Knewton's Alta Module 14
Calculate the hydronium ion concentration of a solution with a pH of −1.070. A) 5.1 M B) 7.7 M C) 9.3 M D) 11.7 M
D) 11.7 M
The initial concentration of base B in solution is 0.72 M. If the pH of the solution at equilibrium is 9.4, what is the percent ionization of the base? A) 12% B) 7.2% C) 2.9% D) 3.5×10−3%
D) 3.5×10−3%
In an acid-base reaction involving neutral base B, what will be the conjugate acid? A) H2O B) H3O+ C) OH− D) HB+
D) HB+
The pH of a solution is equal to: A) -log[H3O+] B) log[H3O+] C) -log[OH−] D) log[OH−]
A) -log[H3O+]
Which of the following is true of water in a base ionization reaction? A) Water loses a proton and is acting as an acid. B) Water loses a proton and is acting as a base. C) Water accepts a proton and is acting as an acid. D) Water accepts a proton and is acting as a base.
A) Water loses a proton and is acting as an acid.
A Bronsted-Lowry base is best described as __________. A) a proton acceptor B) an electron pair donor C) a base capable of accepting exactly two protons D) a base capable of accepting exactly one proton
A) a proton acceptor
If coffee has a [H3O+] of 10−5 M and an [OH−] of 10−9 M, it is: A) acidic B) basic C) neutral D) depends on the temperature
A) acidic
The hydroxide concentration of a solution is equal to: A) −log^pOH B) log^pOH C) 10^−pOH D) 10^pOH
C) 10^−pOH pOH is defined as the negative logarithm of the hydroxide anion concentration (analogous to pH and the hydronium ion concentration), or pOH=−log[OH−]. Use this equation to solve for [OH−]. pOH−pOH[OH−]=−log[OH−]=log[OH−]=10^−pOHRewrite the logarithm as an exponential.
At 10∘C, the ion product of water is 2.93×10−15. What is the concentration of hydronium ions at this temperature? A) 1.46×10−15 M B) 3.84×10−8 M C) 5.41×10−8 M D) There is not enough information.
C) 5.41×10−8 M
Which pOH value corresponds to an acidic solution at room temperature? A) 3.7 B) 5.9 C) 9.2 D) 7
D) 7 If a pH below 7 corresponds to an acidic solution at room temperature, then a pOH above 7 also corresponds to an acidic solution.
Consider the reaction below. H2S+SO2−4⇌HS−+HSO−4 Which of the above chemical species is the Brønsted-Lowry base in the forward reaction?
SO2−4
What is the pOH of a solution at 25.0∘C with [H3O+]=6.6×10−10 M?
pH=4.82
Determine the Kb for the base B given that the equilibrium concentrations are [B]=2.6 M, [HB+]=0.143 M, and [OH−]=6.2×10−2 M.
3.4 x 10^-3
In what ratio will nitric acid and magnesium hydroxide react in a neutralization reaction? HNO3+Mg(OH)2⟶H2O+Mg(NO3)2 A) 1:2 B) 2:1 C) 1:3 D) 3:1
B) 2:1
When a base is dissolved in aqueous solution, water is acting as: A) a base. B) an acid. C) both an acid and a base. D) neither an acid nor a base.
B) an acid.
