General Chemistry
Midterm Test
2008. november 26.
Name:
a.
We mix 100 cm3 solution with pH 4 and 10 cm3 solution with pH 2. What will be the pH
of the mixture (suppose that the volumes are additive)?
pH=:
(3p)
b. We mix 100 cm3 buffer solution with pH=4 (pKa = 4, [HA]=0.1 M, [A-]=0.1M) and 10
cm3 acid solution with pH=2. What will be the pH of the mixture (suppose that the
volumes are additive)?
(5p)
c.
Compare the results in a and b, and explain the difference with the acid-base buffer
capacity:
(6p)
d.
We have 50 cm3 KOH solution with pH=11.70 and a HCl solution with pH 3.5. How
many cm3 HCl solution is needed to neutralize the KOH solution?
V(HCl):
cm3
(3p)
e. The Kacid = 1,8·10−5 for the acetic acid. What is the pH and the percent ionization of the
of the 0.01 mol/dm3 acetic acid solution?
pH:
(3p)
:
(1p)
f. What is the pH of the of the 0.01 mol/dm3 sodium acetate solution?
pH:
g. Titration of a Weak Acid with a Strong Base (show the curve, and explain)
(5p)
(9p)
General Chemistry
Midterm Test
2008. november 26.
Name:
Use the following solubility products:
Ksp(25°C)
1,44·10−10
1,50·10−16
AgCl
AgI
a.
Ksp(25°C)
1,60·10−5
1,35·10−8
PbCl2
PbI2
What is the solubility (S, M=mol/dm3) of the AgI and the PbCl2 in 25°C distilled water?
S(AgI):
M
S(PbCl2):
(2p)
M
(2p)
b. We mix the same volume of saturated PbCl2 and the PbI2 solutions in water at 25°C. Shall we
observe
precipitate?
Explain
all
the
details
(the
volumes
are
Shall we observe precipitate?
If yes, give the formula:
c.
additive).
(3p)
What is the solubility (S) of the PbCl2 in pH=3 HCl solution?
S(PbCl2/HCl):
M
(3p)
d. Effects on the Solubility of PbCl2
add KNO3 to saturated PbCl2 solution
add HCl to saturated PbCl2 solution (draw an approximate solubility diagram versus the
concentration of added salt or acid):
(6p)
General Chemistry
Midterm Test
2008. november 26.
Name:
50.0 ml of 1.0 M NaOH is mixed with 50.0 ml of 1.0 M HCl at 25.0oC. The temperature of
the solution increases to 31.9oC. (c(H2O) = 4.184 J/g)
What is the chemical reaction (1p)?
What is the total heat released (2p)?
How much energy is released per mol of reactant(2p)?
What is the enthalpy (H) for the reaction? (2p)
Give an example for the Hess’s law (6p):
The following standard reduction potentials are given:
Fe2+(aq) + 2e-  Fe(s)
°= −0,440 V
Fe3+(aq) + 3e-  Fe(s)
°= −0,036 V
Calculate the standard reduction potential of
Fe3+ + e-  Fe2+
°= ? V (6p)
This latter half reaction is combined with the
Sn4+ + 2e-  Sn2+
°= +0,150 V
What is the spontaneous chemical reaction that can be derived from these latter two half
reactions? (5p)
What is the equilibrium constant of this chemical reaction at 25 C? (5p)
What is the G° of this chemical reaction? (5p)
Show the cell diagram (5p)
Show Ecell as a function of concentration (10p)