Chapter 17
Calculate the percent ionization of 0.0080 M butanoic acid in a solution containing 0.080 M sodium butanoate. (Ka=1.5×10−5)
0.0187% The difference between the initial and equilibrium concentrations of butanoate is calculated to determine the percent ionization. The variable xx can be used to represent H+ at equilibrium, which is equal to the amount of butanoic acid that was ionized to butanoate. Kax=[H+]eq[CH3CH2CH2COO−]/ eq[CH3CH2CH2COOH]eq =x(0.080+x)/0.0080−x In pure water, the percent ionization of butanoic acid depends on its initial concentration. In contrast, when the common ion of butanoate is already present in solution, the percent ionization of butanoic acid depends only on the concentration of the common ion (while estimating based on the assumption that x is much smaller than the initial concentrations of butanoic acid and butanoate). You can see this when the equation is rearranged to solve for percent ionization. Percent ionization=(Ka/[CH3CH2CH2COO−]init)×100% [(1.5×10−5)/(0.080)]×100%
You add 10.0 grams of solid copper(II) phosphate, Cu3(PO4)2, to a beaker and then add 100.0 mL of water to the beaker at T = 298 K. The solid does not appear to dissolve. You wait a long time, with occasional stirring and eventually measure the equilibrium concentration of Cu2+(aq) in the water to be 5.01×10−8 M. What is the Ksp of copper(II) phosphate? 5.01×10−8 2.50×10−15 4.20×10−15 3.16×10−37 1.40×10−37
1.40×10−37
What is the pH of a solution of 0.20 M HNO2 containing 0.10 M NaNO2 at 25°C, given Ka of HNO2 is 4.5 × 10-4? 3.35 3.05 3.65 2.02
3.05 Construct an ICE table for the reaction of the weak acid HNO2 in water. NO2- is the common ion; therefore, its initial concentration is 0.10 M, not zero in the ICE table.
Calculate the percent ionization of 0.0080 M butanoic acid (Ka=1.5×10−5).
4.3 % The percent ionization is the amount of butanoic acid that is ionized (converted to butanoate ion). The concentration of butanoate ion at equilibrium is divided by the initial concentration of butanoic acid and converted to a percentage. Therefore, the amount of butanoate ion at equilibrium is calculated first. The variable x can be used to represent both the concentration of H+ and CH3CH2CH2COO−, which will be equal at equilibrium. Ka= ([H+]eq[CH3CH2CH2COO−]eq)/ [CH3CH2CH2COOH]eq = x^2/(0.008-x)
What is the pH of a buffer that was prepared by adding 3.96 g of sodium benzoate, NaC7H5O2, to 1.00 L of 0.0100 M benzoic acid, HC7H5O2? Assume that there is no change in volume. The Ka for benzoic acid is 6.3 × 10-5. 4.64 0.439 3.76 4.33
4.64 The applicable equation is the Henderson-Hasselbalch equation: pH = pKa + log [base]/[acid]
Determine the pH of a 0.15 M acetic acid/0.39 M sodium acetate solution where Ka=1.8 x 10-5. 5.16 2.14 7.12 4.32
5.16
The Ksp of Ba(IO3)2 at 25 ∘C is 6.0×10−10. What is the molar solubility of Ba(IO3)2?
5.3×10−4 mol/L
What is the molar solubility of Fe(OH)2 at 25°C if Ksp of the compound is 7.9 × 10-16? 2.8 × 10-8 M 2.0 × 10-16 M 5.8 × 10-6 M 9.2 × 10-6 M
5.8 × 10-6 M The solubility-product expression is: Ksp = [Fe2+][OH-]2
What is a solution that contains conjugate pair of an acid or base that can tolerate addition of a strong acid/base without changing much the pH of the solution?
Buffer
What is the amount of acid or base a buffer can neutralize before the pH changes appreciably. (usually 1 unit of pH)
Buffer capacity
Which buffers exhibit the best buffer capacity?
Buffers with the same concentration of each conjugate pair
Arrange the following solids in order of decreasing solubility, CaF2, K sp=4.0 × 10-11; Ag2CO3, K sp=8.1 × 10-12; Ba3(PO4)2, K sp=6.0 × 10-39; and Ag3(PO4)2, K sp=1.0 × 10-31. Ba3(PO4)2 > CaF2 > Ag3(PO4)2 > Ag2CO3 CaF2 > Ag2CO3 > Ag3(PO4)2 > Ba3(PO4)2 Ba3(PO4)2 > Ag3(PO4)2 > CaF2 > Ag2CO3 Ag2CO3 > Ba3(PO4)2 > Ag3(PO4)2 > CaF2
CaF2 > Ag2CO3 > Ag3(PO4)2 > Ba3(PO4)2 The extent to which solids dissolve in solution is expressed by the magnitude of a solubility equilibrium constant K sp
The shift in equilibrium due to the presence of a common ion of the conjugate pair already in solution is called?
Common ion effect
What is the point in a titration when the mols of acid are equal to the mols of base?
Equivalence point
Which of the following conjugate acid-base pairs will function as a buffer? H2O/OH- HBr/OH- HCl/Cl- HF/F-
HF/F- A buffer resists changes in pH because it contains both an acid, to neutralize added OH- ions, and a base, to neutralize added H+ ions. The acid and base must not completely consume each other through a neutralization reaction; therefore, they must both be weak
In what type of equilibrium are solids or pure liquids not written in the equilibrium constant?
Heterogeneous equilibria
What is a substance that changes color at a certain pH range?
Indicator
Enter the the Ksp expression for C2D3 in terms of the molar solubility x. C2D3 has a solubility product constant of 9.14×10−9. What is the molar solubility of C2D3?