For a weak acid dissociating in water, which of the following is true at equilibrium? A) the rate of the forward reaction is greater than the rate of the reverse reaction B) the rate of the reverse reaction is greater than the rate of the forward reaction C) the rates of the forward and reverse reactions will be equal D) depends on the acid
C) the rates of the forward and reverse reactions will be equal
What is the conjugate base in the forward reaction? C2O4+HC2H3O2⇌HC2O−4+C2H3O2− A) C2O4 B) HC2H3O2 C) HC2O4− D) C2H3O2−
D) C2H3O2−
What products are formed as a result of the dissolution of solid calcium hydroxide (Ca(OH)2) in water? (Ignore stoichiometry.) A) Ca2+(aq) and H2O(l) B) Ca(s) and H2(g) C) Ca(OH)2−4(aq) and H2(g) D) Ca2+(aq) and OH−(aq)
D) Ca2+(aq) and OH−(aq)
What are the expected products of the unbalanced reaction: HNO3(aq)+Ba(OH)2(aq)→? A) Ba(NO3)2(aq) B) O2(g)+Ba(NO3)2(aq) C) H2(g)+Ba(NO3)2(aq) D) H2O(l)+Ba(NO3)2(aq)
D) H2O(l)+Ba(NO3)2(aq)
In a buffer solution made of acetic acid and sodium acetate, if a small amount of acid is added, the added acid will react with which of the following? A) hydronium ions B) sodium ions C) acetic acid D) acetate ions
D) acetate ions
When an acid-base reaction is at equilibrium, the equilibrium constant will be equal to: A) −1 B) 0 C) 1 D) the reaction quotient
D) the reaction quotient
Complete and balance the chemical equation for the neutralization reaction of phosphoric acid (H3PO4(aq)) and sodium hydroxide (NaOH(aq)). Write the chemical equation in molecular form (do not show dissociated ions). Include the state (phase) of each chemical species.
H3PO4(aq)+3NaOH(aq)⟶3H2O(l)+Na3PO4(aq)
Determine the equilibrium concentration of the base NH3 given that pKb=4.76 and the equilibrium concentrations of OH− and NH+4 are 6.5×10−5 M, and 0.42 M respectively.
1.6M
What is the hydroxide concentration in a solution at 25.0∘C with [H3O+]=4.6×10−4 M?
2.2×10−11
When the reaction below is going in the forward direction, which compound acts as the base, according to the Bronsted-Lowry definition? PH+4+H2O↽−−⇀PH3+H3O+ A) H2O B) PH+4 C) H3O+ D) PH3
A) H2O
Choose the option below that is a base ionization reaction. A) H2O+HS−↽−−⇀H2S+OH− B) H2O+HF↽−−⇀F−+H3O+ C) PH+4+H2O↽−−⇀PH3+H3O+ D) H2O+HSO−4↽−−⇀SO2−4+H3O+
A) H2O+HS−↽−−⇀H2S+OH− Base ionization involves the transfer of a proton from water to a base to produce hydroxide ions, or the direct release of hydroxide ions into solution from a metal hydroxide salt.
If acid HX is stronger than acid HY, which statements are true? Select all that apply. A) The Ka of HX is greater than the Ka of HY. B) The Ka of HX is less than the Ka of HY. C) The [H3O+] in the HX solution is smaller than in the HY solution. D) More of the HX is ionized compared to the HY.
A) The Ka of HX is greater than the Ka of HY. D) More of the HX is ionized compared to the HY.
Which of the following is a true statement about the Lewis definition of acids and bases? A) The Lewis definition of acids and bases is based on donating or accepting an electron pair. B) The Lewis definition of acids and bases is based on the production of H3O+ or OH− ions in water solutions. C) The Lewis definition of acids and bases is based on donating or accepting a proton. D) none of the above
A) The Lewis definition of acids and bases is based on donating or accepting an electron pair.
