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Stoichiometry of Precipitation Reactions
What mass of NaCl is needed to react completely with 1.50 L of 0.100 M AgNO
3
?
AgNO
3
+ NaCl → AgCl + NaNO
3
Net ionic:
Ag
+
(aq) + Cl

(aq) → AgCl(s)
1.50 L x 0.100 x
3
AgNO
mol
1
NaCl
mol
1
x 58.45
=
8.77 g NaCl
Mix:
1.25 L of 0.0500 M Pb(NO
3
)
2
2.00 L of 0.0250 M Na
2
SO
4
What mass of PbSO
4
forms?
What amount of what reactant is left over?
Pb(NO
3
)
2
+ Na
2
SO
4
→ PbSO
4
+ 2NaNO
3
Net ionic:
Pb
2+
(aq) + SO
4
2
(aq)
→
PbSO
4
(s)
1.25 L x 0.0500 = 0.0625 mol Pb(NO
3
)
2
2.00 L x 0.0250 = 0.0500 mol Na
2
SO
4
Since the stoichiometric ratio is 1:1, the lower number, 0.0500 mol Na
2
SO
4
is the limiting reactant.
That is 0.0500 mol Na
2
SO
4
reacts with 0.0500 mol Pb(NO
3
)
2
.
Excess:
(0.0625  0.0500) mol Pb(NO
3
)
2
0.0125 mol of Pb(NO
3
)
2
is left over.
To find the mass PbSO
4
formed, work with the limiting reactant.
0.0500 mol Na
2
SO
4
x
4
2
4
SO
Na
mol
1
PbSO
mol
1
x 303
=
15.2 g PbSO
4
formed
Stoichiometry of AcidBase Reactions
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HCl + NaOH → NaCl + HOH
Net ionic:
H
+
(aq) + OH

(aq) → HOH
0.020 L x 0.500 x
NaOH
mol
1
HCl
mol
1
x
= 0.040 L or 40.0 mL HCl
What volume of 0.250 M H
2
SO
4
is required to react completely with 20.0 mL of 0.500 M NaOH?
H
2
SO
4
+ 2NaOH → Na
2
SO
4
+ 2HOH
Net ionic:
H
+
(aq) + OH

(aq) → HOH
0.020 L x 0.500 x
NaOH
mol
2
SO
H
mol
1
4
2
x
= 0.020 L or 20.0 mL H
2
SO
4
Compare the previous two examples, which were identical except for using 0.250 M H
2
SO
4
instead of 0.250 M HCl.
Since H
2
SO
4
has two ionizable hydrogens, there is a 1:2 ratio of H
2
SO
4
with
NaOH, meaning that 20 mL of 0.250 M H
2
SO
4
will react with the same amount of NaOH as
40 mL of 0.250 M HCl.
What amount of water is formed when 25.0 mL of 0.200 M HNO
3
is mixed with
40.0 of 0.100 M NaOH?
HNO
3
+ NaOH → NaNO
3
+ HOH
Net ionic:
H
+
(aq) + OH

(aq)
→
HOH
0.0250 L x 0.500 = 0.00500 mol HNO
3
0.0400 L x 0.100
= 0.00400 mol NaOH
Since stoichiometric ratio between HNO
3
and NaOH is 1:1, the NaOH is the limiting reactant.
Since the stoichiometric ratio between NaOH and H
2
O is also 1:1, 0.00400 mol H
2
O is
formed.
What mass of Ca(OH)
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 Fall '08
 vacillian
 Chemistry, Stoichiometry

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