120 CHEM (Winter 2006)
Test #1
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1. The "lead" in a pencil is actually almost pure carbon. If the mass of "lead" in a small pencil mark is 1 . 2 0 ~o - ~ then how many carbon atoms are there in the pencil mark? 1 g,
2. For the chemical equation below, set the coefficient of Mg3N2equal to one and then balance the equation. Then answer the questions that follow. (Note: The reaction below is not a redox reaction.)
Mg3N2
+
6
H20
-+
3
Mg(OH)2
+
2
NH2 (unbalanced)
What is the coefficient of H 2 0 in the balanced chemical equation? (1 mark) True (T) or False (F)? Magnesium hydroxide, Mg(OH)2, is only slightly soluble in water. (1 mark) True (T) or False (F)? Ammonia, NH3, acts as a strong Bronsted-Lowry base in aqueous solution. (1 mark)
6
7-
F
CHEM 120 (Winter 2006)
Test #1
Page 3 of 7
3. How many grams of Cu(s) can be dissolved in 0.500 L of 0.227 mol L-' HNO,(aq)? The reaction is given below. 3 Cu(s) + 8 HN03(aq) Molar masses, in g mol-':
+
3 Cu(N03)2(aq) + 2 NO(g) + 4 H20(1) HN03, 63.018 C U ( N O ~ )187.57 ~,
Cu, 63.55
4. What is the maximum mass of Pt(NH3)2C12 can be obtained from 14.32 g K2PtC14and that 1.81 g NH3 ? Give your answer in grams. The reaction is given below.
Molar masses: (in g mol-I)
K2PtC14,4 15.1
NH3, 17.034
KCI, 74.55
Pt(NH3)2C12,300.068
A-si...-yg
-tj,\P.,
"LL
iy.32tL-I
C(LPf C l y
-
- -x j o o . 0 6 Y !
1
-
-
lo. 35
7
CHEM 120 (Winter 2006)
Test #1
Page of 4 7
5. Vanillic acid is a compound containing only carbon, hydrogen and oxygen. When a 0.450-g sample of vanillic acid is burned completely in high-purity oxygen, it yields 0.942 g C 0 2 and 0.193 g H20. What is the percentage composition, by mass, of vanillic acid? Molar masses, in g mol-I :
H, 1.008
C, 12.01
0 , 16.00
"/o
0 =
l o o "/, -
", C /
-
% (-I = 3 g . q
6. A 10.50-g sample of a mixture of CuO and Cu20 is reduced to 8.89 g of Cu(s). What is the percentage by mass of CuO in the original mixture? Molar masses, in g mol-I: Cu, 63.55 CuO, 79.55 CuzO, 143.10
CHEM 120 (Winter 2006)
Test #1
Page 5 of 7
7. Classify the following reactions as "redox", "acid-base", "precipitation", or "other". (0.5 marks each)
8. For each of the following, write down the balanced net ionic equation for any ...