Choose the Ka value that corresponds to the strongest acid. A) 7.4×10−7 B) 0.045 C) 1.7×10−5 D) 6.4×10−8
B) 0.045
Water's pH and pOH are both 7 at: A) 0∘C B) 25∘C C) 100∘C D) any temperature
B) 25∘C
The Kb of NH3 is 1.8×10−5. What is the Ka of NH+4, its conjugate acid? A) 1.8×10−5 B) 5.6×10−10 C) 1.8×10−19 D) 3.2×10−10
B) 5.6×10−10
What is the formula for the conjugate acid of acetate, CH3COO−? A) CH3COO B) CH3COOH C) CH2COO2− D) CH3COOH−
B) CH3COOH
Of the following, which are characteristics of basic solutions? (Select all that apply) A) pH levels less than 7 at 25∘C B) Greater concentration of hydroxide ions than hydronium ions C) [H3O+]<[OH−] D) pH levels of 7 at 25∘C
B) Greater concentration of hydroxide ions than hydronium ions C) [H3O+]<[OH−]
In the following reaction, which species acts as an acid? CO2−3+H2S⇌HCO−3+HS− A) CO2−3 B) H2S C) HCO−3 D) HS−
B) H2S
A solution of a compound in water conducts electricity, turns litmus blue, and has a bitter taste. What compound might be in the solution? A) HF B) Mg(OH)2 C) C3H5(COOH)3 D) H2SO4
B) Mg(OH)2
Identify which of following is a base. A) HF B) RbOH C) H2SO4 D) HCO2H
B) RbOH
In the reaction: NaOH⇌Na++OH− where the concentrations for NaOH, Na+, and OH− are each equal to 0.1 M, what is the equation for Kw when finding [H3O+]? A) [0.1 M][0.1 M] B) [H3O+][0.1M] C) [H3O+]/[0.1M] D) [0.1 M]/[H3O+]
B) [H3O+][0.1M]
The equation below is an example of which of the following? CH3COOH+H2O↽−−⇀H3O++CH3COO− A) autoionization B) acid ionization C) base ionization
B) acid ionization
The autoionization of water can be expressed as: A) OH−(aq)+H3O+(aq)⟶2H2O(l) B) OH−(aq)+H+(aq)⟶H2O(l) C) 2H2O(l)⟶H3O+(aq)+OH−(aq) D) 2H2O(l)⟶H3O+(aq)+2OH−(aq)
C) 2H2O(l)⟶H3O+(aq)+OH−(aq)
Which of the following gives the definition of percent ionization? A) Percent ionization is the equilibrium constant for the ionization of a weak acid. B) Percent ionization is the ratio of the concentration of the undissociated acid at equilibrium to its initial concentration times 100%. C) Percent ionization is the ratio of the concentration of the ionized acid at equilibrium to the initial acid concentration times 100%. D) None of the above
C) Percent ionization is the ratio of the concentration of the ionized acid at equilibrium to the initial acid concentration times 100%.
In a buffer solution made of acetic acid and sodium acetate, any base that is added will react primarily with which of the following? A) hydronium B) hydroxide C) acetic acid D) acetate
C) acetic acid
Roughly how many water molecules are ionized at any given time in a sample of room-temperature water? A) one in a thousand B) one in a million C) one in a billion D) one in a trillion
C) one in a billion
When a small amount of a strong acid or a strong base is added to a buffer solution, the pH will: A) decrease if a strong acid is added B) increase if a strong base is added C) remain relatively constant D) it depends on the strength of the acid or base
C) remain relatively constant
The lowest value that is possible on the pH scale is: A) 1 B) 0 C) −1 D) there is no fundamental lower limit
D) there is no fundamental lower limit As this is simply the negative log of the hydronium concentration, each pH unit descended is simply an order of magnitude greater for hydronium concentration, so even at −1, which means 10M in hydronium, there is no theoretical limit at this point. That being said, in the real world, the lowest pH observed is approximately −2, and the highest is approximately 16.
Which base is the weakest when dissolved in water? Kb values are listed next to the base. A) PO3−4 Kb=5.9×10−3 B) NH3 Kb=2.8×10−5 C) C6H5NH2 Kb=4.2×10−10 D) N2H4 Kb=9.5×10−7
The smaller the Kb value, the weaker the base, meaning it ionizes to a lesser extent and creates fewer products. The base with the smallest Kb value is C6H5NH2, which has Kb=4.2×10−10. This means C6H5NH2 is the weakest base listed.
The initial concentration of base B in solution is 0.24 M. If the pH of the solution at equilibrium is 12.53, what is the percent ionization of the base? A) 14.1% B) 20.5% C) 0.71% D) −1.0%
A) 14.1%
H2SO4(aq)+Mg(OH)2(aq)→ __________ + __________ A) 2H2O and MgSO4 B) H2O and MgSO4 C) 2H2O and 2MgSO4 D) 2H2 and MgSO4
A) 2H2O and MgSO4
If we add acid to a buffer containing NaCH3CH2COO and CH3CH2COOH, the acid will react with which of the following? A) NaCH3CH2COO B) CH3CH2COOH C) Na+ D) No reaction will occur.
