Chapter 11 Acids and Bases
Of the following, which acid has the weakest conjugate base? A. HClO4 B. HCOOH C. H3PO4 D. H2CO3
A; A is the strongest acid, making it the weakest conjugate base
What percentage of HF (pKa = 3.17) dissociates in one liter of solution containing two moles of the acid? A. 1.8% B. 32% C. 72% D. 98%
A; HF <--> H+ + F- 1. Convert pKa to Ka (can use pKa of 3) 2. ICE Table 3. Ka = [x][x] / 2 (because 2 moles/1L = 2M) 4. Solve for X 5. Put X over 2 to get percentage of what dissociated, which is about 2%
Consider the reaction: H2CO3 + H2O <--> H3O+ + HCO3- What are the acids and bases in this reaction?
Acids: H2CO3 and H3O+ Bases: HCO3- and H2O
What percent of neutralization reactions go until completion?
All of them
Of the following acids, which would dissociate to the greatest extend (in water) A. HCN (Ka = 6.2 x 10^-10) B. HNCO (Ka = 3.3 x 10^-4) C. HClO (Ka = 2.9 x 10^-8) D. HBrO (Ka = 2.2 x 10^-9)
B
Which one of the following statements concerning 50 mL of basic solution composed of 0.2 MNaH2PO4 and 0.2 M Na2HPO4 is correct? A. The concentration of Na+ is 0.4 M. Your Answer B. The pH of the solution will not change with the addition of 20 mL of water C. The addition of 1 mL of 0.1 M HCl to the reaction will result in a pH of 2. D. With the addition of ammonia, a precipitate should be formed.
B; The correct statement concerning 50 mL of basic solution composed of 0.2 M NaH2PO4 and 0.2 MNa2HPO4 is the pH of the solution will not change with the addition of 20 mL of water. This solution is a buffer. The pH of a buffer does not change with the addition or removal of water.
Which of the following compounds could be added to a solution of HCN to create a buffer? A. HNO3 B. CaCl2 C. NaCN D. KOH
C
Which of the following is an acidic salt? A. KNO3 B. SrCl2 C. CuCl2 D. Ba(CH3COO)2
C
What is the conjugate base of HBrO? A. H+ B. H2BrO2 C. H2BrO+ D. BrO-
D
What is the pH of a solution with an ammonium concentration of 70 mM and an ammonia concentration of 712 mM? (Note: the PKB of ammonia is 3.45) A. 2.45 B. 4.45 C. 9.55 D. 11.55
D
A mixture of acidic wastes is found to be 2 M H2SO4, 0.5 M HI, and 3 M HNO3. What volume of 5 M NaOH solution will be required, per liter of acidic waste, to completely neutralize the acid? A. 3.0 L B. 1.5 mL C. 1.1 L D. 1.5 L
D; A mixture of acidic wastes is found to be 2 M H2SO4, 0.5 M HI, and 3 M HNO3. It will require 1.5 L of a 5 M solution of NaOH to completely neutralize 1 L of the acidic waste in question. The easiest way to answer this question is to determine the molarity of H+ in the acidic wastes. Accounting for all dissociable protons there are 7.5 moles of H+ per liter of solution. Remember, there are two acidic protons on H2SO4. It is then the case that 7.5 moles = 5 MNaOH x ? L solution, resulting in 1.5 L of NaOH solution being necessary for complete neutralization.
List the strong acids
HI HBr HCl HClO4 HClO3 H2SO4 HNO3
NO3-
Nitrate
NO2-
Nitrite
PO4 3-
Phosphate
What does Ka > 1 mean?
Products are favored (strong acid)
What effect does size have of basicity?
Smaller atoms increase basicity F- is more basic than I- OCH3- is more basic than SCH3-
What is Ka?
acid dissociation constant
Is Na(CH3COO) acidic, basic, or neutral?
basic
If pH > pKa, the acid is
deprotonated
Atoms without hydrogen can be acids if...
electron deficient or have large (+) charge
What are Bronstread Lowry bases?
proton acceptors
At low pH, amino acids are
protonated
If pKa > pH, the acid is
protonated
What does Ka < 1 mean?
reactants are favored (weak acid)
What is a neutralization reaction?
reaction between an acid and a base to produce salt and water
The larger the Ka, the _____________________ the acid.
stronger
H2SO4
sulfuric acid
A titration of which of the following aqueous hydrogen halides with NaOH will show an equivalence point above pH = 7? A. HBr (aq) B. HCl (aq) C. HI (aq) D. HF (aq)
D;
Calculate the concentration of F- ions in a 2 M solution of hydrogen fluoride, HF. (The Ka of HF is 6.8 × 10-4.) A. 1.2 × 10-2 M B. 1.8 × 10-2 M C. 1.4 × 10-3 M D. 3.7 × 10-2 M
D;
When designing experiments to study the action of pharmacological agents at physiological pH (~7.3) for use in human blood, which of the following conjugate pairs would serve as the best buffer solution? A. CH3CO2H/CH3CO2-; pKa = 4.8 B. H2CO3/HCO3-; pKa = 6.4 C. HPO42-/ PO43-; pKa = 12.1 D. H2PO4-/HPO42- ; pKa = 7.1
D;
What is the pOH of a mixture made by adding 150 mL of 0.20 M sodium hydroxide to 50 mL of 0.20 M hydrochloric acid? A. 13.0 B. 12.5 C. 1.5 D. 1.0
D; 1. Determine the moles of acid and base each 2. If excess, find the moles of that 3. Plug into pH or POH equation
How do you calculate the pH of a weak acid?
ICE tables
If 99% of the H3O+ ions are removed from a solution whose pH was originally 3, what will be its new pH?
If 99% of H3O+ ions are removed, then only 1% remain. This means the number of H3O+ ions is now only 1/100 of the original. If [H3O+] is decreased by a factor of 100, then the pH increased by 2 - to pH5. New pH = 5
What is a salt?
Ionic compound consisting of a cation and an anion
In its non-ionizes form, an indicator has a particular color. When it has donated a proton to become its conjugate base, what happens?
