Ch.15 - Acid and Base EquilibriumWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

In the 1920s, Gilbert Lewis proposed a new set of definitions for acids and bases. 

Understanding Lewis Acids and Bases

According to the Lewis definition an acid is an electron pair acceptor. 

Concept #1: Understanding Lewis Acids. 

When hydrogen is connected to an electronegative element such as P, O, N, S or halogens then it gains a partially positive charge, which makes hydrogen act as a Lewis acid. 

Since these metal ions accept negative electron pairs then some Lewis Acids may be positively charged. 

If the central element has less than 8 valence electrons around it then it is more likely to accept an electron pair to follow the octet rule. 

According to the Lewis definition a base is an electron pair donor. 

Concept #2: Understanding Lewis Bases. 

Compounds that have lone pair(s) on a central element can act as Lewis bases. 

Compounds that possess a negative charge can act as Lewis Bases. 

Example #1: Identify each of the compounds in the following chemical equation.

Practice: Identify the Lewis acids and bases in the following reactions.

a) H+ + OH ⇌ H2O

b) Cl + BCl3 ⇋ BCl4

c) SO3 + H2O ⇌ H2SO4

Practice: Identify each of the following compounds as either a Lewis acid, a Lewis base or neither.

a)  ZnCl2                                                                                                           b)  CN 

 

c)  NH4+                                                                                                           d) Co3+