A) NaCH3CH2COO
Determine the concentration of hydroxide ions for a 25∘C solution with a pH of 11.75. Your answer should have two significant figures. If reporting your answer in scientific notation form, use the multiplication symbol, ×, not the letter x.
5.6x10^-3
What is the Ka for an acid HA, if the equilibrium concentrations are [HA]=1.34 M, [H3O+]=9.89×10−5 M, and [A−]=9.89×10−5 M? Report your answer in scientific notation. Your answer should have three significant figures.
7.30X 10^-9
A solution has an initial concentration of weak acid (HA) equal to 0.150M and has a pH of 1.900 at equilibrium. What is the percent ionization of the acid?
8.4%
In the earliest of the models to be developed, an acid is defined as something that __________. A) dissolves in water to yield solvated protons, called hydronium ions B) dissolves in water to yield hydroxide ions C) dissolves in water and will produce no ions D) will not dissolve in water
A) dissolves in water to yield solvated protons, called hydronium ions In the Arrhenius model, it is the production of hydronium in water that characterizes an acid.
The reaction 2HCl(aq)+Mg(OH)2(aq)→2H2O(l)+Mg(Cl)2(aq) is an example of what type of reaction? A) neutralization B) dissociation C) oxidation of metals by acid other than water D) reaction of a base with a metal
A) neutralization
During the formation of sodium acetate, NaCH3CO2 , which of the following is are true?1. A solution of the salt NaCH3CO2 contains sodium ions and acetate ions.2. The sodium ion is neither an acid nor a base and thus has no effect on the acidity of the solution.3. The acetate ion, the conjugate base of acetic acid, reacts with water and increases the concentration of the hydroxide ion.4. The acetate ion, the conjugate base of acetic acid, reacts with water and decreases the concentration of the hydroxide ion. A) 1, 2, 4 B) 1, 2, 3 C) 2, 3, 4 D) 1, 3, 4
B) 1, 2, 3
What is the hydronium ion concentration in an aqueous solution with a hydroxide ion concentration of 0.001 M at 25∘C? A) 1×10−8 M B) 1×10−11 M C) 1×10−12 M D) 1×10−14 M
B) 1×10−11 M
Which of the following acids can be found in the human body? A) HF B) HCl C) HNO3 D) H2SO4
B) HCl
According to the Bronsted-Lowry definition, what is the conjugate base when the reaction below proceeds in the forward direction? H2PO−4+H2O⇌H3O++HPO2−4 A) H2O B) HPO2−4 C) H2PO−4 D) H3O+
B) HPO2−4
Consider the reaction of acetic acid CH3CO2H and water. CH3CO2H(aq)+H2O(l)↽−−⇀CH3CO−2(aq)+H3O+(aq) This equation describes the transfer of hydrogen ions, or protons, between the two substances. Which of the following statements about this process is true? A) Proton transfer will continue until equilibrium is reached. B) Proton transfer will continue indefinitely. C) Proton transfer only procedes in one direction. D) None of the above.
B) Proton transfer will continue indefinitely.
The hydronium ion concentration of vinegar is approximately 4×10−3 M. What are the corresponding values of pOH and pH? A) pH = 0.3, pOH = 13.7 B) pH = 2.4, pOH = 11.6 C) pH = 4.7, pOH = 9.3 D) pH = 6.1, pOH = 7.9
B) pH = 2.4, pOH = 11.6 First we calculate the pH using the given hydronium ion concentration of vinegar (4×10−3 M): pH=−log[H3O+]=-log 4×10−3pH=−(−2.3979)=2.3979 Then we use the pH to calculate the pOH: pH+pOH=14.00 pOH=14.00−pH pOH=14.00−2.3979 pOH=11.6
Identify the option below that is a characteristic of acidic solutions. A) [H3O+]<[OH−] B) pOH levels greater than 7 at 25∘C C) pOH levels less than 7 at 25∘C D) pOH levels of 7 at 25∘C
B) pOH levels greater than 7 at 25∘C Acidic solutions have a greater concentration of hydronium ions, H3O+, than hydroxide ions, OH−. The pH level of an acidic solution is less than 7 at 25∘C and the pOH level is greater than 7 at 25∘C.