It becomes a different color
HCN HCN <--> H+ + CN- initial: .2M 0M 0M at equilibrium: (.2-x)M xM xM It is known that the Ka for HCN is 4.9 x 10^-10. Find the [H+]
Ka = [H+][CN-] / .2 -x Ka = [x][x] / .2 (x is negligible) 4.9 x 10^-10 = x^2 / .2 10 x 10^-11 = x^2 1 x 10^-10 = x^2 x = 1 x 10^-5 M
base dissociation constant equation
Kb = [B+][OH-]/[BOH]
Equilibrium constant of water
Keq = [H+][OH-]/[H2O]
Is FeCl3 acidic, basic, or neutral?
acidic
Is NH4Cl acidic, basic, or neutral?
acidic
pH for weak acid
pH = -1/2 log (Ka[WA])
What are Bronstead Lowry acids?
proton donors
What does a large Ka mean?
strong acid
A basic salt contains an ion that is a _______ base
weak
An acidic salt contains an ion that is a _____ acid
weak
What is an indicator?
weak acid that undergoes a color change when it's converted to its conjugate base
The indicator must always be a _________ acid than the one being titrated
weaker
As hydrogen ions are added to an alkaline buffer solution ,what happens to the concentrations of base and conjugate acid?
The base, B, reacts with the added H+ to form HB+, so the base decreases and the conjugate acid increases.
How do group 1 and group II cations react with water?
They do not react
What are amphoteric species?
When a substance can act as an acid or base
H2CrO4
chromic acid
In a neutralization reaction, if equimolar amounts of a strong acid and base react, the resulting solution will be
neutral
Is MgBr2 acidic, basic, or neutral?
neutral
HNO3
nitric acid
HNO2
nitrous acid
Lewis bases act as _________
nucleophiles
Of the following, which contains the lowest concentration of H3O+ ions? A. Lemon juice (pH = 2.3) B. Blood (pH = 7.4) C. Seawater (pH = 8.5) D. Coffee (pH = 5.1)
C
Buffering capacity is generally maintained within ________ pH unit of the pKa value
1
For indicators, we want the pKa to be within ________ of the expected pH
1
How much .1M NaOH solution is needed to neutralize 40mL of a .3M HCl solution?
120 mL
pH + pOH =
14
pKa + pKb =
14
What is the Brønsted-Lowry base in the following reaction? HCl(g) + H2O(l) H3O+(aq) + Cl-(aq) A. H2O B. Cl- C. HCl D. H3O+
A;
Acetylsalicylic acid, also known as aspirin, possesses a pKa of 3.5. What is the pH of a 1 M solution of acetylsalicylic acid? A. 1.8 B. 3.5 C. 5.3 D. 7
A; 1. Convert pKa to Ka (10^-3.5) 2. ICE Table 3. Ka = [x][x] / 1M 4. Sovle for x 5. Plug x into pH equation
The acidic strength of HF is greatly enhanced when it is used in conjunction with SbF5. The resultant system, known as "magic acid", is one of the strongest acids known, and follows the dissociation equation below. HF + SbF5 → H+ + SbF6- A. Lewis base B. Lewis acid C. Brønsted base D. Brønsted acid
B
Which of the following acids (in conjunction with an equal amount of its conjugate base) would be most appropriate to use in order to maintain a buffer solution of pH 7.4 at 25°C? A. H2CO3 (pKa = 6.35) B. H2PO4- (pKa = 7.21) C. HNO2 (pKa = 3.35) D. HCO3- (pKa = 10.33)
B;
A conjugate species will differ from its parent molecule by which of the following? A. A neutron only B. An electron only C. A proton only D. An electron and a proton
C;
Given the pKa values of phenol (C6H5OH) and benzoic acid (C6H5CO2H) are 9.8 and 4.2, respectively, which of the following is the strongest base in water? A. C6H5OH B. C6H5CO2H C. C6H5O- D. C6H5CO2-
C;
Twenty milliliters of a 8.4 x 10-3 M solution of HBr is added to sixty milliliters of water. What is the final pH of the solution? A. 0.6 B. 1.8 C. 2.7 D. 3.3
C; 1. This is a dilution, use M1V1 = M2V2 2. Once you get the new molarity, you can plug it into the pH equation because HBr is a strong acid and it will completely dissociate
The normal range for the pH of blood is between 7.35-7.45. In the absence of blood's normal bicarbonate buffer system, which pair of compounds (in an equimolar mixture) would buffer blood at the same pH? A. HCO2H (pKa = 3.7) and HCO2- B. HF (pKa = 4.8) and F- C. HSO3- (pKa = 7.2) and SO32- D. H3BO3 (pKa = 9.3) and H2BO3-
C; Each of these conjugate pairs will help maintain the pH of a solution containing them around the listed pKa values of the acids. Buffers are most effective one point on either side of their pKa. The buffer system with the acid pKa nearest the physiological pH of blood is HSO3- and SO32- (choice C is correct).
Low lets consider the reverse reaction NH4+ + OH- <—> NH3 + H2O What is the conjugate acid and base?
H2O is the conjugate acid NH3 is the conjugate base
Consider this reaction NH3 + H2O <—> NH4+ + OH- What is the conjugate acid and base?
NH4+ is the conjugate acid (NH3 is the base) OH- is the conjugate base (H2O is the acid)
Is NaNO3 acidic, basic, or neutral?
Neutral
Is Li2CO3 acidic, basic, or neutral?
basic
Of the following anions, which is the strongest base? A. I- B. CN- C. NO3- D. Br-
B
Which of the following is closest to the pH of a solution containing 5 mM H2SO4? A. 1 B. 2 C. 3 D. 4
B pH = -log [H+] pH = -log [2 x 5 x 10^-3M] pH = -log [10 x 10^-3] pH = 2
Ethylenediaminetetraacetic acid (EDTA) is a commonly used scavenger of heavy metals. The molecule has 4 carboxylic acid moieties, with successive pKa values of 1.99, 2.67, 6.16, and 10.26. At neutral pH, what is the predominant charge state of EDTA? A. -1 B. -3 C. -2 D. -4
B; At neutral pH, the predominant charge state of EDTA is -3. The Henderson-Hasselbalch equation (pH = pKa + log ([A-]/[HA])) shows that the deprotonated form of a compound is favored when pH > pKa. At neutral pH this is true for three of the four acidic protons on EDTA, giving a charge state of -3.
