Chemistry Reference
In-Depth Information
Practice Problem 10.21
(a) Calculate the number of millimoles of
that can be produced by treating 2.50 mmol of
PbI
2
Pb(NO
3
)
2
with 5.00 mmol
of NaI. (b) Calculate the number of millimoles of
PbI
2
that can be produced by
treating 2.00 mmol of
Pb(NO
3
)
2
with 1.00 mmol of NaI.
Some quantity of a product of a reaction might be present in a reaction
mixture before the reaction occurs. The tabular method of solving makes this
type of problem as easy as the others. The only difference is a nonzero value
for the initial number of moles of a product.
EXAMPLE 10.22
Calculate the final number of moles of HF, NaF, and NaOH present after 0.750
mol of HF, 0.250 mol of NaF, and 0.400 mol of NaOH are placed in enough
water to make 1.00 L of solution.
Solution
HF reacts with NaOH, but NaF does not react with either of the others. The
equation for the reaction involves the acid reacting with the base, yielding the
salt and water. Tabulating the values given, all in moles, yields:
HF
NaOH
£
NaF
H
2
O
Grams
of first
reactant, A
Grams
of second
reactant, B
Present initially
0.750
0.250
0.400
Change due to reaction
0.250
0.250
0.250
Present finally
0.500
0.000
0.650
Mola
r
mass
Mola
r
mass
Practice Problem 10.22
Calculate the final number of moles of each
reactant and product present after 0.250 mol of HF, 0.150 mol of NaF, and
0.0550 mol of NaOH are placed in 1.000 mol of water.
Moles
of A
Moles
of B
Problems involving limiting quantities may be stated in terms of masses,
rather than moles, and a mass of product might be required. To solve, convert the
masses of reactants to moles, perform the steps given earlier in this section, and
convert the final number of moles of product to a mass, if required. Figure 10.4
summarizes the conversions and procedure.
Balanced ch
emic
al equation,
using lim
iting
reagent
Moles
of product
EXAMPLE 10.23
M
ola
r
mass
What mass of
Na
2
SO
4
will be formed by addition of 14.4 g of
NaHCO
3
in aque-
ous solution to an aqueous solution containing 4.90 g of
H
2
SO
4
?
Solution
Grams
of product
Change the given masses to moles:
a
1 mol NaHCO
3
84.0 g NaHCO
3
14.4 g NaHCO
3
b
0.171
4
mol NaHCO
3
present
Figure 10.4
Procedure for
Solving Problems Involving
Limiting Quantities When Masses
Are Given and Required
a
1 mol H
2
SO
4
98.1 g H
2
SO
4
4.90 g H
2
SO
4
b
0.0499
5
mol H
2
SO
4
present
