Atoms and Atomic Masses - Fundamentals of Chemistry - page 93

3.3 On what standard are all atomic masses presently based? (d) What law allows you to answer each prior part of

this problem?
3.14 A 29.7-g sample of a certain compound contains 85.63%
carbon and 14.37% hydrogen.
(a) How much carbon is in a 9.08-g portion of this
sample?
(b) How much carbon is in 9.08 g of a different sample
of this compound?
3.15 A 4.73-g sample of element A combines completely with
a 12.11-g sample of element B. What is the total mass of
the product?
3.16 A 4.22-g sample of magnesium was burned, yielding
7.00 g of magnesium oxide. How many grams of oxygen
was taken up in the reaction?
3.17 A 6.73-g sample of an element combines completely
with another element to make 12.14 g of a compound.
What mass of the second element reacted?
3.18 Which two types of subatomic particles must be present
in equal numbers for an atom to be neutral?
3.19 (a) Which element has atomic number 23?
(b) Which element has an atomic mass of 23.0 amu (to
three significant figures)?
(c) Locate the elements of part (a) and part (b) on the
periodic table.
3.20 (a) What is the average of a 30.0-g mass and a 46.0-g
mass?
(b) What is the weighted average of eight 30.0-g masses
and twelve 46.0-g masses?
(c) What is the weighted average mass of three chlorine
atoms with mass 35.0 amu each and one chlorine
atom with mass 37.0 amu?
3.21 Why did Mendeleyev not use atomic numbers instead of
atomic masses as the basis for his periodic table?
3.22 In the periodic table (inside front cover), locate five ele-
ments for which mass numbers rather than atomic
masses are given.

3.4 Which of the following are synonyms?

atomic mass

mass number mass of an atom

atomic number atomic weight
3.5 (a) How many protons are in a potassium atom?
(b) What is the atomic number of potassium?
(c) What is the number of positive charges on a
potassium nucleus?
3.6 Which of the three following numbers, each of which ap-
pears on the periodic table inside the front cover, is an
atomic number, which is an atomic mass, and which is a
mass number?
(a) 65 (b) 101.07 (c) (242)
3.7 (a) What is the unit of electric charge used at the atomic
level?
(b) What is the unit of atomic mass?
3.8 What is the weighted average of three masses of 4.21 g,
seven masses of 5.55 g, and two masses of 6.42 g?
3.9 What characteristic of an atom did Dalton think was the
most important?
3.10 What is the difference between the symbol for an ele-
ment and the symbol for an isotope of that element?
3.11 Of atomic number, atomic mass, and mass number,
which two appear with most of the symbols for the ele-
ments in the periodic table?
3.12 What is the difference between the mass of an atom and
the mass number of the atom?
3.13 Potassium and iodine react to form one compound only.
In a certain reaction, 20.0 g of potassium reacts com-
pletely with 64.9 g of iodine to produce potassium
iodide.
(a) How much potassium iodide is produced?
(b) How much iodine would react with 4.00 g of
potassium?
(c) How much iodine would react with 7.29 g of
potassium?

Problems

3.1 Laws of Chemical Combination 3.25 A 7.33-g sample of mercury(I) oxide was decomposed

into mercury and oxygen, yielding 7.05 g of mercury.
(a) What mass of oxygen was obtained?
(b) What fraction of the compound was oxygen?
(c) What percentage of the compound was oxygen?
3.26 A 18.6-g sample of a compound contains 39.35% sodium
and 60.65% chlorine.
(a) Calculate the mass of chlorine present.
(b) Calculate the mass of chlorine present in a 30.0-g
sample of the same compound.

3.23 If 31.9 mg of a compound containing only carbon and
hydrogen is burned completely in oxygen and yields
87.7 mg of carbon dioxide and 71.8 mg of water, how
much oxygen is used up?
3.24 When 7.80 mg of a compound containing only carbon
and hydrogen was burned completely in 28.3 mg of
oxygen, 23.3 mg of carbon dioxide and some water were
formed. Calculate the mass of the water.