Which of the following can behave as a Bronstead-Lowry acid but not a Lewis acid? A. CF4 B. NaAlCl4 C. HF D. Br2
C
Which of the following is an amphoteric species? A. H+ B. S2- C. HS- D. H2S
C
CO3 2-
Carbonate
Methyl red is an indicator that changes from red to yellow in the pH range 4.4-6.2. For which of the following titrations would methyl red be useful for indicating the equivalence point? A. HCN nitrated with KOH B. NaOH titrated with HI C. C6H5COOH (benzoic acid) titrated with LiOH D. C6H5NH2 titrated with HNO3
D
What is the [H3O+] of a 2M aqueous solution of a weak acid HXO2 with a Ka = 3.2 x 10^-5? A. 6.4 x 10^-5 M B. 1.3 x 10^-4 M C. 4.0 x 10^-3 M D. 8.0 x 10^-3 M
D
What is the pH of a solution at 25C whose hydroxide ion concentration is 1 x 10^-4M pOH = -log [OH-] pOH = -log [1 x 10^-4] pOH = 4 pH = 10
D
When a sample of a weak base is completely neutralized with a strong acid, the pH at the equivalence point will be: A. indeterminable given the information provided. B. basic. C. neutral. D. acidic.
D
Which of the following is the conjugate species formed when sodium acetate is added to water? A. Na+ B. H3O+ C. CH3COO- D. CH3COOH
D; When sodium acetate is added to water, acetate removes a proton from water to generate acetic acid and a hydroxide ion. Given that acetate is accepting a proton, it is acting as a base and the conjugate acid formed would be acetic acid, making choice D correct.
What is the dissociation constant for sulfurous acid?
Ka = [H+][SO3-] / [H2SO3]
Ka equation
Ka= [H3O+][A-] / [HA]
Kw of water at 25C
Kw = [H3O+][OH-] = 10^-14
List the strong bases
LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2 NaNH3 O2- OR- NH2- NR2- H- R-
Which cations are stronger acids than water?
NH4+, Be2+, Cu2+, Zn2+, Al3+, Cr3+, and Fe3+
What is the titrant in a titration?
a solution of known concentration
What is a buffer?
a substance that minimizes changes in pH
HClO
hypochlorous acid
pOH equation
pOH=-log[OH-] [OH-] = 10^-pOH
What is buffering capacity?
the ability to which the system can resist changes in pH
What is the base dissociation constant?
𝐾𝑏 is called the base dissociation constant and is a measure of the strength of a base. Strong bases have a higher 𝐾𝑏 than weak bases.
Compared to a 50 mL solution of a 1 M CH3CO2H, the complete neutralization of 50 mL of a 1 MHCl solution will require: A. the same amount of base. B. less base. C. an indeterminable amount of base given the information provided. D. more base.
A
Equal moles of HCl and NaOH are mixed together in an aqueous solution. Which of the following is a true statement if solid NaCl is added to the subsequent solution? A. The pH of the solution remains at 7. B. The pH of the solution decreases below 7. C. A buffer solution will be formed. D. The pH of the solution increases above 7.
A
Given one mole of each of the following substances in one liter of water, which would result in a solution with the highest pH? A. HCN (pKa = 9.2) B. HC5H3N4O3 (pKa = 3.9) C. HC3H5O2 (pKa = 4.9) D. HCHO2 (pKa = 3.7)
A
Question: For a reaction involving a strong base and a weak acid, which of the following indicators would be best to indicate the endpoint of the titration? A. Phenolphthalein (pKa = 9.7) B. Bromothymol (pKa = 7.1) C. Bromocresol (pKa = 4.7) D. Methyl yellow (pKa = 3.3)
A
Which of the following represent chloric acid? A. HClO3 B. ClO3 C. HClO2 D. HClO
A
1 M solution of which of the following compounds would have the lowest pOH? A. KNH2 B. HF C. NH4I D. NaBr
A; A 1 M solution of KNH2 would have the lowest pOH of the four salts listed. As pH = 14 - pOH, very basic solutions will have low values of pOH (high pH), so this question is asking for the most basic compound. HF is a weak acid, and will yield a solution of relatively low pH and high pOH. NH4I is an acidic salt, and gives a solution of relatively high pOH. NaBr is a neutral salt, and therefore a 1 M solution will have both pH and pOH near 7. The anion of KNH2, NH2-, is a strongly basic anion, which will cause KNH2 solutions to be highly basic with low values of pOH.
Addition of sodium acetate to a solution of acetic acid will cause the pH to: A. increase due to the common ion effect. B. remain constant because sodium acetate is a buffer. C. remain constant because sodium acetate is neither acidic nor basic. D. decrease due to the common ion effect.
A; Addition of sodium acetate to a solution of acetic acid will cause the pH to increase due to the common ion effect. Sodium acetate is a basic compound, because acetate is the conjugate base of acetic acid, a weak acid ("the conjugate base of a weak acid acts as a base in water"). The addition of a base to any solution, whether it is buffered or not, will increase the pH. The answer is "increase due to the common ion effect."
Which of the following best accounts for the difference in acid strength between H2S and H2Se? A. Increased stability is observed in HSe- compared to HS-. B. The H—S bond is weaker than the H—Se bond. C. Reactivity of HSe- is increased relative to HS-. D. The bond length observed in H—Se is shorter than that of H—S.
A; At equilibrium, the side of the reaction with the greatest stability predominates. In this instance, if HSe- is more stable than HS-, the dissociation of H2Se will occur to a greater extent and helps explain why H2Se is a stronger acid (choice A is correct, choice C is not correct). A weaker bond between hydrogen and sulfur would not help explain how H2Se is a stronger acid (eliminate choice B), and bond length would have limited impact on acid strength (eliminate choice D).
Because it dissolves carbon dioxide from the atmosphere to make mild carbonic acid, natural rain has a pH of around 5.5. However, due to pollutants such as sulfates from coal-fired power plants and nitrates from car exhausts, the pH of rain can drop to as low as 2. This decrease in pH represents a change in H+ concentration by approximately what factor? A. 3000 B. 300 C. 3.5 D. 35
A; Because it dissolves carbon dioxide from the atmosphere to make mild carbonic acid, natural rain has a pH of around 5.5. However, due to pollutants such as sulfates from coal-fired power plants and nitrates from car exhausts, the pH of rain can drop to as low as 2. This decrease in pH represents a change in H+ concentration by approximately a factor of 3000. Each change by 1 in the pH value corresponds to a change by a factor of 10 in [H+] since pH is a logarithmic scale. Since 5.5 - 2 = 3.5, the factor change in [H+] must be greater than 103 = 1000. More precisely, the change in [H+] is 103.5 = 103 × 100.5 ≈ 1000 × 3 = 3000.
If a solution with a pH of 11 is diluted with pure water until the volume is increased by a factor of 10, the pH will then equal: A. 10 B. 9 C. 12 D. 1
A; If a solution with a pH of 11 is diluted with pure water until the volume is increased by a factor of 10, the pH will then equal 10. Each pH unit corresponds to a 10-fold change in the concentration of H+ (or OH-). Therefore, diluting the basic solution by a factor of ten would result in a solution one pH unit closer to neutrality.