Additional Problems
Which of the following is a Lewis base? A) AlF3 B) H2O C) SiF4 D) C5H12 E) None of the above are Lewis bases.
Which species in the following reaction acts as a Lewis acid?             CuSO4(s) + 4NH3(aq) ⇌ [Cu(NH3)4]2+(aq) + SO42−(aq)       A) Cu2+           B) SO42−          C) [Cu(NH3)4]2+(aq)               D) NH3 E) [Cu(NH3)4]2+(aq) and SO42−
Which of the following are Lewis bases? I)         BCl3 II)        H− III)       H2O IV)       NH3 V)        AlCl3        A) I), II), and IV) B) I), II), and III) C) II), III) and IV) D) I), II), and V) E) III), IV) and V)
Which of the following characteristics is/are  potential identifiers of a Lewis acid? I.  Unfilled octet  II. Double bond present  III. Compounds with metal and hydroxide  A.  Only I       B.  Only II       C.  II and III       D.  I and II       E.  All three
NCl3 would be described as: A) Lewis acid because it can donate electrons B) Lewis acid because it can receive electrons C) Lewis base because it can donate electrons D) Lewis base because it can receive electrons E) This compound is neither acidic or basic
All are examples of Lewis acid-base reactions except: A. Cu2+(aq) + 4NH3(aq)   ⇌   [Cu(NH3)4] 2+(aq) B. HCl(aq) + NH3(aq)   ⇌   NH4Cl(aq) C. H+ (aq) + OH- (aq)   ⇌   H2O(l) D. 2Na(s) + Cl2(g)   ⇌   2NaCl(s)
All are potential Lewis bases except:   A. Ammonia B. Water C. Methane (CH4) D. Cyanide ion (CN-)
Which of the following is the definition of a base in the Lewis system? a. A base is a substance that can accept an H + ion. b. A base is a substance that, when dissolved in water, produces hydroxide ions. c. A base is a substance that contains OH - in its chemical formula d. A base is a substance that that can accept a pair of electrons e. A base is a substance that can donate a pair of electrons.
Which of the following can be a potential Lewis base? a. Ca +2 b. CH4 c. H + d. NH3 e. H3O +
What is the most accurate and complete description of a Lewis Acid? A. proton donor B. proton acceptor C. electron donor D. electron acceptor
In the reaction  SnCl4 + 2Cl− → SnCl62-  identify the Lewis Acid. 1. Cl− 2. SnCl4 3. SnCl62-
True or false: SO3 is a stronger Lewis acid than SO2.
Identify the Lewis acid and Lewis base in the following reactions: (a) CH3OH + H3O+ ⇌ CH3OH2+ + H2O (b) BF3 + NH3 → BF3- + NH3+ (c) Cl2 + AlCl3 → AlCl5  
Draw the product(s) of the following acid-base reaction. Include all lone pairs and formal charges. Use curved arrow(s) to show the electron movement that lead to the formation of the product(s). Finally, label (1) the acid and (2) the base.
The second step in a synthesis of isoamyl acetate, an ester commonly used in the food and cosmetic industries to mimic banana flavor, is represented by the mechanism below. Identify the Lewis acid and the Lewis base.
What feature must any molecule or ion have in order to act as a Lewis acid?
What is the Lewis definition of an acid? Of a base?
What is a general characteristic of a Lewis acid? Of a Lewis base?
In many reactions the addition of AlCl3 produces the same effect as the addition of H+.Draw a Lewis structure for AlCl3 in which no atoms carry formal charges.
For Cu and CH4, which will behave as a Lewis acid toward OH - in water?a. only Cub. only CH4c. Cu and CH4d. neither Cu nor CH4
Which of the following can act as a Lewis base?Cr3+, SO3, CH3NH2, BeCl2 a. Cr3+, BeCl2 b. SO3 onlyc. CH3NH2, BeCl2 d. SO3, CH3NH2 e. CH3NH2 only
Identify the Lewis acid and Lewis base in each of the following reactions.
Classify each of the following as a Lewis acid or a Lewis base.
Identify the Lewis acid and Lewis base in each of the following reactions:a. HNO2(aq) + OH-(aq) ⇌ NO2-(aq)+H2O(l)b. FeBr3(s) + Br-(aq) ⇌ FeBr4-(aq)c. Zn2+(aq) + 4NH3 ⇌ Zn(NH3)42+(aq)d. SO2(g) + H2O(l) ⇌ H2SO3(aq)
Classify each of the following as a Lewis acid or a Lewis base.
For the following reaction, indicate which reactant is the Lewis acid and which is the Lewis base.a. BF3 is the Lewis acid.b. BF3 is the Lewis base.c. CH3OH is the Lewis acid.d. CH3OH is the Lewis base.e. This not a Lewis acid-base reaction.
Classify the following as a Lewis acid or Base:BeCl2, OH-, B(OH)3, CN-
For the following reaction, indicate which reactant is the Lewis acid and which is the Lewis base.SO2 + OH- ⇌ HSO3-a. SO2 is the Lewis acid.b. SO2 is the Lewis base.c. OH- is the Lewis acid.d. OH- is the Lewis base.e. This not a Lewis acid-base reaction.
Which of the following is NOT a Bronsted Acid but IS a Lewis Acid?a. H2Ob. BCl3c. NH3d. NH4+e. HCl
For the following reaction, indicate which reactant is the Lewis acid and which is the Lewis base. 4NH3 + Cu2+ ⇌ Cu(NH3)42+    a. NH3 is the Lewis acid. b. NH3 is the Lewis base. c. Cu2+ is the Lewis acid. d. Cu2+ is the Lewis base. e. This not a Lewis acid-base reaction.