Ksp =108x^5 C2D3(s)⇌2C(aq)+3D(aq) Ksp=[C]^2[D]^3 molar solubility =9.67×10−3 M
It is found that 1.1×10−2g of SrF2 dissolves per 100 mL of aqueous solution at 25 ∘C. Calculate the solubility product for SrF2.
Ksp =2.7×10−9
Enter the Ksp expression for the solid AB2 in terms of the molar solubility x. AB2 has a molar solubility of 3.72×10−4 M. What is the value of the solubility product constant for AB2?
Ksp =4x^3 AB2(s)⇌A(aq)+2B(aq) Ksp =[A][B]^2 Ksp =2.06×10^−10 Ksp=x(2x)^2=4x^3 (plug in given x and solve)
If the molar solubility of CaF2 at 35 ∘C is 1.24×10−3mol/L, what is Ksp at this temperature?
Ksp =7.63×10−9
What is the equilibrium constant for the dissolution of a solid in a saturated solution?
Ksp Solubility Product
There are some data that suggest that zinc lozenges can significantly shorten the duration of a cold. If the solubility of zinc acetate, Zn(CH3COO)2, is 43.0 g/L, what is the solubility product Ksp of this compound?
Ksp=5.15×10−2 Zn(CH3COO)2(s)⇌Zn2+(aq)+2CH3COO−(aq) Ksp=[Zn2+][CH3COO−]^2 number of moles of Zn(CH3COO)2 =0.234 mol [Zn2+] = 0.234 M [CH3COO−] =0.469 M A Ksp of 5.15×10−2 is quite large when compared to many other Kspvalues. This indicates that Zn(CH3COO)2 is relatively soluble in water.
Write the expression for the solubility-product constant for Ca3(PO4)2. Ksp=[Ca2+]^3[PO43-]^2 Ksp=[Ca2+]^2[PO43-]^3 Ksp=[Ca2+]^5[PO43-]^3 Ksp=[Ca2+][PO43-]
Ksp=[Ca2+]^3[PO43-]^2
what are those acids that have more than one proton in their chemical formula?
Polyprotic acids
What forms in a saturated solution?
Precipitate
For the reaction: MgF2(s) ⇌ Mg2+(aq) + 2F- (aq), Ksp= 6.4 × 10-9, the addition of 0.10 M NaF to the solution cause what effect on the solubility equilibrium? Shifts the equilibrium to the right, reduces solubility. Shifts the equilibrium to the left, increases solubility. Shifts the equilibrium to the right, increases solubility. Shifts the equilibrium to the left, reduces solubility.
Shifts the equilibrium to the left, reduces solubility.
What is the amount of material dissolved in a specific amount of solvent at a certain temperature?
Solubility
Ksp may change with temperature? T or F
T
Which of the following would occur if solid NH4Cl was added to an aqueous solution of NH3? NH3 will ionize to a greater extent. The pH increases. The equilibrium constant changes. The pH decreases.
The pH decreases.
In a strong acid-strong base titration how is the pH calculated after the equivalence point stage of the titration? The pH is determined by the concentration of excess strong base in the solution. The pH is determine by using the initial concentration of the strong acid. The pH of the solution is 7.00 because all the acid is consumed and therefore, has no appreciable effect on pH. With the Henderson-Hasselbalch equation.
The pH is determined by the concentration of excess strong base in the solution.
Which of these statements about the common-ion effect is most correct? The common-ion effect does not apply to unusual ions like SO32-. Common ions alter the equilibrium constant for the reaction of an ionic solid with water. The solubility of a salt MA is affected equally by addition of either A− or a non-common ion. The solubility of a salt MA is decreased in a solution that already contains either M+ or A−.
The solubility of a salt MA is decreased in a solution that already contains either M+ or A−.
What is the ratio of HCO−3 to H2CO3 in blood of pH 7.4? What is the ratio of HCO−3 to H2CO3 in an exhausted marathon runner whose blood pH is 7.2?
[HCO−3]/[H2CO3] =11 [HCO−3]/[H2CO3] =7
What are the two ways to prepare a buffer?
a) Mix weak acid or base with the salt of the conjugate pair b) make the conjugate pair in solution
Barium sulfate, BaSO4, is used in medical imaging of the gastrointestinal tract because it is opaque to X rays. A barium sulfate solution, sometimes called a cocktail, is ingested by the patient, whose stomach and intestines can then be visualized via X-ray imaging. If a patient ingests 320 mL of a saturated barium sulfate solution, how much toxic Ba2+ ion has the patient consumed? The solubility product Ksp of BaSO4 is 1.10×10−10.
mass of Ba2+ =4.61×10−4 g BaSO4(s)⇌Ba2+(aq)+SO42−(aq) Ksp=[Ba2+][SO42−] Ksp=[Ba2+]^2 [Ba2+] = 1.05×10−5 M 1.44×10−3 g/L
What are titrations?
neutralization reactions that are performed in order to determine the concentration of solution and the equilibrium constant of an acid or base
Calculate the pH of the solution made by adding 0.50 mol of HOBr and 0.30 mol of KOBr to 1.00 L of water. The value of Ka for HOBr is 2.0×10−9.
pH = 8.48 When the concentrations of acid and base in a buffer solution are equal, [H3O+]=Ka and pH= pKa. When there is more acid than base, [H3O+]>Ka and pH< pKa. The pKa for HOBr is 8.70. As expected, the calculated pH is less than pKa.
What is the Henderson-Hasselbalch equation?
pH = pKa + log [A-]/[HA]
What are titrations used to determine?
the concentration of solution and the equilibrium constant of an acid or base
What is the pH range of a buffer?
the extent of pH scale centered at the buffer pH limited by the buffer capacity
What causes a change in solubility?
whether a dissolution is endothermic or exothermic