Topic 18

Topic 18: Acids and Bases Basic Concepts Additional Concepts Topic 18 Table of Contents Topic 18 Topic 18: Acids and Bases Basic Concepts Additional Concepts

Properties of Acids and Bases Acids and Bases: Basic Concepts Topic 18 Properties of Acids and Bases Although taste is not a safe way to classify acids and bases, you probably are familiar with the sour taste of acids. Lemon juice and vinegar, for example, are both aqueous solutions of acids. Bases, on the other hand, taste bitter.

Properties of Acids and Bases Acids and Bases: Basic Concepts Topic 18 Properties of Acids and Bases Bases have a slippery feel. Like taste, feel is not a safe chemical test for bases, but you are familiar with the feel of soap, a base, on the skin.

Litmus Test and Other Color Changes Acids and Bases: Basic Concepts Topic 18 Litmus Test and Other Color Changes Acids and bases cause certain colored dyes to change color. The most common of these dyes is litmus. When mixed with an acid, litmus is red.

Litmus Test and Other Color Changes Acids and Bases: Basic Concepts Topic 18 Litmus Test and Other Color Changes When added to a base, litmus is blue. Therefore, litmus is a reliable indicator of whether a substance is an acid or a base.

Reactions with Metals and Carbonates Acids and Bases: Basic Concepts Topic 18 Reactions with Metals and Carbonates Another characteristic property of an acid is that it reacts with metals that are more active than hydrogen. This property explains why acids corrode most metals.

Reactions with Metals and Carbonates Acids and Bases: Basic Concepts Topic 18 Reactions with Metals and Carbonates Bases do not commonly react with metals. Click box to view movie clip.

Reactions with Metals and Carbonates Acids and Bases: Basic Concepts Topic 18 Reactions with Metals and Carbonates Another simple test that distinguishes acids from bases is the reaction of acids with ionic compounds that contain the carbonate ion, , to form carbon dioxide gas, water, and another compound.

Submicroscopic Behavior of Acids Acids and Bases: Basic Concepts Topic 18 Submicroscopic Behavior of Acids The submicroscopic behavior of acids when they dissolve in water can be described in several ways. The simplest definition is that an acid is a substance that produces hydronium ions when it dissolves in water. A hydronium ion, H3O+, consists of a hydrogen ion attached to a water molecule.

Submicroscopic Behavior of Acids Acids and Bases: Basic Concepts Topic 18 Submicroscopic Behavior of Acids When HCl dissolves in water, it produces hydronium ions by the reaction shown below. HCl is definitely an acid; it produces H3O+ when dissolved in water.

Acids and Bases: Basic Concepts Topic 18 Acidic Hydrogen Atoms At the submicroscopic level, the reaction of an acid with water is a transfer of a hydrogen ion, H+, from an acid to a water molecule. This transfer forms the positively charged hydronium ion, H3O+, and a negatively charged ion. In an acid, any hydrogen atom that can be transferred to water is called an acidic hydrogen.

Acids and Bases: Basic Concepts Topic 18 Acidic Hydrogen Atoms To help distinguish acids from other hydrogen-containing molecules, acidic hydrogens are written first in the formula. Any time hydrogen is the first element in a formula of a compound, the substance is an acid.

Monoprotic acids contain only one acidic hydrogen. Acids and Bases: Basic Concepts Topic 18 Monoprotic Acids Acids such as acetic acid, HC2H3O2, and hydrochloric acid, HCl, are called monoprotic acids. Monoprotic acids contain only one acidic hydrogen.

Diprotic and Triprotic Acids Acids and Bases: Basic Concepts Topic 18 Diprotic and Triprotic Acids All acids that have more than one acidic hydrogen per molecule are called polyprotic acids. Polyprotic acids with two acidic hydrogens are diprotic acids.

Diprotic and Triprotic Acids Acids and Bases: Basic Concepts Topic 18 Diprotic and Triprotic Acids Those with three acidic hydrogens are triprotic acids.

