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Name______Per______Date______
Honors Chemistry Midterm Exam Thursday, January 19, 2012 7:20 am Room ______
The exam consists of 2 major sections: multiple choice and free response. Note the following important points as you prepare for the exam:
You will be provided a reference booklet, exam, and opscan sheet for multiple choice answers. You will not be permitted to bring additional reference materials to the test room. You will need to bring YOUR OWN CALCULATOR and pencil. You will not be permitted to share or borrow calculators during the exam period.
The attached review packet is meant to assist you in preparing for your exam. However, you should ALSO study concepts and problems from your class notes and chapter assignments. The review packet is intended to be a supplement.
The multiple choice section of the exam is 35 questions with each question being worth 1 point. The free response section is worth 65 points. The following is a list of the possible problem/question topics for the free-response section.
Density Unit Conversions Percent Error and percent yield Percent Composition Empirical/molecular formula Predicting products for chemical reactions (naming/formula writing) Balancing equations and identifying reaction types Net ionic equations and identifying precipitates Molarity problems Stoichiometry (including mass, volume, representative particles, molarity etc.) Limiting and excess reactant problems Identifying oxidation and reduction reactions and assigning of oxidation numbers Wavelength, frequency and energy problems Electron Configurations of all types (full, abbreviated and orbital diagram)
Scenarios with a reading section and multiple choice, problem solving, and short answer questions based on the scenario
Also, you should review the names of common lab equipment and glassware and procedures. 2
1. Introduction
A. Identify each of the following as either a physical or chemical change.
1. Wax melting. 2. Iron rusting. 3. Hydrogen and oxygen combining together to form water. 4. Distillation (boiling) of water.
B. Identify each of the following as either a physical or chemical property.
1. Color 2. Reactivity with oxygen 3. Solubility in water 4. Density 5. If the substance is an acid or a base
C. Identify each of the following as either an extensive or intensive property.
1. Volume 2. Boiling Point 3. Mass 4. Density
D. Distinguish between precision and accuracy.
E. How is percent error calculated?
2. Metric Conversions and Density
A. A solid object with a mass of 22.50 g and a density of 4.50 g/mL is placed in a graduated cylinder with 30.6 mL of water in it. When the object is completely submerged in the water, what will the new volume reading in the cylinder be? 3
B. How many mm are there in 2.95 x 106 km?
C. How many cubic cm are there in 10.8 cubic decameters?
D. The density of potassium dichromate is 2.68 g/cm3. Express this number in pounds per cubic foot. ( 1.00 lb = 454.0 g and 1.00 in = 2.54 cm)
3. Chemical laws
A. Law of conservation of mass B. Law of multiple proportions C. Law of constant composition (definite composition)
For each of the following statements, consider which law above best applies to it. Then, write the letter of the law next to its number.
1. All water is exactly 11.11% hydrogen by mass.
2. In the reaction between hydrogen and oxygen, exactly 2.02 g of H2 react with exactly 32.00 g of O2 to form 34.02 g of H2O.
3. In one compound, 6.00 g of carbon combines with 8.00 g of oxygen. In a second compound, 6.00 g of carbon combines with 16.00 g of oxygen. 4
4. Atomic Structure
A. In one atom of uranium-235,
there are ______protons, ______neutrons and ______electrons.
B. Given an ion of sulfur-34:
1. Write the symbol:
2. List the number of protons______, neutrons______and electrons.
C. List the contributions (experiments and conclusions) of each of the following scientists who helped develop current atomic theory.
1. J.J. Thomson
2. Millikan
3. Rutherford
4. Bohr
5. Lavoisier
6. Mendeleev
D. Define isotope. 5
E. Explain how the atomic masses on the periodic table are calculated from the naturally occurring isotopes.
5. Formulas, mole conversions and molarity
A. Write the formula for each of the following, and classify each as ionic or covalent.
1. aluminum sulfate
2. sulfur trioxide
3. copper (II) hydroxide
4. iron (III) phosphate
B. Define the mole.
C. Distinguish between a strong, weak and non-electrolyte.
D. Calculate the following quantities.
1. How many nitrate ions in 2.50 moles of aluminum nitrate?
2. How many moles of CO2 are there in a 450. g sample of CO2?
3. What is the mass of 8.00 x 1024 formula units of NaCl? 6
4. How many grams of aluminum nitrate are needed to make 350. mL of a 1.45 M solution?
5. If 2.00 g of sodium sulfate are dissolved in 20.0 mL of solution, what is
a. the molarity of the solution?
b. the molarity of the sodium ions?
6. What is the percent by mass of hydrogen in ammonium phosphate?
7. When oxygen is bubbled through a solution of sodium polysulfide, a compound used in photography called “hypo” is produced. What is the empirical formula of hypo if it consists of 29.08% sodium, 40.57% sulfur, and the remainder is oxygen? 7
8. The empirical formula of a compound is C2H3. What is the molecular formula of this compound if the molar mass is 135 g/mole?
6. Equations and stoichiometry
A. First, write a balanced chemical equation for each reaction. Next, classify each reaction(synthesis, decomposition, single replacement, double replacement).
1. nitrogen gas and magnesium metal react to form solid magnesium nitride.
