Chapter 11

Question 1

the actual mass of an atom would be very small, a relative mass scale was

Answer 1

developed

Question 2

one atom was chosen and assigned a

Answer 2

mass value

Question 3

the units are called

Answer 3

atomic mass units

Question 4

the atom that is used to base all other masses on is

Answer 4

carbon-12

Question 5

carbon-12 has an atomic mass of exactly ______ and other atoms have masses relative to that

Answer 5

12 AMU

Question 6

AMU’s are so small that they are ___________ to use in a lab

Answer 6

impractical

Question 7

in a lab _____ would be much easier to use

Answer 7

grams

Question 8

in the early 1800’s Amedeo Avogadro determined the number of atoms needed to make the mass in AMU’s equal to the same value expressed in

Answer 8

grams

Question 9

this number is the same for all elements and is knows as

Answer 9

Avogadro’s number

Question 10

the quantity in Avogadro’s number is

Answer 10

6.02 X 10 to the 23

Question 11

the amount of something that contains the Avogadro’s number (6.02 X 10 23) of that something is called a

Answer 11

mole

Question 12

the idea is the same as calling 12 donuts a dozen donuts; 6.02 X 10 23 donuts would be a mole of

Answer 12

donuts

Question 13

a mole is an unbelievably large number because atoms are very

Answer 13

small

Question 14

most elements are made up of more than one version of an element

Answer 14

isotopes

Question 15

molar mass is the ____ __ _____ of one mole of naturally occurring isotopes of that element

Answer 15

mass in grams

Question 16

the values for molar mass can be found on the

Answer 16

periodic table

Question 17

molar masses of compounds are equal to the ___ of the molar masses of all of its atoms

Answer 17

sum

Question 18

the mass in grams of one mole of any pure substance

Answer 18

molar mass

Question 19

the isotope hydrogen-1 is the standard used for the relative scale of atomic masses

Answer 19

false

Question 20

the mass of an atom of helium-4 is 4 amu

Answer 20

true

Question 21

the mass of a mole of hydrogen atoms is 1.00 X 10 to the 23 amu

Answer 21

false

Question 22

the mass in grams of one mole of any pure substance is called its molar mass

Answer 22

true

Question 23

the atomic masses recorded on the periodic table are weighted averages of the masses of all the naturally occurring isotopes of each element

Answer 23

true

Question 24

the molar mass unit is mol/g

Answer 24

false

Question 25

if the measured mass of an element is numerically equal to its molar mass, then you have indirectly counted 6.02 X 10 to the 23 atoms of the element in the measurement

Answer 25

true

Question 26

the percent by mass of each element in a compound

Answer 26

percent composition

Question 27

formula with the smallest whole number mole ratio of the elements

Answer 27

empirical formula

Question 28

specifies the actual number of atoms of each element in one molecule or formula unit of the substance

Answer 28

molecular formula

Question 29

a compound that has a specific number of water molecules bound to its atoms

Answer 29

hydrate

Question 30

what is the percent composition of a compound?

Answer 30

the percent by mass of each of the elements in a compound

Question 31

describe how to find the percent composition of a compound if you know the mass of a sample of a compound and the mass of each element in the sample

Answer 31

divide the mass of each element by the mass of the sample. Multiply each quotient by 100

Question 32

which information about a compound can you use to begin to determine the empirical and molecular formulas of the compound?

Answer 32

percent composition of the compound

Question 33

you have determined that a compound is composed of 0.300 moles of carbon and 0.600io moles of oxygen. What must you do to determine the mole ratio of the elements in the empirical formula of the compound?

Answer 33

divide each mole value by 0.300 mol

Question 34

the mole ratio of carbon to hydrogen to oxygen in a compound is 1 mol C : 2 mol H : 1 mol O. What is the empirical formula of the compound?

Answer 34

CH2O

Question 35

you calculate the mole ratio of oxygen to aluminum in a compound to be 1.5 mol O : 1 mol Al. What should you do to determine the mole ratio in the empirical formula of the compound?

Answer 35

multiply each mole value by 2

Question 36

what is the relationship between the molecular formula and the empirical formula of a compound?

Answer 36

molecular formula = (empirical formula)n

Question 37

you know that the empirical formula of a compound has a molar mass of 30.0 g/mol. What must you do to determine the value of n in the relationship between the molecular formula and the empirical formula?

Answer 37

divide 60.0 g/mol by 30.0 g/mol

Question 38

you know that the experimental molar mass of a compound is three times the molar mass of its empirical formula. If the compound's empirical formula is NO2, what is its molecular formula?

Answer 38

N3O6

Question 39

a ______ is a compound that has a specific number of water molecules bound to its atoms

Answer 39

hydrate

Question 40

molecules of water that become part of a hydrate are called waters of

Answer 40

hydration

Question 41

in the formula for a hydrate, the number of _______________ associated with each _____________ of the compound is written following a dot

Answer 41

water molecules, formula unit

Question 42

the substance remaining after a hydrate has been heated and its waters of hydration released is called

Answer 42

anhydrous

Question 43

the ratio of the number of moles of __________________ to one mole of the anhydrous compound indicates the coefficient of H2O that follows the dot in the formula of the hydrate

Answer 43

water of hydration

Question 44

because the anhydrous form of the hydrate can absorb water into its _________________, hydrates are used as __________, which are drying agents

Answer 44

crystal structure, desiccants

Question 45

CdSO4 dot H2O

Answer 45

cadmium sulfate monohydrate

Question 46

CdSO4 dot 4H2O

Answer 46

Cadmium sulfate tetrahydrate