Submicroscopic Behavior of Bases Acids and Bases: Basic Concepts Topic 18 Submicroscopic Behavior of Bases The behavior of bases is also described at the molecular level by the interaction of the base with water. A base is a substance that produces hydroxide ions, OH –, when it dissolves in water. There are two mechanisms by which bases produce hydroxide ions when they dissolve in water.

Simple Bases: Metal Hydroxides Acids and Bases: Basic Concepts Topic 18 Simple Bases: Metal Hydroxides The simplest kind of base is a water-soluble ionic compound, such as sodium hydroxide, that contains the hydroxide ion as the negative ion. When NaOH dissolves in water, for example, it dissociates into aqueous sodium ions and hydroxide ions, as shown below.

Other Acids and Bases: Anhydrides Acids and Bases: Basic Concepts Topic 18 Other Acids and Bases: Anhydrides Two related classes of compounds do not fit the previous models of acids and bases, but they still act as acids or bases. These compounds are both oxides, which are compounds containing oxygen bonded to just one other element. These oxides are called anhydrides, which means that they contain no water.

Other Acids and Bases: Anhydrides Acids and Bases: Basic Concepts Topic 18 Other Acids and Bases: Anhydrides Anhydrides differ, depending upon whether the oxygen is bonded to a metal or a nonmetal. Nonmetal oxides form acids when they react with water and are called acidic anhydrides. Metal oxides, on the other hand, react with water to form bases and are called basic anhydrides.

Other Acids and Bases: Anhydrides Acids and Bases: Basic Concepts Topic 18 Other Acids and Bases: Anhydrides In both of these reactions, water is an active reactant. Click box to view movie clip.

Acids and Bases: Basic Concepts Topic 18 Basic Anhydrides These metal oxides are predominantly those of sodium, potassium, and calcium. These metal oxides are ionic so they are solids, even at the high temperature of a roaring fire. They are the major component of the ash that is left when the fire burns out.

The dissociation of the base is complete. Acids and Bases: Basic Concepts Topic 18 Strong Bases Sodium hydroxide, NaOH, is a strong base because when NaOH dissolves in water, all NaOH formula units dissociate into separate sodium and hydroxide ions. The dissociation of the base is complete.

Acids and Bases: Basic Concepts Topic 18 Strong Bases The strength of a base is based on the percent of units dissociated, not the number of OH– ions produced. Some bases, such as Mg(OH)2, are not very soluble in water, and they don’t produce a large number of OH– ions. However, they are still considered to be strong bases because all of the base that does dissolve completely dissociates.

Acids and Bases: Basic Concepts Topic 18 Strong Acids HCl is a strong acid because no HCl molecules are in a water solution of HCl. Because of the strong attraction between the water molecules and HCl molecules, every HCl molecule ionizes.

Acids and Bases: Basic Concepts Topic 18 Weak Acids Acetic acid, HC2H3O2, is a good example of a weak acid. The molecular structure of a weak acid determines the extent to which the acid ionizes in water. A solution of weak acid contains a mixture of un-ionized acid molecules, hydronium ions, and the corresponding negative ions.

Acids and Bases: Basic Concepts Topic 18 Weak Acids The concentration of the un-ionized acid is always the greatest of the three concentrations.

Acids and Bases: Basic Concepts Topic 18 Weak Bases Ammonia is a weak base because most of its molecules don’t react with water to form ions. Other examples of bases that produce so few OH– ions that they are considered to be weak bases are Al(OH)3, and Fe(OH)3.

Strength Is Not Concentration Acids and Bases: Basic Concepts Topic 18 Strength Is Not Concentration Although the terms weak and strong are used to compare the strengths of acids and bases, dilute and concentrated are terms used to describe the concentration of solutions. The combination of strength and concentration ultimately determines the behavior of the solution.

