CHEM 211 Ch.18 Smartbook
A buffer is made up using 2.5 L of 0.25 M sodium phenolate (C6H5ONa) and solid phenol (C6H5OH; pKa = 10.0). The desired buffer pH is 9.82. Which of the following options correctly show the calculations required to calculate the mass of phenol needed? Select all that apply.
Mass of phenol required = 2.5 L × 0.38mol/1L × 94.11g/1mol [phenol] = 0.25/10^−0.18 9.82 = 10.00 + log0.25/[phenol]
Match each of the following cations with the anion used to precipitate it selectively in a qualitative analysis procedure.
Pb2+ matches Cl- Cu2+ matches S2- Fe2+ matches OH- Ba2+ matches CO32-
Match each of the following cations with the anion used to precipitate it selectively in a qualitative analysis procedure.
Ag2+ - Cl^- Hg2+ - S2^- Co2+ - OH^- Ca2+ - CO3^2-
Which of the following statements correctly describe a strong acid-weak base titration curve?
Before the equivalence point is reached, the weak base and its conjugate acid are both present in solution. The pH at the equivalence point is < 7.00.
The solubility of MgCO3 in water at 25oC is equal to 1.6 x 10-3 g per 100 mL. Select the options that correctly reflect the steps required to calculate Ksp for this compound.
Calculate molar solubility by converting g/100 mL to mol/L. Calculate the molar mass for MgCO3. The molar solubility will give both [Mg2+] and [CO32-]. Multiply the calculated values of [Mg2+] and [CO32-] to determine Ksp.
Match each condition with its effect on the solubility of a sparingly soluble ionic compound.
Change in pH= can either decrease or increase solubility, depending on the compound addition of a common ion= decreases solubility formation of a complex ion= increases solubility
Which of the following statements describes the common ion effect?
For a solution of a weak acid in water, addition of the conjugate base will shift the ionization equilibrium. Reason: Addition of the conjugate base will shift the equilibrium toward the weak acid.
When can Ksp values be used to compare the relative solubilities of two ionic compounds?
If the formulas of the compounds contain the same total number of ions
Calculate the Ksp of Fe(OH)3 given the equilibrium concentrations [Fe3+] = 9.3 × 10-11 M and [OH-] = 2.8 × 10-10 M.
Ksp = 2.0 × 10-39 Reason: Ksp = (9.3 × 10-11)(2.8 × 10-10)3
Match the relationship between Q and Ksp to the correct description.
Q<Ksp = solution is unsaturated and no precipitate forms Q= Ksp solution is saturated and no change occurs Q<Ksp= precipitate forms until solution becomes saturated
Which of the following statements correctly defines qualitative analysis?
Qualitative analysis is the determination of the types of ions present in a solution
Consider the reaction PbSO4 (s) ⇌ Pb2+ (aq) + SO42- (aq). When Na2SO4 is added to the system, the presence of the common ion _____ (give the name or formula, including the charge) causes the equilibrium to shift toward the ______ and the solubility of PbSO4 will ______ , in accordance with Le Chatelier's principle.
SO42-, left, decrease
When comparing the titration curve for a weak base-strong acid titration and a strong acid-strong base titration the following differences are found. Choose all that apply.
The curve for the weak base-strong acid titration drops gradually before the steep drop close to the equivalence point. The pH at the equivalence point is below 7.00 for the weak base-strong acid titration.
When comparing the titration curve for a weak acid-strong base titration and a strong acid-strong base titration the following differences are found. Choose all that apply.
The pH at the equivalence point is above 7.00 for the weak acid-strong base titration. The curve for the weak acid-strong base titration rises gradually before the steep rise to the equivalence point.
A given mass of solid KOH is added to an aqueous solution of Cu(NO3)2 of known concentration. Select all the options that correctly reflect the information required to determine whether or not a precipitate forms in this solution.
The volume of the Cu(NO3)2 solution The molar mass of KOH Ksp of Cu(OH)2
Select the least soluble compound from the following list.
