Ch 10: Acids and Bases and Equilibrium
Naming Acids
-Acids with a hydrogen ion (H+) and a nonmetal (or CN-) ion are named with the prefix hydro and end with ic acid. HCL hydrochloric acid -Acids with a hydrogen ion (H+) and a polyatomic ion are named by changing the end of the name of the polyatomic ion from ATE to IC ACID or ITE to OUS ACID ClO3- chlorate ClO2- chlorite HClO3 chloric acid HClO2 chlorous acid
Weak Acids Table 10.3
-Make up most of the acids -Have strong conjugate base pairs
10.6 Reactions of Acids and Bases
Gastric acid contains HCl and is produced by parietal cells that line the stomach. When protein enters the stomach, HCl is secreted until the pH reaches 2, optimum for digestion.
NH3, a Bronsted-Lowry Base
In the reaction of ammonia and water, -NH3 acts as the base that accepts H+ -H2O acts as the acid that donates H+
Strong Acids: Table 10.3
There are six common strong acids.
Strong vs. Weak Acids
-A STRONG ACID completely ionizes (100%) in aqueous solutions. HCl(g) + H2O(l) --------> H3O+(aq) + Cl-(aq) -A WEAK ACID dissociates only slightly in water to form a few ions in aqueous solutions. H2CO3(aq) + H2O(l) -------->H3O+ + HCO3-(aq)
Strong and Weak Acids
-In an HCl solution, the strong acid HCl dissociates 100% to form H+ and Cl-. -A solution of the weak acid HC2H3O2 contains mostly molecules of HC2H3O2 and a few ions of H+ and C2H3O2-.
10.3 Acid-Base Equilibrium
-Oxygen transport involves an equilibrium between hemoglobin (Hb), oxygen, and oxyhemoglobin (HbO2). Hb(aq) + O2(g)------> HbO2(aq) Hypoxia may occur at high altitudes with a lower oxygen concentration.
10.5: The pH Scale
-The pH scale is used to describe the acidity of solutions. Cranberry juice is very acidic, with a pH of 2.9.
10.2: Strengths of Acids and Bases
-Weak acids only partially dissociate in water. -Hydrofluoric acid (HF) is the only halogen that is a weak acid.
Study Check: 1. Write the conjugate base for each of the following acids: A. HBr B. H2S C. H2CO3 2. Write the conjugate acid for each of the following bases: A. NO2- B. NH3 C. OH-
1. A) H+ + Br- B) H+ + HS- C) H+ + HCO3- 2. A) HNO2 B) NH4+ C) H2O
Study Check: Select the correct name for each of the following acids: 1. HBr 2. H2CO3 3. HBrO2
1. Br-, bromide HYDROBROMIC ACID 2. CO3^2-, carbonate CARBONIC ACID 3. HBrO2 BrO2-, bromite BROMOUS ACID
pH of Common Substances
On the pH scale, values below 7.0 are acidic, a value of 7.0 is neutral, and values above 7.0 are basic.
Study Check: What is the molarity of an HCl solution if 25.5 mL of 0.438 M NaOH is required to neutralize 0.0250L of HCl? HCl(aq) + NaOH(aq) ----> NaCl(aq) + H2O(l)
1. 2. 3. 4.
Components of a Buffer
A BUFFER SOLUTION -contains a combination of acid-base conjugate pairs, a weak acid and a salt of its conjugate base such as HC2H3O2(aq) and C2H3O2-(aq) weak acid salt of conjugate base -has equal concentrations of a weak acid and its salt.
Study Check: which of the following combinations make a buffer solution? A. HCl and KCl B. H2CO3 and NaHCO3 C. H3PO4 and NaCl D. HC2H3O2 and KC2H3O2
A buffer consists of a weak acid and a salt of its conjugate base. A. Not a buffer B. buffer, a weak acid and its salt C. Not a buffer D. buffer, a weak acid and its salt.
10.7 Buffers
A buffer solution maintains the pH by neutralizing small amounts of added acid or base. An acid must be present to react with any OH- added, and a base must be present to react with any H3O+ added.
