11. Which of the following compounds has the smallest mass percent chlorine? A)

Question

11. Which of the following compounds has the smallest mass percent chlorine?
A) BeCl2
B) MgCl2
C) CaCl2
D) SrCl2
E) BaCl2
12. Ascorbic acid contains 40.92% C, 4.58% H and 54.50% O by mass. What is the empirical formula of
ascorbic acid?
A) C2H4O
B) C4H3O4
C) C3H4O
D) C3H3O
E) C3H4O3
13. Solid lithium hydroxide is used in space vehicles to remove the carbon dioxide exhaled by
astronauts. The hydroxide reacts with the carbon dioxide to form solid lithium carbonate and liquid
water. How many grams of carbon dioxide can be absorbed by 1.00 g of lithium hydroxide?
A) 1.89 g
B) 0.919 g
C) 1.84 g
D) 3.67 g
E) 0.500 g

Consider the complete combustion of octane, C8H18. How many grams of O2 are needed to burn
1.50 mol of octane?
A) 800 g
B) 267 g
C) 400 g
D) 384 g
E) 600 g
15. Magnesium metal burns in air with a dazzling brilliance to produce magnesium oxide. When 5.50 g
of Mg burns, what is the theoretical yield of magnesium oxide?
A) 5.50g
B) 9.12 g
C) 0.226 g
D) 4.56 g
E) 18.2 g
16. Mercury(II) oxide decomposes upon heating to mercury metal and oxygen gas. Upon heating a
sample of HgO the reaction container and its contents decreased in mass by 0.250 g. What mass of
HgO reacted?
A) 0.845 g
B) 0.250 g
C) 0.500 g
D) 1.69 g
E) 3.38 g

When a mixture of 10.0 g of acetylene (C2H2) and 10.0 g of oxygen (O2) is ignited, the resulting
combustion reaction produces CO2 and H2O. Assuming the reaction goes to completion, how
many grams of C2H2 are present after the reaction?
A) 6.75 g
B) 3.26 g
C) 5.93 g
D) 4.07 g
E) 0.00 g
18. A sample of 0.30 mol of potassium phosphate is added to 20.0 mL of 0.15 M silver nitrate, resulting
in the formation of a precipitate. Calculate the theoretical yield, in moles, of the precipitate that
forms.
A) 0.0010 mol
B) 0.0020 mol
C) 0.0030 mol
D) 0.0060 mol
E) 0.0090 mol
19. You are presented with a white solid and told that due to careless labeling it is not clear if the
substance is barium chloride, lead chloride, or zinc chloride. When you transfer the solid to a
beaker and add water, the solid dissolves to give a clear solution. Next, a Na2SO4 (aq) solution is
added and a white precipitate forms. What is the identity of the unknown white solid?
A) BaCl2
B) PbCl2
C) ZnCl2
D) PbCl
E) BaCl

20. EXTRA CREDIT. Which of the following metals will react in acid solutions to form H2 gas? [You
must select all correct answers.]
A) Mg
B) Al
C) Fe
D) Cu
E) Ag

Explanation / Answer

11. Which of the following compounds has the smallest mass percent chlorine?
A) BeCl2    Cl %   = 71*100/80 = 88.75%
B) MgCl2    Cl%   = 71*100/95   = 74.73%
C) CaCl2     Cl%   = 71*100/111 = 63.96%
D) SrCl2      Cl% = 71*100/158.5 = 44.8%
E) BaCl2     Cl%   = 71*100/208      = 34.13 % least percentage

40.92% C, 4.58% H and 54.50% O

12.

Element    %        A. Wt        Relative number    simple ratio         simplest ratio

C              40.92   12            40.92/12 = 3.4         3.4/3.4 = 1             1*3   = 3

H                4.58     1               4.58/1   = 4.58      4.58/3.4   = 1.35     1.35*3   = 4

O              54.5      16            54.5/16    = 3.4      3.4/3.4     = 1           1*3     = 3

Empirical formula    C3H4O3

E) C3H4O3

13. 2LioH + Co2 ---------> Li2CO3 + H2O

     2 moles of LiOH react with 1 mole of Co2

    2*24g of LiOH react with 44g of Co2

     1g of LiOH react with = 44*1/2*24   = 0.916 moles

B) 0.919 g

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