Zn(OH)2 (Ksp = 3 x 10-16)
Consider a buffer solution consisting of 0.35 M HNO2 and 0.50 M KNO2, which has an initial pH of 3.30 (Ka for HNO2 = 7.1 × 10-4). If 0.030 mol of HCl are added to 1.0 L of this solution, select all the options that correctly reflect the steps required to calculate the change in pH.
[H3O+] = 7.1 × 10-4 × 0.380/.470 Reason: Correct. 0.03 mol of HCl will react with 0.030 mol NO2- to give [NO2-] = 0.47 M. 0.030 mol HNO2 are formed so that [HNO2] = 0.38 M. pH = -log(7.1×10−4×0.38/0.47) = 3.24
150 mL of 0.15 M Na2SO4 is mixed with an equal volume of 0.050 M AgNO3. Select all the options that correctly show the steps used to determine whether or not a precipitate will form, if Ksp for Ag2SO4 = 1.5 × 10-5.
[SO42-] = 7.5 × 10-2 M Reason: Since equal volumes are mixed [SO42-] is halved. Q = (0.025)^2(0.075) Reason: [Ag+] = 0.05020.0502 because 1 mol of AgNO3 produces 1 mol of Ag+ ions in solution, and the final volume is twice the original volume. By the same argument, [SO42-] = 0.1520.152.
One type of acid-base buffer is composed of a weak _____, which will react with any added base, and its conjugate _____, which will react with any added acid.
acid, base
When Na2CO3 is added to a saturated solution of BaCO3, the equilibrium will shift so as to ______ the quantity of carbonate ions in solution, thus ______ the solubility of BaCO3.
decrease, decreasing Reason: The equilibrium will shift to use up the excess CO32- ions, toward the undissociated salt, and the solubility of BaCO3 will decrease.
The solubility of a substance can be expressed in terms of the mass of the substance in ______ present in 1 L of a saturated solution, or in terms of the ______ solubility, which is the number of moles present in 1 L of a saturated solution
grams; molar
Match each stage of a weak acid-strong base titration with the correct description of how to calculate [H3O+], [OH-], and/or pH.
initial pH matches Choice, use Ka and [HA]init to calculate [H3O+] = [A-] use Ka and [HA]init to calculate [H3O+] = [A-] before equivalence point matches Choice, pH = pKa + log[A-][HA]; [A-] = molesOH-addedtotalvolume pH = pKa + log[A−][HA][A-][HA]; [A-] = moles OH− addedtotal volumemoles OH- addedtotal volume at equivalence point matches Choice, [OH-] = Kb×A- where [A-] = molesofHAinittotalvolume [OH-] = Kb×[A−]‾‾‾‾‾‾‾‾‾‾√Kb×A- where [A-] = moles of HAinittotal volumemoles of HAinittotal volume after equivalence point matches Choice, pH depends on moles excess OH- added pH depends on moles excess OH- added
A slightly soluble ionic compound will dissolve to a small extent in H2O and a saturated solution is formed at a fairly ________ solute concentration. At this point there is a(n) between undissolved solid and the dissociated in solution.
low; equilibrium; solute
Consider a buffer solution consisting of 1.0 M HF and 1.0 M NaF, which has an initial pH of 3.14 (Ka for HF = 7.2 × 10-4). Use the Henderson-Hasselbalch equation to determine the new pH after 0.10 mol of NaOH is added to 1.0 L of this solution.
pH = 3.23 Reason: Addition of a base will cause the pH to increase. pH = pKa + log [conjugate base]/[acid] The 0.10 mol of OH- will react with 0.10 of HF to produce 0.10 mol of F- then [HF] = 0.90 M and [F-] = 1.10 M. pH = -log (7.2 × 10-4) + log 1.10/0.90 = 3.14 + 0.09 = 3.23.
Which of the following is the correct expression to calculate the molar solubility of Ag3PO4 in water at 25oC if Ksp = 2.6 × 10-18?
s= 4 Sqr root^ (2.6 x 10^-18 / 27)
True or false: For complex ion formation, a Kf that is >> 1 indicates that a given complex ion is stable, and likely to form.
true; Reason: Correct. The complex ion is the product of the equilibrium equation, so a large Kf value means that complex ion formation is favored.
