Chapter 18
Correctly order the steps necessary to solve weak-acid equilibria problems.
1. Write the balanced equation and Ka expression 2. Define X as the unknown change in concentration that occurs in the reaction and assume X is small compared to [HA] initial
Calculate [OH -] in the solution that has [H3O+] = 6.7 x 10^-2 M. Is the solution acidic or basic?
1.5 x 10^-13 M [OH-] = Kw/ [H3O+] The solution is acidic [H3O+] > [OH-], so the solution is acidic.
Calculate the Kb value for the acetate ion (CH3COO) if the Ka value for acetic acid (Ch3COOH) is 1.8 X 10^-5
5.6 x 10 ^-10
Place the following pH values in order of increasing [H3O]. Start with the pH that corresponds to the lowest [H3O+] at the top of the list. 4.3 8.5 7.2
8.5 7.2 4.3
Describe the relationship between the species in the reaction HSO3- + CH3NH2 ----> SO3^2- + CH3NH3+ A) HSO3- is the conjugate acid of SO3^2-. B) CH3NH is the conjugate base for HSO3- C) The base in the foward reaction is CH3NH2 D) The base in the reverse reaction is CH3NH3+ F) BD are a conjugate acid-base pair
A) HSO3- is the conjugate acid of SO3^2-. C) The base in the foward reaction is CH3NH2 F) BD are a conjugate acid-base pair
A Bronsted - Lowry base is proton _____. A Bronsted - Lowry base must contain an available _______ pair of ______ in its formula in order to form a(n) ____ to H+.
Acceptor lone electron covalent
Which of the following is present in the greatest concentration in a 1.0 M solution of CH3COOH? OH- H3O CH3COOH CH3COO
CH3COOH
Select ALL the weak bases from the following list. (CH3)2NH CH3NH2 LiOH NH3
Compounds with electron- rich N atoms are weak bases. NH3 (CH3)2NH CH3NH2
Finding the pH a weak base solution is very similar to that weak acid. What is the only step that is necessary in the calculations of pH of a weak base and not a weak acid?
Convert [OH] to [H3O+]
True or False ac For any acid-base reaction Ka x Kb = Kw for the reating acid and base.
False Ka x Kb= Kw is only for conjugate acid- base pair, not for the acid and base reacting.
A species that contains one or more _____ atoms as well as one or more _____ electron pairs can act as either an acid or a base, depending on the reaction. Such a species is describes as being ___
H Lone Amphoteric
Depicts the net ionic equation for the reaction of a strong acid (HNO3) with a strong base (KOH)?
H+ (aq) + OH- (aq) --> H2O (l) This is the net neutralization reaction for the reaction of a strong acid with a strong base.
Which of the following is NOT a conjugate acid-base pair? H3PO4 / H2PO4 H2PO4/ PO4^3- NH3/NH2 H2S/ HS HCO3/ CO2^2-
H2PO4/ PO4^3- Conjugate acid-base pairs differ by a single proton (H+). The conjugate acid of PO4^3- is HPO4^2-,not H2PO4-
The pH of a solution is measure of its ________ concentration.
H30+ ion
Strong acid * Weak acid
H3O+, A - If Ha is a strong acid, it dissociates completlely to form ions. No undissociated HA molecules remain in solution. *HA If Ha is a weak acid, most of its molecules remain undissociated.
Select all the strong acids from the following CH3COOH HI HBr HCLO4 HNO3 HF H2SO4 HF HNO2
HBr HI HCLO4 HNO3 H2SO4
Ka values provided, select all the equilibrium acid- base reactions that will favor the products.
HF + OCL
Which of the following monoprotic acids would give a solution with the lowest pH at the same molarity? CH3COOH (pka= 4.74) HNO2 (pka = 3.15) HSO-4 (pka =1.99) HBrO (pka = 3.15)
HSO-4 (pka =1.99) has the lowest pka value and is therfore teh strongest acid with the lowest pH for solutions of the same concentration.
Two types of strong acids are binary containing hydrogen bonded to a(n) ______ atom and oxoacids in which the number of ionizable protons by _____ or more.
Halogen ; 2 All hydrogen halides except HF are strong acids.
