Ch 7 Section 4

Question 1

when a new substance is synthesized or discovered, it is analyzed

Answer 1

quantitatively to reveal its percentage composition

Question 2

from these data (percentage composition), the

Answer 2

empirical formula is determined

Question 3

an empirical formula consists of the symbols for the elements combined in a compound, with subscripts showing

Answer 3

the smallest whole-number mole ratio of the different atoms in the compound

Question 4

for an ionic compound, the formula unit is usually

Answer 4

the compound’s empirical formula

Question 5

for a molecular compound, the empirical formula does not necessarily indicate the

Answer 5

actual numbers present in each molecule

Question 6

to determine a compound’s empirical formula from its percentage composition, begin by

Answer 6

converting percentage composition to a mass composition

Question 7

(conversion of percentage comp. to mass comp.) assume that you have a

Answer 7

100.0 g sample of the compound

Question 8

(conversion of percentage comp. to mass comp.) then calculate the amount of each

Answer 8

element in the sample

Question 9

next, the mass composition of each element is converted to a

Answer 9

composition in moles by dividing the appropriate molar mass

Question 10

to find a ratio of smallest whole numbers, divide each number of moles by the

Answer 10

smallest number in the existing ratio

Question 11

because of rounding/ experimental error, a compound’s mole ratio sometimes consists of numbers close to

Answer 11

whole numbers instead of exact whole numbers.

Question 12

in such a case (close to whole #s instead of exact) the differences from whole numbers may be

Answer 12

ignored and the nearest whole number taken

Question 13

sometimes mass composition is known instead of

Answer 13

percentage composition

Question 14

to determine the empirical formula in this case (when mass comp. is known as percentage comp.) convert mass composition

Answer 14

to composition in moles and calculate the smallest whole-number mole ratio of atoms

Question 15

the molecular formula is the actual formula of a

Answer 15

molecular compound

Question 16

an empirical formula may or may not be a

Answer 16

correct molecular formula

Question 17

the relationship between a compound’s empirical formula and its molecular formula can be written as follows:

Answer 17

x(empirical formula)=molecular formula

Question 18

the number represented by x is a whole number multiple indicating the factor by which the

Answer 18

subscripts in the empirical formula must be multiplied to obtain the molecular formula.

Question 19

the value of x is sometimes

Answer 19

1

Question 20

x(empirical formula mass) =

Answer 20

molecular formula mass

Question 21

to determine the molecular formula of a compound, you must know

Answer 21

the compound’s formula mass

Question 22

because a compound’s molecular formula mass is numerically equal to its molar mass, a compound’s molecular formula can also be found given the compound’s

Answer 22

empirical formula and its molar mass