Exam III Spots
1. Provide balanced chemical equations for the following reactions
(a)
Au2S3 (s)
+
H2(g)
--------->
Au (s)
+
H2S (g)
(b) Solid elemental phosphorous, P4, reacts with fluorine gas to produce gaseous phosphorous trifluoride.
(include the proper states/phases in your equation)
(c) Nitrogen dioxide reacts with water to produce nitric acid and nitrogen monoxide.
(d) Combustion of ethanol CH3CH2OH, a fuel additive.
2
2. For each of the following, predict the products of the reaction by writing a balance net ionic equation for
each. If no reaction is expected, then write NO REACTION.
(a)
ZnCl2 (s) added to CsOH (aq)
(b)
BaBr2 (aq) added to AgNO3 (aq)
(c)
Pb(NO3)2 (aq) mixed with NaI (aq)
(d)
AgNO3 (aq) mixed with K3PO4 (aq)
(e) Na2SO4 (aq) and LiOH (aq)
(f)
(NH4)2CrO4 (aq) and Pb(NO3)2 (aq)
(g)
Ba(ClO4)2 (aq) mixed with KBr (aq)
(a)
3
For the following compounds, describe what specific reagents (chemicals) you would mix in order to
obtain the desired product (many possible combinations).
You must choose entire chemicals
(solutions or solids).
Cr(OH)3 (s)
(b)
BaSO4 (s)
(c)
NH4Cl (aq)
4.
(a)
Consider the following reaction between lead (II) nitrate and sodium phosphate
Predict the products and Write the balance net ionic equation
(b)
Write the balanced full molecular equation
(c)
Write the balanced complete ionic equation
(d)
If 25 mL of 0.125 M Pb(NO3)2 (aq) is mixed with 35 mL of 0.300 M Na3PO4 (aq), how much lead (II)
phosphate will be formed.
3.
4
A particular chemical procedure calls for 50 mL of a 0.125 M solution of NaOH. Describe (in words and
specific quantities) how you would prepare 50 mL of a 0.125 M solution of NaOH (aq) (mol. wt. of NaOH
= 40.00 g/mol) using:
(a) solid NaOH
5.
(b) a 3.00 M NaOH (aq) stock solution.
6. Emer’gen-C Energy drink mix contains among other things Mg2+. A solution of this flavorful lemon-lime
drink is made by dissolving 6 grams of the solid mix into 177 ml of water. When this solution is treated
with excess Na3PO4 (aq) (Mol Wt. = 163.94 g/mol), 0.216 g of magnesium phosphate, Mg3(PO4)2 (Mol Wt.
= 262.85 g/mol), precipitate out of solution. What is the concentration (in molarity) of the Mg2+ ion in this
solution?
5
7.
Describe (in words and specific quantities) how you would prepare 0.10 L of a 4.25 M solution of NH4Cl
(aq) (mol. wt. of NH4Cl = 53.491 g/mol). The following materials and chemicals are available for your
use:
A balance, pipettes, 10 mL, 25ml, 50 mL, 100 mL, 500 mL and 1L Volumetric Flasks
1 L of 5 M NH4Cl (aq) stock solution, 1 L of 5 M NaCl (aq), 1 L of 5 M AgNO3 (aq)
100 g of NH4Cl (s)
8.
100 g of NaCl (s)
distilled water
100 g of AgCl (s)
You are asked to remove Ba2+ ion from 50 mL of a 0.150 M Ba(NO3)2 solution. You are given the
following 0.500 M solutions: NaI, HCl, AgNO3, Li2SO4, NaOH. Determine the minimum amount of the
appropriate reagent that you will need to use to completely remove the barium ion.
9.
6
For each of the following predict whether or not a reaction will take place to any significant extent.
If a reaction does take place, write out the balanced net ionic equation for it.
(a)
PbCl2 (aq) mixed with Na2SO4 (aq)
(b)
NaOH (aq) added to CoCl2 (aq)
(c)
(NH4)3PO4 (aq) mixed with AgNO3 (aq)
(d)
NH4Br (aq) mixed with NaClO4
(e)
Ca(NO3)2 (aq) added to Na2CO3 (aq)
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10.
Describe exactly (in words and in quantities) how you would go about preparing 50 mL a 0.0175 M BaCl2
(aq) solution. The following solutions are available for your use:
(a) 100 mL of 0.45 M Ba(NO3)2,
(c) 100 ml 0.005 M BaCl2 (aq)
(b) 100 ml 0.15 M BaCl2 (aq)
(d) 50 ml 0.25 M BaCl2 (aq)
(Hint: DON’T MAKE THIS PROBLEM HARDER THAN IT IS. If you are unable to come up with a
number, please make a reasonable guess and describe how you would prepare the solution)
11. A particular metal (III) chloride was analyzed and found to contain 50.83% by mass chloride. Determine
the identity of the metal and write the chemical formula for the compound.
