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Calculate the molar mass of calcium carbonate. b. A certain sample of calcium carbonate contains 4.86 moles. What is the mass in grams of this sample? What.
Typology: Summaries
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A chemical compound is a collection of atoms. The mass of 1 mole of methane can be found by summing the masses of carbon and hydrogen present:
Mass of 1 mole C
12.01 g
Mass of 4 mole H
1.008 g
Mass of 1 mole CH
4
16.04 g
The
molar mass
of a substance is the mass in grams of
one mole of the compound.
Sample Exercise 3.
Juglone, a dye known for centuries, is produced from thehusks of black walnuts. It is also a natural herbicide (weedkiller) that kills off competitive plants around the blackwalnut tree but does not affect grass and othernoncompetitive plants. The formula for juglone is C
10
a. Calculate the molar mass of juglone. b. A sample of 1.
2
g of pure juglone was
extracted from black walnut husks. How many moles of juglone does this sample represent?
P.
Sample Exercise 3.
Calcium carbonate (CaCO
), also called calcite, is the 3
principal mineral found in limestone, marble, chalk, pearls,and shells of marine animals such as clams. a. Calculate the molar mass of calcium carbonate. b. A certain sample of calcium carbonate contains 4.
moles. What is the mass in grams of this sample? What is the mass of the CO
(^23)
ions present?
Sample Exercise 3.
Isopentyl acetate (C
14
) is the compound responsible 2
for the scent of bananas. A molecular model of isopentylacetate is shown in the margin below. Interestingly, beesrelease about 1
g (
6
g) of this compound when
they sting. The resulting scent attracts other bees to jointhe attack. How many molecules of isopentyl acetate arereleased in a typical bee sting? How many atoms of carbonare present?
Sample Exercise 3.8 Solution To find the number of molecules released in a sting, wemust first determine the number of moles of isopentylacetate in 1
6
g:
Isopentyl acetate is released whena bee stings.
There are two common ways of describing the composition of a compound: in terms of the numbers ofits constituent atoms. The percentages (by mass) of itselements.
For ethanol, which has the formula C
OH, the mass 5
of each element present and the molar mass are obtainedas follows:
Mass of C
24.02 g
Mass of H
6.048 g
Mass of O
16.00 g
Mass of 1 mol C
46.07 g
The
mass percent
(often called the weight percent) of
carbon in ethanol can be computed by comparing the massof carbon in 1 mole of ethanol to the total mass of 1 moleof ethanol and multiplying the result by 100:Mass percent of C
Mass percent of H
Mass percent of O
mass of C in 1 mol C
H 2
OH 5
mass of 1 mol C
H 2
OH 5
Sample Exercise 3.10^ Solution^ The molar mass of penicillin F is computed as follows:
168.1 g
120.16 g
28.02 g
32.07 g
64.00 g
Mass of 1 mol C
14
20
4
312.4 g
Mass percent of C
Mass percent of H
Mass percent of N
Mass percent of S
Mass percent of O
Reality Check:
The percentages add up to 99.99%.
A device is shown in Fig. 3.5. Suppose a substance has been prepared that is composed of carbon, hydrogen, and nitrogen. When0.1156 gram of this compound is reacted with oxygen,0.1638 gram of carbon dioxide (CO
) and 0.1676 gram of 2
water (H
O) are collected. 2
Figure 3. A schematic diagram of the combustion device used to analyzesubstances for carbon and hydrogen. The sample is burned inthe presence of excess oxygen, which converts all its carbon tocarbon dioxide and all its hydrogen to water. These products arecollected by absorption using appropriate materials, and theiramounts are determined by measuring the increase in massesof the absorbents.
The remainder must be nitrogen:
In the present case, 38.67% carbon by mass means 38.67 grams of carbon per 100.00 grams of compound;16.22% hydrogen means 16.22 grams of hydrogen per100.00 grams of compound; and so on.
%C
%H
To determine the formula, we must calculate the number of carbon atoms in 38.67 grams of carbon, thenumber of hydrogen atoms in 16.22 grams of hydrogen,and number of nitrogen atoms in 45.11 grams of nitrogen.
We can find the smallest whole-number ratio of atoms in this compound :
