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InClass Problem Set #1Answer Sheet
29 Aug 1996 Name ______________________________
1. Reagent grade aqueous ammonia is 14.5 M. Directions call for using 5 mL of 6M NH3 to clean each of your three sintered glass crucibles. How will you make the 6 M NH3?
A. How much 6 M NH3 should you make up? Why?
3 crucibles x 5 mL each = 15 mL
B. How many moles of NH3 will the solution in "A" contain?
15 mL
|
Liter
|
6
mole
|
| 1000
mL
|
Liter
|
C. How many mL of the 14.5 M NH3 solution will we need?
0.090 moles
|
Liter
|
1000
mL
|
| 14.5
moles
|
Liter
|
D. What is the procedure for making the 6 M NH3?
Add 6.2 mL of 14.5 M NH3 to about 15 - 6.2 = 8.8 mL of H2O. [More accurate solutions require a volumetric flask.]
2. How many grams of AgNO3 are required to make 500 mL of 0.1M AgNO3?
A. How many moles of AgNO3 are in 500 mL of 0.1M AgNO3?
0.500 L
|
0.1
mole AgNO3
|
| L
|
B. How many grams will these moles weigh? (The formula weight of AgNO3 is 169.837 grams/mole)
0.0500 moles AgNO3
|
169.837
grams
|
| mole
|
3. How much 0.1 M AgNO3 will be required to precipitate 0.2000 g of unknown chloride, if the sample is 60% chloride? (atomic wt. of Cl is 35.453)
A. How many grams of chloride are in the sample?
0.200 g unknown
|
0.60
g Cl-
|
| g
unknown
|
B. How many moles of chloride are in the sample?
0.12 g Cl-
|
mole
Cl-
|
| 35.453
g Cl-
|
C. How many moles of silver are required to precipitate the chloride? (Hint: Write the balanced chemical reaction between Ag+ and Cl-.)
Ag+ + Cl- = AgCl (s)
3.385 x 10-3 moles Cl-
|
1
mole Ag+
|
| 1
mole Cl-
|
D. How many mL of 0.1M AgNO3 are required to precipitate the chloride?
3.385 x 10-3 moles Ag+
|
liter
|
1000
mL
|
| 0.1
moles Ag+
|
liter
|
= 33.9 mL