19. general national chemistry competition · 2021. 2. 3. · 1111111111111111111111111111 19....
TRANSCRIPT
∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞
19. General national chemistry competitionfor high school students
Wednesday February 19, 2020
time: 8-10 (120 min.)
∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞∞
Háskóli Íslands
Tandur hf
19. Chemistry competitionFebruary 19 2020
Name: _____________________________________________________Kennitala: _____________________________________________________
Phone number: _____________________________________________________Email: _____________________________________________________
School: _____________________________________________________Year of study: 1st year 2nd year 3rd year 4th year
General instructions
1. 1 This booklet contains 21 questions on 15 enumerated pages, as well as a formula sheet and aperiodic table. make sure that you have all the pages.The first 10 questions give 3 points each, the next 8 give 5 points each and finally, the last 3questions give 10 points each.
2. 2 Your results and answers must be written in the exam papers (this booklet). Answers on onscratch papers will not be graded.
3. There will be no negative marking for wrong answers.
4. 4 You are only allowed to use a non-programmable calculators and the next two pages, whichinclude formulas, constants and the periodic table. You may tear the formula sheets from theproject.
5. In the multiple choice questions, there is only one correct answer to each question.
6. Some of the questions are in several sections. If any section is answered incorrectly and theanswer is used in subsequent sections there will not be deducted any points in the later sectionsas long as the calculations are correct.
Formulas and constants
∆G = ∆H − T∆S ∆G◦ = ∆H◦ − T∆S ◦ ∆G = ∆G◦ + RT ln Q
∆x =∑
mynd x −∑
hvar f x p =∑
i pi[H3O+] = Ka
2
(−1 +
√1 + 4C0
Ka
)k = Ae−
EaRT ln
(k1k2
)= −Ea
R
(1
T1− 1
T2
)E = E◦ − RT
nF ln Q
∆G◦ = −RT ln K = −nFE◦ q = C∆T q = mc∆T
pH = − log[H3O+] pKa = − log Ka pH = pKa + log [A−]
[HA]
A = εbc PV = nRT E = hcλ
NA = 6.0223 · 1023mól−1 F = 96485 Cmól e− TK = T◦C + 273.15
1atm = 760torr = 101325Pa Kw = 1.00 · 10−14 1bar = 105Pa = 0.9869atm
h = 6.626 · 10−34J · s c = 3 · 108m/s R = 8.3144 JK·mól = 0.08206 L·atm
K·mól
A = A0 · e−kt 1J = 1kg ·m2 · s−2 1 calorie = 4.184J
ax2 + bx + c = 0⇒ x = −b±√
b2−4ac2a
3
lithi
umLi
6,94
1
11
sodi
um
Na
22,9
9
19
pota
ssiu
mK 39,1
0
37
rubi
dium
Rb
85,4
7
55
caes
ium
Cs
132,
9
87
fran
cium
Fr (223
)
4
bery
llium
Be
9,01
2
12
mag
nesi
umM
g24
,31
20
calc
ium
Ca
40,0
8
38
stro
ntiu
m
Sr 87,6
2
56
bari
umBa
137,
3
88
radi
um
Ra
226
21
scan
dium
Sc 44,9
6
39
yttr
iumY 88
,91
71
lute
tium
Lu
175,
0
103
law
renc
ium
Lr
(262
)
22
titan
ium
Ti 47,8
8
40
zirc
oniu
m
Zr
91,2
2
72
hafn
ium
Hf
178,
5
104
ruth
erfo
rdiu
m
Rf
(261
)
23
vana
diumV 50
,94
41
nubi
dium
Nb
92,9
1
73
tant
alum
Ta 180,
9
105
dubn
ium
Db
(262
)
24
chro
miu
m
Cr
52,0
0
42
mol
ybde
num
Mo
95,9
4
74
tung
sten
W 183,
8
106
seab
orgi
umSg (2
66)
25
man
gane
seM
n54
,94
43
tech
netiu
m
Tc
(98) 75
rhen
ium
Re
186,
2
107
bohr
ium
Bh
(264
)
26 ironFe 55,8
5
44
ruth
eniu
m
Ru
101,
1
76
osm
ium
Os
190,
2
108
hass
ium
Hs
(269
)
27 coba
lt
Co
58,9
3
45
rhod
ium
Rh
102,
9
77
irid
ium
Ir 192,
2
109
mei
tner
ium
Mt
(268
)
28 nick
el
Ni
58,6
9
46
palla
dium
Pd 106,
4
78
plat
inum
Pt 195,
1
110
darm
stad
tium