Red wines are generally acidic, with proper pH values near 3.6. At this pH, which of the following organic acids commonly found in wine have the highest proportion of molecules in the -1 charge-state? (note: pKa1 denotes the pKa of the most acidic proton on the compound; the pKa values of all subsequent protons on the compounds of interest are all near pH = 6) A. Maleic acid (pKa1 = 1.90) B. Citric acid (pKa1 = 3.09) C. Succinic acid (pKa1 = 4.05) D. Tartaric acid (pKa1 = 2.95)
A; Red wines are generally acidic, with proper pH values near 3.6. At this pH, maleic acid will have the highest proportion of molecules in the -1 charge-state. As this is a question asking for extremes, it is safe to eliminate tartaric and citric acids for having the non-extreme pKa values. The Henderson-Hasselbalch equation states that pH = pKa + log ([A-]/[HA]), where A- is the molecule in the -1 charge state, and HA is the protonated, neutral molecule. Rearranging this equation and substituting the given pH yields: log ([A-]/[HA]) = 3.6 - pKa. The acid that gives the largest positive number for the right side of this equation is the one with the smallest pKa, maleic acid.
The resulting solution made from the combination of 50 mL of 1.0 M LiOH with 50 mL of 1.0 MHBr will be identical in all respects to 100 mL of: A. 0.5 M LiBr. B. 1 M LiBr. C. a saturated solution of LiBr(s). D. 2 M LiBr.
A; The resulting solution made from the combination of 50 mL of 1.0 M LiOH with 50 mL of 1.0 MHBr will be identical in all respects to 100 mL of 0.5 M LiBr. The best way to approach this question is to ignore OH- and H+, because they will neutralize each other when mixed. Thus, in this question we are mixing 50 mL of 1.0 M Li+ and 50 mL of 1.0 M Br-. Since the solution volume is doubling, the concentration of each ion is expected to decrease by a factor of 2. Therefore, the correct choice is "0.5 M LiBr".
Given the self-ionization of water is endothermic, what is the value of the sum pH + pOH at 50 C? A. Less than 14 B. Equal to 14 C. Greater than D. Cannot be determined
A; This is Le Chat's principle. Since the reaction is endothermic, heat is a reactant. Increase in temperature shifts the reaction to the right. Shifting to the right means that at equilibrium, [H+] and [OH-] will increase. So pH and pOH will both be lower than 7 at 50C, and the sum of pH and pOH will be less than 14 at 50C.
In a 1M aqueous solution of boric acid (H3BO3, Ka = 5.8 x 10^-10), which species will be present in solution in the greatest quantity? A. H3BO3 B. B2BO3- C. HBO3 2- D. H3O+
A; ◦ H3BO3 (aq) + H2O (l) <—> H3O (aq) + H2BO3- (aq); Boric acid is a weak acid. Since H3BO3 is a weak acid, equilibrium will lie to the left. Making the answer A.
What is a strong acid?
An acid which completely splits up into its ions in water. E.g. when HCl is in water all the HCl molecules split up into H⁺ and Cl⁻
What is a weak acid?
An acid which will have some molecules which do not split up into their ions. E.g. in ethanoic acid only some of the molecules will have split up into the ethanoate ion and H⁺ ions.
A 25 mL solution of .2 M acetic acid (pKa = 4.76) is mixed with a solution with 50mL of 1.0 M sodium acetate (pKb = 9.24). What is the final pH? A. 4.8 B. 5.8 C. 9.2 D. 10.2
B
List the following compounds by increasing pKa: I. HsSO4 II. NH3 III. CH3CH2COOH IV. HF A. I < III < II < IV B. I < IV < III < II C. III < I < IV < II D. II < III < IV < I
B
The conjugate bases of HSO4-, CH3OH, and H3O+ are, respectively: A. SO4-, CH2OH-, H2O B. SO42-, CH3O-, H2O C. SO4-, CH3O-, OH- D. SO42-, CH2OH-, OH-
B
What is the pH of a solution with a hydronium (H3O+) ion concentration of 3 × 10-1 M? A. 2.0 B. 0.5 C. 1.5 D. 1.0
B
Which of the following bases is the weakest? A. KOH B. NH3 C. CH3NH2 D. Ca(OH)2
B
Which of the following best characterizes the ionization constant of a strong acid? A. 0 < Ka < 0.1 B.Ka > 1 C.Ka < 0 D. 0.1 < Ka < 1
B
Which of the following combinations will form a solution with the greatest buffering capacity? A. 0.2 M HCl and 0.2 M NaCl B. 0.2 M CH3CO2H and 0.2 M NaCH3CO2 C. 0.02 M CH3CO2H and 0.02 M NaCH3CO2 D. 0.02 M HCl and 0.02 M NaCl
B
A salt solution contains ammonium cation (Ka = 5.7 × 10-10) and nitrite anion (Kb = 1.4 × 10-11) in equal proportions. The pH of the solution will be: A. acidic because nitrite has a higher Kb value than the Ka of ammonium. B. acidic because ammonium has a higher Ka value than the Kb of nitrite. C. basic because ammonium has a higher Ka value than the Kb of nitrite. D. basic because nitrite has a higher Kb value than the Ka of ammonium.
B;
4-Nitrophenol (pKa = 7.08) is an indicator that is yellow when deprotonated and colorless when protonated in solution. If a solution has a pOH of 10, its color will be: A. indeterminable from the information given. B. colorless. C. light yellow because both acid and conjugate base will be present in equal amounts. D. yellow.
B; 4-Nitrophenol (pKa = 7.08) is an indicator that is yellow when deprotonated and colorless when protonated in solution. If a solution has a pOH of 10, its color will be colorless. Since pH + pOH = 14, we know that the pH of the solution in question is 4. Since this pH is less than the pKa of the indicator, the 4-nitrophenol will be protonated. Therefore, the solution will be colorless.