Strength Is Not Concentration Acids and Bases: Basic Concepts Topic 18 Strength Is Not Concentration For example, it is possible to have a concentrated solution of a weak acid or weak base or a dilute solution of a weak acid or weak base. Similarly, you can have a concentrated solution of a strong acid or strong base, as well as a dilute solution of a strong acid or strong base.

Acids and Bases: Basic Concepts Topic 18 The pH Scale In most applications, the observed range of possible hydronium or hydroxide ion concentrations spans 10–14 M to 1M. This huge range of concentrations presents a problem when comparing different acids and bases. To make this range of possible concentrations easier to work with, the pH scale was developed by S.P.L. Sørenson.

Acids and Bases: Basic Concepts Topic 18 The pH Scale pH is a mathematical scale in which the concentration of hydronium ions in a solution is expressed as a number from 0 to 14. A scale of 0 to 14 is much easier to work with than a range from 1 to 10–14 (100 to 10–14). The pH scale is a convenient way to describe the concentration of hydronium ions in acidic solutions, as well as the hydroxide ions in basic solutions.

A solution with a pH of 4 has a hydronium ion concentration of 10–4M. Acids and Bases: Basic Concepts Topic 18 The pH Scale Think about the pH numbers 0 to 14 and the hydronium ion concentration range. Notice that the pH value is the negative of the exponent of the hydronium ion concentration. For example, a solution with a hydronium ion concentration of 10–11M has a pH of 11. A solution with a pH of 4 has a hydronium ion concentration of 10–4M.

Indicators register different colors at different pHs. Acids and Bases: Basic Concepts Topic 18 Measuring pH pH is convenient because there are simple methods for measuring it in the lab or in the field. Indicators register different colors at different pHs. pH meters are instruments that measure the exact pH of a solution.

Interpreting the pH Scale Acids and Bases: Basic Concepts Topic 18 Interpreting the pH Scale pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic. As the pH drops from 7, the solution becomes more acidic. As pH increases from 7, the solution becomes more basic.

Acids and Bases: Basic Concepts Topic 18 pH of Common Materials In a neutral solution, the concentration of hydroxide ions and the concentration of hydronium ions are equal.

Types of Acid-Base Reactions Acids and Bases: Basic Concepts Topic 18 Types of Acid-Base Reactions The reaction of an acid and a base is called a neutralization reaction. Click box to view movie clip.

Types of Acid-Base Reactions Acids and Bases: Basic Concepts Topic 18 Types of Acid-Base Reactions Consider the following neutralization reaction.

Types of Acid-Base Reactions Acids and Bases: Basic Concepts Topic 18 Types of Acid-Base Reactions Hydrochloric acid, HCl, is a common household and laboratory acid. Muriatic acid is the common household name of hydrochloric acid.

Neutralization Reactions Acids and Bases: Basic Concepts Topic 18 Neutralization Reactions A solution of hydrochloric acid, HCl, is added to exactly the amount of a solution of basic sodium hydroxide, NaOH, that will react with it. Click box to view movie clip.

Neutralization Reactions Acids and Bases: Basic Concepts Topic 18 Neutralization Reactions Litmus papers show that the resulting salt solution is neither acidic nor basic. Click box to view movie clip.

Strong Acid + Strong Base Acids and Bases: Basic Concepts Topic 18 Strong Acid + Strong Base A typical type of acid-base reaction is one in which both the acid and base are strong. The reaction of aqueous solutions of hydrochloric acid and sodium hydroxide is a good example of this type of reaction. HCl is the acid; NaOH is the base. The products are NaCl, which is a salt, and water. Now take a closer look at these reactants and their products.

Strong Acid + Strong Base Acids and Bases: Basic Concepts Topic 18 Strong Acid + Strong Base You also know that sodium hydroxide in water completely dissociates into sodium ions and hydroxide ions because NaOH is a strong base.

