07/07/16
CHEM 1A
ANSWER KEY
Name _________________________________
Quiz 5 (30 points)
1. (4 points) Briefly answer the following questions.
(a) Compare the passage of electricity through a wire and through a solution.
Through a wire electrons are moving; through a solution ions are moving.
(b) How can it be that aqueous solutions of all ionic compounds conduct electricity but
aqueous solutions of covalent molecular compounds may or may not conduct electricity?
Ionic compounds are made up of ions. When an ionic compound dissolves in water, ions go into
the solution. In the solutions, the ions can move freely. When most covalent compounds
dissolve in water, the solution contains only molecules that carry no net charge. However, all
acids and ammonia that are covalent compounds conduct electricity when dissolved in water.
Molecules of acids and ammonia react with water molecules to produce ions.
2. (5 points) Give the chemical formula for each of the following molecules, ions, or formula units.
H3PO4
phosphoric acid
HPO42−
dihydrogen
phosphate ion
hydrogen
phosphate ion
PO43−
phosphate ion
H2PO4−
calcium dihydrogen
Ca(H2PO4)2 phosphate
H2CO3
carbonic acid
HNO2
nitrous acid
HCO3−
hydrogen carbonate
ion
NO2−
nitrite ion
CO32−
carbonate ion
N3−
nitride ion
C4−
carbide ion
NH3
ammonia
Mg(HCO3)2
magnesium
hydrogen carbonate
NH4NO2
ammonium
nitrite
3. (8 points) In the presence of a catalyst, 44.01 grams of carbon dioxide enter a reaction with
10.08 grams of hydrogen gas that produces methyl alcohol, CH3OH, and water. Assuming that
the reaction yield was 25%, fill the blanks in the following table.
Balanced Chemical
Equation
CO2
Mass before the reaction
44.01 g
Molar mass
L.R.
44.01 g/mol
+
3 H2
10.08 g
→
CH3OH
0g
+
H2 O
0g
2.016 g/mol 32.04 g/mol 18.02 g/mol
Moles before the reaction
1.0 mol
5.0 mol
0 mol
0 mol
Moles consumed
(–) or moles produced (+)
−0.25 mol
−0.75 mol
+0.25 mol
+0.25 mol
Moles after the reaction
0.75 mol
4.25 mol
0.25 mol
0.25 mol
Mass after the reaction
33.01 g
8.56 g
8.01 g
4.51
PLEASE TURN OVER!!!
4. (5 points) An experiment is conducted in which varying amounts of solid iron are added to a
fixed volume of liquid bromine. The product of the reaction is a single compound, which can
be separated from the product mixture and weighed. The graph shows the relationship between
the mass of iron in each trial versus the mass of the product compound.
What is the formula of the product compound? Show calculations.
Fe
2.0 g ×
Br
9.0 g ×
1 mol
55.85
1 mol
79.90 g
0.0358 mol
= 0.0358 mol
0.0358
0.1126 mol
= 0.1126 mol
0.0358
= 1.0 mol
= 3.1 mol
Formula of the product: FeBr3
5. (8 points) A solution containing 0.200 moles of barium nitrate is mixed with a solution
containing 0.100 moles ammonium sulfate.
(a) Write the full-formula, complete ionic, and net ionic equation (FFE, CIE, and NIE) for the
reaction occurred. In each equation, indicate physical state of each reactant and product:
(s), (l), (g), (aq).
FFE: Ba(NO3)2(aq) + (NH4)2SO4(aq) → BaSO4(s) + 2 NH4NO3(aq)
CIE: Ba2+(aq) + 2NO3−(aq) + 2NH4+(aq) + SO42−(aq) → BaSO4(s) + 2NH4+(aq) + 2NO3−(aq)
NIE: Ba2+(aq) + SO42−(aq) → BaSO4(s)
(b) Complete the following table.
Barium ion
Moles before the
reaction
Moles consumed (–)
or moles produced (+)
Moles after the
reaction
0.200
−0.100
0.100
Nitrate ion
Ammonium ion
Sulfate ion
spectator ion
spectator ion
L.R.
0.400
0.200
0
0
0.400
0.200
0.100
−0.100
0