Study Check: Identify each solution as ACIDIC, BASIC, or NEUTRAL. A. _____________HCl with a pH = 1.5 B. _____________ pancreatic fluid, [H3O+]= 1 x 10^-8M C. ____________ Sprite soft drink, pH=3.0 D. ____________ pH=7.0 E. ____________[OH-]= 3 x 10^-10M F. ____________ [H3O+]= 5 x 10^-12
A. Acidic B. Basic C. Acidic D. Neutral E. Acidic F. Basic
Endpoint of Titration
At the ENDPOINT, -the moles of base are equal to the moles of acid in the solution. -the concentration of the base is known. -the volume of the base used to reach the endpoint is measured. -the molarity of the acid is calculated using the neutralization equation for the reaction.
Buffers
When an acid or base is added to water, the pH changes drastically. In a BUFFER SOLUTION, the pH is maintained; the pH does not change when acid or base is added.
pH Calculation: If a solution of aspirin has a [H3O+] = 1.7 x 10^-3M, what is the pH of the solution?
1. GIVEN: [H3O+]= 1.7 x 10^-3M NEED: pH KNOW: pH=-log[H3O+] 2. pH=-log[H3O+]= -log[1.7 x 10^-3] PROCEDURE: Enter 1.7 and press EE or Exp. Calculator Display: 1.7^00 or 1.700 or 1.7E00 Enter 3 and press +/- to change sign Calculator Display: 1.7^-03 or 1.7-03 or 1.7E-03 3. PROEDURE: log +/- Calculator Display: 2.769551079 Combining Steps: pH= -log[1.7 x 10^-3] = 1.7 EE or Exp. 3 +/- log +/- =2.769551079 COEFFICIENT: POWER of 10 1.7 x 10^-3M H=-log[1.7 x 10^-3M] = 2.77
Study Check: Match the formulas with their names. 1. ____________HNO2 2. ____________Ca(OH)2 3. ____________H2SO4 4. ___________HIO3 5. __________NaOH
1. NITROUS ACID 2. CALCIUM HYDROXIDE 3. SULFURIC ACID 4. IODIC ACID 5. SODIUM HYDROXIDE
Study Check: An important reaction in the body fluid is H2CO3(aq) + H2O(l)------> H3O+(aq) + HCO3-(aq) <----- Use Le Chatelier's principle to predict whether the system shifts in the direction of PRODUCTS or REACTANTS for each of the following: A. Adding some H3CO3(aq) B. Removing some HCO3-(aq) C. Adding some H3O+(aq)
A. Adding some H2CO3(aq) -The concentration of the reactant H2CO3 increases -The rate of the forward reaction increases to shift the system in the direction of the PRODUCTS until equilibrium is reestablished. B. Removing some HCO3-(aq) -When the concentration of the product HCO3- decreases, the rate of the reverse reaction decreases. -The system shifts in the direction of the PRODUCTS until equilibrium is reestablished. C. Adding some H3O+(aq) -When the concentration of the product H3O+ increases, the rate of the reverse reaction increases. -The system shifts in the direction of the REACTANTS until equilibrium is reestablished.
Study Check: Complete each of the following with EQUAL, or NOT EQUAL, FASTER or SLOWER, or CHANGE or DO NOT CHANGE: A. Before equilibrium is reached, the concentrations of the reactants and products __________________________________. B. Initially, reactants have a rate of reaction ______________________ than the rate of reaction of the products. C. At equilibrium, the rate of the forward reaction is ________________________ to the rate of the reverse reaction. D. At equilibrium, the concentrations of the reactants and products _______________________________.
A. CHANGE B. FASTER C. EQUAL D. DO NOT CHANGE.
Study Check: Use Table 10.3, identify the stronger acid in each pair. A. HNO2 or H2S B. HCO3- or HBr C. H3PO4 or H3O+