A 2 M solution of the potent organic pollutant sodium methylthiolate (NaSCH3) is titrated to its endpoint with 2 M HCl. Which of the following best approximates the pH of the resultant solution? (pKb of SCH3- = 3.6) A. -log (1 × 10^-3.6) B. -log (1 × 10^-5.2) C. -log (2 × 10^-5.2) D. -log (1 × 10^-1.8)
B; A 2 M solution of the potent organic pollutant sodium methylthiolate (NaSCH3) is titrated to its endpoint with 2 M HCl. -log (1 × 10-5.2) best approximates the pH of the resultant solution. (pKb of SCH3- = 3.6) The result of the titration will be a 1 M solution of methylthiol, HSCH3 since the initial 2 Msolution has been doubled in volume during the titration. Since we know the pKb of its conjugate base SCH3- is 3.6, then we know the pKa of HSCH3 is 10.4. Therefore, at equilibrium: 10-10.4 = (x)(x)/(1-x) Where x = [H+] = [SCH3-], at equilibrium. As the resultant value of x is negligibly small compared to 1, we ignore x in the denominator and say that x = [H+] = [SCH3-] = (10-10.4)(0.5) giving 1 × 10-5.2. The answer -log (2 × 10-5.2) would be correct if the resultant solution was 2 M in concentration. The answer -log (1 × 10-1.8) is the result of using the pKb of the methylthiolate anion in the calculation rather than the pKa of HSCH3, and -log (1 × 10-3.6) would be the result of a similar a calculation using this pKb value, while not taking the square root.
Which of the following salts will produce a basic solution when added to pure water? A. KCl B. NaClO C. NH4Cl D. MgBr2
B; Choice B will dissociate into Na+ and ClO-. Na+ does nothing, but ClO- is the conjugate base of a weak acid. Therefore, the solution will be basic. A has no effect on pH C and D leave it on the acidic side.
Enough HF (Ka = 7.4 × 10-4) is added to water to create a pH = 2.1 solution. The addition of which of the following would have the least impact on the pH of this solution? A. NH4F B. PbF2 C. Na2CO3 D. NaF
B; Enough HF (Ka = 7.4 × 10-4) is added to water to create a pH = 2.1 solution. The addition of PbF2 would have the least impact on the pH of this solution. Both NaF and NH4F are soluble salts, and will decrease the solubility (acidity) of HF due to the common ion effect, so both of these answer choices can be eliminated. Na2CO3 is a soluble salt and CO32- is the conjugate base of a weak acid, so it will act to increase the pH. PbF2 is essentially insoluble in water, and therefore will have the least effect on the pH, making it the best answer.
An unknown quantity of KOH was added to a liter of water in order to prepare a stock solution. The pH of the solution was measured to be 10.0. Assuming there were no other compounds in the solution, what quantity of KOH was added to the water? A. 10-2 moles B. 10-4 moles C. 10-10 moles D. 10-14 moles
B; Given the final pH was measured at 10.0, the concentration of hydronium ion is 10-10 M and we can calculate the quantity of hydroxide in solution to be 10-4 M (given Kw = 10-14). A pure water solution would already contain 10-7M OH-, but as this number is so much smaller than the final concentration (10-4M), the quantity of KOH added was likely very close to 10-4 moles (answer B is correct).
Two moles of propanoic acid, CH3CH2CO2H (pKa = 4.9), are added to a liter of water. What is the pH once equilibrium has been reached? A. 0.47 B. 2.3 C. 4.6 D. 7.7
B; Here we are asked to find the pH of a solution containing a weak acid (HA). To do this, we can use an ICE table to find the solution (note: we round the pKa to 5.0). Since pH = -log[H+], and log 10A = A, we can estimate that the pH of the solution is between 2 and 3 because the exponent is between -2 and -3.
The indicator bromothymol blue has a pKa near the pH of neutral water. Its basic form is a deep blue whereas its acidic form is a pale yellow. Near pH = 7 the indicator is green. If a solution of CsOH was slowly added to a solution of bromothymol blue in distilled water, what color change would be observed? A. Yellow to blue B. Green to blue C. Green to yellow D. Blue to green
B; If a solution of CsOH was slowly added to a solution of bromothymol blue in distilled water, the solution would change from green to blue. When bromothymol blue is initially added to distilled water (pH = 7), the solution is green. As the base CsOH is added to solution, the pH of the solution increases and the basic form of the indicator dominates, giving a blue color. A change to yellow, or a change from blue to green, would indicate a decrease in pH.
Which of the following salts would yield acidic aqueous solutions when dissolved in water? I. NH4ClO4 II. AgNO3 III. NaC2H3O2 A. I only B. I and II only C. III only D. I and III only
B; If the cation of a salt is the conjugate acid of a weak base, it will make a solution acidic. Similarly, if the anion of a salt is the conjugate base of a weak acid, it will make a solution basic. Ammonium perchlorate, NH4ClO4, contains the conjugate base (ClO4-) of a strong acid, which will have no reaction with water, and a conjugate acid (NH4+) of the weak base, NH3, which should make the solution acidic. Roman numeral I is therefore true (eliminate choice C). Silver nitrate, AgNO3, also contains the conjugate base (NO3-) of a strong acid, and its cation is reactive with water to form an insoluble hydroxide. Since Ag+ pulls hydroxide out of the solution, it lowers the pH of the solution by producing excess hydrogen ions (Ag+ + H2O → AgOH + H+). Roman numeral II is therefore also true (eliminate choices A and D). The anion in sodium acetate (C2H3O2-) is the conjugate base of a weak acid and will therefore make the solution basic according to the following hydrolysis equation: C2H3O2- + H2O → HC2H3O2 + OH-. The Na+ ion is not reactive with water since it is from the strong base NaOH.
Addition of which of the following compounds to a 1 M solution of H2C2O4(pKa = 1.2) would best help maintain the pH of a solution at 1.5? A. H2C2O4 B. HC2O4- C. HCl D. NaCl
B; If the goal is to maintain pH, we are attempting to create a buffer. Buffers are composed of conjugate pairs (weak acids and/or bases). Addition of more of the same acid would have no impact on the buffering potential of this solution (eliminate choice A). Addition of a different and strong acid would drop the pH dramatically, so eliminate choice C. Sodium chloride would not affect the pH (eliminate choice D). The answer should be the conjugate base of oxalic acid (H2C2O4), which is hydrogen oxalate (HC2O4-), or choice B.
What is the final pH after 30 milliliters of 3 x 10-3 M HBr is mixed with 20 milliliters of 4 x 10-3 M NaOH? A. 2.5 B. 3.7 C. 7.0 D. 11.5
B; In the reaction of a strong acid and a strong base, protons generated by the acid react with hydroxide ions generated by the base and any remaining protons or hydroxide ions are then responsible for the final pH of the solution. Here we have (0.03 L)(3 x 10-3 M) = 9 x 10-5 mol H+ and (0.02 L)(4 x 10-3 M) = 8 x 10-5 mol OH- resulting in 1 x 10-5 mol of H+ remaining. This means the solution should be acidic, so we can eliminate choices C and D. The final proton concentration is 1 x 10-5 mol/0.05 L = 0.2 x 10-3 = 2 x 10-4M H+ resulting in a pH of 3.7 (choice B is correct).
