CHEM*131 (W 2004)
REVIEW LAB FOR MIDTERM EXAM
PAGE - 1
1.
0.10 M of HClO4(aq) and 0.10 M of HNO2(aq) will have the same pH.
TRUE
/
FALSE
2.
The pH of a solution of 0.20 M Ca(OH)2 is lower than that of 0.20 M KOH(aq).
TRUE
/
FALSE
3.
The Kb for pyridine, C5H5N, is 1.8 × 10!9 M, and Kw for water is 1.0 × 10!14 M2.
4.
(a)
The pH of 0.10 M solution of C5H5N is:
(b)
The percent ionization of 0.10 M C5H5N is equal to:
(c)
Write an expression that defines Ka of C5H5NH+(aq).
(d)
Ka of C5H5NH+(aq) is equal to:
Circle the salts listed below which will form a basic solution when dissolved in water.
Al(ClO4)3
5.
Na2CO3
Ba(NO3)2
LiCN
HCOOH
(CH3)2NH2Cl
Arrange the following 0.10 M solutions in order of increasing pH. Given that Ka(HNO2) = 5.0 × 10!4;
Ka(HF) = 6.8 × 10!4; Kb(NH3) = 1.8 × 10!5 and Kb((CH3)3N) = 6.0 × 10!5.
KF
HNO2
LiOH
HI
(CH3)3N
NH4ClO4
Na2SO4
Lowest pH
6.
7.
8.
K2HPO4
Highest pH
Hydrosulfuric acid, H2S, is a diprotic acid with Ka1 = 9.0 × 10!8 M and Ka2 = 1.0 × 10!12 M.
(a)
The formula for the conjugate acid of HS! is:
(b)
Write a net ionic equation to show that HS! acts as an acid in water.
(c)
Kb for the sulfide ion, S2!, is equal to:
(d)
The equilibrium constant for the reaction HS! + H2O º H2S + OH! is:
When 1.0 L of 0.25 M NH3 (Kb = 1.8 × 10!5) is mixed with 1.0 L of 0.25 M NH4Cl,
(a)
a 1:1 buffer is produced with pH equal to 7.0.
TRUE
/
FALSE
(b)
the best buffer zone is between 3.74 and 5.74.
TRUE
/
FALSE
(c)
the pH remains unchanged upon dilution with water.
TRUE
/
FALSE
(d)
an increase in NH4+ concentration will have higher buffer capacity
against the addition of HCl addition.
TRUE
/
FALSE
An aqueous buffer is prepared from 0.10 M hypochlorous acid, HClO (Ka = 3.0 × 10!8), and 0.1 M sodium
hypochlorite, NaClO(aq).
(a) The pH at the half-equivalence point is:
(b)
HClO, ClO!, Na+ and H+ are the major species present at the
half-equivalence point.
TRUE
(c)
At pH 7.00, the percent of HClO in the buffer system is equal to:
(d)
When 100 mL of 0.10 M HClO(aq) and 200 mL of 0.10 M NaClO(aq)
are mixed, the pH of the resultant solution is:
(e)
0.025 mol of HCl solution is added to 1.0 L of this HClO!ClO! buffer solution.
(i)
Write the net ionic equation for the reaction that takes place.
(ii)
The equilibrium constant, Kc, for the reaction is equal to:
(iii)
The pH of the solution after the addition of 0.025 mol HCl is:
/
FALSE
CHEM*131 (W 2004)
9.
REVIEW LAB FOR MIDTERM EXAM
PAGE - 2
100 mL of 0.20 M solution of trimethylammonium chloride, (CH3)3NHCl(aq), and a bottle of 0.10 M NaOH
are provided to prepare a basic buffer at pH 9.25. The Kb for trimethylamine, (CH3)3N, is 6.0 × 10!5.
(a) Write the net ionic equation for the reaction that takes place.
(b)
The equilibrium constant, Kc, for the reaction is equal to:
(c)
When equal volumes of 0.10 M NaOH and 0.20 M (CH3)3NH+(aq) are mixed,
the pH of the resulting solution is equal to the pKa of (CH3)3NH+(aq).
TRUE
(d)
The volume of 0.10 M NaOH required to reach pH 9.25 is:
(e)
At the equivalence point,
(i)
the concentrations of (CH3)3N(aq) and (CH3)3NHCl(aq) are equal.
(f)
/
FALSE
mL
(ii)
the volume of NaOH required to reach the equivalence point is:
(iii)
the concentration of (CH3)3N(aq) is equal to:
(iv)
the pH of the resultant buffer solution is:
Methyl red (Ka = 10!5) is a suitable indicator for the titration of
(CH3)3NHCl(aq) with NaOH.
TRUE
/
FALSE
mL
TRUE
/
FALSE
10.
A raw sewage sample contains 320 mg L!1 organic matter of formula C5H10O7
(182.1 g mol!1). The BOD of the sewage water, in ppm, of O2 (32.0 g mol!1) is:
11.
It has been suggested that the partial pressure of CO2 may reach 600 ppmv within a century. Given that the
Henry’s law constant for CO2 is 3.4 × 10!2 M atm!1at 25oC and Ka for H2CO3 is 4.2 × 10!7.