A. HNO2 is the stronger acid B. HBr is the stronger acid C. H3O+ is the stronger acid.
Study Check: In each of the following equations, identify the Bronsted-Lowry acid and base in the reactants: A. HNO3(aq) + H2O (l)-------> H3O+(aq) + NO3-(aq) B. HF(aq) + H2O (l) ----------> H3O+(aq) + F-(aq)
A. HNO3(aq) acid; H2O(l) base B. HF(aq) acid; H2O(l) base
Study Check: Write balanced equations for the following reactions: A. MgCO3(s) + HBr(aq)------> B. HCl(aq) + NaHCO3(aq)------>
A. MgBr2(aq) + CO2(g) + H2O(l) B. NaCl(aq) + CO2(g) + H2O(l)
Study Check: Identify each of the following as a strong or weak acid or base: A. HBr B. HNO2 C. NaOH D. H2SO4 E. Cu(OH)2
A. Strong acid B. Weak acid C. Strong base D. Strong acid E. Weak base
Study Check: Determine the [H3O+] for solutions having each of the following pH values: A. 3.0 B. 3.42
A. [H3O+]= 1 x 10^-3M B. 1.GIVEN: pH=3.42 NEED: [H3O+] KNOW: [H3O+]=10^-pH 3.42 +/- Calculator Display: -3.42 2. 2nd 10^x or inv log Calculator Display: 3.801893963^-04 or 3.801893963E^-04 3. [H3O+]= 3.8 x 10^-4M
10.1 Acids
ARRHENIUS ACIDS: -produce hydrogen ions (H+) ions when they dissolve in water. -are also electrolytes because they produce H+ in water -have a sour taste -turn blue litmus red -corrode some metals
Bases
ARRHENIUS BASES -produce hydroxide ions (OH-) in water -taste bitter or chalky -are also electrolytes because they produce hydroxide ions (OH-) in water -feel soapy and slippery -turn litmus indicator paper blue and phenolphthalein indicator pink.
Bronsted-Lowry Acids and Bases
According to the Bronsted-Lowry theory, -an acid is a substance that donates H+ -a base is a substance that accepts H+
Acids, Carbonates, Bicarbonates
Acids react -with carbonates and hydrogen carbonates -to produce carbon dioxide gas, a salt, and water.
Reactions of Acids
Acids react with -metals to produce salt and hydrogen gas -bases to produce a salt and water -bicarbonate and carbonate ions to produce carbon dioxide gas. A salt is an ionic compound that does not have H+ as the cation or OH- as the anion.
Acids and Metals
Acids react with metals -such as K, Na, Ca, Mg, Al, Zn, Fe, and Sn -to produce hydrogen gas and the salt of the metal.
Basic Solutions
Adding a base to pure water -increases the [OH-] -causes the [OH-] to exceed 1.0 x 10^-7M -decreases the [H3O+] [H3O+] < [OH-] The solution is basic
Acidic Solutions
Adding an acid to pure water -increases the [H3O+] -causes the [H3O+] to exceed 1.0 x 10^-7M -decreases the [OH-] [H3O+] > [OH-] The solution is acidic
How Buffers Work
Buffers work because -they resist changes in pH from the solution of acid or base. -in the body, they absorb H3O+ or OH- from foods and cellular processes to maintain pH. -they are important in the proper functioning of cells and blood -they maintain a pH close to 7.4 in blood. A change in the pH of the blood affects the uptake of oxygen and cellular processes.
Working Buffers
Buffers work because the weak acid in a buffer neutralizes bases and the conjugate base in the buffer neutralizes acids. The buffer described here consists of about equal concentrations of acetic acid (HC2H3O2) and its conjugate base, acetate ion (C2H3O2-). -Adding H3O+ to the buffer reacts with C2H3O2- whereas adding OH- neutralizes HC2H3O2. -The pH of the solution is maintained as long as the added amounts of acid or base are small compared to the concentrations of the buffer components.
Concentration Changes, Equilibrium
Given the equilibrium reaction, adding MORE HF, HF(aq) + H2O(l)------> F-(aq) + H3O+(aq) -increases the concentration of HF -puts stress on the system that is relieved by increasing the rate of the forward reaction add HF HF(aq) + H2O(l)------> F-(aq) + H3O+(aq) -Le Chatelier's principle states that adding more reactant causes the system to shift the direction of the products until equilibrium is reestablished. Given the equilibrium reaction, removing some of the HF Remove HF HF(aq)+ H2O(l)------> F-(aq) + H3O+(aq) -Le Chatelier's principle states that the stress of removing some of the reactant causes the system to shift in the direction of the reactants until equilibrium is reestablished. Given the equilibrium reaction, adding MORE F- HF(aq) + H2O(l)------> F-(aq) + H3O+(aq) <------ -increases the concentration of F- -puts stress on the system that is relieved by increasing the rate of the reverse reaction HF(aq) + H2O(l)------> F-(aq) + H3O+(aq) <----- Add F- Le Chatelier's principle states that the addition of more product to the system causes the system to shift in the direction of the reactants.