At 100∘C, the ion product of water is 5.13×10−13. What is the concentration of hydronium ions at this temperature? A) 2.56×10−13 M B) 5.06×10−7 M C) 7.16×10−7 M D) There is not enough information.
C) 7.16×10−7 M
Strong acids are paired with: A) strong conjugate bases. B) water. C) weak conjugate bases. D) weak conjugate acids.
C) weak conjugate bases.
Which acid is the strongest when dissolved in water? Ka values are listed next to the acid. A) CH3COOH, Ka=1.8×10−5 B) HNO2, Ka=4.0×10−4 C) HF, Ka=6.8×10−4 D) HClO2, Ka=1.1×10−2
D) HClO2, Ka=1.1×10−2 The larger the Ka value, the stronger the acid, meaning it ionizes to a greater extent. The acid with the largest Ka value is HClO2, which has Ka=1.1×10−2. This means HClO2 is the strongest acid listed.
Methylamine (CH3NH2) is a weak base like ammonia (NH3). Write the chemical equation for the dissociation of aqueous methyl amine. Be sure to show all charges and include all products.
Methylamine has no OH− anion to dissociate directly. Instead, like ammonia, it has a nitrogen with a lone-pair of electrons that can accept a proton from water, leading to the protonated formula CH3NH+3(aq). The water molecule minus a proton gives the hydroxide anion, OH−(aq). The completed reaction is shown below. CH3NH2(aq)+H2O(l)⇌CH3NH+3(aq)+OH−(aq)
Sulfuric acid reacts with sodium carbonate to form water, a salt, and a gas. Write the formulas for the salt and other compound that are formed in the reaction. Na2CO3(aq)+H2SO4(aq)⟶H2O(l)+?+?
The formula for sulfuric acid is H2SO4, and the formula for sodium carbonate is Na2CO3. The gas evolved in the reaction of a carbonate with an acid is carbon dioxide, or CO2. Water is also given as one of the products. So part of the reaction will be as shown below. Na2CO3(aq)+H2SO4(aq)⟶CO2(g)+H2O(l)+? The sodium ions and the sulfate ion from the reactants are missing in the products. They must be added. Recall that a sodium ion has a charge of plus one and a sulfate ion has a charge of minus two. The complete reaction is shown below. Na2CO3(aq)+H2SO4(aq)⟶CO2(g)+H2O(l)+Na2SO4(aq) Besides water, the products are CO2 gas and sodium sulfate, Na2SO4.
The reactants zinc and hydrochloric acid are involved in a redox reaction. Which of the following is a product of the reaction?
The reaction is Zn(s)+2HCl(aq)⟶ZnCl2(aq)+H2(g).
A metal and an acid react violently to form sodium sulfate and hydrogen gas. What are the acid and the metal? Write chemical formulas separated by a comma. Do not include the state of matter of the species in your answers.
When an acid oxidizes a metal, the products are hydrogen gas and a salt that consists of a cation of the metal and the anion of the acid. The formula for sodium sulfate is Na2SO4, because the sodium ion has a charge of +1 and the sulfate ion has a charge of −2. Therefore, the metal will be elemental sodium, Na, and the acid will be sulfuric acid, H2SO4. The equation of the very explosive reaction is shown below. 2Na(s)+H2SO4(aq)⟶Na2SO4(aq)+H2(g)
A solution has a pOH of 6.50 at 50∘C. What is the pH of the solution given that Kw=6.22×10−15 at this temperature? The equation relating pH and pOH at any temperature is pKw=pH+pOH Where pKw=−logKw. It is given that Kw=6.22×10−15 at 50∘C. Therefore, we can solve for the pH as follows: pH=pKw−pOH =−log(6.22×10−15)−6.50 =14.206−6.50=7.71
pH=7.71
