Jay Krishnan
Chemistry I
8.29.11
High School Knowledge Exam
1) If 0.821 atm krypton gas is confined to a 19.2 L container at 29.7oC, how many moles
of krypton gas are present in the container? (R = 0.08206 L·atm/mol·K)
PV = nRT
T = 29.7 + 273 = 302.7
0.821 * 19.2 = n * (.08296) * (302.7)
n = .635 moles
2) Select the answer that expresses the result of (30.297 ÷ 5.112) – 5.88 with the
correct number of significant figures.
30.297/5.112 = 5.927
5.927 – 5.88 = 0.05
3) How many grams of aluminum are needed to form 275 g of aluminum chloride?
3Al + 3NH ClO → Al O + AlCl + 3NO + 6H O
4
4
2 3
3
2
Molar Mass of AlCl3 = 133.339
275g/133.339 = 2.06 moles of AlCl3
Al =6.18 moles
26.98 g/mol * 6.18 moles = 167 grams
4) Calculate the molar mass of ammonium nickel sulfate, (NH4)2Ni(SO4)2.
Nitrogen = 2 * 14 = 28
Hydrogen = 4 * 2 = 8
Nickel = 58.69 = 58.69
Sulfur = 32.06 * 2 = 64.12
Oxygen = 16 * 8 = 128
Molar Mass = 286.81 g/mol
o
5) A 0.794 mole sample of radon gas is confined to a 20.4 L container at 31.3 C.
What is the pressure of the gas? (R = 0.08206 L·atm/mol·K)
PV = nRT
T = 31.3 + 273 = 304.3
P * 20.4 = .794 * .08206 * 304.3
P = .972 atm
6) Consider an isotope of samarium, samarium-144, 144
62 Sm . Select the combination
which lists the correct atomic number, mass number, and neutron number, respectively.
Atomic Number: 62
Mass Number: 144
Neutron Number: 144 – 62 = 82
7) What is the stoichiometric coefficient in front of NaOH when the reaction below is
balanced with the lowest whole number coefficients?
B O + NaOH → Na BO + H O
2
3
3
3
2
B O + 6NaOH → 2Na BO + 3H O
2
3
The answer is 6.
3
3
2
8) The chemical equation 2NO (g) + O (g) → 2NO (g) informs us that Magnesium
2
2
oxide is used in the manufacturing of cement and as an antacid. Which of the
following gives the correct formula and bonding for magnesium oxide?
MgO; Ionic bonding
9) Sucrose has the molecular formula C12H22O11. What is the percent of carbon in
sucrose by mass?
Molecular Weight for C12H22O11:
Carbon = 12 * 12 = 144
Hydrogen = 22 * 1 = 22
Oxygen = 16 * 11 = 176
Molar Mass = 342 g/mol
Percent of Carbon = 144 / 342 = 42.1%
10) How many grams of calcium phosphate are needed to form 172 g of calcium silicate?
2Ca3(PO4)2 + 6SiO2 + 10C → 6CaSiO3 + P4 + 10CO
Molar Mass for Calcium Silicate:
Calcium = 40
Silicon = 28
Oxygen = 3 * 16 = 48
Molar Mass = 116 g/mol
Moles of CaSi03 = 172/116 = 1.48 moles
Moles of Calcium Phosphate = .493 moles
Grams of Calcium Phoshate = .493 moles * 310.176722 = 152.917 grams
11) What is the stoichiometric coefficient in front of H2O when the reaction below is
balanced with the lowest whole number coefficients?
BF3 + H2O → B2O3 + HF
A: 2BF3 + 3H2O → B2O3 + 6HF
12) The chemical equation Fe2O3 (s) + 3CO (g) → 2Fe (s) + 3CO2 (g) informs us that
…unfinished question.
13) What is a chemical property of chlorine?
A Nonmetal gas that burns in Sodium Vapor
14) What is the pH of a 0.20M HCl solution?
pH = -log(.20) = 0.7 = H+ concentration
15) A sample of oxygen gas at 41.4 oC and 0.500 atm has a volume of 11.41 L. What is
its volume when the temperature is -10.8 oC and its pressure is 0.500 atm?
