CHEM 209 Midterm 2
DATE ____________
NAME ___Key____
NAvogadro = 6.02 1023
Activity Series of Metals
Li>K>Ba>Ca>Na>Mg>Al>Mn>Zn>Fe>Cd>Co>Ni>Sn>Pb>H2>Cu>Ag>Pt>Au
1.(2pts) Using the template below, give the electron configuration of element manganese
in cell diagram notations
3d
3p
4p
4s
3s
2s
2p
1s
2. (2pts) Using the template below, give the electron configuration of element germanium
in cell diagram notations
3d
3p
3s
2s
2p
1s
3. (2pts) Name these compounds:
Na2S sodium sulfide
Cl2O7 dichlorine heptoxide
4p
4s
4. (1pt) The chemical formula of copper(I) sulfide is:
(a) CuSO4
(b) CuS
(c) Cu2S
(d)
CuSO3
(e) CoS
5. (1pt) The proper name for Pb(NO3)2 is:
(a) Lead(IV) nitrate
(b) Potassium nitrate
(d) Lead(II) nitride
(c) Lead(II) nitrate
(e) Lead(II) nitrite
6. (4pts) Write the chemical formulas for the following:
iodine heptafluoride __IF7____
iron(II) phosphate __Fe3(PO4)2__
calcium nitride _____ Ca3N2____
sodium hydrogen phosphate _ Na2HPO4_
7. (2pts) Compile Lewis electron-dot formula for the following:
|Ö|
2|
sulfite ion
|Ö – S – Ö|
sulfur
trioxide
|Ö|
|
|O = S – Ö|
|O|
|Ö|
||
|
 |Ö – S – Ö|  |Ö – S = O|
8. (2pts) Identify polar molecular compound(s) out of the following:
(a)
CoCl3
(b)
COCl2
(c)
CCl4
(d)
CaCl2
In 9 to 11, for bromate ion, BrO3- :
9. (1pt) Compile its Lewis electron-dot formula.
|Ö|
26e
|
|Ö – Br – Ö|
10.(1pt) Select out of the following & sketch its electron configuration:
(a)
tetrahedral
(b)
trigonal bipyramid
(c)
trigonal planar
(d)
square planar
Br
O
O
O
11. (2pts) Select out of the following & sketch its molecular geometry:
(a)
tetrahedral
(b)
trigonal pyramid
Br
O
(c)
trigonal planar
(d)
O
square pyramid
O
In 12 to 15, for potassium dichromate, K2Cr2O7
12. (2pts) Calculate its molar mass 2x39+2x52+7x16 = 294 g/mol
13. (3pts) Determine its mass percent composition
%K = (2x39/294)x100% = 26.3%
%Cr = (2x52/294)x100% = 35.5%
%O = (7x16/294)x100% = 38.2%
14. (2pts) Determine the oxidation number of chromium in it (circle one):
-2
+2
+4
+6
+7
15. (2pts) How many moles of potassium dichromate are there in 100.00 g of K2Cr2O7?
100/294 = 0.340 mol
16. (2pts) Oxidation number of sulfur in pyrosulfate ion, S2O72- is (circle one):
(a) -2
(b) +2
(c) +6
(d) +7
(e) +14
17. (2pts) Determine the molecular formula of a compound containing 40.0 %C, 6.67%
H, the rest being oxygen, if its estimated molar mass is about 60g/mol. C2H6O2
C = 40.0/12 = 3.333 H=6.67/1 = 6.67 O = (100-40.0 – 6.67)/16 = 3.333
Divide by 3.333:
C2H4O2
18. (2pts) Which of the following compounds contains an element in its zero oxidation
state?
(a) C6H12O6
(b) Al2(SO4)3
(c) H2O
(d) ICl3
(e) OF2
19. (4pts) Which of the following contains the highest mass percent of hydrogen?
(a) LiH
(b) LiAlH4
(c) NaBH4
(d) LiBH4
(e) H2O
20. (2pts) How many moles of sulfur are there in 39.0 g of sodium sulfide, Na2S? (circle
one)
(a) 1
(b) 0.5
(d) 1.2.1024
(c) 39
(e) 6.02.1023
21. (1pt) How many moles of ions are released in a solution when 1 mole of MgCl2
dissolves in water? (circle one)
(a) 1
(b) 2
(c) 3
(d) 4
(e) 5
22. (2pts) The number of all atoms in 2 moles of NO2 is (circle one):
(a) 2
(b) 4
(c) 6
(e) 6.02.1023
(d) 3.6.1024
23. (2pts) Finish (including balancing) the chemical equation for a reaction between
calcium chloride and silver nitrate in aqueous solution. Indicate the physical state of the
products. Compile the ionic & net ionic equations for that reaction.
CaCl2(aq) + AgNO3(aq)  Ca(NO3)2(aq) + 2AgCl(s)
Cl-(aq) + Ag+(aq)  2AgCl(s)
24. (2pts) For the (unbalanced) chemical equation:
2 Fe2O3 + 6 Cl2 4 FeCl3
the proper set of stoichiometric coefficients is:
(a)
(b)
(c)
(d)
(e)
1
2
1
2
2
3
3
1
6
4
2
2
2
4
6
3
3
3
3
3
+3O2
25. (2 pts) For the reaction in the previous problem (#24), the element that is
oxidized___O____& reduced__Cl___ are:
(a) iron & oxygen
(b) chlorine & oxygen
(d) iron & chlorine
(c) chlorine & iron
(e) oxygen & chlorine
26. (4pts)
Finish (including balancing) the chemical equations for those reactions
below that are possible. If the reaction would not go, state so (X).