For the following reaction, indicate which reactant is the Lewis acid and which is the Lewis base. a. Benzene is the Lewis acid. b. Benzene is the Lewis base. c. Br+ is the Lewis acid. d. Br+ is the Lewis base. e. This not a Lewis acid-base reaction.
Classify each of the following as a Lewis acid or a Lewis base:
Which are Lewis acids and which are Lewis bases?(a) Mg2+ (b) OH− (c) SiF4 (d) BeCl2
Identify the Lewis acid and Lewis base in the reaction:(a) Na+ + 6H2O ⇌ Na(H2O)6+ 
Identify the Lewis acid and Lewis base in the reaction:(b) CO2 + H2O ⇌ H2CO3
Identify the Lewis acid and Lewis base in the reaction:(c) F− + BF3 ⇌ BF4−
We have seen an introductory definition of an acid: An acid is a compound that reacts with water and increases the amount of hydronium ion present. In the chapter on acids and bases, we saw two more definitions of acids: a compound that donates a proton (a hydrogen ion, H+) to another compound is called a Brønsted-Lowry acid, and a Lewis acid is any species that can accept a pair of electrons. Explain why the introductory definition is a macroscopic definition, while the Brønsted-Lowry definition and the Lewis definition are microscopic definitions.
Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:(a) CO2 + OH− ⟶ HCO3−
Identify the Lewis acid and Lewis base in the reaction:(a) Fe3++ 2H2O ⇌ FeOH 2++ H3O+
Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:(b) B(OH)3 + OH− ⟶ B(OH)4−
Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:(c) I− + I2 ⟶ I3−
Identify the Lewis acid and Lewis base in the reaction:(b) H2O + H− ⇌ OH− + H2
Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:(d) AlCl3 + Cl− ⟶ AlCl4− (use Al-Cl single bonds)
Identify the Lewis acid and Lewis base in the reaction:(c) 4CO + Ni ⇌ Ni(CO)4
Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:(e) O2− + SO3 ⟶ SO42−
Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:(a) CS2 + SH− ⟶ HCS3−
Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:(b) BF3 + F− ⟶ BF4−
Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:(c) I− + SnI2 ⟶ SnI3−
Classify the following as Arrhenius, Brønsted-Lowry, or Lewis acid-base reactions. A reaction may fit all, two, one, or none of the categories:(b) H2SO4 + NH3 ⇌ HSO4− + NH4+
Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:(d) Al(OH)3 + OH− ⟶ Al(OH)4−
Classify the following as Arrhenius, Brønsted-Lowry, or Lewis acid-base reactions. A reaction may fit all, two, one, or none of the categories:(c) 2HCl ⇌ H2 + Cl2
Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:(e) F− + SO3 ⟶ SFO3−
Using Lewis structures, write balanced equations for the following reactions:(d) NH4+ + C2H5O− ⟶
Using Lewis structures, write balanced equations for the following reactions:(c) CaO + SO3 ⟶
Using Lewis structures, write balanced equations for the following reactions:(b) H3O+ + CH3− ⟶
Using Lewis structures, write balanced equations for the following reactions:(a) HCl(g) + PH3(g) ⟶
In dilute aqueous solution HF acts as a weak acid. However, pure liquid HF (boiling point = 19.5°C) is a strong acid. In liquid HF, HNO3 acts like a base and accepts protons. The acidity of liquid HF can be increased by adding one of several inorganic fluorides that are Lewis acids and accept F– ion (for example, BF3 or SbF5). Write balanced chemical equations for the reaction of pure HNO3 with pure HF and of pure HF with BF3.
Boric acid, H3BO3, is not a Brønsted-Lowry acid but a Lewis acid.(a) Write an equation for its reaction with water.
Boric acid, H3BO3, is not a Brønsted-Lowry acid but a Lewis acid.(b) Predict the shape of the anion thus formed.
Boric acid, H3BO3, is not a Brønsted-Lowry acid but a Lewis acid.(c) What is the hybridization on the boron consistent with the shape you have predicted?
Classify each of the following as either a Lewis acid or a Lewis base.a. Fe3+b. BH3c. NH3d. F–
Identify the Lewis acid and Lewis base from among the reactants in each of the following equations.Fe3+(aq) + 6H2O(l) ⇌ Fe(H2O)63+(aq)
Consider the following reaction:Identify the Lewis acid in the reaction.
Identify the Lewis acid and Lewis base from among the reactants in each of the following equations.Zn2+(aq) + 4NH3(aq) ⇌ Zn(NH3)42+(aq)
Identify the Lewis acid and Lewis base from among the reactants in each of the following equations.(CH3)3N(g) + BF3(g) ⇌ (CH3)3NBF3(s)
Consider the following reaction:Identify the Lewis base in the reaction.
Identify the Lewis acid and Lewis base from among the reactants in each of the following equations.Ag+(aq) + 2NH3(aq) ⇌ Ag(NH3)2+(aq )
Identify the Lewis acid and Lewis base from among the reactants in each of the following equations.AlBr3 + NH3 ⇌ H3NAlBr3
The fluoride ion reacts with water to produce HF. Is fluoride acting as a Lewis acid or as a Lewis base when reacting with water?
