Acids and Bases

Acids and Bases

ACIDS AND BASES 1 Weak Weak Stron g Acetic Acid 7 NH3 HCl

Stron g NaOH H2 O Acid Ex. HCl HSO3

H+ OH- Base Ex. NaOH KOH 14 ARRHENIUS ACIDS Substances that produce H+ (hydrogen ion, proton) in soln. Properties of acids are related to the H+ ions they

produce Increase H+ concentration when added to H2O Decrease OH- concentration when added to H2O Decreases pH, x<7 Turn blue litmus paper red Sour No effect on phenolphthalein, stays colorless React with certain metals to produce salt and H2 ARRHENIUS ACIDS Not all compounds that contain hydrogens are acids. Ex. CH3COOH : acetic acid, i.e. Vinegar

Only hydrogens in very polar bonds are ionizable. Hydrogen ions are stabilized by solvation. Some definitions: Monoprotic Acids acids that contain one ionizable hydrogen. Ex. HNO3 Diprotic Acids acids that contain two ionizable hydrogens. Ex. H2SO4 Triprotic Acids acids that contain three ionizable hydrogens. Ex. H3PO4 ARRHENIUS BASE Substances that produce OH- (hydroxide ion) in soln.

Properties of bases are related to the OH- ions they produce Increase OH- concentration when added to H2O Decrease H+ concentration when added to H2O Increases pH, x>7 Turn red litmus paper blue Bitter and slippery Turns colorless phenolphthalein, pink. Most bases are ionic compounds. Bronsted-Lowry Acid

Substances that DONATE H+ (hydrogen ion, proton) in rx. H2O is an acid b/c it gives up an H+ and becomes OH- (a base) Bronsted-Lowry Base Substances that

ACCEPT H+ in rx. NH3 is a base b/c it accepts the H+ and becomes NH4+ (an acid) Bronsted- Lowry Theory CONJUGATE ACIDS & BASES Conjugate - coupled, connected, or related, in

particular. In the case of the reverse reaction the conjugate acid is the acid; H+ donor on the product side the conjugate base is base; H+ acceptor on the product side. In essence, the reversible reaction of ammonia and water has two acids and two Bronsted- Lowry Theory CONJUGATE ACIDS & BASES

Which substance is the B-L acid (H+ donor)? Which substance is the B-L base (H+ acceptor)? What substance is the conjugate base? What substance is the conjugate acid? Bronsted- Lowry Theory CONJUGATE ACIDS & BASES Conjugate acids are always paired with a base, and conjugate bases are always paired with an

acid. A conjugate acid-base pair consists of two ions or molecules related by the loss or gain of one hydrogen ion. Bronsted- Lowry Theory CONJUGATE ACIDS & BASES Which substance is the B-L acid (H+ donor)? Which substance is the B-L base (H+ acceptor)?

What substance is the conjugate base? What substance is the conjugate acid? Bronsted- Lowry Theory CONJUGATE ACIDS & BASES Which substance is the B-L acid (H+ donor)? Which substance is the B-L base (H+ acceptor)? What substance is the conjugate base?

Bronsted- Lowry Theory AMPHOTERIC SUBSTANCES A substance that can act as either an acid or a base is said to be amphoteric. Water is amphoteric. In the reaction with hydrochloric acid, water accepts a proton and is therefore a base. In the reaction with ammonia, water donates a proton and is therefore an acid.

LEWIS ACIDS AND BASES A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond. A Lewis base is a substance that can donate a pair of electrons to form a covalent bond. The Lewis definitions include all the BrnstedLowry acids and bases. ACID BASE THEORIES SUMMARY Acid-Base Definitions Type Acid

Base Arrhenius H+ producer OH producer Brnsted-Lowry H+ donor Lewis H+ acceptor

electron-pair acceptor electron-pair donor PRACTICE PROBLEM Identify the Lewis acid and the Lewis base in this reaction between ammonia and boron trifluoride. NH3 + BF3 NH3BF3 When a Lewis acid reacts with a Lewis base, the base donates a pair of electrons and the acid accepts the donated pair. ADDITIONAL

PRACTICE PROBLEMS Identify the Lewis acid and Lewis base in each of the reactions. 1. H+ + H2O H3O+ 2. AlCl3 + Cl- AlCl43. Would you predict PCl3 to be a Lewis acid or a Lewis base in a typical reaction? Explain your prediction. 4. KOH + HBr KBr + H2O 5. HCl + H O H O+ + Cl- QUESTION #7 ON PAGE 593 7. Write equations for the ionization of HNO 3,in water and the reaction of CO32- with water. For

each equation, identify the hydrogen-ion donor and the hydrogen-ion acceptor. Then label the conjugate acid-base pairs in each equation. HNO3 + H2O H3O+ + NO3Hydrogen-ion donor (Acid): HNO3 Conjugate Base: NO3Hydrogen- ion acceptor (Base): H2O Conjugate Acid: H3O+ ACID BASE INDICATORS Substances that change colors in the presence of an acid or base. SECTION 2

Hydrogen Ions and Acidity ION PRODUCT CONSTANT FOR WATER The ionization of water is a reversible reaction, so Le Chteliers principle applies. Adding either hydrogen ions or hydroxide ions to an aqueous solution is a stress on the system. In response, the equilibrium will shift toward the formation of water. The concentration of the other ion will decrease.

