Quiz 2 1998 Answers

1.  e (it contains two nonmetals)

2.  d  nitrite is NO₂^-, nitrate is NO₃^-

3.  a  an ionic solid consists of alternating positive and negative ions in three dimensions, so each + ion will typically be surrounded by 6 - ions.

4.  e 

5.  c  % =  ( mass K / total mass ) * 100% = [ 3 * 39.10 amu) / (3 * 39.10 + 1 * 238.03) amu ] x 100% = 32.9%

6.    a       CxHy   x = amount of C in mol, y = amount of H in mol;  assume 100 g to make this easier:

    C (92.3 g / 12 g/mol)  H (7.7 g / 1 g/mol) = C_7.69 H _7.7 = CH

7.  b

         2 C₂H₆     +         7 O₂  -->  4 CO₂ + 6 H₂O

n        3                        10

            3                        3 x 7/2 = 10.5          if all C2H6 reacts, not enough O2

        2/7 x 10 = 2.86        10                         if all O2 reacts, 2.86 mol C2H6 is required. 

         So C2H6 is excess reagent, 0.14 mol remains.

8.      a      

K₂CrO₄ and Pb(NO₃)₂?

2 K⁺  + CrO₄^2-  + Pb²⁺ + 2 NO₃^- -->  PbCrO₄ + 2 K⁺ + 2 NO₃^-

9.  b

n = CV = 16.7 mL x 0.35 mol/L x  1 L / 1000 mL = 0.00585 mol H2SO4

0.00585 mol H2SO4 x (2 mol H+ /mol H2SO4) = 0.0117 mol H+

1 mol H+ reacts with 1 mol OH-

10. b

q = m * SH * DT = 200 J = 45 g * SH * 4.23^oC;  SH = 1.05 J/g^oC.