An indicator is a(n)_____ organic acid that has a different color than its _____base. Each indicator changes color over a specific _____range.
weak, conjugate, pH
Which of the following combinations could be used in an acid-base buffer system?
-NH3/ NH4Cl Reason: This is a buffer because it contains a weak acid-base pair. In this case NH3 is a weak base and NH4Cl is its conjugate acid. KNO2/HNO2 Reason: HNO2 is a weak acid; therefore a solution containing HNO2 and NO2- would function as a buffer. -CH3COOH/NaCH3COO-
Select all the statements that correctly describe the solubility product constant Ksp for a slightly soluble substance.
-The value of Ksp indicates how far a dissolution equilibrium proceeds in favor of dissolved solute. -Ksp is a particular form of a general equilibrium constant (Kc).
A buffer used in food products is the benzoic acid/benzoate buffer, which has a pKa = 4.19. If you need to maintain a pH of 3.50 using this buffer system, what concentration of benzoate ion would you need if you have 0.05 M benzoic acid?
0.01 M benzoate ion Reason: 3.50 = 4.19 + log[benzoate]/0.05 so [benzoate]/0.05 = 10^-0.69 and [benzoate] = 0.05 × 10^-0.69 = 0.01 M.
In order for a solution of a weak acid and its conjugate base to be considered a buffer, the ratio of base concentration to acid concentration must be within the range _____
0.1 < [base]/[acid] < 10
Which of the following can NOT be used as an acid-base buffer solution?
0.5 M HNO3 and 0.5 M NaNO3 Reason: HNO3 is a strong acid. An acid-base buffer must consist of a conjugate acid-base pair of a weak acid or base. 0.3 M HCl and 0.3 M NaOH Reason: HCl and NaOH are not a conjugate acid-base pair
Rank the following compounds from greatest solubility (top of the list) to lowest solubility (bottom of the list).
1. CaCO3 ( Ksp=8.7 x 10^-9) 2.BaSO4 (Ksp=1.1 x 10^10) 3. FeS( Ksp= 6.3 x 10^-18)
In a standard qualitative analysis scheme, cations in a solution can be separated by stepwise addition of precipitating agents. Place the precipitating agents in the correct order for this procedure, starting with the first compound added at the top of the list.
1. HCl 2.H2S 3. NaOH 4. Na2CO3
Order the steps for preparing a buffer correctly, starting with the first step at the top of the list.
1. choose an appropriate conjugate base pair 2. calculate the ratio of buffer component concentrations needed 3.convert the ratio to molar quantities of the two buffer components 4. mix components together and correct pH if needed.
30.0 mL of a 0.15 M solution of the weak acid HClO is titrated with 0.20 M NaOH. Which of the following options correctly reflect how to calculate the pH after the addition of 16.5 mL of NaOH? Select all that apply. (The equivalence point has not yet been reached.) Ka for HClO is equal to 3.0 × 10-6.
1.2 × 10-3 moles of HClO remain in solution. pH = -log(3.0 × 10-6) + log3.3×10−31.2×10−33.3×10-31.2×10-3 Reason: The Henderson-Hasselbalch equation can be used to calculate pH at this point. The ratio moles ClO−/moles HClO= [ClO-]/[HClO] at this point. 3.3 × 10-3 moles of OH- have been added. Reason: 16.5 mL × 1L/1000mL× 0.20mol/1L = 3.3 × 10-3 mol OH- added.
In order for a solution of a weak acid and its conjugate base to be an effective buffer, the ratio of weak acid to weak base (or vice versa) must be ______-fold or less. Multiple choice question.
10
Calculate the molar concentration of Pb2+ ions at equilibrium in an aqueous solution of PbF2(s) if Ksp for PbF2 is 3.6 x 10-8.
2.1 × 10-3 M Reason: Let [Pb2+] = x, then 3.6 × 10-8 = (x)(2x)2 = 4x3 and x = 3.6×10−84‾‾‾‾‾‾‾√33.6×10-843.