10.4 Dissociation of Water
H2O(l) + H2O(l)------> H3O+(aq) + OH-(aq)
Weak Acids
In WEAK ACIDS, -only a few molecules dissociate -most of the weak acid remains as the undissociated (molecular) form of the acid. -the concentration of the H3O+ and the anion (A-) are small. H2CO3(aq) + H2O(l) -->H3O+(aq) + HCO3-(aq)
Acids and Hydroxides: Neutralization
In a neutralization reaction, -an acid reacts with a base to produce salt and water -the salt formed is the anion from the acid and the cation from the base. HCl(aq) + NaOH(aq)------> NaCl(aq) + H2O(l)
Equilibrium
In an equilibrium reaction, -two reactions are taking place -a reversible reaction proceeds in both the forward and reverse directions. FORWARD REACTION: HF(aq) + H2O(l)----->F-(aq) + H3O+(aq) REVERSE REACTION: F-(aq) + H3O+(aq)----->HF(aq) + H2O(l) Equilibrium is reached when -there are no further changes in the concentrations of the reactants and products. -the rate of the forward reaction is equal to the rate of the reverse reaction.
Conjugate Acid-Base Pairs
In any acid-base reaction, there are two conjugate acid-base pairs, and -each pair is related by the loss and gain of H+ -one pair occurs in the forward direction -one pair occurs in the reverse direction In this acid-base reaction, -the first conjugate acid-base pair is HF, which donates H+ to form its conjugate base, F- -the other conjugate acid-base pair is H2O, which accepts H+ to form its conjugate acid, H3O+ -each pair is related by a loss and gain of H+ In the reaction, NH3 and H2O, -one conjugate acid-base pair is NH3/NH4+ -the other conjugate acid-base pair is H2O/H3O+
Neutralization Reactions
In neutralization reactions, one H+ always reacts with one OH-. -If we write the strong acid and strong base as ions, we see that H+ reacts with OH- to form water, leaving the ions Na+ and Cl- in solution: H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)----> Na+(aq) + Cl-(aq) + H2O(l) -The overall reaction occurs as the H+ from the acid and OH- from the base form water: H+(aq) + OH-(aq)----> H2O(l) Net ionic equation
Pure Water Is Neutral
In pure water, the ionization of water molecules produces small but equal quantities of H3O+ and OH- ions. [H3O+] = 1.0 X 10^-7M [OH-]= 1.0 X 10^-7M [H3O+] = [OH-] Pure water is neutral
Concentration Changes, Equilibrium: Table 10.4
In summary, Le Chatelier's principle indicates that a stress caused by adding a substance at equilibrium is relieved when the system shifts the reaction away from that substance.
How Buffers Work
In the buffer with acetic acid (HC2H3O2) nd sodium acetate (NaC2H3O2), -the salt produces acetate ions and sodium ions NaC2H3O2(aq)----> C2H3O2-(aq) + Na+(aq) -the salt is added to provide a higher concentration of the conjugate base C2H3O2- than from the weak acid alone HC2H3O2(aq) + H2O(l) -----> C2H3O2-(aq) + H3O+ (aq) <----- Large amount Large amount
Strong Acids
In water, the dissolved molecules of HA, a STRONG ACID, -dissociate into ions 100% -give large concentrations of H3O+ and the anion (A-) HCl(g) + H2O(l) ------> H3O+(aq) + Cl-(aq)
Acid-Base Titration Calculations: What is the molarity of an HCl solution if 18.5 mL of 0.225M NaOH is required to neutralize 0.0100L of HCl? HCl(aq) + NaOH(aq) ------> NaCl(aq) + H2O(l)
SOLUTION: 1. 2. 3. 4.