Ds
(281
)
29 copp
erC
u63
,55
47 silv
er
Ag
107,
9
79 gold
Au
197,
0
111
roen
tgen
ium
Rg
(272
)
30 zincZn
65,3
9
48
cadm
ium
Cd
112,
4
80
mer
cury
Hg
200,
6
112
cope
rnic
ium
Cn
(285
)
13
alum
inum
Al
26,9
8
31
galli
umG
a69
,72
49
indi
umIn 114,
8
81
thal
lium
Tl
204,
4
113
unun
triu
m
Uut
50 tinSn 118,
7
82 leadPb 207,
2
114
flero
vium
Fl (289
)
83
bism
uth
Bi
209,
0
115
unun
pent
ium
Uup
57
lant
hanu
m
La
138,
9
58 ceri
umCe
140,
1
59
pras
eody
miu
mPr 14
0,9
60
neod
ymiu
mN
d14
4,2
61
prom
ethi
umPm (1
45)
62
sam
ariu
m
Sm 150,
4
63
euro
pium
Eu
152,
0
64
gado
liniu
mG
d15
7,3
65
terb
ium
Tb
158,
9
66
dysp
rosi
umD
y16
2,5
67
holm
ium
Ho
164,
9
68
erbi
umEr
167,
3
69
thul
ium
Tm
168,
9
70
ytte
rbiu
mY
b17
3,0
89
actin
ium
Ac
(227
)
90
thor
ium
Th
232,
0
91
prot
actin
ium
Pa 231,
0
92
uran
ium
U 238,
0
93
nept
uniu
mN
p(2
37)
94
plut
oniu
mPu (2
44)
95
amer
iciu
m
Am
(243
)
96
curi
um
Cm
(247
)
97
berk
eliu
m
Bk
(247
)
98
calif
orni
um
Cf
(251
)
99
eins
tein
ium
Es
(252
)
100
ferm
ium
Fm (257
)
101
men
dele
vium
Md
(258
)
102
nobe
lium
No
(259
)
5
boro
nB10
,81
14 silic
onSi 28,0
9
32
germ
aniu
mG
e72
,61
33
arse
nic
As
74,9
2
51
antim
ony
Sb 121,
8
52
tellu
rium
Te 127,
6
84
polo
nium
Po (209
)
85
asta
tine
At
(210
)
116
liver
mor
ium
Lv
(293
)
117
unun
sept
ium
Uus
1
hydr
ogen
H 1,00
8
6
carb
onC 12,0
1
7
nitr
ogen
N 14,0
1
15
phos
phor
usP
30,9
7
8
oxyg
enO 16,0
0
16 sulf
urS32
,07
34
sele
nium
Se 78,9
6
9
fluor
ine
F19
,00
17
chlo
rine
Cl
35,4
5
35
brom
ine
Br
79,9
0
53 iodi
neI12
6,9
2
heliu
m
He
4,00
3
10 neonNe
20,1
8
18 argo
nA
r39
,95
36
kryp
ton
Kr
83,8
0
54 xeno
nX
e13
1,3
86 rado
n
Rn
(222
)
118
unun
octiu
m
Uuo
Part I - 3 point questions
Question 1
Which one of the following elements is an alkaline earth metal?
Zink (Zn)
Silver (Ag)
Magnesium (Mg)
Lithium (Li)
Nickel (Ni)
Question 2
Valgerður the scientist must pour 20.0 mL of strong acid into her solution. The acid is stored in a largeglass bottle. How should Valgerður measure the volume she needs?
Pour from the bottle into a beaker and read from the scale.
Pipette from the bottle into her solution.
Pour from the bottle into a beaker and from the beaker into a graduated cylinder.
Pour from the bottle straight into the solution.
Pour from the bottle into a volumetric flask and fill up to the line with deionised water.
Question 3
Aluminum in the Earth is mostly on the form of alumina. Another name for alumina is aluminumoxide. What is the chemical formula for aluminum oxide?
Al2O
Al3O2
AlO3
Al2O3
Al2O
1
Question 4
Guttormur the bull is probably the most loved Icelandic bull of all time. Icelanders loved it so muchthat some argued that it was worth its weight in gold. When Guttormur was at his heaviest he weighed942 kg. How many moles of gold (Au) was Guttormur worth?
4780 moles
1.86 · 108 moles
1.86 · 105 moles
4.78 moles
2.09 · 10−4 moles
Question 5
Mercury (Hg) is the only metal that is in liquid phase at room temperature. When this metal reactswith chlorine it produced HgCl2 which is, on the other hand, a solid at room temperature.What is the number of protons (p), neutrons (n) and electrons (e) in the mercury ion 200Hg2+ in theHgCl2?
80 p, 120 n, 80 e
80 p, 120 n, 82 e
78 p, 200 n, 78 e
80 p, 120 n, 78 e
82 p, 200 n, 78 e
Question 6
Gunnar wants to prepare a buffer solution with pH around 4.7. What two substances could he mixtogether to achieve such a solution?