Which of the following statements is true about a solution of acetic acid in equilibrium? CH3CH2COOH (aq) <--> H+ (aq) + CH3CH2COO- (aq) A. When HI is added, CH3CH2COOH acts as a Brønsted-Lowry acid. B. When HCl is added, CH3CH2COO- acts as a Brønsted-Lowry base. C. When NaOH is added, CH3CH2COOH acts as a Lewis acid. D. When HF is added, CH3CH2COOH acts as an Arrhenius base.
B; It is true about a solution of acetic acid in equilibrium that when HCl is added, CH3CH2COO-acts as a Brønsted-Lowry base. CH3CH2COOH (aq) H+ (aq) + CH3CH2COO- (aq) In the presence of a strong acid, CH3CH2COO- will behave as a Brønsted-Lowry base by accepting a proton and the equilibrium will shift to the left. In the presence of a strong base, H+ and not CH3CH2COOH will behave as a Lewis acid and accept electrons from OH-. CH3CH2COOH does not contain the hydroxide ion, even though the formula for a carboxylic acid (COOH) might suggest that. Therefore, it cannot behave as an Arrhenius base.
The Ka of formic acid (HCOOH) is 1.8 × 10-4. What is the pKb of the formate ion? A. -14 - log (1.8 × 10-4) B. 14 + log (1.8 × 10-4) C. -14 + log (1.8 × 10-4) D. 14 - log (1.8 × 10-4)
B; The Ka of formic acid (HCOOH) is 1.8 × 10-4. The pKb of the formate ion is 14 + log (1.8 × 10-4). For a conjugate pair, such as formic acid and the formate ion, the product of the Ka of the acid and the Kb of the base is equal to 10-14. The equation KaKb = 10-14 is equivalent to the equation pKa + pKb= 14. Therefore, pKb = 14 - pKa = 14 - [-log (1.8 × 10-4)]=14 + log (1.8 × 10-4)
Methyl red (pKa = 5.1) undergoes a color change from red at a pH of approximately 4.1 to yellow at a pH of approximately 6.1. Which of the following best explains this transition? A. The increased alkaline nature of the solution results in decomposition of the indicator into a yellow intermediate. B. Different proportions of the acid and conjugate base predominate at differing pHs. C. Acidic methyl group protons are being lost, resulting in a change in the length of the conjugated system of the acid. Your Answer D. The weak acid forms a weak bond with its proton which only becomes strong enough to change the color at higher pHs.
B; The protonated and deprotonated form of most indicators generate a different color based upon the length of their conjugated systems. When the pH of a solution changes, the proportion of the acid and conjugate base forms of the indicator change and result in a color change (choice B is correct, D is incorrect). When the pH of the solution is equal to the pKa of the indicator, we would expect equal amounts of the protonated form of the indicator and its conjugate base (and a mixing of the two colors). As you move one pH unit from the pKa, you have 90% of one form and only 10% of the other (explaining why you see little color change beyond the pH values listed above). If an indicator decomposed, it would not likely be a reversible process (eliminate choice A). Methyl protons are very poor acids and will not dissociate near the pH values described here (eliminate choice C).
Which of the following is a contributing factor to the relative acidity of HF compared to HCl? A. HCl exhibits stronger hydrogen bonding. B. HF has a greater boiling point. C. F- is less stable in solution than Cl-. D. HCl has a shorter bond length.
C
The Ka of a buffer is 4.5 × 10-4. If the concentration of undissociated weak acid is equal to the concentration of the conjugate base, the pH of this buffer system is between: A. 5 and 6. B. 2 and 3. C. 3 and 4. D. 4 and 5.
C; The Ka of a buffer is 4.5 × 10-4. If the concentration of undissociated weak acid is equal to the concentration of the conjugate base, the pH of this buffer system is between 3 and 4. The pH of a buffer can be calculated using the Henderson-Hasselbalch equation, pH = pKa + log ([conjugate base]/[conjugate acid]) When the concentrations of the acid and base are equal, the fraction on the right-hand side is 1; since log 1 = 0, we have pH = pKa. If the Ka of the acid is 4.5 × 10-4, which is between 10-4 and 10-3, the pKa (and, therefore, the pH) is between 3 and 4.
Which of the following would exhibit a color change only at the end of the titration of 20 milliliters of 0.75 M NaOH into 60 milliliters of 0.25 MHClO4? A. Thymol blue (pKa = 1.7) B. Methyl orange (pKa = 3.5) C.Bromothymol blue (pKa = 7.1) D. Phenolphthalein (pKa = 9.7)
C; The number of moles of the acid and base can be determined by multiplying the molarity and the volume. Thus 0.75 M NaOH * 0.020 L gives 0.150 mol NaOH and 0.25 M HClO4 * 0.060 L gives 0.150 mol HClO4. The neutralization reaction here involves equal quantities of a strong acid and strong base resulting in a neutral solution (pH = 7). The appropriate indicator will not change color until all the acid has been neutralized by the addition of the full amount of base. An indicator's given color is dictated by its protonation state, since it is itself a weak acid. When the solution pH approaches that of the pKa of the indicator, the protonation state of the compound changes and the color of the indicator changes. Therefore, we will select an indicator with a p?Ka nearest the pH we wish to see a color change (choice C is correct).
Which one of the following best approximates the pH of a solution when 99.9% of the acid in a pH 1 solution is neutralized? A. 7 B. 1 C. 4 D. 6.7
C; The pH of a solution when 99.9% of the acid in a pH 1 solution is neutralized is 4. The neutralization of 99.9% of acid tells us that for every one thousand H+ originally in solution, only one remains. A change in [H+] by a factor of 103 corresponds to a change of 3 pH units. If the initial pH was 1.0, then the final pH must be 4.