Study Check: Find the pH of a solution with a [H3O+] of 4.0 x 10^-5.
STEP 1: STEP 2: STEP 3:
Study Check: Select the correct group of coefficients for each of the following neutralization reactions. 1. HCl(aq) + Al(OH)3(aq)----> AlCl3(aq) + H2O(l) 2. Ba(OH)2(aq) + H3PO4(aq)----> Ba3(PO4)2(s) + H2O(l)
STEP 1: 1. HCl(aq) + Al(OH)3(aq)----> salt + H2O(l) 2. Ba(OH)2(aq) + H3PO4(aq)----> salt + H2O(l) STEP 2: 1. 3HCl(aq) + Al(OH)3(aq)----> salt + H2O(l) 2. 3Ba(OH)2(aq) + 2H3PO4(aq)----> salt + H2O(l) STEP 3: 1. 3HCl(aq) + Al(OH)3(aq)----> salt + 3H2O(l) 2. 3Ba(OH)2(aq) + 2H3PO4(aq)----> salt + 6H2O(l) STEP 4: 1. 3HCl(aq) + Al(OH)3(aq)----> AlCl3(aq) + 3H2O(l) ANSWER: 3, 1, 1, 3 2. 3Ba(OH)2(aq) + 2H3PO4(aq)--->Ba3(PO4)2(s) + 6H2O(l) ANSWER: 3, 2, 1, 6
Guide to Writing Conjugate Acid-Base Pairs
STEP 1: Identify the reactant that loses H+ as the acid. STEP 2: Identify the reactant that gives H+ as the base. STEP 3: Write the conjugate acid-base pairs.
Guide to Calculating [H3O+] and [OH-] in Aqueous Solutions
STEP 1: State the given and needed quantities STEP 2: Write the Kw, for water and solve for the unknown [H3O+] or [OH-] STEP 3: Substitute the known [H3O+] or [OH-] into the equation and calculate.
Guide to Calculations for Acid-Base Titrations
STEP 1: State the given and needed quantities STEP 2: Write a plan to calculate the molarity or volume. STEP 3: State equalities and conversion factors, including concentrations. STEP 4: Set up the problem to calculate the needed quantity.
Guide to Calculating [H3O+] from pH
STEP 1: State the given and needed quantities. STEP 2: Enter the pH value into the inverse log equation and change the sign. STEP 3: Adjust the SFs in the coefficient.
Guide to Calculating the pH of a Solution
STEP 1: State the given and needed quantities. STEP 2: enter the [H3O+] into the pH equation STEP 3: Press the log key and change the sign. Adjust the number of SFs on the right of the decimal point.
Study Check: If lemon juice has [H3O+] of 2.0 x 10^-3M, what is the [OH-] of the solution?
STEP 1: State the given and needed quantities. Given: [H3O+]= 2.0 x 10^-3M Need: [OH-] Known: Kw= [H3O+][OH-]= 1.0 x 10^-14 STEP 2: Write the Kw, for water and solve for the unknown [H3O+] or [OH-]. Kw= [H3O+][OH-]= 1.0 x 10^-14 [OH-]= Kw/[H3O+] STEP 3: Substitute known [H3O+] or [OH-] and calculate. [OH-]= 1.0 x 10^-14/[2.0 x 10^-3]= 5.0 x 10^-12M Because the [H3O+] concentration 2.0 x 10^-3M is greater than the [OH-] of 5.0 x 10^-12M, the solution is acidic.
Balancing Neutralization Reactions: Write the balanced equation for the neutralization of solid magnesium hydroxide and nitric acid.
STEP 1: Write the reactants and products. STEP 2: Balance the H+ in the acid with the OH- in the base. STEP 3: Balance the H2O with the H+ and the OH-. STEP 4: Write the salt from the remaining ions.
Guide for Balancing Neutralization Reactions
STEP 1: Write the reactants and products. STEP 2: Balance the H+ in the acid with the OH- in the base. STEP 3: Balance the H2O with the H+ and the OH-. STEP 4: Write the salt from the remaining ions.