HCl and NaOH
Acetic acid (CH3COOH) and HCl
NH3 and NaOH
NaCl and NaOH
Acetic acid (CH3COOH) and NaOH
2
Question 7
Electromagnetic rays that have energies between 6.63·10−17 J and 6.63·10−15 J are classified as X-rays.What is the lowest and highest possible wavelenght of an X-ray?
0.03 and 3.00 nm
1.00 · 1017 and 1.00 · 1019 nm
0.03 and 3.00 m
450 and 700 nm
3.00 and 300 nm
Question 8
Fire extinguishers contain carbon dioxide (CO2) under high pressure which causes it to be on a liquidstate, but when it is sprayed out of the extinguisher it turns into gas. 5 L fire extinguisher contains2.00 kg af CO2. What will the volume of the gas be at 25 ◦C and 1.00 atm once all the substance inthe extinguisher has been sprayed out?
93.3 L
9.50 · 103 L
1.12 · 105 L
1.11 · 103 L
473 L
Question 9
The following reaction is exothermic. Which change will shift the equilibrium to the right?
2SO2(g) + O2(g) 2SO3(g)
Raising the temperature
Adding SO2
Removing O2
All of the above
None of the above
3
Question 10
Iceland spar is a mineral called "silver rock" in Icelandic. Despite the name, Iceland spar does notcontain any silver. It is pure crystallized calcium carbonate (CaCO3). In order to be classified as acrystal, the crystal must have at least 1 ·1014 CaCO3 units. What is the lowest possible mass of Icelandspar so that it can be classified as a crystal?
11.31 ng
16.62 ng
11.31 g
6.809 · 1015 g
1.001 · 1016 g
4
Part II - 5 point questions
Question 11
A buffer solution is 0.100 M CH3COONa and 0.100 M CH3COOH. 12.36 mL of 0.134 M HCl wasadded to 25.00 mL of the solution. What is the pH after the addition? pKa(CH3COOH) = 4.76.
4.07
4.29
4.76
5.07
5.23
Question 12
Kinetic measurements were done on the transformation of cyclopropane to propene. The values of therate constant were collected at different temperatures. Two measurements were used to determine theactivation energy of the reaction. At 750 K the rate constant was k = 0.00018 s−1 and at 850 K therate constant was k = 0.030 s−1. What is the activation energy for the reaction?
6.7 · 10−3 J/mól
17 kJ/mól
33 kJ/mól
1.2 · 102 kJ/mól
2.7 · 102 kJ/mól
5
Question 13
The mass percent of oxygen (O) in the human body is 65%, but the atomic percent is 24%. What isthe total number of all atoms in a human body which weighs 62 kg?
6.32 · 1030 atoms
1.62 · 1030 atoms
6.32 · 1027 atoms
1.62 · 1027 atoms
1.52 · 1027 atoms
Question 14
Consider the following reaction
Al2S3(s) + 6H2O(l)→ 2Al(OH)3(s) + H2S(g)
What amount of Al2S3 remains after the reaction of 0.133 mol Al2S3 and 0.111 mol H2O?
17.2 g
28.3 g
14.0 g
8.33 g
19.8 g
6
Question 15
When sulfite reacts with permanganate the following oxidation-reduction reaction takes place:
SO 2−3 + MnO −
4 → SO 2−4 + MnO2
Write the balanced equation for the raction when it takes place in a basic solution.
Balanced chemical equation:________________________________________________________
Question 16Aspartame is a sweetener which is 200 times sweeter than sugar. There are five functional groups inan aspartame molecule. Draw circle around these functional groups and write their names.
7
Question 17
The concentration of solutions can be determined by using spectroscopy. Fanney chemistry studentmeasured the absorbance of a CuCl2 solution, in order to determine the concentration of Cu2+ in thesolution. The graph below shows the absorbance (Abs) of the solution as a function of wavelength. Atthe maximum absorbance the extinction coefficient was ε = 12.39 L
mol·cm .
a) Use Beer’s law (A = εbc) to calculate the molarity of Cu2+ in the solution.
CCu2+ = ___________________ M
b) What is the electron configuration of the Cu2+ ion?