Which of the following options correctly describes the function of an acid-base buffer?
A buffer minimizes changes in pH when acid or base is added to the solution. Reason: A buffer minimizes changes in pH when an acid or base is added to the solution.
In a standard qualitative analysis scheme, cations in a solution can be separated by stepwise addition of precipitating agents from Group 1 to Group 2. Select the correct separation method for the Group listed. Select all that apply.
Adding H2S will precipitate Group 2 cations. Add HCl will precipitate Group 1 cations.
Consider the following complex ion equilibria: Ag+ + 2NH3 ⇌ Ag(NH3)2+ Kf = 1.5 x 107 Ag+ + 2CN- ⇌ Ag(CN)2- Kf = 1.0 x 1021 If a solution containing equal concentrations of both cyanide ions and ammonia was added to a solution of silver ions, which complex ion would form?
Ag(CN)2- Reason: Formation of Ag(CN)2- is favored, since it has a much larger Kf value than Ag(NH3)2+.
Select all the statements that correctly describe a saturated aqueous solution of a slightly soluble ionic compound that is in contact with undissolved solute.
An equilibrium exists between the undissolved and dissolved solute. The dissolved solute is assumed to be dissociated into ions.
Which of the following steps correctly show how to calculate the solubility for Pb(IO3)2Pb(IO3)2 given that Ksp = 2.6×10−13Ksp = 2.6×10-13?
Assume that Pb2+=s, then IO3-=2s. Ksp=4s3
Which of the following options correctly describe how to calculate the pH at various stages during the titration of a strong acid against a strong base? Select all that apply.
At the equivalence point pH = 7.00. Reason: pH = 7.00 at the equivalence point for any strong acid-strong base titration. Initial pH = -log[HA]. Reason: Since HA is a strong acid, [H3O+]init = [HA]init.
Select the statements that correctly describe how to calculate the pH at various points during the titration of a weak acid against a strong base.
At the equivalence point the pH calculation is based on the reaction of the conjugate base A- with H2O. The initial [H3O+] is calculated from [HA]init and Ka
Which of the following quantities must be known in order to calculate the pH of an acid-base buffer solution using the Henderson-Hasselbalch equation?
Concentration of weak acid Ka of weak acid or Kb of weak base Reason: The Henderson-Hasselbalch equation relates pH to the pKa of the weak acid component. As long as one ionization constant of the acid-base pair is known, the other can be calculated using the relationship Ka x Kb = Kw. Concentration of conjugate base
Match each slightly soluble salt with the correct Ksp expression.
Fe(OH)2 = Ksp = [Fe^2+][OH-]^2 Fe(OH)3= Ksp= [Fe^3+][OH-]^3
Which of the following can affect the solubility of a sparingly soluble ionic compound?
Formation of complex ions Solution pH Presence of a common ion
Which of the following conjugate acid-base pairs is the best choice to prepare a buffer of pH 3.50?
HCOOH/HCOONa (pKa of HCOOH = 3.74) Reason: The pKa of the weak acid component should be as close as possible to the desired pH.
Which of the following are examples of complex ions?
HgCl42- Fe(SCN)(H2O)52+ Ag(NH3)2+
Under what conditions will a precipitate not form when an aqueous solution of AgNO3 is added to an aqueous solution of NaCl?
If Q < Ksp
The solubility of Ag2CrO4 in water is equal to 0.029 g per 1 L of solution at 25°C. Select all the options that correctly reflect the steps required to calculate Ksp for this compound from the given information.
Ksp = 2.5 × 10-12 [CrO42-] = 8.7 × 10-5 M Molar solubility = 0.029g1L0.029g1L × 1mol331.8g1mol331.8g = 8.7 × 10-5 M Ag2CrO4 Reason: Ksp = (2 × 8.7 × 10-5)2(8.7 × 10-5) Molar solubility = 0.029g1L0.029g1L × 1mol331.8g1mol331.8g = 8.7 × 10-5 M Ag2CrO4
Which of the following is the correct Ksp expression for the reaction Al(OH)3 (s) ⇌ Al3+ (aq) + 3OH- (aq)?