(R = 0.08206 L·atm/mol·K)
V1/T1 = V2/T2
T1 = 41.4 + 273 = 314.4 K
T2 = -10.8 + 273 = 262.2 K
(11.41)/(314.4) = V2/(262.1)
V2 = 9.512L
16) Which of the following gives the correct formula and bonding for sodium sulfide?
Na2S; Ionic Bonding
17) Lithium forms compounds which are used in dry cells and storage batteries and in
high-temperature lubricants. It has two naturally occurring isotopes, 6Li (isotopic mass =
6.015121 amu) and 7Li (isotopic mass = 7.016003 amu.) Lithium has an atomic mass of
6.9409 amu. What is the percent abundance of lithium-6?
6.015121(L6) + 7.016003(1-L6) = 6.9409
L6 = .075103
Percent of L6 = 7.5%
18) An enclosed mixture has a mass of 4.37010 ± 0.00003 g, and after a chemical change
occurs the mixture has a mass of 4.37012 ± 0.00003 g. These results show that…
The Law of Conservation remains true because after the chemical change the mass
remains the margin of error.
19) Select the answer that expresses the result of (44.318 ÷ 8.712) – 4.75 with the correct
number of significant figures.
44.318/8.721 = 5.087
5.087 – 4.75 = .34
20) A flask has a mass of 68.20 g when empty and 567.12 g when filled with water.
When the same flask is filled with concentrated phosphoric acid, H3PO4, its mass is
911.37 g. What is the density of concentrated phosphoric acid? (Assume that water has a
density of 1.00 g/cm3 at the temperature of the measurement.)
Mass of Water = 567.12 – 68.20 = 498.92 grams
Mass of H3PO4 = 911.37 – 68.20 = 843.17 grams
Since water has a density of 1 the volume must be equal to the mass of water; hence
the Volume of the flask is 498.92 ml
Density of phosphoric acid = 843.17/498.92 = 1.6900 g/ml
21) A scientist must determine the density of a mineral sample. Her five trials yield
densities of 3.73 g/cm3, 3.64 g/cm3, 3.84 g/cm3, 3.87 g/cm3, and 3.69 g/cm3. Independent
studies found the correct density to be 3.75 g/cm3. Which of the following statements
represents the best analysis of the data?
Her data is more accurate than it is precise.
22) Express 0.006917 cm using three significant figures.
6.92 X 10^-3
23) How many grams of N2 gas occupy 39.2 L at STP?
(R = 0.08206 L·atm/mol·K)
1 mol = 22.4L
Xmol = 39.2L
X = 1.75 moles
N2 = 28g/mol * 1.75 moles = 49 grams
24) Which of the following properties of argon gas is an extensive property?
Number of molecules; Extensive properties have to do with quantity… Intensive are
properties where quantity doesn’t matter
25) A flask has a mass of 71.25 g when empty and 593.17 g when filled with water. When
the same flask is filled with concentrated nitric acid, HNO , its mass is 812.38 g. What is the
3
3
density of concentrated nitric acid? (Assume that water has a density of 1.00 g/cm at the
temperature of the measurement.)
Mass of Water = 593.17 – 71.25 = 521.92 grams
Mass of HNO3 = 812.38 – 71.25 = 741.13 grams
Since water has a density of 1 the volume must be equal to the mass of water; hence
the Volume of the flask is 521.92 ml
Density of nitric acid = 741.13/521.92 = 1.4200 g/ml
26) Calculate the molar mass of ceric ammonium nitrate, (NH ) Ce(NO ) .
4 2
3 6
Nitrogen = 14 * 8 = 112
Hydrogen = 1 *8 = 8
Oxygen = 16 * 18 = 288
Cerium = 140.116
Molar Mass = 548.1 amu
27) Which of the following elements are the least reactive?
Noble Gases
28) Sucrose has the molecular formula C12H22O11. What is the percent of hydrogen in
sucrose by mass?