Strong Acid + Strong Base Acids and Bases: Basic Concepts Topic 18 Strong Acid + Strong Base An overall equation for the reaction between NaOH and HCl shows each substance involved in the reaction. An overall equation does not indicate whether these substances exist as ions. The best way for you to model the submicroscopic behavior of an acid-base reaction is to show reactants and products as they actually exist in solution.

Strong Acid + Strong Base Acids and Bases: Basic Concepts Topic 18 Strong Acid + Strong Base Instead of an overall equation, an ionic equation, in which substances that primarily exist as ions in solution are shown as ions, can be written.

Strong Acid + Strong Base Acids and Bases: Basic Concepts Topic 18 Strong Acid + Strong Base How can a lithium battery have an aqueous electrolyte? Two facets of the construction of this new battery keep the lithium metal from reacting with water. First, the lithium is in the form of individual atoms embedded in a material such as manganese (IV) oxide, rather than as a solid metal.

Strong Acid + Strong Base Acids and Bases: Basic Concepts Topic 18 Strong Acid + Strong Base Second, the electrolyte is full of dissolved lithium salts, so the lithium ions that are produced travel to the site of reduction without reacting with water.

Spectator Ions and the Net Ionic Reaction Acids and Bases: Basic Concepts Topic 18 Spectator Ions and the Net Ionic Reaction Note that the ionic equation gives more information about how a strong acid-strong base reaction occurs. When you examine the two sides of the ionic equation, you see that Na+ and Cl– are present both as reactants and as products.

Spectator Ions and the Net Ionic Reaction Acids and Bases: Basic Concepts Topic 18 Spectator Ions and the Net Ionic Reaction Although they are important components of an overall equation, they do not directly participate in the chemical reaction. They are called spectator ions because they are present in the solution but do not participate in the reaction.

Spectator Ions and the Net Ionic Reaction Acids and Bases: Basic Concepts Topic 18 Spectator Ions and the Net Ionic Reaction Just as in a mathematical equation, items common to both sides of the equation can be subtracted. This process simplifies the equation so that the reactants and products that actually change can be seen more clearly.

Spectator Ions and the Net Ionic Reaction Acids and Bases: Basic Concepts Topic 18 Spectator Ions and the Net Ionic Reaction When ions common to both sides of the equation are removed from the equation, the result is called the net ionic equation for the reaction of HCl with NaOH.

Spectator Ions and the Net Ionic Reaction Acids and Bases: Basic Concepts Topic 18 Spectator Ions and the Net Ionic Reaction The net ionic equation describes what is really happening at the submicroscopic level. Although solutions of HCl and NaOH are mixed, the net ionic equation is hydrogen ions reacting with hydroxide ions to form water.

Consider the reaction of hydrobromic acid and aluminum hydroxide. Acids and Bases: Basic Concepts Topic 18 Strong Acid + Weak Base Consider the reaction of hydrobromic acid and aluminum hydroxide. The overall equation shows the reactants and products.

Hydrobromic acid, a strong acid, completely ionizes in water. Acids and Bases: Basic Concepts Topic 18 Strong Acid + Weak Base Hydrobromic acid, a strong acid, completely ionizes in water. All of the Al(OH)3 that dissolves dissociates, so it is technically a strong base. However, because it is so insoluble, few OH– ions are produced, and Al(OH)3 acts as a weak base.

Therefore, the ionic equation shows little dissociation of the base. Acids and Bases: Basic Concepts Topic 18 Strong Acid + Weak Base Therefore, the ionic equation shows little dissociation of the base. The dissociated salt, AlBr3, is also shown as ions.

The spectator ions in this equation are bromide ions. Acids and Bases: Basic Concepts Topic 18 Strong Acid + Weak Base The spectator ions in this equation are bromide ions. They are removed from both sides of the equation to produce the net ionic equation.

A solution of ammonia is best represented by NH3(aq). Acids and Bases: Basic Concepts Topic 18 Strong Acid + Weak Base A solution of ammonia is best represented by NH3(aq). A solution of HCl, as in the last case, is best represented as H+ (aq) and Cl– (aq). The ionic reaction is written by representing what is actually in the reactant and product solutions. The ionic salt NH4Cl is written as dissociated ions.