8
Question 18
Gunnar the chemist is interested in kinetics and decided to study the following reaction:
2HgCl2(aq) + C2O 2−4 (aq)→ 2Cl−(aq) + 2CO2(g) + Hg2Cl2(s)
He measured the initial rate of the reaction with different initial concentrations of HgCl2 and C2O 2 –4
and gathered the following results:
Measurement [HgCl2] [M] [C2O 2−4 ] [M] Initial rate [mol L−1min−1]
1 0.105 0.15 1.8 · 10−5
2 0.052 0.30 7.1 · 10−5
3 0.052 0.15 8.9 · 10−6
The rate law of the reaction has the form
rate = k[HgCl2]a[C2O 2−4 ]b
Determine the values of a and b in the kinetic equation.
a = ___________________
b = ___________________
9
Part III - 10 point questions
Question 19 Methanol
Methanol (CH3OH) is used as a substitute for gasoline in some vehicles. To design engines that willrun on methanol, we must understand its thermochemistry
Standard enthalpy of formation for a few substances are given in the following table
Substance ∆Hof [kJ/mol]
CH3OH(l) −238.66CH3OH(g) −200.66
CO2(g) −393.51CO2(aq) −413.80H2O(l) −285.83H2O(g) −241.82
a) The methanol in an automobile engine must be in the gas phase before it can react. Calcula-te the heat (in kJ) that must be added to 1.00 kg liquid methanol to increase its temperaturefrom 25.0 ◦C to its boiling point, 65.0 ◦C. The molar heat capacity of liquid methanol is81.6 J K−1 mól−1.
q = ____________________ kJ
b) Calculate the heat that must be added to vaporize 1.00 kg of methanol. The molar enthalpy ofvaporization for methanol is 38 kJ mól−1.
q = ____________________ kJ
10
c) Once it is in the vapor phase, the methanol can react with oxygen in the air according to
CH3OH(g) +32
O2(g)→ CO2(g) + 2H2O(g)
Calculate the heat of cumbustion of methanol (in kJ/mol), that is, calculate ∆Ho for the reaction.
∆Ho = ____________________ kJmol
d) Calculate the heat released when 1.00 kg of gaseous methanol is burned in air at constantpressure.
q = ____________________ kJ
e) Suppose that the methanol is burned inside the cylinder of an automobile. Taking the radius ofthe cylinder to be 4.0 cm and the distance moved by the piston during one stroke to be 12 cm.The work done by the gas is called work (w) and is given by w = −P∆V , where P is the externalpressure and ∆V is the volume change. Calculate the work done (in J) per stroke as the gasexpands against an external pressure of 1.00 atm. (1 L · atm = 101.3 J and the volume of acylinder is πr2h).
w = ____________________ J
11
Question 20 Equilibrium constant
Air pollution contains, among other substances, NO, NO2 and SO2. These substances are released tothe atmosphere when oil is burned. The equilibrium constants for the following reactions are knownat 25 ◦C:
SO2(g) +12
O2(g) SO3(g) Kc1 = 2,2 (1)
NO(g) +12
O2(g) NO2(g) Kc2 = 0,25 (2)
The equilibrium constant, Kc, for the reaction of SO2 with NO2, is unknown.
SO2(g) + NO2(g) SO3(g) + NO(g) Kc =? (3)
a) Use the information given for equations (1) and (2) to determine the value of the equilibriumconstant for reaction (3) at 25 ◦C.
Kc = ____________________
b) Kp and Kc have a known relation of Kp = Kc(RT )∆n, where ∆n is the change in number ofgaseous molecules in the chemical equation. Calculate the equilibrium constant Kp for reaction(3) at 25 ◦C. If you could not solve part a), then use the value Kc = 10.
Kp = ____________________
12
c) SO2 and NO2 was put into an empty reaction vessel at 25 ◦C and allowed to reach equilibrium.At equilibrium the partial pressures of the substances were measured as follows:
Substance Partial pressure, Pi
SO2 0.2 atmNO2 0.15 atmSO3 0.3 atm
Calculate the partial pressure of NO at equilibrium. If you could not solve part b), then use thevalue Kp = 12.
PNO = ___________________ atm
d) Again, SO2 and NO2, was put into an empty reaction vessel at 25 ◦C. The initial pressure ofSO2 was 0.20 atm and the initial pressure of NO2 was 0.10 atm. Calculate the partial pressureof NO when the reaction has reached equilibrium. If you could not solve part b), then use thevalue Kp = 12.
PNO = ___________________ atm
13
Question 21 Organic Chemistry
In organic chemistry the Diels-Alder reaction is an important way to synthesize ring structures. Oneof the starting materials in the reaction is a diene, a chemical that has conjugated double bonds. Thediene reacts with another double bond to form a ring. The mechanism for the reaction is shown below.The curved arrows show the movement of electrons during the reaction.
If the diene or the other alkene have any side groups (R) they stay relative to each other as shownbelow.
As you can see, the alkene can react with the diene in two possible ways, depending on how the alkeneis flipped.
14
a) What two products can be formed when the following molecules react? Draw the products.
Compound A was synthesized with the Diels-Alder reaction.
b) Draw the two compounds that were used to synthesize compound A.
c) What is the name of compound A according to the IUPAC naming system?
15