ION PRODUCT CONSTANT FOR WATER The ionization of water is a reversible reaction, so Le Chteliers principle applies. In any aqueous solution, when [H+] increases, [OH] decreases. Likewise, when [H+] decreases, [OH] increases. ION PRODUCT CONSTANT FOR WATER Acidic HCl(aq) H+(aq) + Cl(aq) A solution in which [H+] is

greater than [OH] is an acidic solution. The [H+] is greater than 1 107M. Basic NaOH(aq) Na+(aq) + OH(aq) A basic solution is one in which [H+] is less than [OH]. The [H+] is less than 1 107M. AKA alkaline solutions ION PRODUCT CONSTANT

FOR WATER For aqueous solutions, the product of the hydrogen-ion concentration and the hydroxideion concentration equals 1.0 1014. The product of the concentrations of the hydrogen ions and the hydroxide ions in water is called the ion-product constant for water (Kw). Kw = [H+] [OH] = 1.0 1014 Sample Problem 19.2 USING THE ION PRODUCT CONSTANT FOR WATER

If the [H+] in a solution is 1.0 105M, is the solution acidic, basic, or neutral? What is the [OH] of this solution? [H+] is 1.0 105M, which is greater than 1.0 107M. Rearrange Kw = [H+] [OH] [OH] = Kw [H+] [OH ] = 1.0 109M

RELATING PH TO H ION CONCENTRATION + Mathematically, pH is defined as the log of H+ ion concentration of a soln. pH = -log[H+] or [H+] = 10-pH pH is a measure of how much H+ are in a solution . If H+ concen. Is not given as 1 x 10-x : Ex. [H+] = 5.4 x 10-8M pH = -log(5.4 x 10-8) = 7.3

CALCULATING PH To calculate the pH of an aqueous solution you need to know the concentration of the hydronium ion in moles per liter (molarity). The pH is then calculated using the expression: pH = - log [H3O+] Example: Find the pH of a 0.0025 M HCl solution. The HCl is a strong acid and is 100% ionized in water. The hydronium ion concentration is 0.0025 M. Thus: pH = - log (0.0025) = - ( - 2.60) = 2.60

CALCULATING PH MORE PROBLEMS Example: What is the pH of a solution with a hydrogen-ion concentration of 4.2 1010M? pH = - log [H3O+] pH = - log [4.2 x 10-10M] pH = - (-9.37675) pH = 9.38 (Base) BELL RINGER ACTIVITY 1.

2. pH = - log [H3O+] CALCULATING THE HYDRONIUM ION CONCENTRATION FROM PH The hydronium ion concentration can be found from the pH by the reverse of the mathematical operation employed to find the pH. [H3O+] = 10-pH Example: What is the hydronium ion concentration in a solution that has a pH of 8.34? 8.34 = - log [H3O+]

- 8.34 = log [H3O+] + -8.34 -9 CALCULATING THE HYDRONIUM ION CONCENTRATION FROM PH The pH of an unknown solution is 6.35. What is the hydrogen-ion concentration? 6.35 = - log [H3O+] - 6.35 = log [H3O+]

[H3O+]= 10-6.35 = 4.5 x 10-7 M Practice Problems Calculate the [H+] for each solution. A. pH = 5.00 B. pH = 12.38 When the pH is a whole number, you can assume the coefficient to be 1 When the pH is a decimal, use the antilog. What are the hydrogen ion concentrations for solutions with the following pH values? C. pH = 4.00

D. pH = 11.55 Relationship between pH and pOH. pH scale ranges from 014. For aqueous solutions, the product of the hydrogenion concentration and the hydroxide-ion concentration equals 1.0 1014. [H+] + [OH] = 1.0 1014

CALCULATING POH To calculate the pOH of a solution you need to know the concentration of the hydroxide ion in moles per liter (molarity). The pOH is then calculated using the expression: pOH = - log [OH-] Example: What is the pOH of a solution that has a hydroxide ion concentration of 4.82 x 10-5 M? pOH = - log [4.82 x 10-5] = - ( - 4.32) = 4.32

CALCULATING PH FROM [OH] If you know the [OH] of a solution, you can find its pH. 1. You can use the ion-product constant to determine [H+] for a known [OH]. 2. Then you use [H+] to calculate the pH. PRACTICE PROBLEM What is the pH of a solution if the [OH-] = 4.0 x 10-11M? 1. Start with the ion-product constant to find

Kw [H+]. + + Kw = [OH ] [H ] [H ] = [OH ] 2. Rearrange the equation to solve for [H ].