Acids and Bases: Basic Concepts Topic 18 Strong Acid + Weak Base A quick look at the ionic reaction shows that the chloride ion is a spectator ion because it appears on both sides of the reaction. You get the net ionic equation by subtracting the spectator Cl– from both sides of the ionic equation.

A Broader Definition of Acids and Bases Acids and Bases: Basic Concepts Topic 18 A Broader Definition of Acids and Bases The reaction of a strong acid with a weak base demonstrates the need for a slightly broader definition of acids and bases.

A Broader Definition of Acids and Bases Acids and Bases: Basic Concepts Topic 18 A Broader Definition of Acids and Bases As you learned in the last chapter, much of the behavior of acids and bases in water can be explained by a model that focuses on the hydrogen ion transfer from the acid to the base. This model will also help explain why every acid-base reaction does not result in a neutral solution.

A Broader Definition of Acids and Bases Acids and Bases: Basic Concepts Topic 18 A Broader Definition of Acids and Bases In the more inclusive Brønsted-Lowry model, an acid is a hydrogen-ion donor and a base is a hydrogen-ion acceptor. When a Brønsted-Lowry acid donates a hydrogen ion, a conjugate base is formed. When a Brønsted-Lowry base accepts a hydrogen ion, a conjugate acid is formed. Two substances related to each other by the donating and accepting of a single hydrogen ion are a conjugate acid-base pair.

Identifying Conjugate Acid-Base Pairs Acids and Bases: Basic Concepts Topic 18 Identifying Conjugate Acid-Base Pairs Identify the conjugate acid-base pairs in this reaction. A hydrogen ion is donated by HClO2, which is the Brønsted-Lowry acid in the forward reaction. The resulting conjugate base is ClO2–. The base in the forward reaction is H2O, which accepts a hydrogen ion to form the conjugate acid H3O+.

Identifying Conjugate Acid-Base Pairs Acids and Bases: Basic Concepts Topic 18 Identifying Conjugate Acid-Base Pairs As in the case of the weak base-strong acid reaction, mixing equal moles of acid and base does not produce a neutral solution. Because the final pH in this case is basic, more hydroxide than hydronium ions must be present in the final reaction mixture.

Weak Acid + Strong Base— Equations—Weak Acid, Strong Base Acids and Bases: Basic Concepts Topic 18 Weak Acid + Strong Base— Equations—Weak Acid, Strong Base Write the overall, ionic, and net ionic equations for the reaction of phosphoric acid with lithium hydroxide. Phosphoric acid, H3PO4, is a weak acid. Lithium hydroxide, LiOH, is a strong base.

Weak Acid + Strong Base— Equations—Weak Acid, Strong Base Acids and Bases: Basic Concepts Topic 18 Weak Acid + Strong Base— Equations—Weak Acid, Strong Base Write a balanced equation for the overall reaction. The salt is lithium phosphate, Li3PO4. Water is also a product. You’ll need three moles of LiOH for each mole of H3PO4. Three moles of water will be produced.

Weak Acid + Strong Base— Equations—Weak Acid, Strong Base Acids and Bases: Basic Concepts Topic 18 Weak Acid + Strong Base— Equations—Weak Acid, Strong Base Now, write the ionic equation. Because H3PO4 is a weak acid, it is only partially ionized, and you write it in the ionic equation as H3PO4. LiOH is completely dissociated, as is the salt lithium phosphate. Be careful to keep the ionic equation balanced.

Weak Acid + Strong Base— Equations—Weak Acid, Strong Base Acids and Bases: Basic Concepts Topic 18 Weak Acid + Strong Base— Equations—Weak Acid, Strong Base Check for spectator ions. Li+ is a spectator ion. Subtract Li+ from both sides of the equation to get the net ionic equation.