Squaric acid, shown below, has two acidic protons with pKa values of 1.5 and 3.4. If 10 mL of a 1 M sample of squaric acid is titrated with 10 mL of a 2 Msolution of NaOH, the pH of the resultant solution will be in which of the following ranges? A. 0 - 4 B. 4 - 7 C. 7 - 11 D. 11 - 14
C; The pKa values given (1.5 and 3.4) indicate that while the first proton is a reasonably strong acid, the second is weaker, but still acidic. After neutralizing all the H+s in squaric acid with an equivalent amount of OH-from NaOH (a strong base), the pH of the solution will be greater than 7 (eliminate choices A and B). The final solution will be 0.5 M sodium squarate, a weak base with pKb = 10.6. This will result in a mildly basic solution between 7 and 11. For those who need proof:
Mixing which of the following with an equal volume of 1 M HCl would generate a final solution with pH 7? A. 1 M H2SO4 B. 1 M Mg(OH)2 C. 1 M KOH D. 1 M CH3COOH
C; This question is asking about a neutralization reaction. If equal quantities of the acid and base in question are mixed and generate a pH of 7, the two species have to be a strong acid and a strong base (if it were a weak acid and a strong base, the result would have been a basic solution, while if it were a strong acid and a weak base, the result would have been an acidic solution). Choices A and D are acids, so should be eliminated. Between choices B and C, only KOH is a strong base, and moreover has one equivalent of hydroxide to neutralize the hydrogen ions, making choice C correct.
Chlorosulfonic acid (HSO3Cl) is stronger than sulfuric acid when solvated in water, yet it is far less acidic in common organic solvents. When 1.16 g of HSO3Cl is dissolved in 10 mL of hexane, spectroscopic methods determine the [SO3Cl-] to be 2.2 × 10-3 M. Which of the following is closest to the pKa of chlorosulfonic acid in hexane? A. 6.2 B. 2.8 C. 5.4 D. 0.2
C; When 1.16 g of HSO3Cl is dissolved in 10 mL of hexane, spectroscopic methods determine the concentration of [SO3Cl-] to be 2.2 × 10-3 M. The pKa of chlorosulfonic acid in hexane is closest to 5.4. The molecular weight of HSO3Cl is ~116 g/mol, so the initial concentration for HSO3Cl in 10 mL of hexane is 1 M. If [SO3Cl-] is 2.2 × 10-3 M, then the Ka ([SO3Cl-][H+]/[HSO3Cl]) in question can be expressed as (2.2 × 10-3)2/(1 - 2.2 × 10-3). The denominator can be safely simplified to 1, giving Ka = ~4 × 10-6. Since -log (4 × 10-6) is between 5 and 6, 5.4 is the only possible answer.
What would be the predicted pH of a potassium malate (KC4H5O5) solution? A. < 7 B. 7 C. > 7 Correct Answer D. Inadequate information to determine the pH
C; When confronted with an unfamiliar salt, we must evaluate each ion individually in order to determine the overall pH of the solution. Potassium is a group I metal and is therefore neutral in water (it fails to react with water). The anion malate is not a conjugate base of one of the strong acids you must recognize for the MCAT. You should therefore conclude it is the conjugate base of a weak acid, and is therefore a basic anion (it reacts with water by accepting a proton). Overall, this salt generates a basic solution with a pH > 7, so choice C is correct.
A titration is performed on 100 mL of a 1 M solution of nitrous acid (Ka = 4 × 10-4) using a 2 MNaOH solution. Upon addition of 25 mL NaOH, the pH of the solution will be closest to: A. 5.4 B. 1.4 C. 7.4 D. 3.4
D
Binary mixtures of equal moles of which of the following acid-base combinations will lead to a complete (99+%) neutralization reaction? I. HCl and NaOH II. HF and NH3 III. HNO3 and NaHCO3 A. I only B. I and II only C. II and III only D. I, II, and III
D
The Ka of HSCN is equal to 1 x 10^-4. The pH of a HSCN solution: A. Will be approximately 4 B. Will be approximately 10 C. Will increase as [HSCN] increases D. Cannot be determined from the information given
D
Which of following acids would dissociate to the greatest degree? A. HCN (Ka = 6.2 x 10^-10) B. H3BO3 (Ka = 5.4 x 10^-10) C. HNO2 (Ka = 4.0 x 10^-4) D. H2SO3 (Ka = 1.4 x 10^-2)
D
Ba(NO2)2 is a basic salt due to the interaction of the nitrite ion with water according to the following reaction: NO2- + H2O HNO2 + OH- Why does the equilibrium shown favor the left side of the reaction? A. H2O is a stronger acid than HNO2. B. H2O is a weaker base than OH−. C. NO2− is a stronger base than OH−. D. NO2− is a weaker base than OH−.
D; Ba(NO2)2 is a basic salt due to the interaction of the nitrite ion with water according to the following reaction: NO2- + H2O HNO2 + OH- The equilibrium shown favors the left side of the reaction because NO2− is a weaker base than OH−. Acid/base equilibria always favor the weaker acid/base pair. Since NO2- has a negative charge and no proton to donate, it must be the base, making water the acid. If the equilibrium favors the left hand side of the reaction, NO2- and H2O must be the weakest base and acid, respectively, eliminating these choices. While the choice, "H2O is a weaker base than OH−" is a true statement, water is not acting as a base in this particular reaction so this choice is not a good justification.
Which of the following compounds is a weak electrolyte? A. BaCl2 B. CH3OH C. KOH D. CH3COOH
D; CH3COOH is a weak electrolyte. Strong electrolytes dissociate into ions when dissolved in water, yielding a solution that conducts electricity. Weak electrolytes partially dissociate in solution. Both the strong base KOH and salt BaCl2 are strong electrolytes because they are ionic compounds, and can therefore be eliminated. Answer choices CH3COOH and CH3OH are covalently bonded molecular compounds, but only CH3COOH partially dissociates due to the slightly acidic nature of the COOH group. CH3OH does not dissociate to any appreciable extent and is a non-electrolyte.
Given that 0.0040% of a 0.5 mole sample of HCN dissociates in one liter of solution, what is the approximate pKa of HCN? A. 4.2 B. 5.2 C. 7.2 D. 9.2
D; Given 0.0040% of the acid has dissociated, we know that [CN-]/([HCN]-[CN-]) = 4 x 10-5. We can assume the [CN-] to be negligible compared to the [HCN], which allows us to remove [CN-] from the denominator. The [HCN] is 0.5 M, so we can calculate [CN-] to be 2 x 10-5M. These equilibrium concentrations can be substituted into the Ka expression to get a value for Ka, and from there we can find our pKa. (2 x 10-5)2/0.5 = 8 x 10-10 = Ka, which gives us a pKa between 9 and 10 (choice D is correct).
The addition of 1 g of which of the following compounds to distilled water would cause the least change in pH? A. LiH B. HCl C. LiOH D. CsOH
D; The addition of 1 g of CsOH to distilled water would cause the least change in pH. Since the question posits that 1 g of each strong electrolyte (which undergoes complete dissociation) is added to distilled water, the compound with the highest molecular weight will yield the lowest molar concentration of either H+ or OH-. Cesium hydroxide (MW = ~150) is far heavier than any of the other compounds in question and is therefore the correct answer. LiH is a strong base, and when added to water will undergo the reaction LiH + H2O ? LiOH + H2. Hence the resultant pH from 1 g of LiH will be just slightly higher than 1 g of LiOH.
