Acids. Strong Acids: Two types of strong acids, with examples that you should memorize , are 1.The hydrohalic acids HCl, HBr, and HI
This model focuses on the nature of acids and bases and the reactions between them.
Acid – proton (H+ ion) donor
Base – proton (H+ ion) acceptor
In an acid-base reaction, a proton is transferred from an acid to a base:
HB + A-⇌ HA + B-
Conjugate base: the species formed when a proton is removed from the acid.
Conjugate acid: the species formed when a proton is added to a base.
H2O + H2O ⇌ H3O+ + OH-
What is the conjugate acid and base for
The ionization of water can be simplified to the ionization of one water molecule:
H2O ⇌ H+(aq) + OH-(aq)
The ion product constant of water @ 25⁰C:
Kw = [H+] [OH-] = 1.0 x 10-14
pH = -log[H+] = -log[H3O+]
or the same formula can be used to determine the [H+] concentration by: [H+] = 10-pH
A similar approach is used to determine the hydroxide ion concentration:
pOH = -log[OH-]
Because [H+] [OH-] = 1.0 x 10-14 then the pH and pOH are connected by the following:
pH + pOH = 14.00
Weak acids react reversibly with water to form H+ ions.
HNO2 (aq) + H2O ⇌ H3O+ (aq) + NO2- (aq)
NH4+ (aq) + H2O ⇌ H3O+ (aq) + NH3 (aq)
The equilibrium constant for a weak acid:
HX ⇌ H+ + X-
Ka = [H+] [X-]
*the smaller the Ka value the weaker the acid.
% ionization = [H+] x 100 [HX]
These are acids that have more than one ionizable hydrogen ion. These acids ionize in steps, with a separate equilibrium constant for each one:
H2C2O4 (aq) ⇌ H+ (aq) + HC2O4- Ka1 = 5.9 x 10-2
HC2O4- (aq) ⇌ H+ (aq) + C2O4-2 Ka2 = 5.2 x 10-5
The anion formed in step one produces another H+ ion in the next step.
The Ka becomes smaller with each successive step:
Ka1 > Ka2 > Ka3
NH3(aq) + H2O ⇌ NH4+(aq) + OH-(aq)
F- (aq) + H2O ⇌ HF (aq) + OH- (aq)
(A) Na+(B) Cl¯(C) CH3COO¯(D) Mg2+(E) Al3+
(A) HCO3¯(B) H2PO4¯(C) NH4+(D) H2O(E) HS¯
(A) H2SO4 molecules(B) H3O+ ions(C) HSO4¯ ions(D) SO42¯ ions(E) All species are in equilibrium and therefore have the same concentrations.
(A) H3O+ + OH¯ ---> 2 H2O(B) HCN + OH¯ ---> H2O + CN¯(C) Cu(H2O)42+ + 4 NH3 ---> Cu(NH3)42+ + 4H2O(D) H2SO4 + H2O ---> H3O+ + HSO4¯(E) H2O + HSO4¯ ---> H2SO4 + OH¯
(A) 0.08%(B) 0.2%(C) 1%(D) 2%(E) 4%
(A) H2O(B) NH3(C) S2¯(D) NH4+(E) HCO3¯
(A) The acid strength varies unpredictably.(B) The acid strength decreases only if X is a nonmetal.(C) The acid strength decreases only if X is a metal.(D) The acid strength decreases whether X is a nonmetal or a metal.(E) The acid strength increases.
(A) 5.0 x 10¯7(B) 2.0 x 10¯7(C) 5.0 x 10¯6(D) 5.0 x 10¯3(E) 2.0 x 10¯3
In the equilibrium represented above, the species that act as bases include which of the following?
I. HSO4¯ II. H2O III. SO42–
(A) II only(B) III only(C) I and II(D) I and III(E) II and III
(A) 5 x 10¯2(B) 5 x 10¯5(C) 2.5 x 10¯6(D) 5 x 10¯7(E) 2.5 x 10¯8
(A) NaNO3(B) Na2CO3(C) NH4Cl(D) NaHSO4(E) Na2SO4
(A) 10(B) Between 7 and 10(C) 7(D) Between 4 and 7(E) 4
(A) HNO2 + Na+ + OH¯ ---> NaNO2 + H2O(B) HNO2 + NaOH ---> Na+ + NO2¯ + H2O(C) H+ + OH¯ --->H2O(D) HNO2 + H2O ---> NO2¯ + H3O+(E) HNO2 + OH¯ ---> NO2¯ + H2O
(A) 2.5 x 10¯11(B) 2.5 x 10¯10(C) 5.0 x 10¯10(D) 5.0 x 10¯6(E) 5.0 x 10¯4
(A) accepts a proton from water(B) accepts a pair of electrons to form a bond(C) donates a pair of electrons to form a bond(D) donates a proton to water(E) has resonance Lewis electron-dot structures
A pure 14.85 g sample of the weak base ethylamine, C2H5NH2 , is dissolved in enough distilled water to make 500. mL of solution.
The aqueous ethylamine reacts with water according to the equation below.
C2H5NH2(aq) + H2O(l) C2H5NH3+(aq) + OH-(aq)
HF(aq) + H2O(l) H3O+(aq)+ F–(aq) Ka = 7.2×10–4
Hydrofluoric acid, HF, dissociates in water as represented by the equation above.
HF(aq) reacts with NaOH(aq)according to the reaction represented below.
HF(aq) + OH–(aq) H2O(l) + F–(aq)
A volume of 15 mL of 0.40 M NaOH(aq) is added to 25 mL of 0.40 M HF(aq) solution. Assume that volumes are additive.
HC3H5O2(aq) ↔ C3H5O2– (aq) + H+(aq)Ka = 1.34 x 10–5
Propanoic acid, HC3H5O2, ionizes in water according to the equation above.
The methanoate ion, HCO2–(aq) reacts with water to form methanoic acid and hydroxide ion, as shown in the following equation.
HCO2–(aq) + H2O(l) ↔ H2CO2(aq) + OH–(aq)
Hypochlorous acid, HOCl, is a weak acid commonly used as a bleaching agent. The acid–dissociation constant, Ka, for the reaction represented above is 3.2×10–8.
Give a brief explanation for each of the following.