Acids and Bases: Basic Concepts Topic 18 Weak Acid + Weak Base The strong-strong reaction plus the two types of weak-strong reactions are the favorable acid-base reactions. Looking at an acid-base reaction as occurring by H+ transfer helps you to understand why the weak-weak reaction is not considered a favorable reaction.

Acids and Bases: Basic Concepts Topic 18 Weak Acid + Weak Base Because neither a weak acid nor a weak base has a strong tendency to transfer a hydrogen ion, transfer between the two may occur, but it is uncommon. Reactions between a weak acid and a weak base generally do not play an important role in acid-base chemistry.

Question 1 Find the pH of the following solution. Basic Assessment Questions Topic 18 Question 1 Find the pH of the following solution. The hydronium ion concentration equals: 10–2M.

Basic Assessment Questions Topic 18 Answer pH = 2

Question 2 Find the pH of the following solution. Basic Assessment Questions Topic 18 Question 2 Find the pH of the following solution. The hydroxide ion concentration equals: 10–8M.

Basic Assessment Questions Topic 18 Answer pH = 6

Basic Assessment Questions Topic 18 Question 3 Write the net ionic equation for sulfuric acid, H2SO4, and strontium hydroxide, Sr(OH)2.

Basic Assessment Questions Topic 18 Answer

Basic Assessment Questions Topic 18 Question 4 Identify the conjugate acid-base pairs in the following reaction.

Basic Assessment Questions Topic 18 Answer

Acids and Bases: Additional Concepts Topic 18 Additional Concepts

Acids and Bases: Additional Concepts Topic 18 Buffers Defined A buffer is a solution that resists changes in pH when moderate amounts of acids or bases are added. Click box to view movie clip.

Acids and Bases: Additional Concepts Topic 18 Buffers Defined It contains ions or molecules that react with OH– or H+ if one of these ions is introduced into the solution. Buffer solutions are prepared by using a weak acid with one of its salts or a weak base with one of its salts

If an acid is added, NH3 reacts with the H+. Acids and Bases: Additional Concepts Topic 18 Buffers Defined For example, a buffer solution can be prepared by using the weak base ammonia, NH3, and an ammonium salt, such as NH4Cl. If an acid is added, NH3 reacts with the H+.

If a base is added, the NH4+ ion from the salt reacts with the OH–. Acids and Bases: Additional Concepts Topic 18 Buffers Defined If a base is added, the NH4+ ion from the salt reacts with the OH–.

Acids and Bases: Additional Concepts Topic 18 Buffers Defined Look at another system that contains the weak acid acetic acid, HC2H3O2, and the salt sodium acetate, NaC2H3O2. If a strong base, OH–, is added to the buffer system, the weak acid reacts to neutralize the addition.

This reaction takes care of the added OH–. Acids and Bases: Additional Concepts Topic 18 Buffers Defined This reaction takes care of the added OH–. If H+ is added, the acetate ion from the NaC2H3O2 is available to neutralize the added H+.

These two buffer systems are common ones used in many laboratories. Acids and Bases: Additional Concepts Topic 18 Buffers Defined These pH changes are insignificant when you compare them to the changes that occur in the unbuffered solution. These two buffer systems are common ones used in many laboratories. Blood has many buffer systems to maintain its constant pH of 7.4.

Acids and Bases: Additional Concepts Topic 18 Acid-Base Titrations The general process of determining the molarity of an acid or a base through the use of an acid-base reaction is called an acid-base titration. Click box to view movie clip.

Acids and Bases: Additional Concepts Topic 18 Acid-Base Titrations The known reactant molarity is used to find the unknown molarity of the other solution. Solutions of known molarity that are used in this fashion are called standard solutions. In a titration, the molarity of one of the reactants, acid or base, is known, but the other is unknown.

You know that NaOH and HCl react completely. Acids and Bases: Additional Concepts Topic 18 Acid-Base Titrations You know that NaOH and HCl react completely. You know the concentration of the NaOH solution, so it is your standard solution.