Molar Mass of Sucrose:
Carbon: 12 * 12 = 144
Hydrogen: 1 * 22 = 22
Oxygen: 16 * 11 = 176
Formula Weight = 342 g/mol
22*100/342 = 6.43%
29) What is a covalent compound?
A covalent bond is a form of chemical bonding that is characterized by the sharing
of pairs of electrons between atoms, and other covalent bonds. In short, the stable
balance of attractive and repulsive forces between atoms when they share electrons
is known as covalent bonding. [wiki]
30) Which assumptions of Dalton’s atomic theory had to be revised or discarded because
of the discovery of stable isotopes?
All atoms of a given element are identical, and the atoms of a given element are
different from those of any other element
31) Which procedure can be used to demonstrate experimentally that the reaction obeys
the Law of Conservation of Matter?
2Mg + O2  2MgO
Determine the mass of sealed flash-bulb containing magnesium and
oxygen, ignite the mixture, cool, and compare the final mass of the bulb
plus contents to the original mass of the bulb plus contents
32) An enclosed mixture has a mass of 6.82021 ± 0.00004 g, and after a chemical
change occurs the mixture has a mass of 6.82024 ± 0.00004 g. These results show
that
The Law of Conservation remains true because after the chemical change the mass
remains the margin of error.
33) Atoms D, X, Q and Z have the following nuclear compositions… which two are
isotopes?
318
121 X
321
124 A
328
124 Z
318
120Q
A and Z are isotopes… same atomic number different atomic mass.
79
34) Bromine has two naturally occurring isotopes, Br (isotopic mass =
81
78.9183376 amu) and Br (isotopic mass = 80.916291 amu). Bromine has an atomic
mass of 79.904 amu. What is the percent abundance of bromine-81?
78.9183376(1 - B81) + 80.916291(B81) = 79.904
2(B81) = .9856624
B81 = .4928312
Percent of B81 = 49.28312%
35) How many grams of O gas occupy 43.7 L at STP?
2
(R = 0.08206 L·atm/mol·K)
1 mol = 22.4 L
X mol = 43.7 L
X mol = 1.95
1.95 mol * 32 g/mol = 62.4 grams
36) Which of the following properties of xenon gas is an extensive property?
Number of molecules; Extensive properties have to do with quantity… Intensive are
properties where quantity doesn’t matter
o
37) A sample of xenon gas at 48.2 C and 0.680 atm has a volume of 12.87 L. What is its
o
volume when the temperature is -12.4 C and its pressure is 0.680 atm?
(R = 0.08206 L·atm/mol·K)
V1/T1 = V2/T2
T1 = 48.2 + 273 = 321.2 K
T2 = -12.4 + 273 = 260.6 K
(12.87)/(321.2) = V2/(260.6)
V2 = 10.44 Liters
38) Consider an isotope of europium, europium-153, 15363 Eu Select the combination
which lists the correct atomic number, mass number, and neutron number,
respectively.
Atomic number = 63; Mass number = 153;
Neutron number = 153 – 63 = 90
39) Express 0.082033 cm using three significant figures.
8.20 X 10^-2
40) At 25 °C. the concentration of the hydroxide ion in moles per liter in a
solution that has a pH of 8 is
-log(OH-) = 6
OH- Molarity = 10^-6 moles/liter
41) Air is sealed in a vessel at 273 °C and then cooled to 0 °C. If the vessel itself
does not contract, the pressure inside the vessel will become
When the temperature goes down, the pressure goes down.
42) The density of carbon tetrachloride is 1.60 g·mL–1. How many moles are there
in a liter of the pure CCl4?
Density = 1.6 g/ml
In one liter there are 1600 grams.
Molecular weight of CCl4 = 153.8236 g/mol
Moles of CCl4 = 1600g/153.8236 g/mol = 10.40 moles
43) If the formula of an oxide is X2O3, what is the formula of the chloride of X?
X = +3
XCl3
44) What formula would be expected when Ba and N combine to form a binary
compound?
Ba3N2