Ksp = [Al3+][OH-]3
A chemist titrates a 25.00-mL portion of 0.25 M HNO3 with a 0.25 M solution of NaOH. Which of the following options correctly reflect the steps required to calculate the pH once 35.00 mL of NaOH has been added? Select all that apply.
Moles of OH- added = 8.75 × 10-3 Reason: 35.00 mL × 1L/1000mL × 0.25moles/1L = 8.75 × 10-3 moles OH- added pH = 12.62 Reason: [OH-] = 2.5×10−3mol/0.0600 L = 0.042 [H3O+] = 1×10−14/0.042= 2.4 × 10-13 and pH = -log(2.4 × 10-13) = 12.62 Moles of OH- in excess = 2.5 × 10-
Which slightly soluble ionic salts will become more soluble at lower pH?
Salts that contain the anion of a weak acid
Consider the ionization of the weak acid HClO2: HClO2 (aq) + H2O (l) ⇌ ClO2- (aq) + H3O+ (aq) Select all the statements that correctly describe the effect of adding KClO2 to this system.
The % ionization of HClO2 will decrease. The solution pH will increase.
Fractional precipitation is a method of separating ions in aqueous solution. A reagent is slowly added that forms an insoluble salt with one or more of the ions present. Fractional precipitation is based on what property?
The Ksp value of the insoluble compounds. Reason: The relative values of the solubility product constant Ksp is the property used to separate.
Consider a general buffer system made from a weak acid, HA, and its conjugate base A-. Select all the statements that describe the behavior of this system when strong acid is added to it.
The [A-] in solution will decrease. Reason: Some of the A- in solution must be used up to react with the excess H3O+ added. The overall pH will decrease only slightly. The ratio [HA]/[A−]will increase. Reason: Equilibrium shifts toward the unionized HA, to use up the excess H3O+ added.
Which of the following descriptions are correct for an acid-base indicator?
The color of the indicator changes over a specific pH range. A typical indicator changes color over a range of about 1.5 - 2 pH units.
If NaClO (aq) is added to the reaction shown below, which of the following statements would be true? Select all that apply. HClO (aq) + H2O (l) ⇌ ClO- (aq) + H3O+ (aq)
The concentration of HClO (aq) would increase. The pH of the solution would increase. Reason: NaClO contains the ion ClO-, which is also part of the equilibrium system. Adding NaClO causes the equlibrium to shift to the left, decreasing [H3O+] and increasing pH.
Why does the equivalence point for a weak base-strong acid titration occur at a pH < 7.00?
The conjugate acid of the weak base reacts with H2O to give a solution with pH < 7.00.
Select all the options that correctly describe the formation constant (Kf) for a complex ion.
The larger the value for Kf, the more stable the complex ion. Kf is also known as the stability constant for the complex ion.
Which of the following statements correctly describe the titration curve for the titration of a strong acid with a strong base?
The pH rise is very steep close to the equivalence point of the titration. The equivalence point is at a pH of 7.00.
Which of the following should be considered when selecting/preparing a buffer solution?
The pKa of the weak acid component of the buffer should be close to the desired pH. The ratio of conjugate base to weak acid should be less than 10 and greater than 0.1.
Which statement correctly defines the equivalence point in an acid-base titration?
The point at which the number of moles of -OH added equals the number of H+ ions present Reason: The equivalence point is the point at which neutralization is complete. This occurs when equimolar amounts of acid and base have been combined.
For a weak acid that has been dissolved in water, the ionization equilibrium will shift toward the reactants if a quantity of the conjugate base is added to the solution. This is an example of the ____ ______ effect.
common ion
The ______ point of a titration is the point at which the indicator changes color. The indicator is chosen so that the color change occurs at a pH as close as possible to the pH of the _____ point.
end; equivalence
Match each term to the correct definition, with reference to an acid-base titration.
endpoint; the point at which the indicator changes color equivalence point; the point at which the moles of -OH added are equal to the moles of H3O+ originally present
In an acid-base titration, the point at which equimolar amounts of acid and base have been combined is called the ______ point.
equivalence
True or false: Qualitative analysis is the determination of the identity and amount of substance(s) present in a sample.
false; Reason: Qualitative analysis only determines the presence of a given substance not the amount.