Strong Bases
STRONG BASES -are formed from metals of Groups 1A(1) and 2A(2) -include LiOH, NaOH, KOH, Ba(OH)2, Sr(OH)2, and Ca(OH)2. -dissociate completely in water. KOH(s)------> K+(aq) + OH-(aq)
Acid-Base Titration
TITRATION -is a laboratory procedure used to determine the molarity of an acid. -uses a base such as NaOH to neutralize a measured volume of an acid. -requires a few drops of an indicator such as phenolphthalein to identify the endpoint. In the following titration, a specific volume of acidic solution is titrated to the endpoint with a known concentration of NaOH.
Names of Common Acids Table 10.1
Table 10.1: Names of Common Acids and their Anions
Indicator
The INDICATOR phenolphthalein -is added to identify the endpoint -turns pink when the solution is neutralized.
Function of Conjugate Base in a Buffer
The function of the acetate ion, C2H3O2-, is to neutralize H3O+ from acids. The acetic acid produced contributes to the available weak acid.
Function of a Weak Acid in a Buffer
The function of the weak acid in a buffer is to neutralize a base. the acetate ion produced in the neutralization reaction adds to the concentration of acetate already in solution from the salt. HC2H3O2 + OH- -----> C2H3O2- + H2O acetic acid base acetate ion water
Ion Product Constant, Kw
The ion product constant for water, Kw, is defined -as the product of the concentrations of H3O+ and OH- -as equal to 1.0 X 10^-14 at 25 degrees C (the concentration units are omitted). When -the [H3O+] and [OH-] are equal, the solution is neutral -the [H3O+] is greater than the [OH-], the solution is acidic -the [OH-] is greater than the [H3O+], the solution is basic
The pH Scale
The pH of a solution -is used to indicate the acidity of a solution. -has values that usually range from 0 to 14. -is ACIDIC when the values are less than 7. -is NEUTRAL at a value of 7. -is BASIC when the values are greater than 7. ACIDIC SOLUTION pH<7 [H3O+]> 1 x 10^-7M NEUTRAL SOLUTION pH=7.0 [H3O+]= 1 x 10^-7M BASIC SOLUTION pH>7 [H3O+]< 1 x 10^-7M
pH Measurement
The pH of a solution can be determined using (a) a pH meter, (b) pH paper, and (c) indicators that turn different colors corresponding to different pH values.
The pH scale
The pH of a solution is commonly measured using -a pH meter in the laboratory -pH paper, an indicator that turns specific colors at specific pH values. The pH of a solution is found by comparing the colors of indicator paper to a chart.
Calculating the pH of Solutions
The pH scale -is a logarithmic scale that corresponds to the [H3O+] of aqueous solutions. -is the negative logarithm (base 10) of the [H3O+] pH= -log[H3O+] -To calculate the pH, the negative powers of 10 in the molar concentrations are converted to positive numbers. If [H3O+] is 1.0 x 10^-2M, pH= -log[1.0 x 10^-2]= -(-2.00)= 2.00
Naming Bases
Typical Arrhenius bases are named as hydroxides. NaOH SODIUM HYDROXIDE KOH POTASSIUM HYDROXIDE Ba(OH)2 BARIUM HYDROXIDE Al(OH)3 ALUMINUM HYDROXIDE
Ionization of Water
Water is AMPHOTERIC-it can act as an acid or a base. In water, -H+ is transferred from one H2O molecule to another -one molecule acts as an acid, while another acts as a base. -equilibrium is reached between the conjugate acid-base pairs.
Calculating [H3O+]
What is the [H3O+] of a solution if [OH-] is 5.0 x 10^-8M? SOLUTION: 1. State the given and needed quantities. 2.Write the Kw, for water and solve for the unknown [H3O+] or [OH-] 3. Substitute the known [H3O+] or [OH-] and calculate.
Le Chatelier's Principle
When we alter the concentration of a reactant or product of a system at equilibrium, -the rates of the forward and reverse reactions will no longer be equal. -a stress is placed on the equilibrium. Le CHATELIER'S PRINCIPLE: states that when equilibrium is disturbed, the rates of the forward and reverse reactions change to relieve that stress and reestablish equilibrium.