Small Ka Value
High Pka Value
The stronger the acid, the ___________ the [ H3O+] at equilibrium, and the ________ the value of Ka
Higher ; larger
Describe the constant Ka
Ka is the acid-dissociation acid [H2O] is not included in the ka expression for a particular acids.
Select all the expression that correctly express the relationship between Ka and Kb for a conjugate acid- base pair.
Ka x Kb = Kw Ka= (Kw/Kb)
Large Ka value
Low Pka Value
The two general types of weak base include molecules that contains one or more _____ atoms, and the anions of weak ______
N Acids
The reaction of an acid and a base in aqueous solution, in which all H+ ions from the acid react with all the OH- ions from the base is called______.
Neutralization
Arrhenius acid
Produces H+ ions when dissolved in aqueous solutions
Which of the following options correctly describes the structural characteristics of strong and weak bases? Ch3OH contains OH in its formula and is therefore a strong base Soluble hydroxides are strong bases Compounds that contain electron- rich N are weak bases. Amines such as CH3CH2NH are weak bases.
Soluble hydroxides are strong bases Compounds that contain electron- rich N are weak bases. Amines such as CH3CH2NH are weak bases.
The direction of an acid-base equilibrium depends on the relative strength of the acid and bases involved. Since strong acids and strong bases readily accept and donate protons, the equilibrium will always favor the reaction of the ________ acid and base and the formation of the _____ acid and base.
Stronger ; Weaker
How does a conjugate acid differ from its conjugate base?
The conjugate acid of a neutral base will have a charge of +1 A conjugate base may be positively charged, neutral, or negatively charged. The conjugate acid has one more H than its conjugate base.
Describe the Bronsted- Lowry acid-base reactions?
The reactions and products contains an acid and a base. Some species can act as either an acid or a base depending on the other species present.
Which of the following statements correctly decsribes a 1.0 M of KCN? A) The solution contains a significant concentration of the weak base CN- B) The solution is baisc C) The solution contains a significant concentration of weak acid HCN D) The solution is acidic
The solution contains a significant concentration of the weak base CN- (the CN- anion is the conjugate base of a weak acid. CN- reacts with H2O to produce OH- ions, making the solution basic. K+ has no effect on the pH of the solution. ) The solution is basic (KCN is a soluble ionic salt and dissociates completely to give K+ and CN- ions. CN- is a weak base and its concentration will remain significant, although it will react with H2O to produce a small amount of HCN)
A(n) ______ acid is one that dissociated only slightly in water, whereas a(n) _____ acid dissociates completely into ions.
Weak ; Strong
Given the acid-base equilibrium HCN (aq) + HCO- (aq) ---> CN- (aq); pKa for HCN= 9.2 and pKa for H2CO3 = 6.3. HCN is a ______ acid than H2CO3 and the equilibrium as written will lie to the _____ and favor the formation of the ______.
Weaker ; Left; Reactants Remember the higher pKa the maller Ka value indicates Weaker acid.
In general the stronger an acid is, the ______ its conjugate base will be. Thus the conjugate base Cl- is _____ because its conjugate acid HCl is strong.
Weaker ; weak
Match the relative concentrations of hydronium and hydroxide with the type of solutions Acidic solution Basic solution Neutral solutions
[H3O+] > [OH-] [OH-]> [H3O+] [H3O+] = [OH-]
Bronsted - Lowry base
accepts an H+
Lewis acid
accepts an electron pair
The strength of a weak base is indicated by its ______ - ionization constant Kb. The greater the value kb the _____ the base.
base stronger
Bronsted - Lowry acid
donates H+
Lewis base
donates an electron pair
Arrhenius base
forms OH- in aqueous solution
The autoionization of water is a process where water ionizes slightly to form ______ ions and ______ ions.
hydronium OH-
A monoprotic acid has _____ ionizable protons, whereas a diprotic acid has _____ ionizable protons
one two
In an organic acid such as CH3CH2COOH, the ionizable H atoms is/ are______.
only the H of the COOH group
Basic Solution Neutral Solution Acidic Solution
pH > 7.00 pH = 7.00 pH < 7.00
According to the Bronsted- Lowry definition, an acid donated H+ to a base. An acid-base reaction can therefore be described as a(n) _____ transfer reaction.
proton
If you are given pH and asked to calculate [H+] you would _______.
raise 10 to the power of the negative pH value.