The equilibrium constant Kf is known as the ______ constant for a complex ion, and measures the tendency of a metal ion to form a particular complex ion.
formation
The pH at the equivalence point for a weak acid-strong base titration is _____ than 7.00 because at this point the major species in solution is the conjugate _____ of the weak acid. This species reacts with H2O to form a(n) _____ solution.
greater; base; basic
Compared to a strong acid-strong base titration, the curve for a weak acid-strong base titration begins at a ______ pH, and has a ______ vertical section as the equivalence point is reached.
higher; smaller
At the equivalence point of a weak acid-strong base titration, all the acid has been neutralized. However, the pH of the solution is not 7.0 because of the _____ of the conjugate base to produce OH- ions.
hydrolysis
At the equivalence point of a weak base-strong acid titration, all the base has been neutralized. However, the pH of the solution is not 7.0 because of the ______ of the conjugate acid to produce H3O+ ions.
hydrolysis
Copper(II) sulfide (CuS) is sparingly soluble in water (Ksp = 6.0 x 10-37). The addition of ammonia, which forms a stable complex ion with Cu2+, will ______ the solubility of copper sulfide in water.
increase
Formation of a stable complex ion will generally ______ the solubility of a sparingly soluble substance.
increase
Adding a strong acid to a slightly soluble ionic compound will _____ its solubility if it contains the anion of a weak acid.
increase Reason: The anion of a weak acid is itself a weak base, which will react with the strong acid added. The equilibrium will shift to form more of the anion, increasing the solubility of the salt.
A chemist titrates a 25.00-mL portion of 0.15 M HCl with a 0.20 M solution of KOH. Which of the following options correctly describe how to calculate the pH at the beginning of this titration AND after 15.00 mL of base has been added? Select all that apply.
initial pH = -log(0.15) = 0.82 [H3O+] after base has been added = 7.5×10^−4/0.0400L initial moles of H3O+ = 3.75 × 10-3 Reason: 25.00 mL × 1L/1000mL x 0.15mol/1L= 3.75 × 10-3 moles H3O+
Match each point in a strong acid-base titration with the correct procedure for calculating the pH and/or [H3O+].
initial pH= matches Choice, [H3O+] = [HA] and pH = -log[H3O+] before equivalence point= Moles H3O+ remaining = (initial moles H3O+) - (moles H3O+reacted); use total volume to calculate new [H3O+] and pH after equivalence point= Moles excess OH- present = (moles OH-added) - (moles OH-reacted); use total volume to calculate new [OH-]; calculate pH from pOH
For ionic compounds that have the same total number of _____ in their formulas, the larger the Ksp value, the _____ soluble the compound.
ions; more Reason: The overall charge of an ionic compound is always zero. The solubilities of two ionic compounds can meaningfully be compared using Ksp if the total number of ions in the formula is the same, for example, CaF2 and Ag2SO4, since both compounds have a total of 3 ions per formula unit. The larger the value of Ksp, the more soluble the compound.
Consider the equilibrium system NH3 (aq) + H2O (l) ⇌ NH4+ (aq) + OH- (aq). If some solid NH4Cl were added to the system, the equilibrium would shift to the _____ and the [OH-] would _____.
left; decrease Reason: NH4Cl dissociates in aqueous solution to release NH4+ ions and Cl- ions. The added NH4+ ions will cause the equilibrium to shift to the left, thus decreasing the [OH-].