Acids and Bases: Additional Concepts Topic 18 Acid-Base Titrations You can use the reaction, the volumes of acid and base used, plus the molarity of the base to determine the molarity of the unlabeled HCl.

Determining Concentration: Using Stoichiometry Acids and Bases: Additional Concepts Topic 18 Determining Concentration: Using Stoichiometry From the balanced equation for the reaction, you know that one mole of HCl reacts with one mole of NaOH. Therefore, the number of moles of HCl in 20.0 mL of the HCl solution equals the number of moles of NaOH in 19.9 mL of 0.100M NaOH solution.

Determining Concentration: Using Stoichiometry Acids and Bases: Additional Concepts Topic 18 Determining Concentration: Using Stoichiometry Now, use the factor label method to solve this solution stoichiometry problem, just as you used it to solve other stoichiometry problems. Because you know the concentration of the NaOH solution, first find the number of moles of NaOH involved in the reaction.

Determining Concentration: Using Stoichiometry Acids and Bases: Additional Concepts Topic 18 Determining Concentration: Using Stoichiometry Next, examine the balanced equation for the reaction and determine that, because their coefficients are the same, equal numbers of moles of NaOH and HCl react.

Determining Concentration: Using Stoichiometry Acids and Bases: Additional Concepts Topic 18 Determining Concentration: Using Stoichiometry Because 1.99 x 10–3mol NaOH react, 1.99 x 10–3 mol HCl present in solution also react. Finally, use the volume to find the molarity of the acid.

Determining Concentration: Using Stoichiometry Acids and Bases: Additional Concepts Topic 18 Determining Concentration: Using Stoichiometry Based on your single titration, the molarity of the HCl solution is 0.0995M. However, before you put this value on the label, you probably would repeat the titration for several additional trials in order to verify your analysis and be more confident of the value on the label.

Acids and Bases: Additional Concepts Topic 18 Finding Molarity A 15.0-mL sample of a solution of H2SO4 with an unknown molarity is titrated with 32.4 mL of 0.145M NaOH to the bromothymol blue endpoint. Based upon this titration, what is the molarity of the sulfuric acid solution?

Acids and Bases: Additional Concepts Topic 18 Finding Molarity Because the molarity of the NaOH solution is known, the number of moles of NaOH involved in the titration can be calculated. The corresponding number of moles of H2SO4 can then be determined, and this figure can be used to calculate the molarity of the acid.

Acids and Bases: Additional Concepts Topic 18 Finding Molarity Write the balanced equation for the reaction. Remember that sulfuric acid is a diprotic acid. Because the concentration of the NaOH solution is known, find the number of moles of NaOH used in the titration.

Find the concentration of the H2SO4. Acids and Bases: Additional Concepts Topic 18 Finding Molarity Using the balanced equation, find the number of moles of H2SO4 that react with 4.70 x 10–3 mol NaOH. Find the concentration of the H2SO4.

Acids and Bases: Additional Concepts Topic 18 pH and pOH Because the concentrations of H+ ions are often very small numbers, the pH scale was developed as a more convenient way to express H+ ion concentrations. The pH of a solution equals the negative logarithm of the hydrogen ion concentration.

The pH scale has values from 0 to 14. Acids and Bases: Additional Concepts Topic 18 pH and pOH The pH scale has values from 0 to 14. Acidic solutions have pH values between 0 and 7, with a value of 0 being the most acidic. The pH of a basic solution is between 7 and 14 with 14 representing the most basic solution. A neutral solution has a pH of 7.

Acids and Bases: Additional Concepts Topic 18 pH and pOH Chemists have also defined a pOH scale to express the basicity of a solution. The pOH of a solution is the negative logarithm of the hydroxide ion concentration.

