NAME:
Midterm Exam 1
Cemistry 211
Sept. 16,1997
PAGE 1 0f 5
- Show all work.
- Work problems to proper number of significant figures.
- Be sure to include units in your answers.
- Circle your final answers.
- Put your name on ALL pages.
(3 pts) 1. A solution of 2.5 g of table sugar dissolved in 5.0 ml of water contains a
sugar concentration of
(a) 0.50 mg/ml.
(b) 0.50 g/ml.
(c) 5.0 x 102 mg/cm3 .
(d) 5.0 x 102 g/L.
(3 pts) 2. Which of the following represents the greatest percent uncertainty?
(a) A thermometer reading of 100o C ± 3o C.
(b) The specific heat of Cd is measured to be 0.197 J/g Co
(the theoretical value is 0.231 J/g Co ).
(c) The melting point of tin is measured to be 244o C (the theoretical
value is 232o C).
(d) A balance measured the mass of a 1.000 g standard as 0.9981 g.
(3 pts) 3. Which of the following are chemical changes?
(a) milk souring
(b) silver tarnishing
(c) butter melting
(d) coal burning
(3 pts) 4. The elements whose symbols are Mg, Ba, and Pt are
(a) manganese, barium, and plutonium.
(b) mercury, beryllium, and polonium.
(c) manganese, barium, and platinum.
(d) mendelevium, bromine, and protactinium.
(3 pts) 5. The neutral atom 6 5Cu contains
(a) 29 neutrons.
(b) 29 protons.
(c) 65 neutrons.
(d) 65 electrons
(3 pts) 6. The ion 5 9Co2+ contains
(a) 59 neutrons and 27 protons.
(b) 29 protons and 27 electrons.
(c) 27 protons and 32 neutrons.
(d) 27 protons and 27 electrons.
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(4 pts) 7. Compounds in which the anion is O2+ and the cation
is either Fe2+ or Fe3+ can have the formulae
(a) O2 Fe3 or Fe3 O2
(b) FeO or FeO2
(c) Fe2 O or Fe3 O
(d) Fe2 O3 or FeO
(3 pts) 8. Which of the following staements are(is) true?
(a) The atomic number of an element is equal to the number of protons in
the nucleus of an atom of that element.
(b) Isotopes of the same element have different atomic numbers.
(c) 2 3Na has a mass number of 23.
(d) An anion is a negatively charged ion.
(4 pts) 9. Which of the following are(is) FALSE?
(a) Carbon is a metal.
(b) The mass number is twice the atomic number.
(c) The formula of calcium chloride is Ca2 Cl.
(d) The elements of the first period are known as the noble gases.
(4 pts) 10. Yttrium-90 is a radionuclide which is being studied for use in the
treatment of cancer. Which of the following describes the 9 0Y3+ ion?
(a) It has 36 electrons.
(b) It has 39 neutrons.
(c) It has 51 neutrons.
(d) It can form 9 0Y(NO3 )3
(4 pts) 11. Vitamin C, C6 H8 O6 ,
(a) has an empirical formula of C3 H4 O3 .
(b) contains 40.92% carbon by mass.
(c) contains 6 moles of carbon atoms per mole of molecules of Vitamin C.
(d) has a molecular mass of 176.12.
(4 pts) 12. Balance the equation
__Ca(OH)2 (aq) + __H3 PO4 (aq)-------------->__H2 O(g) + __Ca3 (PO4)2 (s)
(3 pts) 13. Consider the reaction
Mg(s) + I2 (s) ------> MgI2 (s)
Under which of the following reaction conditions will Mg be the limiting reagent?
(a) 200 atoms of Mg and 300 molecules of I2
(b) 0.16 mol Mg and 0.25 mol I2
(c) 100 atoms of Mg and 100 molecules of I2
(d) 0.12 mol Mg and 0.08 mol I2
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(3 pts) 14. Consider the reaction
2 SO2 (g) + O2 (g) -------> 2 SO3 (g)
What is the largest number of SO3 molecules which could be made from
381 SO2 molecules and 185 O2 molecules?
(a) 381
(b) 370
(c) 185
(d) 92
(3 pts) 15. One atom of an element has a mass of 9.123 X 10-23 g. There is only
one isotope of the element. The element is
(a) manganese.
(b) chlorine.
(c) chromium.
(d) argon.
(5 pts) 16. If the fertilizers listed below are priced according to their nitrogen
content, which will be the least expensive per 50 lb. bag?
(a) urea (NH2 )2 CO
(b) ammonia NH3
(c) ammonium nitrate NH4 NO3
(d) guanidine HNC(NH2 )2
(6 pts) 17. Indicate which of the following ions have a noble-gas electron arrangement
and, for such ions, identify the corresponding noble gas.
(a) Cs+
(b) I+
(c) S2-
(d) P3-
(e) Al3+
(f) O-
18. An analysis of nicotine, a compound found in the leaves of tobacco, shows that it is
74.0% C, 8.65% H and 17.35% N. Its molar mass is 162 g/mol.
(7 pts)
a) Determine the empirical formula of nicotine.
(7 pts)
b) What is the molecular formula?
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19.Aspirin, C9 H8 O4 (s), can be produced by reacting salicylic acid, C7 H6 O3 (s), with acetic
anhydride, C4 H6 O3 (l). Water is a side product of this reaction. Initially, you have 14.43 g
of salicylic acid and 10.38 g of acetic anhydride. Upon completion of this reaction you
obtain 6.26 g of pure aspirin.
(4 pts) a) Write a balanced equation for this reaction.
(4 pts) b) What is the limiting reagent?
(5 pts) c) Determine the theoretical yield of aspirin.
(4 pts) d) Calculate the percent yield for this reaction.
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(8 pts) 20. Fill in the blanks in the following table:
Symbol
Atomic
Number
Number of
Neutrons
31
36
8
27
?
?
Xe
Mass Number
15
58
133
(15 pts) EXTRA CREDIT. Calculate the percent abundances of chlorine-35 and chlorine37 if the atomic weight is 34.453 amu and the exact masses of the isotopes are
35
Cl = 34.968853 amu and 3 7Cl = 36.9659 amu. Assume no other isotopes exist.