Chemistry Reference
In-Depth Information
(b)
Even though the amount of money is sufficient to purchase 13.5 lb of
nuts, the store does not have that much. The maximum quantity that can
be purchased is the 12.5 lb on hand. The nuts are said to be available in
limited quantity. No matter how much more money is available, the
quantity of nuts limits the purchase.
Practice Problem 10.16
How many pounds of cashew nuts, at
$8.00 per pound, can be purchased with $150.00 if the store has 20.0 pounds
of the nuts?
EXAMPLE 10.17
(a)
Calculate the quantity of calcium metal required to react with 1.50 mol
of aqueous hydrochloric acid.
(b)
Calculate the quantity of calcium that will react with 1.50 mol of HCl if
1.00 mol of calcium is present.
(c)
Calculate the quantity of calcium that will react with 1.50 mol of HCl if
0.500 mol of calcium is present.
Solution
(a)
The quantity of calcium is determined in the same way as the quantity of
hydrogen was in Example 10.3:
Ca(s)
2 HCl(aq) £ CaCl
2
(aq)
H
2
(g)
Balanced
chemical
equation
Moles
of HCl
Moles
of Mg
a
1 mol Ca
2 mol HCl
1.50 mol HCl
b
0.750 mol Ca
(b)
In part (a), we determined that 0.750 mol of Ca will react with 1.50 mol
of HCl. Because more calcium is present in this case, 0.750 mol will be
used up, and the remaining 0.25 mol will not react. Ca is
in excess.
(c)
In part (a), we showed that 0.750 mol of Ca is required to react with
1.50 mol of HCl, but in this case, not that much calcium is present.
Calcium is
in limiting quantity,
and the entire 0.500 mol of Ca will react
with 1.00 mol of HCl:
a
2 mol HCl
1 mol Ca
0.500 mol Ca
b
1.00 mol HCl
The hydrochloric acid is in excess. The number of moles of HCl that will be
left unreacted is the difference:
1.50 mol HCl present
mol HCl reacts
0.50 mol HCl unreacted
1.00
Practice Problem 10.17
Calculate the number of moles of hydro-
gen gas that will be produced in each part of Example 10.17.