14 1.0 10 = 0.25 103M 3. [H+] = 4.0 1011 + [H+] = 2.5 104M 4. pH = log[H+]

= log(2.5 104) = (3.60205) pH = 3.60 PRACTICE PROBLEMS 1. Calculate the pH of each solution A. [OH-] = 4.3 x 10-5M B. [OH-] = 4.3 x 10-11M 2. Calculate the pH of each solution A. [H+] = 5.0 x 10-5M B. [H+] = 8.3 x 10-10M

MORE PRACTICE PROBLEMS Find the pH and the pOH of each solution. A. [H+] = 1 x 10-4M B. [H+] = 0.0015M What are the pH and pOH values of the following solutions, based on their hydrogen-ion concentrations? C. [H+] = 1 x 10-12M D.[H+] = 0.045M Use either pH Calculations worksheet #1 or #2 here Complete Topic 8 Acids, Bases, and Salts note packet page 146, practice problems # 26-29.

RELATIVE H CONCENTRATIONS OF SOLUTIONS The lower the pH, the more H+ ions are in a soln. + As [H+] in a soln. increases, pH of the soln. decreases. Ex. A soln. with a pH of 3 has more H+ ions then a soln. of pH 4 Difference in H+ of two soln. = 10

That Means: (difference in pH) RELATIVE H+ CONCENTRATIONS OF SOLN. Complete Topic 8 Acids, Bases, and Salts note packet page 146, practice problems # 30-32. STRONG VS WEAK ACIDS Determined by degree in which the acid dissociates in water. Strong Acid completely ionized in aqueous

soln. HCl(g) + H2O(l) H3O+(aq) + Cl High concentration of H3O+ (aq) Ex. Weak Acid partially ionized in aqueous soln. + + Low concentration of H O

3 CH3COOH(aq) + H2O(l) H3O (aq) + CHEx. COO(aq) 3 ACID DISSOCIATIONK a CONSTANT; Acid dissociation constant (Ka) is the ratio of the concentration of the dissociated form of an acid to the

concentration of the undissociated form. Ka reflects the fraction of an acid that is ionized Ka = Weak acids have small Ka values. Strong acids have large Ka values. Dissociation/ ionization is more complete Example: Nitrous acid (HNO2) has a Ka of 4.4 104 : strong Ethanoic acid (CH3COOH) has a Ka of 1.8 105 : weak ACID DISSOCIATION K a

CONSTANT; Example CH3COOH(aq) + H2O(l) H3O+(aq) + CH3COO(aq) [H O+] [CH COO] 3 3 Keq= [CH3COOH] [H2O] CALCULATING DISSOCIATION CONSTANTS

You can find the Ka of an acid in water by substituting the equilibrium concentrations of the acid, [HA], the anion from the dissociation of the acid, [A], and the hydrogen ion, [H+], into the equation below. [H+][A] Ka = [HA] CALCULATING DISSOCIATION CONSTANTS

In a 0.1000M solution of ethanoic acid, [H+] = 1.34 103M. Calculate the Ka of this acid. Refer to the table for the ionization equation for ethanoic acid. 1. Start by determining the equilibrium concentration of the ions. + 3 [H ] = [CH3COO ] = 1.34 10 M (0.1000 0.00134)M = 0.0987M

Concentration [CH3COOH] [H+] [CH3COO] Initial 0.1000 0

0 Change 1.34 103 1.34 103 1.34 103 Equilibrium

0.0987 1.34 103 1.34 103 STRONG VS WEAK BASES Determined by degree in which the metal ions and hydroxide ions dissociate in water. Strong Base completely ionized in aqueous soln. NaOH(aq) + H2O(l) OH-(aq) + Ex.

Na+(aq) Weak Acid partially ionized in aqueous soln. + NH3(aq) + H2O(l) NH4 (aq) + OH(aq) Ex. Bas Conjugat Conjugat Aci e d

e Acid e Base NEUTRALIZATION A rx between an acid and a base to produce water and a salt. Generally a double replacement reaction TITRATION A lab process used for determining the concen. Of an unknown soln. by reacting it

with a soln. of known concen. Involves an acid and a base When moles of H+ and OH- are equal, neutralization has occurred, and the endpoint of the titrations is reached. Indicators are used to identify the endpoint. Change in indicator color = endpoint reached. SALTS Ionic compounds composed of a positive ion (other than H+) and a negative ion (other than OH-) Salt is one of the products of an acid-base

neutralization rx Salts are electrolytes (conduct electricity when dissolved in H2O) Soluble salts are better electrolytes than insoluble salts Table F can be used to determine soluble and insoluble salts ELECTROLYTES Substances that can conduct electricity when dissolved in H2O Dissolve in H2O to produce a

soln. with + and ions. Conduct electricity b/c of mobile ions in the soln. Acids (Table K), bases (Table L), and salts are electrolytes

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