Of the following, which statement best explains why HF is a weak acid, but HCl, HBr, and HI are strong acids? A. F has a greater ionization energy than Cl, Br, or I B. F has a larger radius than Cl, Br, or I C. F- has a larger radius than Cl-, Br-, or I- D. F- has a smaller radius than Cl-, Br-, I-
D; The more stable an acid's conjugate base is, the stronger the acid. Larger anions are better able to spread out the negative charge, making them more stable.
Consider this reaction: AlCl3 + H2O <--> (AlCl3OH)- + H+ What are the Lewis acids and bases?
Lewis acids: H+, AlCl3 Lewis bases: AlCl3OH-, H2O AlCl3 and H+ are acids because they accept electron pairs H2O and AlCl3OH- are bases because they donate electron pairs
What effect do negative charges have on basicity?
More negative charges increases basicity OH- is more basic than H2O CO3 2- is more basic than HCO3 2-
What effect do positive charges have on acidity?
More positive charges, increases acidity NH4+ is more acidic than NH3 Fe3+ is more acidic than acidic than Fe2+
What happens when both ions contribute to the solution?
Need to look at Ka values
SO4 2-
Sulfate
As hydrogen ions are added to an acidic buffer solution, what happens to the concentrations of undissociated acid and conjugate base?
The conjugate base, A-, reacts with the added H+ to form HA, so the conjugate base decreases and the undissociated acid increases.
What effect does size have on acidity?
The larger the atom, the more acidic HI is more acidic than HF H2S is more acidic than H2O
What effect does electronegativity have on basicity?
The less electronegative the atom, the more basic NH3 is more basic than HF CH3NH2 is more basic than CH3OH
What effect does electronegativity have on acidity?
The more electronegative at the atom, the more acidic H2O is more acidic than CH4 HCl is more acidic than H2S
What is the autoionization of water?
Water acting as acid and base, giving us Kw where Kw=[H+][OH-] and Kw=1*10^-14
What is the buffering domain on a titration curve?
When we initially add large amounts of strong acid/base to a weak base/acid respectively, and there is little change in pH. After this part, there is little weak acid left and the OH- concentration in solution is not that much different from the NaOH concentration in the titrant, where the curve levels off.
Orange juice has a pH of 3.5. What is its [H+]?
[H+] = 3.2 x 10^-4 M
What is the half equivalence point?
[HF] at half equiv = [F-] at half-equiv The pKa of HF equals the pH at the half-equivlance point
Neutralization equation
a x [A] x Va = b x [B] x Vb a = number of acidic hydrogens b = constant that tells us how many H+ ions the base came accept
A 50 mL solution of HCOOH (formic acid) is titrated with .2M NaOH. The equivalence point is reached when 40 mL of the NaOH solution has been added. What was the original concentration o the formic acid solution.
a[A]Va = b[B]Vb [A] = .16M
Two most common buffers on the MCAT
acetic acid and its salt (sodium acetate) ammonia and its salt, ammonium chloride
Buffer is a mature of an ______ and a salt of its ________ _______
acid conjugate base
What does polyprotic mean?
an acid that can donate more than one proton
Is NaF acidic, basic, or neutral?
basic
The conjugate base of a strong acid has no _________ properties in water
basic
H3BO3
boric acid
Let's consider HF titrated with NaOH. As HF is neutralized, the pH will increase. But from the titration curve, we see it does not change rapidly. The region where the pH changes gradually is called the __________ domain
buffering
H2CO3
carbonic acid
HClO3
chloric acid
HClO2
chlorous acid
phenolphthalein is an indicator with a pKa of about 9.0. When added to a solution where the pH is less than 8, its color is _________; If the solution pH is above 10, it will turn __________
colorless; magenta
For an indicator, when the pKa is equal to the pH of the solution it is in, it will __________
deprotonate
at high pH amino acids are
deprotonated
What are Lewis acids?
electron pair acceptors
What are lewis bases?
electron pair donors
Acids generally have more _________ atoms bonded to hydrogen
electronegative
Lewis acids act as _________
electrophiles
The point at which the indicator changes its final color is the
endpoint
Neutralization reactions are always
exothermic
Bases generally have _________ electronegative atoms with lone pairs
less
What is the pH of 25 mL of .065 CH3COOH? (Ka = 1.8 x 10^-5)
pH = -1/2 log (1.8 x 10^-5[6.5 x 10^-2]) pH = -1/2 (12 x 10^-7) pH = -1/2 (1.2 x 10^-6) pH = -1/2 (-6) pH = 2 < pH < 3
What is the pH of a 25mL of .025M HCl?
pH = -log [.025M] pH = -log (2.5 x 10^-2) pH = -(-2) pH = ~2
How do you calculate the pH of a strong acid?
pH = -log[H+]
pH equation
pH = -log[H+] [H+] = 10^-pH
Henderson-Hasselbalch equation
pH = pKa + log [A-]/[HA]
How would you make a pH 4.5 buffer from 1M acetic acid if pKa = 4.5
pH = pKa + log [A-]/[HA] 4.5 = 4.5 + log [A-]/[HA] 0 = log [A-]/[HA]
pKa equation
pKa = -logKa
pKb equation
pKb=-logKb
What is the pH of 1 L of 2.9 x 10^- M Ca(OH)2?
pOH = -log (2 x 3 x 10^-4) pOH = -log (6 x 10^-4) pOH = -(-4) pOH = 4 (actual value = 3.24) 3 < pOH < 4 pH = 14-3 > pH > 14-4 pH = 11 > pH > 10
pOH for strong bases
pOH = -log[OH-]
How do weak acids dissociate?
partially
HClO4-
perchloric acid
H3PO4
phosphoric acid
The strength of an acid is directly related to how much the...
products are favored over the reactants
What are amphoteric compounds?
substances that can act as an acid or a base
What is buffering capacity?
the amount of acid or base a buffer can neutralize
What is a conjugate acid?
the particle formed when a base gains a hydrogen ion
What is the equivalence point?
the point at which neutralization occurs moles OH- added = moles of H+ initially present
What is a conjugate base?
the species that remains after a Bronsted-Lowry acid has given up a proton
Give an example of an amphoteric compound?
water, amino acids