Balanced chemical equation:
Type: ______
2. Aqueous silver nitrate and nickel metal react to form silver metal + aqueous nickel (III) nitrate.
Type:______
3. Solid Platinum (IV) fluoride reacts to form platinum metal and fluorine gas
Type: ______
4. When a solution of sodium sulfate is added to a solution of iron (III) nitrate, a precipitate forms.
a. Write the complete balanced equation for the reaction.
b. Identify the precipitate: ______8
c. Identify the type of reaction: ______
d. Identify the spectator ion(s):______
e. Write the net ionic equation:
B. Redox Equations
1. Identify the oxidation numbers in each of the following:
-2 +1 NaClO C2O4 NH4
2. What are the defining characteristics of each of the following types of equations?
Oxidation –
Reduction –
3. Given the following UNBALANCED equation:
C3H8 (g) + O2 (g) CO2 (g) + H2O (l)
a. If you react 2.00 g of C3H8 with 8.00 g of O2, what mass of water is formed? 9
b. If 2.25 g of water is produced experimentally, what is the % yield?
4. Ammonia, NH3, is used to make fertilizers for lawns and gardens by reacting nitrogen gas with hydrogen gas.
a. Write a balanced equation with the smallest whole-number coefficients for this reaction.
b. How many moles of ammonia are formed when 1.34 moles of nitrogen react?
c. How many grams of hydrogen are required to produce 2.75x103 g of ammonia?
7. Light and Electron Configuration
A. State the relationship between frequency, wavelength and the speed of light. 10
B. Determine the number of:
1. electrons occupying the p orbitals in the arsenic atom?
2. orbitals in the third energy level?
3. d orbitals in a d sublevel?
4. valence electrons in an atom of sulfur?
C. Define the term isoelectronic.
D. What ion with a charge of -2 is isoelectronic with an argon atom?
E. Write both the complete and the abbreviated (short-hand or core) electron configuration of:
1. an aluminum atom
2. a sulfide ion
3. an atom of uranium
F. Draw an orbital diagram (orbital configuration or notation) of the following. DO NOT use abbreviated (short-hand) notation.
1. a phosphorus atom 11
2. a strontium ion
H. Distinguish between ground and excited state for an atom.
I. The laser in a CD player uses light with a wavelength of 780 nm. Calculate the energy of this radiation, in joules per photon. 12
10. Science Scenario Question
Directions: Read the following article. Using the article, answer the questions on the next page.
Let us examine and interpret an investigation as it might have appeared in an article, “Global Warming?” The Chickadees Don’t Mind.” Printed in a magazine called Feathered Friends Digest. (Note: Both the magazine title and the article are fictitious.)
Bird enthusiasts in Anytown, Pennsylvania, have recently completed a study of the effect of climate change on the chickadee population. The chickadee is a small, seed-eating songbird, common in the Northeastern United States through out the year.
The study compares the mean (average) June and December temperatures, as reported by the National Weather Service, with the number of chickadees counted by the Audubon Society during its December and June bird counts. The Audubon Society is a recognized group of bird experts that conducts nationwide bird counts around June 21 and December 21 each year. The table below lists the number of chickadees counted in Anytown during the two annual counts each year, and the mean temperature during the month preceding the count that year.
During the 10 year period of the study, there has been a 3.9ºC in crease in the mean June temperature, from 23.3 ºC to 27.2 ºC. In that time, the summer count of chickadees increased almost 70 percent, from 89 to 147 birds. The man December temperature increased 2.7 ºC, from 1.7 ºC to 4.4 ºC, with an increase in the winter count of chickadees of nearly 75 percent.
We conclude that whatever harm global warming may do to the environment, it does not endanger the chickadee population. In fact, as the climate continues to become warmer, we can look forward to ever-increasing numbers of these delightful songbirds.
Year Mean temperature Number of chickadees Mean temperature in Number of chickadees in June ºC found in summer December ºC found in winter count 1997 23.3 89 1.7 95 1998 23.9 91 1.7 98 1999 22.2 92 0.6 101 2000 24.4 95 1.7 102 2001 24.4 94 2.8 102 2001 25 110 2.8 120 2003 26.1 122 3.9 133 2004 26.7 134 3.3 145 2005 26.7 146 5.6 160 2006 27.2 147 4.4 162
Now, let us analyze the article and the validity of its conclusions. Should we assume that the data are accurate? Since both the National Weather Service and The Audubon Society are reliable and impartial sources, we believe the data to be accurate. 13
However, we must question the validity of the conclusion. This conclusion was not based on a controlled experiment. There may have been other reasons for the change in the chickadee population. In addition, the sample size was very small considering the large number of chickadees that can be found throughout the United States. If we were to graph this data, we would notice that in 2002 there was a sudden large increase in the bird population without a corresponding jump in temperature. A good scientific analysis of this data must include an explanation of all the observations, not just those that support one particular explanation.
Questions
1. What hypothesis did the author of this article propose?
2. Which of the following conclusions is not supported by the data?
A. More chickadees are seen in December that in June B. Over the 10-year period, the mean June temperature has generally increased. C. Over the 10-year period, the chickadee population has generally increased. D. Global warming is causing an increase in the bird population.
Base your answers to questions 3 and 4 on the following article, “Seed Sales Level Off,” which appeared the following month in Feathered Friends Digest. (Note: As before, both the magazine and the title of the article are fictitious.)
The Munchies Seed Company, which specializes in distributing seed for songbirds to homeowners in Pennsylvania, has reported that after the enormous growth in sales that began in 2002, sales for the year 2007 are slightly below last year’s levels. Company officials go on to state that they knew that the enormous growth in the number of people actively feeding songbirds could not go on indefinitely.
3. What alternative explanation for the increase in the chickadee population is provided by the data in this second article?
4. The mean temperature in Anytown, Pennsylvania, in June 2007 was 27.8 ºC. Predict the (approximate) number of chickadees that will be counted by the Audubon Society during the summer count; justify your prediction.