Chemistry Reference
In-Depth Information
EXAMPLE 11.21
Calculate the number of millimoles of present in a sample if it takes
27.17 mL of 2.500 M HCl to convert the sample to NaCl,
Na
2
CO
3
CO
2
,
and
H
2
O.
Solution
Na
2
CO
3
(s)
2 HCl(aq) £ 2 NaCl(aq)
CO
2
(g)
H
2
O(
/
)
a
2.500 mmol HCl
1 mL HCl
a
1 mmol Na
2
CO
3
2 mmol HCl
27.17 mL HCl
b
b
33.96 mmol Na
2
CO
3
Practice Problem 11.21
Calculate the number of millimoles of
in a sample if it takes 27.17 mL of 2.500 M HCl to convert the sam-
ple to NaCl,
NaHCO
3
CO
2
,
and H
2
O.
EXAMPLE 11.22
An unknown acid with only one ionizable hydrogen atom per formula unit, rep-
resented as HA, is prepared in the laboratory. Calculate the molar mass of the
acid if it takes 33.48 mL of 0.5000 M NaOH to neutralize a solution prepared
by dissolving 3.172 g of the acid in water. The reaction may be represented as
follows:
HA(aq)
NaOH(aq) £ NaA(aq)
H
2
O(
/
)
Solution
The number of moles of base is calculated first:
1 L
1000 mL
a
0.5000 mol NaOH
1 L NaOH
33.48 mL NaOH
a
b
b
0.01674 mol NaOH
The number of moles of acid is
1 mol HA
1 mol NaOH
0.01674 mol NaOH
a
b
0.01674 mol HA
The molar mass is the number of grams per mole:
3.172 g HA
0.01674 mol HA
189.5 g/mol
Snapshot Review
❒
Atitration is a controlled reaction used to determine the number of
moles of one substance by treatment with a known number of moles
of a second substance. The known number of moles is calculated as a
volume times a molarity of the solution of known concentration. The
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