Ch.15 - Acid and Base EquilibriumSee all chapters
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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

Lewis Acid and Base

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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
Which of the following is a Lewis acid? A) BBr3 B) CCl4 C) NH3 D) CHBr3 E) None of the above are Lewis acids.
Briefly describe the difference between Bronsted acid and bases and Lewis acid and bases. For example, are all Bronsted acids also Lewis acids; are all Lewis acids also Bronsted acids?
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.
Classify each of the following as either a Lewis acid or a Lewis base.?1. B(OH)32. P(CH3)33. BeCl24. CN-
Classify each of the following as a Lewis acid or a Lewis base: B(OH) 3OF2Cl-SO3 Na+
Which of the following could act as a Lewis base?a. H2Ob. PCl3c. Lu3+d. FeCl3e. Both (a) and (b) are Lewis bases
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
Express your answer as a chemical equation. Identify all of the phases in your answer.a. For NH4+, write an equation that shows how the cation acts as an acidb. For Co3+, write an equation that shows how the cation acts as an acidc. For CH2NH3+, write an equation that shows how the cation acts as an acid.
Classify each of the following as a Lewis acid or a Lewis base. BeCl2, NH3, O2-, SO3, Fe2+
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
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.
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. 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.
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
Match each of the following definitions with the correct term. Lewis Acid                   Arrhenius Acid                         Bronsted-Lowry Acid               Arrhenius Base                                     Bronsted-Lowry Base                          Lewis Base.                  a. Increases the H + concentration when dissolved in a solvent.b. Increases the OH– concentration when dissolved in a solvent.c. A proton (H +) donor.d. A proton (H +) acceptor.e. An electron pair acceptor.f.  An electron pair donor
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 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. 
Classify each of the following as a Lewis acid or a Lewis base.