is the solvent, which acts as the medium that holds the other parts dissolved or dispersed. Water is a very common solvent, so aqueous solutions are common on Earth. A solute is the component present at a much lower concentration than the solvent. Chemists often...

electrolyte and nonelectrolyte solutions

Conductivity in Electrolyte Solutions

Electrolyte solutions conduct electricity because they contain mobile ions. The amount of current depends on how many ions are present in the aqueous solution. A solution with more dissolved ions conducts better, while a solution with few or no ions conducts poorly. Strong electrolytes dissociate completely in water. This complete dissociation is shown with a single forward arrow. Water-soluble ionic compounds such as sodium chloride split into sodium cations and chloride anions in solution.

solubility of ionic compounds

Solubility Rules for Ionic Salts

Solubility rules help predict whether ionic salts will dissolve in water. Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a set temperature and pressure. It is often measured in molarity, or moles per liter (mol/L). A compound is soluble if it dissolves in water. When a soluble salt dissolves, its ions separate and spread evenly through the solution. This physical change is called dissociation. Potassium chloride, KCl, is a simple example. Water...

Aqueous reactions are chemical reactions that take place in water. Water is a good solvent, so it can dissolve many substances. Because of that, many chemical reactions happen in aqueous solution. In high school chemistry, these reactions are often grouped into three common patterns: precipitation, acid-base, and oxidation-reduction. A precipitation reaction happens when ions in two aqueous ionic compounds exchange partners and form an insoluble salt, called a precipitate. In an acid-base...

precipitation reactions

Predicting Precipitation in Aqueous Reactions

Precipitation reactions happen when two aqueous solutions of soluble salts are mixed and an insoluble ionic compound forms. That solid is called a precipitate. The ions in solution exchange partners, so these reactions are also called double displacement, double replacement, exchange, or metathesis reactions. These reactions are useful in chemistry for identifying metal ions in a compound. They also support gravimetric methods, which measure composition by the mass of a substance. Whether a...

oxidation-reduction reactions

Redox Reactions and Oxidation Numbers

Redox reactions are chemical changes in which electrons move between reactants, and oxidation numbers help track that change. The term oxidation once referred only to reactions with molecular oxygen, but it now covers a wider reaction class called oxidation-reduction, or redox, reactions. Some redox reactions form ionic products. A simple example is the reaction between sodium and chlorine that produces sodium chloride. To follow what happens to each reactant, chemists often write...

oxidation numbers

Assigning Oxidation States in Redox Reactions

Oxidation states help track electron transfer in redox reactions. An oxidation number, also called an oxidation state, is a hypothetical number that shows the effective charge of an atom or element. Chemists assign it by using a set of rules. In an ionic compound, oxidation numbers are based on how many electrons move between reacting species. For example, when calcium chloride forms, calcium loses two valence electrons and the two chlorine atoms each gain one electron. In CaCl2, calcium has...

acids, bases and neutralization reactions

How Acids and Bases Form Ions

Acids and bases form ions in water through acid-base reactions. These reactions move a hydrogen ion, H+, from one chemical species to another. They matter in many natural and technological processes, from chemistry inside cells and in lakes and oceans to the large-scale production of fertilizers, pharmaceuticals, and other useful substances. In water, an acid is a substance that produces hydrogen ions. This is the Arrhenius definition of an acid. The H+ ion is also called a proton. In...

synthesis and decomposition reactions

Building and Breaking in Chemical Reactions

Synthesis and decomposition are two redox reactions that show how substances can be built up or broken down. Synthesis means to make something, while decomposition means to break something apart. These reactions also involve chemical changes and energy changes. Synthesis reactions are also called combination reactions. In a synthesis reaction, two or more substances join to form one more complex substance. They are often written as A + B → AB or A + B → C. One example is the formation of...

key terms and concepts

Learn how precipitation, acid-base, and redox reactions happen in water, and how molecular, complete ionic, and net ionic equations show them.

Aqueous Reactions and Ionic Equations | JoVE K12

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Matter And Its Interactions

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New York State Science Learning Standards

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Ionization Energy

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Electron Affinity

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PS.Chm.2.2

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PS.Chm.3.1

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Aqueous Reactions and Ionic Equations

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