Round 4
Friday, December 4, 2015
HighFourChemistry
Category C: Grades 9 – 10
The use of calculator is required.
Answer #1:
Solution:
39.33
The chemical reaction is as follows:
Hg
+
S
1mol
→
HgS
1 mol S
32.07g
246 g HgS �
Hg� �
� � 1mol S� = 39.33 g S
200.59g
1 mol Hg
Answer#2:
Explanation:
Na > Mg > Al > P > Cl
One of the guidelines for the periodic trend for atomic size is that atomic
size decreases when going across a period from left to right. This is
attributed to the increasing pull of the nucleus on the electrons in the
outermost main energy level.
All elements stated fall in Period 3. Since sodium (Na) is at the leftmost, it
has the biggest atomic size. Refer to the image below regarding positions of
the elements in the periodic table.
Answer#3:
Explanation:
Hg
The chemical symbol of mercury, the only other element in the periodic
table that is liquid at a room temperature of 25°C, is Hg.
Answer#4:
Explanation:
solid
The melting and boiling points of carbon (3500 & 4827°C, respectively) are
very high. This means that carbon is solid at a room temperature of 25°C.
This can be explained by the kinetic molecular theory. A solid material is
held together by strong bonds, therefore, it will need more energy (in this
case, heat energy) to break the bonds.
Answer#5:
Explanation:
3
The electron configuration for nitrogen, N, is 1s22s22p3. The number of
electrons in the p orbital is 3.
Round 4
Friday, December 4, 2015
HighFourChemistry
Category C: Grades 9 – 10
The use of calculator is required.
Answer#6:
Solution:
vanadium oxide
Convert given quantities of reactants into mols
1mol
1.54x103 g V2 O5 �
V O � = 8.47 mols V2 O5
181.88g 2 5
1mol
1.96x103 g Ca �
Ca� = 48.90 mols Ca
40.08g
Based on the chemical equation: 1 mol V2 O5 ≈ 5 mol Ca
5 mol Ca
8.47 mols V2 O5 �
1 mol V
2 O5
� = 42.35 mol
There is an excess amount of calcium since it would only require 42.35 mols
of Ca to react with 8.47 mols of V2O5. Therefore, Ca is the excess reactant
and V2O5 is the limiting reactant.
Answer#7:
Solution:
862.92
The computations for the theoretical yield of V will be based on the limiting
reactant, which is the V2O5.
2 mols V
Answer#8:
Solution:
Answer#9:
Explanation:
Answer#10:
Explanation:
8.47 mols V2 O5 �
1 mol V
2 O5
50.94 g
��
mol
V� = 862.92 g V
93.06
Percent yield (% yield) can be obtained by dividing the actual yield (which
was given in the problem) with the theoretical yield computed from the
previous problem.
803g
% yield =
x 100 = 93.06
862.92g
semiconductors
Semiconductors are normally not conductors, but they will conduct
electricity at elevated temperatures, or when combined with a small
amount of certain other elements. Some examples of semiconductors are
germanium and silicon which are commonly used in transistors and solar
cells.
12, 10
Magnesium, in its stable form, has 12 protons and 12 electrons. However,
when ionized, magnesium tends to lose its two outermost electrons –
therefore, making magnesium positively-charge.
Round 4
Friday, December 4, 2015
HighFourChemistry
Category C: Grades 9 – 10
The use of calculator is required.
Answer#11:
Solution:
13341
By stoichiometry analysis:
1 kmol CaO
1 kmol CO
44.01 kg
1.7x1010 kg CaO �
� �1 kmol CaO2 � �
56.08 kg CaO
Answer#12:
Explanation:
Answer#13:
Solution:
Release of CO2 = 13341 x 109 grams
kmol
1000 g
CO2 � �
1 kg
1
� �1x109 �
trigonal planar
In the most stable arrangement, the three BF bonds point to the corners of
an equilateral triangle with boron (B) in the center of the triangle. Each of
the three FBF angles is 120°.
47.53
Solve for the mass of chlorine in AgCl:
1 mol
1 mol Cl
35.45 g Cl
gramsCl = 1.088 g AgCl �
AgCl� �
� � 1 mol Cl � = 0.2691 g
143.32 g
1 mol AgCl
Since it was treated with excess AgNO3, we assume that all chloride ions in
the original compound were precipitated to AgCl. Hence, the mass of Cl in
AgCl is also the same amount of Cl in the original compound.
0.2691g
x 100 = 47.53%
%Cl in cmpd =
0.5662g
Answer#14:
Explanation:
6
The following is the balanced chemical equation:
P4O10 + 6H2O → 4H3PO4
It would take 6 moles of water to balance the equation.
Answer#15:
Solution:
Pb
To compare, convert each of them to its mass equivalent in grams.
1molePb
207.20g
2 atoms Pb �
��
6.02283x1023 atoms
4g
mol
Pb� = 6.88 x 10−22 g Pb
5.1 x 10−23 mol He �
He� = 2.04 x 10−22 g He
1mol
6.88 x 10−22 g Pb > 2.04 x 10−22 g He
Round 4
Friday, December 4, 2015
HighFourChemistry
Category C: Grades 9 – 10
The use of calculator is required.
Answer#16:
Explanation:
997.50
By dimensional analysis:
1g
$10.5
9.5x103 cg �
� �1 g Au� = $997.50
100cg
Answer#17:
Explanation:
1:1:5
The chemical formula for ammonium hydroxide is NH4OH. It has 1 nitrogen
(N) atom, 1 oxygen (O) atom, and 5 hydrogen (H) atoms. Therefore, the
ratio of N:O:H atoms is 1:1:5.
Answer#18:
Explanation:
magnesium
The dots which appear to be circling/orbiting around the nucleus are the
electrons. By counting the number of electrons, we can identify the
element since the no. of electron of an element in its ground state is also
the atomic number. In this case, the element has 12 electrons, identifying it
as magnesium.
Answer#19:
Explanation:
Fe+3 / Fe+3
Answer#20:
Explanation:
I- / ITo determine the element, we identify the number of protons in the
element since the number of protons is equivalent to the atomic number:
p+ = 127 – 74 = 53 (this identifies the element as Iodine (I) )
This isotope of iodine has 54 electrons. Therefore, the anion is I-.