12.
(a)
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Before cardiologists can treat heart attack survivors and others suffering from heart disease, they need to
know the condition of the heart. Radioactive imaging gives physicians a noninvasive way to distinguish
between functional and nonfunctional heart tissue. A radioactive form of technetium, technetium-99m or
99mTc, is superior for medical imaging. This radioisotope is readily available, and its short half-life
reduces handling problems and patient exposure. Drs. Edward A. Deutsch and Kenneth A. Glavan
developed complexes of 99mTc that are positively charged and strongly attracted to mitochondria, cellular
organelles that are abundant in functional heart tissue. One such complex is sold by Dupont under the
trade name “Cardiolite”. Cardiolite has the molecular formula Tc(C5H9NO)6+.
Calculate the molecular weight of the Tc(C5H9NO)6+ ion to 5 significant figures. (show some work, 15
pts)
(b) Determine the weight percent for the following elements in Cardiolite, Tc(C5H9NO)6+. (15 pts)
(i) Tc
(ii) C
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13. A 0.250 g sample of the biologically important molecule Urea was analyzed and found to contain 19.99 %
C, 6.714 % H, 26.64% O and 46.65 % N by mass. Determine the empirical formula for Urea
14. A particular unknown organic compound thought to contain C, H, N, and O was analyzed and found to
contain 37.02% C, 18.50% N, and 2.22% H by mass. Determine the empirical formula of this compound.
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15. Surfactants are bifunctional molecules that contain a polar “head” group and a long hydrophobic, non-polar
tail. Surfactants are commonly used to help solubilize non-polar, organic substances in aqueous solutions.
At the proper concentrations, the surfactants molecules surround the non-polar substance and form a micelle
with the polar head groups directed out towards the water as shown below. One such surfactant has the
chemical formula C10H21SO3Na.
SO3 Na
NaO3 S
NaO3 S
SO3 Na
SO3 Na
hydrocarbon
NaO 3S
SO 3Na
SO 3Na
NaO3 S
NaO 3S
NaO3 S
SO3 Na
NaO 3S
In one typical experiment, 0.845 g of surfactant, C10H23SO3Na (molar mass = 246.34 g/mol) is required to
solubilize 0.150 g of a hydrocarbon in 250.0 mL of water.
(a) Calculate the number of surfactant “molecules” (C10H23SO3Na) that are needed to solubilize the hydrocarbon
(20 pts)
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16. The thermite reaction has been used for welding railroad rails, in incendiary bombs, and to ignite solid fuel
rockets. The reaction involves combining Fe2O3 (MM = 159.69 g/mol) with solid Al to produce molten iron
and Al2O3 (s) (MM = 101.96 g/mol) according to the balanced equation shown below.
Fe2O3 (s) + 2 Al (s) ---------> 2 Fe (l) + Al2O3 (s)
(a) If 15 grams of each reactant is combined together, how much molten Fe will be produced? (20 pts)
(b) Which reactant and how much of it remains after the reaction has been completed? (15 pts)
(c) If only 6.55 g Fe was recovered, what is the percent yield of this reaction (5 pts)
17.
12
Aqueous solutions of copper nitrate, Cu(NO3)2 (Mol. wt 187.56 g/mol) react with aqueous solutions of
potassium iodide, KI (Mol. wt. 166.00 g/mol), to produce solid CuI (Mol wt.: 190.45 g/mol) as the
infamous “mustard” colored solid according to the following balanced equation:
4 KI (aq)
+
2 Cu(NO3)2 (aq)

2 CuI (s)
+ 4 KNO3 (aq) + I2 (aq)
(a)
Write the complete ionic equation for this reaction
(b)
If 25 mL of 0.025 M KI (aq) is mixed with 50 mL of 0.030 M Cu(NO3)2 (aq), how many grams of CuI (s)
will be produced?
(c)
If 0.014 g of the CuI produced above is dissolved in enough THF (tetrahydrofuran, an organic solvent) to
give 400 mL of solution, what will be Molarity of this solution?
18.
13
As we observed in the laboratory, copper sulfate solution reacts with aluminum wire to produce solid
copper metal. The balanced chemical equation is shown below”
2 Al (s) + 3 CuSO4 (aq) 
Al2(SO4)3 + 3 Cu (s)
(a)
If 3.50 g of Aluminum is placed in a 200 mL flask containing 75.0 mL of 1.800 M CuSO4 (mol. mass =
159.60 g/mol). How much Cu will be produced? (for full credit you must show all work)
(b)
If only 3.75 g of Cu were isolated in the reaction, determine the percent yield. (If, AND ONLY IF, you
failed to answer part (a) assume 5.0 g of Cu for part (a) (10 pts)