Ag + HCl(aq)  X
Zn + 2HCl(aq)  ZnCl2 + H2
2Al + 3CuCl2(aq)  2AlCl3 + 3Cu
Cu + ZnSO4(aq)  X
27. (2pts) The net ionic equation for the reaction (in an aqueous solution):
BaCl2 + Na2SO4  BaSO4 + 2NaCl
contains the following species (select one):
(a) BaCl2, Ba2+, Cl-
(b) Na2SO4, Na+, SO42-
(d) Na+, Cl-, NaCl
(c) Ba2+, SO42-, BaSO4
(e) Cl-, SO42-, NaCl
28. (2pts)
Which of the following reactions in an aqueous solution will NOT go to
completion (circle one)?
(a) Pb(NO3)2 + Na2S  PbS + 2NaNO3
(b) 3CaCl2 + 2Na3PO4  Ca3(PO4)2 + 6NaCl
(c) KCl + NaNO3  KNO3 + NaCl
(d) NaHCO3 + HCl  H2O + CO2 + NaCl
(e) Ca(OH)2 + 2HCl  CaCl2 + H2O
(g) FeCl3 + 3NaOH  Fe(OH) 3 + 3NaCl
29. (2pts)
Phosphorus, P, is completely oxidized with oxygen producing
diphosphorus pentoxide. Haw many grams of phosphorus are necessary to prepare 19.7 g
of P2O5?
4P + 5O2  2P2O5
P(g) =
19.7 g P2O5
1 mol P2O5
142 g P2O5
4 mol P
2 mol P2O5
31 g P
1 mol P
= 8.60 g P
30. (4pts)
Silver bromide for photography is produced by precipitation reaction
between solutions of silver nitrate and magnesium bromide. How many moles of silver
bromide will be produced when a solution containing 0.49 mol of AgNO3 is mixed with a
solution containing 0.29 mol of MgBr2?
2AgNO3 + MgBr2 => 2AgBr + Mg(NO3)2 react 2mol AgNO3 per 1 mol MgBr2
there are 0.49 mol AgNO3 per 0.29 mol MgBr2
i.e. less than necessary AgNO3 for 0.29 mol MgBr2
Hence AgNO3 is limiting reagent:
AgBr(mol) = 0.49mol AgNO3(1molAgBr/1molAgNO3) = 0.49 mol AgBr
31. (2pts)
In an experiment described in the previous problem, after isolating,
washing, filtering & drying the precipitate, its mass was measured as 87.31 g. What was
the percent yield of that operation?
Theor Yield: 0.49 mol AgBr => 0.49g x (107.9+79.9)g/mol = 92.02 g AgBr
%Yield = (87.31/92.02)x100% = 95%
32. (2pts) When a double displacement reaction is driven by precipitation, the ions that
do not form the precipitate (circle one):
(a)
evaporate
(b) are cations only
(c) are left in the solution & called spectator ions
(d) form a second insoluble compound
(e) none of the above
33. (2pts) The net ionic reaction between aqueous lead nitrate and potassium iodide is
(circle one):
(a)
Pb(NO3)2(aq) + KI(aq) → PbI2(s) + KNO3(aq)
(b) Pb2+(aq) + NO3-(aq) + K+(aq) + I-(aq) → PbI2(s) + K+(aq) + NO3-(aq)
(c)
Pb2+(aq) + 2I-(aq) → PbI2(s)
(d)
2Pb(NO3) 2 (s) → 2PbO + 4NO2 + O2(g)
(e)
Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq)
34. (1pt) When the following equation is balanced, what is the stoichiometric coefficient
for H2O? (circle one)
Ca(OH)2(aq) + H3PO4(aq) → Ca3(PO4)2(s) + H2O(aq)
2
3
4
5
6
35. (1pt) The reaction HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) may be classified as
(circle one):
(a) acid-base
(b) neutralization
(d) all of the above
(c)
(e)
double replacement
none of the above
36. (2pts) Which of the gases below has the lowest molar mass? (circle one)
(a)
argon
(b)
(d)
nitrogen
fluorine
(e)
(c)
neon
oxygen
37. (1pt) Which of the following statements is not true? (circle one)
(a)
When a metal reacts with a nonmetal, an ionic compound is formed
(b)
(c)
A metal-nonmetal reaction can always be assumed to be an oxidation-reduction
reaction
Two nonmetals can undergo an oxidation-reduction reaction
(d)
When two nonmetals react, the compound formed is ionic
(e)
A metal-nonmetal reaction involves electron transfer
38. (1pt) The molar mass of magnesium hydroxide is (circle one):
(a)
19.0 g/mol
(d)
(b)
42.0 g/mol
30.0 g/mol
(c)
(e)
58.3 g/mol
41.3 g/mol
39. (1pt) Which of the following contain the smallest number of molecules? (circle one)
(a)
5.0 g CO2
(d)
(b)
5.0 g H2O
5.0 g O2
(e)
(c)
5.0 g NH3
40. (1pt) A reaction that involves a transfer of electrons is called (circle one):
(a)
precipitation
(b) neutralization
(c)
oxidation-reduction
(d) double displacement
(e)
none of the above
5.0 g N2