Name__________________________________________ Answers to Sample Exam Questions #1 Chemistry 112 Multiple Choice 1. Which of the following statements best describes what happens when chocolate melts? a) This is a physical change, and the molecules move farther apart. b) This is a chemical change, and the molecules move farther apart. c) This is a physical change, and the molecules move closer together. d) This is a chemical change, and the molecules move closer together. 2. Which of the following is not part of Dalton’s atomic theory? a) All matter is composed of indivisible atoms. b) Atoms of the same element can be different. c) Compounds form when atoms combine in whole number ratios. d) A chemical reaction involves rearrangement of atoms. 3. Which of the following pairs of compounds illustrates the law of multiple proportions? a) Fe, FeO3 b) Cl, Cl2 c) H2SO4, NaOH d) H2O, H2O2 4. Which of the following elements would you expect to behave most like magnesium? a) sodium b) calcium c) aluminum d) scandium 5. Which of the following has the longest wavelength? a) X rays b) microwaves c) green light
d) UV light
6. Which of the following represents the correct formula of the compound formed by fluorine and aluminum? a) Al3F7 b) Al5F c) AlF3 Al7F3 7. Which of the following is an ionic compound? a) N2O b) CO
c) HCl
8. What is the molar mass of acetaminophen, shown here? a) 151 g/mol b) 48 g/mol c) 120 g/mol d) 132 g/mol
d) Na2O OH O
N H acetaminophen
9. Which of the following is most likely to lose electrons in an ionic compound? a) oxygen (O) b) hydrogen (H) c) lead (Pb)
d) carbon (C)
10. Which of the following is the least active metal? a) aluminum b) gold c) iron
d) magnesium
11. Which statement best describes the chemistry of soaps? a) They contain both a nonpolar group and a polar group b) They contain only a nonpolar group c) They contain only a charged group d) They are highly polar, charged compounds 12. Which of the following is not true about acid-base indicators? a) They act as sensors of H+ by changing color. b) They account for the fact that roses are red and violets are blue. c) They are found in pH paper. d) They form the basis of the Scott test for cocaine. 13. Isomers are molecules with the same a) kinds and number of atoms but a different arrangement of these atoms b) number of electrons and protons but a different number of neutrons c) net dipole but different atoms involved in the bond d) molecular formula but a different overall charge 14. Which of the following elements has the greatest electronegativity? a) S b) He c) Fr
d) Cl
15. Your friend is abroad this semester in London. She reports that the temperature there is 4°C. You know that the conversion to Fahrenheit involves multiplying by 1.8 and adding 32°F. What is the London temperature in Fahrenheit with the correct number of significant figures? a) 39.2°F b) 39°F c) 40°F d) 4°F
Short Answer. 1. Put a check in the box in front of the oxidation-reduction reactions below and circle the material undergoing oxidation. N2 + O2 2 NO
6 CO2 + 6 H2O C6H12O6 + 6 O2
PbCl2 + KI KCl + PbI2
Mg + 2 HCl MgCl2 + H2
CuO + H2 Cu + H2O
HCl + NaOH H2O + NaCl
2. Give an example of an oxidation-reduction reaction common to everyday life. What is being oxidized in your example? What is being reduced? Examples mentioned in class include batteries, rusting metal, burning fuels, reaction of rocket fuel, reaction of gun powder, respiration, and photography.
2
3. Circle any of the following that indicate an acid. [H+] = 1.0 x 10-8 mol/L pH = 6.5 turns litmus blue NH3 + H2O NH4+ + OH-
(compound in bold font)
HCl + H2O H3O+ + Cl-
(compound in bold font)
4. Briefly describe an example of an acid-base reaction common to everyday life. Many possibilities. See pp 104-111 in text.
5. Circle all the homogeneous mixtures below. Gatorade
Jello
Cappuccino
Orange Juice
Blood
6. Circle any of the following formulas that could be real compounds. H2P
MgS2
Fr2Cl
Na3N
K2O
7. Use the models below for this question. (p= protons; n = neutrons; e = electrons)
4 p, 4n
5 p, 6n
4 p, 6n
4e
5e
4e
Atom 1
Atom 2
Atom 3
a) What is the relationship between Atom 1 and Atom 3? (One word is sufficient.) Isotopes b) Write each of the atoms above in the shorthand notation that describes the most common isotope of hydrogen as H-1. Atom 1: Be-8
Atom 2: B-11
Atom 3: Be-10
c) Briefly comment on the proportions of these atoms as they are depicted here. The nucleus is far too big relative to the electron cloud.
d) How many valence electrons does Atom 2 have? 3 3
8. For each of the following compounds, a) Circle the correct type of bonding. You may need to circle two choices for one compound. b) Predict whether the compound dissolves significantly in water. (Necessary electronegativity values are as follows: C = 2.5; H = 2.1; O = 3.5; N =3.0) a) Type of bonding?
b) Dissolves in water?
CH4
ionic
polar covalent
nonpolar covalent
Yes
No
HCN
ionic
polar covalent
nonpolar covalent
Yes
No
polar covalent
nonpolar covalent
Yes
No
(C is the central atom)
CaO
ionic
9. Draw the Lewis dot structure for each compound in the boxes provided. a) CH4
H
H C H
b) HCN
c) CaO Ca2+
H:C:::N:
O
2-
H
10. Rank CH4, HCN, and CaO in terms of expected boiling point. CH4 HCN _______ __________ lowest intermediate
CaO _______ highest
Problems. You must clearly show your work for full credit. 1. Assume that the element with atomic number 113 has just been discovered in two different forms: one with 139 neutrons and one with 145 neutrons. If the first form occurs 75% of the time, what atomic mass should be listed on the periodic table for this element? (113 + 139) * 0.75 + (113 + 145) * 0.25 = 253.5 amu
2. If exactly one mole of pennies were divided equally among the world’s population (assume 5.5 x 109 people), how many dollars would each person receive? Please report your answer with the correct number of significant figures. 6.02 x 1023 pennies/5.5 x 109 people = 1.09 x 1014 cents = 1.1 x 1012 dollars
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3. The fermentation of glucose (C6H12O6) produces ethanol (C2H6O) and carbon dioxide. a) Write a balanced equation for this reaction. C6H12O6 2 C2 H6O + 2 CO2
b) What is the molar mass of glucose? 6 x 12.01 g/mol + 12 x 1.008 g/mol + 6 x 16.00 g/mol = 180.2 g/mol
c) What mass of ethanol is produced if 360 grams of glucose undergoes complete fermentation? 360 g glucose x 1 mole glucose 180 g glucose
x 2 moles ethanol x 46 g ethanol 1 mole glucose mole ethanol
= 184 g
4. A closed vessel contains 52 g of C2H2 and 200 g of O2, which react to form CO2 and H2O. a) How many molecules of C2H2 are in the vessel? 52 g x 1 mole x 6.02 x 1023 molecules = 1.2 x 1024 molecules 26 g mole
b) Write a balanced equation for the reaction. 2 C2 H2 + 5 O2 4 CO2 + 2 H2 O
c) After the reaction is complete, how many grams of each material will be found in the vessel? 2 moles C2H2 (see part a) x 5 moles O2 x 32 g O2 = 160 g O2 used, so 40 g remain. All C2H2 used. 2 mol C2H2 mole 2 moles C2H2 x 4 moles CO2 x 44 g CO2 = 176 g CO2 produced. 2 mol C2H2 mole 2 moles C2H2 x 2 moles H2 O x 18 g H2O = 36 g H2 O produced. 2 mol C2H2 mole Final answers: 0 g C2 H2
40 g O2
176 g CO2
5
36 g H2O
