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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
95
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 10
Practice Problems
11. Calculate the number of atoms in 2.00 g of platinum.
12. How many sulfur atoms are in a metric ton (1.00 ϫ 10 6 g) of
sulfur?
13. How many grams of mercury are in 1.19 ϫ 10 23 atoms of
mercury?
14. What is the mass in grams of 3.01 ϫ 10 19 atoms of iodine?
15. The EPA limit for lead in the water supply is 15 parts per
billion by mass. Calculate the number of lead ions present in
1.00 kg of water that is at the EPA limit for lead.
10.3 Moles of Compounds
Recall that a mole is Avogadro’s number (6.02 ϫ 10 23 ) of particles
of a substance. If the substance is a molecular compound, such as
ammonia (NH 3 ), a mole is 6.02 ϫ 10 23 molecules of ammonia. If
the substance is an ionic compound, such as baking soda (sodium
hydrogen carbonate, NaHCO 3 ), a mole is 6.02 ϫ 10 23 formula units
of sodium hydrogen carbonate. In either case, a mole of a compound
contains as many moles of each element as are indicated by the subscripts in the formula for the compound. For example, a mole of
ammonia (NH 3 ) consists of one mole of nitrogen atoms and three
moles of hydrogen atoms.
Molar mass of a compound The molar mass of a compound is
the mass of a mole of the representative particles of the compound.
Because each representative particle is composed of two or more
atoms, the molar mass of the compound is found by adding the
molar masses of all of the atoms in the representative particle. In the
case of NH 3 , the molar mass equals the mass of one mole of nitrogen atoms plus the mass of three moles of hydrogen atoms.
molar mass of NH 3 ϭ molar mass of N ϩ 3(molar mass of H)
molar mass of NH 3 ϭ 14.007 g ϩ 3(1.008 g) ϭ 17.031 g/mol
You can use the molar mass of a compound to convert between mass
and moles, just as you used the molar mass of elements to make
these conversions.
▲
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
95
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 10
Practice Problems
11. Calculate the number of atoms in 2.00 g of platinum.
12. How many sulfur atoms are in a metric ton (1.00 ϫ 10 6 g) of
sulfur?
13. How many grams of mercury are in 1.19 ϫ 10 23 atoms of
mercury?
14. What is the mass in grams of 3.01 ϫ 10 19 atoms of iodine?
15. The EPA limit for lead in the water supply is 15 parts per
billion by mass. Calculate the number of lead ions present in
1.00 kg of water that is at the EPA limit for lead.
10.3 Moles of Compounds
Recall that a mole is Avogadro’s number (6.02 ϫ 10 23 ) of particles
of a substance. If the substance is a molecular compound, such as
ammonia (NH 3 ), a mole is 6.02 ϫ 10 23 molecules of ammonia. If
the substance is an ionic compound, such as baking soda (sodium
hydrogen carbonate, NaHCO 3 ), a mole is 6.02 ϫ 10 23 formula units
of sodium hydrogen carbonate. In either case, a mole of a compound
contains as many moles of each element as are indicated by the subscripts in the formula for the compound. For example, a mole of
ammonia (NH 3 ) consists of one mole of nitrogen atoms and three
moles of hydrogen atoms.
Molar mass of a compound The molar mass of a compound is
the mass of a mole of the representative particles of the compound.
Because each representative particle is composed of two or more
atoms, the molar mass of the compound is found by adding the
molar masses of all of the atoms in the representative particle. In the
case of NH 3 , the molar mass equals the mass of one mole of nitrogen atoms plus the mass of three moles of hydrogen atoms.
molar mass of NH 3 ϭ molar mass of N ϩ 3(molar mass of H)
molar mass of NH 3 ϭ 14.007 g ϩ 3(1.008 g) ϭ 17.031 g/mol
You can use the molar mass of a compound to convert between mass
and moles, just as you used the molar mass of elements to make
these conversions.
▲