12.
(a)
The concentration of dissolved CO2 in water at 25oC is:
(b)
The pH of rainwater in equilibrium with 600 ppmv of CO2(g) is:
Circle the ionic compounds listed below which are not soluble in water.
Al(OH)3
13.
(NH4)2SO4
PbBr2
Ba(OH)2
FeCO3
15.
Na2S
Rank the following ionic compounds according to the increasing order of solubility in water.
ZnS
(Ksp = 2.8 × 10!25 M2)
Ag2CO3
(Ksp = 8.5 × 10!12 M3)
!38
4
Fe(OH)3
(Ksp = 1.0 × 10 M )
Ca3(PO4)2 (Ksp = 1.3 × 10!32 M5)
Least soluble
14.
AgI
Most soluble
Ksp for copper (II) hydroxide, Cu(OH)2, is 2.2 × 10!20 M3 at 25oC. Molar mass of Cu(OH)2 is 97.56 g mol!1.
(a) Write the Ksp expression for Cu(OH)2(s).
(b)
The solubility of Cu(OH)2 in pure water is equal to:
(c)
The Cu2+ ion concentration in a saturated solution of Cu(OH)2 is:
(d)
The pH of a saturated solution of Cu(OH)2 is:
(e)
The solubility of Cu(OH)2 in a solution of 1.0 × 10!4 M CuCl2(aq) is:
(f)
The Cu2+ ion concentration in a solution which has had KOH added
to make the pH 10.00 is:
g L!1
An aqueous solution of 0.20 L of 0.20 M barium nitrate is mixed with 0.050 L of 0.050 M NaF. A white
insoluble salt may produce. The white solid has a Ksp of 1.0 × 10!6 M3.
(a)
Write the net ionic equation for the precipitation reaction.
(b)
The chemical formula of the white insoluble salt is:
(c)
Qsp (Ion Product) for this white solid product is equal to:
(d)
Since Qsp is larger than Ksp, the precipitation will occur.
TRUE
/
FALSE
(e)
Addition of AgF to the system will produce more white precipitates.
TRUE
/
FALSE
(f)
Write a net ionic equation when dilute HCl(aq) is added to the solution.
CHEM*131 (W 2004)
REVIEW LAB FOR MIDTERM EXAM
PAGE - 3
Data Information
Ka (HA) '
[A !] [H3O %]
[HA]
'
Kw
Kb (A !)
Kb (A !) '
[HA] [OH !]
[A !]
'
Kw
Ka (HA)
Henderson-Hasselbalch Equation
pH ' pKa % log
For
1:1 electrolyte
1:2 electrolyte
1:3 electrolyte
[Weak Base (A !)]
[Weak Acid (HA)]
pH = ! log [H3O+]
pOH = ! log [OH!]
pKa = ! log Ka
Ksp = s2
Ksp = 4s3
Ksp = 27s4
ANSWERS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
FALSE
FALSE
(a) 9.13
(b) 0.013%
(c) Ka(C5H5NH+) = [C5H5N] [H3O+] / [C5H5NH+]
(d) 5.6 × 10!6 M
Na2CO3, LiCN, K2HPO4
(lowest pH) HI < HNO2 < NH4ClO4 < Na2SO4 < KF < (CH3)3N < LiOH (highest pH)
(a) H2S
(b) HS!(aq) + H2O(R) º S2!(aq) + H3O+(aq)
(c) 1.0 × 10!2 M
(d) 1.1 × 10!7 M
(a) FALSE
(b) FALSE
(c) TRUE
(d) FALSE
(a) 7.52
(b) FALSE
(c) 76.8%
(d) 7.82
(e) (i)
ClO!(aq) + H3O+(aq) ÿ HClO(aq) + H2O(R)
(ii) 3.3 × 107 M!1
(iii) 7.30
(a) (CH3)3NH+(aq) + OH!(aq) ÿ (CH3)3N(aq) + H2O(R)
(b) 1.7 × 104 M!1
(c) TRUE
(d) 46 mL
(e) (i)
FALSE
(ii) 200 mL
(iii) 0.067 M
(iv) 11.30
(f)
FALSE
225 ppm
(a) 2.0 × 10!5 M
(b) 5.57
Al(OH)3, PbBr2, FeCO3, AgI
(Least soluble) ZnS < Fe(OH)3 < Ca3(PO4)2 < Ag2CO3 (Most soluble)
(a) Ksp [Cu(OH)2(s)] = [Cu2+(aq)] [OH!(aq)]2
(b) 1.7 × 10!5 g L!1
(c) 1.8 × 10!7 M
(d) 7.55
(e) 7.4 × 10!9 M
(f)
2.2 × 10!12 M
(a) Ba2+(aq) + 2 F!(aq) ÿ BaF2(s)
(b) BaF2
(c) 1.6 × 10!5 M3
(d) TRUE
(e) TRUE
(e) BaF2(s) + 2 H3O+(aq) ÿ Ba2+(aq) + 2 HF(aq) + 2 H2O(R)