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Home , Empirical formula

CHEMISTRY 101 SPRING 2002 EXAM 1 FORM A SECTIONS 501-509 DR. KEENEY-KENNICUTT

Directions: (1) Put your name, S.I.D. number and signature on the free response part of the exam where indicated. (2) Each multiple choice question is actually 2 questions on your scanning sheet. If you are sure of an answer, put the same answer down for both questions for 5 pts. If you cannot decide between two answers, put one answer down for one question and the other answer down for the other question. If you get one correct you'll get half credit for 2.5 pts. If there is an ambiguous multiple choice question, use the last page to explain your answer. (3) Do NOT write on the envelope. (4) Bubble in OPTION A on the scanning sheet IF you want your grade posted. (5) When finished, put the free response answers in the envelope with the scanning sheet. You can keep the multiple choice part - the answers will be given to you as you leave. (6) There are a total of 29 questions (17 actual questions).

PART 1

1&2. Which of the following name/symbol pairs is incorrect?

(a) chromium/Cr (b) tungsten/W (c) potassium/K (d) tin/Ti (e) silver/Ag

3&4. The correct name for CH3COCH3 is:

(a) benzene (b) (c) methanol (d) ethanol (e)

5&6. Two moles of Ca(CH3COO)2 contain:

(a) 2 units of Ca(CH3COO)2 (b) 2 Ca2+ cations - (c) 4 moles of CH3COO anions (d) 2 x Avogadro's number of (e) 2 moles of atoms

ã Keeney-Kennicutt, 2002 A1

7&8. The molecular formula of an organic compound is C9H12O3. Its empirical formula is ______.

(a) C2H3O (b) C9H12O3 (c) C3H4O (d) C4H6O (e) C3H3O

9&10. The minimum daily requirement of the amino acid lysine (C6H14N2O2) is 5.5 mmol. How many grams is this?

(a) 8.0 g (b) 0.80 g (c) 0.008 g (d) 80. g (e) 0.080 g

11&12. One of the organic bases most often found in nucleotides (the building blocks of nucleic acids) is thymine. Its elemental composition by mass is 47.6% C, 4.80% H, 25.4% O and 22.2%N. If its true molecular formula is the same as its empirical formula, its true molecular formula is ______.

(a) C2H2ON (b) C3H3ON (c) C6H6O2N2 (d) C5H5O2N2 (e) C5H6O2N2

ã Keeney-Kennicutt, 2002 A2 13&14. Which of the following statements is FALSE for the balanced equation given below?

CS2 + 3O2 ® CO2 + 2SO2

(a) Sixty four (64) grams of O2 will produce 128 grams of SO2.

(b) One mole of CS2 will produce two moles of SO2.

(c) Three of gas requires one of CS2 for reaction.

(d) The reaction of one mole of O2 will produce 2/3 mole of SO2.

(e) The reaction of 76 g of CS2 produces 44 g of CO2.

15&16. A student weighed out 70.0 g of CaBr2. To what volume should she dissolve and dilute this to make a

solution that is 3.00 M CaBr2?

(a) 942 mL (b) 117 mL (c) 455 mL (d) 1080 mL (e) 269 mL

ã Keeney-Kennicutt, 2002 A3 17&18. Concentrated phosphoric acid is 85.0% H3PO4 by weight and has a density of 1.69 g/mL. One (1.00) liter

of concentrated phosphoric acid contains ______of H3PO4.

(a) 1995 g (b) 509 g (c) 1440 g (d) 734 g (e) 913 g

19&20. Every hemoglobin molecule (molecular weight - 64,456 amu/molecule) contains 4 iron atoms. What is the percent iron in hemoglobin?

(a) 1.5% (b) 0.21% (c) 0.69% (d) 0.35% (e) 6.0%

ã Keeney-Kennicutt, 2002 A4 21&22. What volume of 2.00 M HCl acid must you use to prepare 100. mL of 0.500 M HCl?

(a) 400. mL (b) 200. mL (c) 100. mL (d) 50.0 mL (e) 25.0 mL

23&24. Zinc is more active chemically than is silver; it may be used to remove dissolved silver ions from solution:

Zn(s) + 2AgNO3(aq) ® Zn(NO3)2(aq) + 2Ag(s)

What mass of Zn metal would be consumed by 25.45 mL of 1.015 M AgNO3, assuming 100% efficiency?

(a) 0.8446 g (b) 0.4012 g (c) 1.355 g (d) 0.6259 g (e) 0.7112 g

ã Keeney-Kennicutt, 2002 A5

ã Keeney-Kennicutt, 2002 A6

CHEMISTRY 101 SPRING 2002 NAME EXAM 1 S 501-509 ID Signature Form A

PART 2

25. Suppose you have 2 samples of sulfur. Sample #1 has 1 mole of S6 molecules and Sample #2 has 3 mole

of S2 molecules. Answer the following questions and show your work to get full credit.

(3 pts) (a) Which sample has more molecules? Explain.

(7 pts) (b) Calculate the number of sulfur atoms in each sample. What does your answer show? Draw a picture to illustrate your answer.

OVER Þ

ã Keeney-Kennicutt, 2002 A7 (10 pts) 26. Convert the following chemical reaction written in words to , then balance the equation:

When aluminum nitrate reacts with calcium hydroxide, the two products are aluminum hydroxide and calcium nitrate.

(5 pts) 27. Chalcocite, Cu2S, is a mineral containing copper. What mass of chalcocite contains 20.0 g of copper?

ã Keeney-Kennicutt, 2002 A8 (7 pts) 28. Octane, C8H18, is a component of gasoline. A spark is used to ignite 1.56 g of octane and 6.77 g of

oxygen gas in a sealed container. What mass of carbon dioxide, CO2, is produced? The unbalanced equation is below:

C8H18(l) + O2(g) ® CO2(g) + H2O(g) UNBALANCED - you need to balance this

OVER Þ

ã Keeney-Kennicutt, 2002 A9 (8 pts) 29. The reaction of finely divided aluminum and iron(III) oxide, Fe2O3, is called the thermite reaction. It produces a tremendous amount of heat, making the welding of railroad track possible in the last

century. If the reaction has a percent yield of 80.0%, how much Fe2O3 is necessary to produce 100.0 g of Fe in this very useful reaction?

Fe2O3(s) + Al(s) ® Fe(s) + Al2O3(s) UNBALANCED - you need to balance this

ã Keeney-Kennicutt, 2002 A10 SCRAP PAPER OR COMMENTS ON EXAM

CHEMISTRY 101 Spring 2002 NAME EXAM 1 Form A S 501-509

ã Keeney-Kennicutt, 2002 A11