The following example problem shows you how to calculate pH and pOH. Acids and Bases: Additional Concepts Topic 18 pH and pOH If either pH or pOH is known, the other may be determined by using the following relationship. The pH and pOH values for a solution may be determined if either [H+] or [OH–] is known. The following example problem shows you how to calculate pH and pOH.

Calculating pH and pOH from [H+] Acids and Bases: Additional Concepts Topic 18 Calculating pH and pOH from [H+] If a certain carbonated soft drink has a hydrogen ion concentration of 7.3 x 10–4M, what are the pH and pOH of the soft drink? Because [H+] is given, it is easier to calculate pH first.

Calculating pH and pOH from [H+] Acids and Bases: Additional Concepts Topic 18 Calculating pH and pOH from [H+] A log table or calculator shows that log 7.3 = 0.86 and log 10–4 = – 4. Substitute these values in the equation for pH. The pH of the soft drink is 3.14.

Calculating pH and pOH from [H+] Acids and Bases: Additional Concepts Topic 18 Calculating pH and pOH from [H+] To find pOH, recall that pH + pOH = 14.00. Isolate pOH by subtracting pH from both sides of the equation.

Calculating pH and pOH from [H+] Acids and Bases: Additional Concepts Topic 18 Calculating pH and pOH from [H+] Substitute the value of pH and solve. The pOH of the solution is 10.86. As you might expect, the carbonated soft drink is acidic.

Calculating ion concentrations from pH Acids and Bases: Additional Concepts Topic 18 Calculating ion concentrations from pH When the pH of a solution is known, you can determine the concentrations of H+ and OH–. First, recall the equation for pH. Multiply both sides of the equation by –1.

Calculating ion concentrations from pH Acids and Bases: Additional Concepts Topic 18 Calculating ion concentrations from pH Now take the antilog of both sides of the equation. Rearrange the equation. A similar relationship exists between [OH–] and pOH.

Calculating [H+] and [OH–] from pH Acids and Bases: Additional Concepts Topic 18 Calculating [H+] and [OH–] from pH What are [H+] and [OH–] in an antacid solution with a pH of 9.70? Use pH to find [H+]. Use a log table or calculator to find that the antilog of – 9.70 is 2.0 x 10–10.

Calculating [H+] and [OH–] from pH Acids and Bases: Additional Concepts Topic 18 Calculating [H+] and [OH–] from pH To determine [OH–], first use the pH value to calculate pOH. Now use the equation relating [OH–] to pOH.

Calculating [H+] and [OH–] from pH Acids and Bases: Additional Concepts Topic 18 Calculating [H+] and [OH–] from pH A log table or calculator shows that the antilog of – 4.30 is 5.0 x 10–5. As expected, [OH–] > [H+] in this basic solution.

Additional Assessment Questions Topic 18 Question 1 A 0.100M LiOH solution was used to titrate an HBr solution of unknown concentration. At the endpoint, 21.0 mL of LiOH solution had neutralized 10.0 mL of HBr. What is the molarity of the HBr solution?

Additional Assessment Questions Topic 18 Answer 0.210M HBr

Additional Assessment Questions Topic 18 Question 2 Calculate the pH and pOH of aqueous solutions having the following ion concentrations.

Question 2a Answer 2a pH: 14.00; pOH: 0.00 Topic 18 Additional Assessment Questions Topic 18 Question 2a Answer 2a pH: 14.00; pOH: 0.00

Question 2b Answer 2b pH: 6.75; pOH: 7.25 Topic 18 Additional Assessment Questions Topic 18 Question 2b Answer 2b pH: 6.75; pOH: 7.25

Additional Assessment Questions Topic 18 Question 3 The pH is given for two solutions. Calculate [H+] and [OH–] in each solution.

Question 3a Answer 3a pH = 2.80 Topic 18 Additional Assessment Questions Topic 18 Question 3a pH = 2.80 Answer 3a

Question 3b Answer 3b pH = 13.19 Topic 18 Additional Assessment Questions Topic 18 Question 3b pH = 13.19 Answer 3b

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