Chemistry Reference
In-Depth Information
The equation gives the
mole ratios,
so we need to convert the mass of phos-
phorus to the number of moles of phosphorus, and then we can proceed as in
Section 10.1:
Note that the coefficient in the
balanced equation has nothing
to do with the molar mass.
a
1 mol P
31.0 g P
2.88 g P
b
0.0929 mol P
a
5 mol Cl
2
2 mol P
0.0929 mol P
b
0.232
3
mol Cl
2
The coefficients in the equation
relate the number of moles of
one substance to the number
of any other substance.
Finally, convert the number of moles of chlorine to the mass of chlorine:
a
70.9 g Cl
2
1 mol Cl
2
0.232
3
mol Cl
2
b
16.5 g Cl
2
As usual, we could combine all these steps into a single calculation:
Balanced
chemical
equation
Grams
of P
Molar
mass
Moles
of P
Moles
of Cl
2
Molar
mass
Grams
of Cl
2
a
1 mol P
31.0 g P
a
5 mol Cl
2
2 mol P
a
70.9 g Cl
2
1 mol Cl
2
2.88 g P
b
b
b
16.5 g Cl
2
Practice Problem 10.6
Calculate the mass of phosphorus pentachlo-
ride that will be produced by the reaction in Example 10.6.
EXAMPLE 10.7
Electrolysis of concentrated aqueous sodium chloride solution (called brine)
yields aqueous sodium hydroxide, hydrogen gas, and chlorine gas—three impor-
tant industrial chemicals. Calculate the mass of chlorine that can be produced
by electrolysis of 50.0 kg of sodium chloride in concentrated aqueous solution:
Electricity
2 NaOH(aq)
2 H
2
O(
/
)
----------
¡
2 NaCl(aq)
Cl
2
(g)
H
2
(g)
Solution
Kilograms
of
NaCl
Balanced
chemical
equation
Definition
of kilo
Grams
of NaCl
Molar
mass
Moles
of NaCl
Moles
of Cl
2
Molar
mass
Grams
of Cl
2
(
)
(
)
(
)
(
)
3.03
10
4
g Cl
2
1000 g NaCl
1 kg NaCl
1 mol NaCl
58.5 g NaCl
1 mol Cl
2
2 mol NaCl
70.9 g Cl
2
1 mol Cl
2
50.0 kg NaCl