A complex ion consists of a central _______ cation covalently bonded to two or more anions or molecules, which act as Lewis _____.
metal; base
In the separation of two ionic compounds by selective precipitation, a solution of a precipitating ion is added to the mixture until the Q of the ______ soluble compound is almost equal to its Ksp. This ensures that the Ksp of the ______ soluble compound is exceeded as much as possible and a maximum amount of it will precipitate.
more, less
A buffer solution consists of 0.45 M HCOOH and 0.63 M HCOONa (pKa for HCOOH = 3.74). Which option shows the correct calculation for the pH of the buffer after 0.020 mol of solid NaOH is added to 1.0 L of the solution?
pH = 3.74 + log0.65/0.43 Reason: 0.020 mol of NaOH reacts with HCOOH so that [HCOOH] = 0.43 M. [HCOONa] increases correspondingly.
Consider a buffer made by combining equal volumes of 0.15 M CH3COOH and 0.32 M NaC2H3O2. What is the pH of this buffer if the Ka for CH3COOH is 1.8 × 10-5?
pH = 5.07 Reason: pH = -log(1.8 × 10-5) + log0.320.150.320.15 = 4.74 + 0.33 = 5.07
Match the pH of the titration end point with the indicator that could be used to indicate the endpoint.
pH = 7.00 =bromothymol blue pH = 2.00 = thymol blue pH = 9.00 =phenolphthalein
Which of the following is the correct expression for the Henderson-Hasselbalch equation, which is used to calculate the pH of an acid-base buffer solution?
pH = pKa + log([base][acid])
Consider a buffer solution consisting of 1.0 M HF and 1.0 M NaF, which has an initial pH of 3.14 (Ka for HF = 7.2 × 10-4). If 0.10 mol of NaOH is added to 1.0 L of this solution, select all the options that correctly reflect the steps required to calculate the change in pH. Assume no volume changes.
pHafter addition = -log (5.89 × 10-4) = 3.23 Reason: pHafter addition = -log(7.2×10−4×0.901.10)7.2×10-4×0.901.10 = -log (5.89 x 10-4) = 3.23 After OH- has been consumed, [HF] = 0.90 M, [F-] = 1.10 M. Reason: 0.10 mol of OH- will react with 0.10 of HF to produce 0.10 mol of F-. [H+]after addition = 7.2 × 10-4 × 0.901.100.901.10 Reason: Ka = [H+]after addition[F−][HF][H+]after addition[F-][HF] = (x)(1.10)0.90(x)(1.10)0.90 = 7.2 × 10-4 [H+]after addition = 7.2 x 10-4 x 0.901.10 pHafter addition = -log(7.2×10−4×0.901.10) Reason: pHafter addition = -log(7.2×10−4×0.901.10)7.2×10-4×0.901.10 = -log (5.89 x 10-4) = 3.23
According to the Le Chatelier's principle, the addition of an ion in common with a weak acid will _____, thus changing the pH from that of the pure acid.
shift the equilibrium to the left Reason: When a product species is added to an equilibrium system Le Chatelier's principle states the system will shift away from the products to relieve the stress. For a weak acid this reduces the [H+]eq and the pH increases.
For a buffer system composed of a weak acid-conjugate base, [H+] = Ka [HA]/[A−]. As long as the amounts of HA and A- are large relative compared to the amounts of OH- or H+ added, the change in [HA]/[A−] will be ______ and the change in [H+], and thus pH, will be ________.
small, small
When a strong acid or base is added to a buffer system, there is a ______ change in the [HA]/[A−] ratio and thus a ______ change in pH.
small; small Reason: A buffer reacts with added acid or base so that there is only a small change in the [HA][A−][HA][A-] ratio, which in turn results in only a small change in pH.
For a slightly soluble ionic compound such as Ag2S, the expression Ksp = [Ag+]2[S2-] is called the _____ product constant for the compound.
solubility
Match each term to its correct definition with regard to a slightly soluble ionic compound.
solubility= The number of grams of compound dissolved in a liter of saturated solution molar solubility=The number of moles of compound dissolved in a liter of saturated solution
Consider a buffer consisting of a weak acid (HA) and the corresponding conjugate base (A-). The buffer initially contains equal amounts of HA and A-. Match each picture to the correct representation of the buffer after the change indicated. Instructions
strong acid has been added= A strong base has been added=B
