Round2
Monday, October12, 2015
HighFourChemistry
Category D: Grades 11 – 12
The use of calculator is required.
Answer #1: Extensive
Answer#2: 4
Solution:
Tabulate all data and computed values.
Basis: 100 grams of caffeine
Component
Mass (g)
Atomic weight
(g/mol)
Carbon
49.5
12.01
Hydrogen
5.2
1.01
Nitrogen
28.8
14.01
Oxygen
16.5
16.00
Mole (mol)
Mole Ratio
49.5
= 4.12
12.01
5.2
= 5.15
1.01
28.8
= 2.06
14.01
16.50
= 1.03
16.00
4.12
=4
1.03
5.15
=5
1.03
2.06
=2
1.03
1.03
=1
1.03
With the given mole ratio, the chemical formula derived is now C4H5N2O with a molecular
weight of (4 x 12.01) + (5 x 1.01) + (2 x 14.01) + (1 x 16.00) = 97.11 g/mol.
Since the computed molecular weight (97.11 g/mol) is not equal to 194.20 g/mol, then
C4H5N2O is the empirical formula and not yet the molecular formula.
To find the molecular formula: (C4H5N2O)X; x =
MW of molecular formula
MW of empirical formula
Molecular formula: C8H10N4O2
Number of atoms of nitrogen, N in molecular formula: 4
=
194.20
97.11
= 2.00
Answer#3: Ketone
Explanation:
In ketones, the carbonyl carbon is connected to two other carbon atoms. As for acetone, two
methyl groups (-CH3) are connected to the carbonyl carbon.
Round2
Monday, October12, 2015
HighFourChemistry
Category D: Grades 11 – 12
The use of calculator is required.
Answer #4: 129.14
Solution:
Balance the given chemical equation:
MWCaCl2 = 110.98 g/mol
MWAgCl = 143.32 g/mol
CaCl2
grams of AgCl produced = 50.0 g CaCl2 �
grams of AgCl produced = 129.14 g
+ 2AgNO3
→
2AgCl
+
Ca(NO3)2
2 mol AgCl 143.32 g AgCl
1 mol CaCl2
��
��
�
1 mol CaCl2
110.98 g CaCl2 1 mol CaCl2
Answer #5: 1,010
Solution:
P1 = 800 mmHg
V1 = 1,515 mL
P2 = ???
V2 = 1.2 L = 1,200 mL
P1 V1 = P2 V2
P2 =
(P1 V1 ) (800 mmHg)(1,515 mL)
=
= 1,010 mmHg
V2
1,200 mL
Answer#6: +6
Explanation: Chromium is classified as a group 6 element and has three oxidation states: +2;
+3, and +6.
Answer#7: Ag
Explanation: This expression is a shorthand notation to provide a more convenient way of
writing the electronic configuration of elements with large atomic numbers. Krypton (atomic
no. 36) has 36 electrons. There 11 more electrons in the configuration (from subshells 4d and
5s). The total number of electrons is now 47 (36 + 11), thus identifying the element as Ag
(chemical name: silver).
Round2
Monday, October12, 2015
HighFourChemistry
Category D: Grades 11 – 12
The use of calculator is required.
Answer#8: Charles’ Law
Explanation:
Charles’ Law states that:
At constant pressure, the volume of a given sample of gas is directly proportional to its
absolute temperature.
Answer#9: 1.5
Solution:
Ionization of HCl can be expressed as:
HCl
↔
H+
[H+] = [HCl] = 0.030
pH = -log[H+]
pH = -log(0.030)
pH = 1.5
Answer#10: 0.062
Solution:
Use the formula: P =
P=
m
�9.8 s2�
1
kg∙m
N∙s2
�13,600
P = 6330.8 Pa �
g
gc
ρh
kg 4.75
m� = 6330.8 Pa
��
m3 100
1atm
� = 0.06248 ≈ 0.062
101,325Pa
Answer#11: Aluminum Sulfate
+
Cl-
Round2
Monday, October12, 2015
HighFourChemistry
Category D: Grades 11 – 12
The use of calculator is required.
Answer#12: 3.4
Solution:
MWC3H8 = 44.11 kg/kmol
Use the formula: PV =
m
MW
RT and manipulate to arrive at ρ =
kg
(200 kPa) �44.11
�
kg
P ∙ MW
kmol
=
=
3.4
ρ=
3
m kPa
m3
R∙T
� (40 + 273)
�8.314
Answer#13: Chloride
m
V
=
P∙MW
R∙T
kmol∙K
Answer#14: Propane
Explanation: Its equivalent chemical formula is C3H8.
Answer#15: 342.17
Solution:
2 Al atoms x
3 S atoms x
12 O atoms x
26.98 g/mol
32.07 g/mol
16.00 g/mol
=
=
=
53.96 g/mol
96.21 g/mol
192 g/mol _
342.17 g/mol
Answer#16: Ammonium / ammonium ion
Explanation: A conjugate acid is formed when a base accepts a proton. In this case, NH3 (a
base) accepts a proton – NH4+.
Answer#17:179.5
Solution:
heat produced, kJ = 45.7 g CO �
220 kJ
1 mol CO
��
� = 179.5 kJ
28.01 g CO 2 mol CO
HighFourChemistry
Category D: Grades 11 – 12
The use of calculator is required.
Answer#18: NaOH
Answer#19: +4
Solution:
6x + 18(-2) = -12
x = +4
Answer#20: 0.14
Solution:
k=
ln 2
0.559
ln 2
=
=
1.24 yrs
yr
t1
2
Use the formula ln
ln
Nt
N0
= −kt to solve for Nt.
Nt
0.559
= −�
� 3.72 yr
1.12
yr
Solving for Nt: 0.14 grams
Round2
Monday, October12, 2015