Mid1AnsKey10 - Introductory Chemistry Fall 2010 Midterm 1...

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Introductory Chemistry Name (print) Answer Key Fall 2010 - Midterm 1 Section 2 - Prof. Draper 4 pages - 6 problems – 92 points total Be sure to show computations and reasoning where requested Periodic Table is the last page – you may tear it off and use it for scratch paper Periodic table is last page exam Avogadro ʼ s Number = 6.022 x 10 23 E = Q 1 Q 2 /(4 π ε 0 r) μ = QR μ(Debye) = δ (R/0.2082 Å) ε 0 = 8.854 x 10 -12 C 2 J -1 m -1 e = 1.602 x 10 -19 Coulomb 1 Å = 10 -10 m 1 a. (6 pts) Atomic structure. Fill in the blanks: protons neutrons valence electrons Chemical symbol, atomic mass number , and charge (i) 50 64 ____4 _______ 114 Sn_ (neutral) (ii) 82 _ 122 ___ 2 204 Pb +2 b. (8 pts) Molecular formulas. By combustion analysis, a chemical compound is found to have the follow mole ratios of elements: 1 C : 0.714 H : 0.429 N : 0.857 O From measurements of the grams of compound present as a gas in a particular volume, the molecular mass is computed as 227.1 gm/mol. What is the molecular formula of the compound? (You may round atomic masses to one decimal place.) the molecular weight must be an integral multiple of: (1*12.0 + 0.714*1.0 + 0.429*14.0 + 0.857*16.0) = 32.43 gm/mol 227.1/32.43 = 7.00 The molecular formula is therefore C7 H5 N3 O6 (trinitrotoluene) C____ H____ N ____ O_____
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Name: ___________________________ page 2 2. Stoichiometry a. (6 pts) Balance the following chemical reactions: 1 C 2 H 6 + _7/2_O 2 _2 _CO 2 + _3 _H 2 O _1_ Cl 2 O 7 + _1 _H 2 O
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