05/15/14
CHEM 1A Final Exam
Name: ________________________________
Please read the following. To receive full credit for a question or a problem, in addition to the
correct answer, you must show a neat, complete, and logical method of solution where each
number is labeled with the appropriate unit and the final answer is rounded to the correct
number of significant digits. The correct answer without any work shown will generally get
zero credit! When an explanation is required, it should be brief, but accurate and complete.
There are 16 questions for a total of 200 points.
1.
(12.5 points) A 10-L container at 0ºC is filled with 0.200 moles of oxygen, 0.500 moles
carbon dioxide, and 0.300 moles of methane.
(a) How many substances are present in the container?
(b) How many elements are present in the container?
(c) How many molecules are present in the container?
(d) How many atoms are present in the container?
(e) How many compounds are present in the container?
(f) What is the density of the material inside the container?
(g) What is the pressure inside the container?
2. (12.5 points) Complete the following table.
Name
Formula
sulfurous acid
IF7
ammonia
AlN
SnF2
calcium peroxide
AgClO3
potassium hydrogen phosphate
ammonium sulfide
NO2
manganese(II) sulfate
Pb(C2H3O2)2
calcium hypochlorite
FeO
3. (12.5 points) Examine the following list of chemical substances to answer questions (a), (b),
(c) and (d).
CH3OH
NH4ClO3
Na2O2
Al2S3
SO3
NH2OH
KMnO4
HClO4
(a) Which of the substances contain(s) a polyatomic cation?
(b) Which of the substances contain(s) a polyatomic anion?
(c) Which of the substances contain(s) both ionic and covalent bonds?
(d) Which of the substances contain(s) no ionic bonds?
4. (12.5 points) Trinitrotoluene (TNT) is one of the most commonly used explosives for
military and industrial applications. It is a compound of carbon, nitrogen, hydrogen, and
oxygen. Carbon occurs in two forms: graphite (the material in “lead pencils”) and diamond.
Oxygen and nitrogen comprise over 98% of the atmosphere of Earth. Hydrogen is an
element which reacts explosively with oxygen. Which of the properties of the elements
determines the properties of TNT? Briefly explain.
5. (12.5 points) Fill the blanks in the table below.
Formula
Name
Lewis Structure
(single structure or
several resonance
structures;
Dots & Dashes Style)
Number of Atoms
Number of Protons
Number of Electrons
Number of Valence
Electrons
Number of Bonding
Electron Pairs
Number of Lone
Electron Pairs
Formal Charge on Sulfur
Atom
Oxidation State of
Sulfur Atom
Electron Cloud
Geometry
Name of the Geometric
Arrangement of Atoms
Sketch of the Geometric
Arrangement of Atoms
and Lone Pairs around
the Central Atom
Predicted Ideal Bond
Angle
Deviation from the Ideal
Bond Angle (yes or no?)
Bonds Are of the Same
Length (yes or no?)
SO3
SO32−
6. (12.5 points) Place X in all appropriate boxes to indicate types of chemical bonds and
intermolecular forces responsible for the interactions between atoms, ions and molecules in
each sample of matter. (You may use the space below the table to sketch the shapes of
molecules under consideration.)
7. (12.5 points) The following diagram represents a cross-sectional area of a steel tank filled
with hydrogen gas at 20°C and 3 atm pressure. (The dots represent the distribution of H2
molecules.)
Which of the following diagrams illustrate the distribution of H2 molecules in the steel tank
if the temperature is lowered to – 20°C? Briefly explain your choice.
(A)
(B)
(C)
(D)
8. (12.5 points) Relative humidity is the ratio of the pressure of water vapor in the air to the
pressure of water vapor in air that is saturated with water vapor at the same temperature.
Often this quantity is multiplied by 100 to give the percent relative humidity.
relative humidity =
actual partial pressure of H 2O
×100%
partial pressure of H 2O vapor if saturated
Suppose the percent relative humidity is 80.0% at 35.0°C. How many grams of water are
present in each cubic meter of the air?
9. (12.5 points) Ozone, O3, absorbs ultraviolet radiation and dissociates into O2 molecules and
O atoms:
O3 + hν → O2 + O
A 1.65 L sample of air at 22°C and 748 mmHg contains 0.25 ppm of O3. How much
energy, in joules, must be absorbed if all the O3 molecules in the sample of air are to
dissociate? Assume that each photon absorbed causes one O3 molecule to dissociate, and
that the wavelength of the radiation is 254 nm.
10. (12.5 points) Consider the reaction of combustion of propane, C3H8. (This reaction is used
in barbecue grills.)
(a) Write a balanced chemical equation for the reaction of combustion of one mole of
propane. All reactants and products are gases.
(b) Calculate the enthalpy of the reaction using the standard enthalpies of formation.
(c) Calculate the enthalpy of the reaction using the bond energies values.
(d) Compare the two methods of calculating ΔHºrxn. Are the results of calculations similar?
(e) Why all combustion reactions of organic compounds are exothermic? Explain this in
terms of bond energies.
11. (12.5 points) It is difficult to prepare many compounds directly from their elements, so
ΔH°f values for these compounds cannot be measured directly. For most organic
compounds, it is easier to measure the standard enthalpy of combustion by reaction of the
compound with excess O2(g) to form CO2(g) and H2O(l). The standard enthalpy of
combustion of n-butanol, C4H10O(l), is ‒ 2676 kJ/mol at 25°C.
(a) Determine ΔH°f of n-butanol. (Hint: Write the thermochemical equation for the
reaction of combustion of n-butanol.)
(b)
Write the thermochemical equation for the reaction of formation of n-butanol.
12. (12.5 points) 8.00 g HCl is allowed to react with 10.0 g HNF2 according to the balanced
chemical equation given below.
3 HCl + 3 HNF2 → 2 ClNF2 + NH4Cl + 2 HF
In the course of the chemical reaction, only 15% of the limiting reactant has been
consumed. Determine which substances and how many moles of each will be present after
the reaction.
13. (12.5 points) In standardizing hydrochloric acid, 22.5 mL were required to neutralize 25.0
mL of 0.0500 M solution of sodium carbonate.
(a) What is the molarity of the HCl solution?
(b) How much water must be added to 200 mL of it to make it 0.100 M?
14. (12.5 points) An 8.129 g sample of MgSO4∙xH2O is heated until all the water of hydration
is driven off. The resulting anhydrous compound, MgSO4, weighs 3.967 g. What is the
formula of the hydrate?
(a) What is the formula of the hydrated salt?
(b) What is the name of the hydrated salt?
15. (12.5 points) The unit cell of graphite is shown below. The cell volume can be calculated
using the formula: 𝑉 =
√3 2
𝑎 𝑐.
2
Calculate the density of graphite.
16. (12.5 points) Using the half-equation method, write the balanced ionic equation and the
balanced full-formula equation for of the following reaction.
(K+)2Cr2O 72 − + (Na+)2SO 32 − + (H+)2SO 24 − → (Cr3+)2(SO 24 − )3 + (K+)2SO 24 − + (Na+)2SO 24 − + H2O