Chloral (Cl3C—CH=O) forms a monohydrate, chloral hydrate, the sleep-inducing depressant called “knockout drops” in old movies. (a) Write two possible structures for chloral hydrate, one involving hydrogen bonding and one that is a Lewis adduct. 
Many molecules with central atoms from Period 3 or higher take part in Lewis acid-base reactions in which the central atom expands its valence shell. SnCl4 reacts with (CH3)3N as follows:(a) Identify the Lewis acid and the Lewis base in the reaction.
Many molecules with central atoms from Period 3 or higher take part in Lewis acid-base reactions in which the central atom expands its valence shell. SnCl4 reacts with (CH3)3N as follows:(b) Give the nl designation of the sublevel of the central atom in the acid before it accepts the lone pair.
Chlorobenzene, C6H5Cl, is a key intermediate in the manufacture of dyes and pesticides. It is made by the chlorination of benzene, catalyzed by FeCl3, in this series of steps:(1) Cl2 + FeCl3 ⇌ FeCl5 (or Cl+FeCl4−)(2) C6H6 + Cl+FeCl4− ⇌ C6H6Cl+ + FeCl4−(3) C6H6Cl+ ⇌ C6H5Cl + H+(4) H+ + FeCl4− ⇌ HCl + FeCl3(a) Which of the step(s) is (are) Lewis acid-base reactions?
Chlorobenzene, C6H5Cl, is a key intermediate in the manufacture of dyes and pesticides. It is made by the chlorination of benzene, catalyzed by FeCl3, in this series of steps:(1) Cl2 + FeCl3 ⇌ FeCl5 (or Cl+FeCl4−)(2) C6H6 + Cl+FeCl4− ⇌ C6H6Cl+ + FeCl4−(3) C6H6Cl+ ⇌ C6H5Cl + H+(4) H+ + FeCl4− ⇌ HCl + FeCl3(b) Identify the Lewis acids and bases in each of those steps.
Esters, RCOOR′, are formed by the reaction of carboxylic acids, RCOOH, and alcohols, R′OH, where R and R′ are hydrocarbon groups. Many esters are responsible for the odors of fruit and, thus, have important uses in the food and cosmetics industries. The first two steps in the mechanism of ester formation areIdentify the Lewis acids and Lewis bases in these two steps.
Classify each of the following as either a Lewis acid or a Lewis base.
Identify the Lewis acid and the Lewis base in the following reaction.a. B(OH)3(aq) + H2O(l) ⇌ B(OH)4-(aq) + H+(aq)
Identify the Lewis acid and the Lewis base in the following reaction.b. Ag+(aq) + 2NH3(aq) ⇌ Ag(NH3)2+(aq)
Identify the Lewis acid and the Lewis base in the following reaction.c. BF3 (g) + F -(aq) ⇌ BF4-(aq)
Identify the Lewis acid and the Lewis base in the following reaction.a. Fe3+(aq) + 6H2O(l) ⇌ Fe(H2O)63+(aq)
Identify the Lewis acid and the Lewis base in the following reaction.b. H2O(l) + CN -(aq) ⇌ HCN(aq) + OH -(aq)
Identify the Lewis acid and the Lewis base in the following reaction.c. HgI2(s) + 2I-(aq) ⇌ HgI42-(aq)
Would you expect Fe3+ or Fe2+ to be the stronger Lewis acid? Explain.
Use the Lewis acid–base model to explain the following reaction.CO2(g) + H2O(l) → H2CO3(aq)
Which are Lewis acids and which are Lewis bases?(a) Cu2+ (b) Cl− (c) SnCl2 (d) OF2
Which are Lewis acids and which are Lewis bases?(a) Na+ (b) NH3 (c) CN− (d) BF3
Which are Lewis acids and which are Lewis bases?(a) BF3 (b) S2− (c) SO32− (d) SO3
Which of the following can act as a Lewis base? Cr3+, SO3, CH3NH2, BeCl2A. SO3 onlyB. SO3, CH3NH2C. CH3NH2 onlyD. CH3NH2, BeCl2E. Cr3+, BeCl2
Classify each of the following as a Lewis acid or a Lewis base. H-, I- Fe3+ NO2 SnCl4 CH3OH (CH3)3N
Classify each of the following as a Lewis acid or a Lewis base:Fe3+ BCl3 S2-H2OSO3
Classify each of the following as either a Lewis acid or a Lewis base:H+ B(OH)3Cl-P(CH3)3
Identify the Lewis acid and Lewis base in each of the following reactions. HNO2(aq) + OH−(aq) ⇌ NO2−(aq) + H2O(l) SO2(g) + H2O(l) ⇌ H2SO3(aq)
Which of the following is a Lewis acid?A) BBr3B) CCl4C) NH3D) CHBr3E) None of the above are Lewis acids.
Which of the following could act as a Lewis base?a. H2Ob. PCl3c. Lu3+d. FeCl3e. Both (a) and (b) are Lewis bases
For the following reaction, indicate which reactant is the Lewis acid and which is the Lewis base.Al3+ + 6H2O ⇌ Al(OH)3 + 3H3O+a) Al3+ is the Lewis acid.b) Al3+ is the Lewis base.c) H2O is the Lewis acid.d) H2O is the Lewis base.e) This is not acid-base reaction.
Is SiF4 a lewis base or lewis acid?
Classify each of the following as a Lewis acid or a Lewis base: B(OH) 3OF2Cl-SO3 Na+
Classify each of the following as a Lewis acid or a Lewis base.
Classify each of the following as a Lewis acid or a Lewis base. 
Classify each of the following as either a Lewis acid or a Lewis base.?1. B(OH)32. P(CH3)33. BeCl24. CN-
Of the following list of molecules and ions, which can behave as Lewis bases: CO3-2, NH4+, Na+, OH-?  (i) NH4+ only (ii) NH4+ and OH- (iii) CO3-2 and Na+ (iv) CO3-2 and OH- (v) OH- only
Why is BCl3 a Lewis acid?
Classify each of the following as a Lewis acid or a Lewis base. 
Classify each of the following as a Lewis acid or a Lewis base.BeCl2, NH3, O2-, SO3, Fe2+