Module 7 Test

Question 1

What is Avogadro’s number equal to?

Answer 1

6.022 x 1023 units/mol

Question 2

A mole is defined by?

Answer 2

The number of atoms in the exact amount of a unit

Question 3

A unit can be what?

Answer 3

Atoms, molecules, ions

Question 4

What do you use as a conversion factor when asked “how many molecules are in a ____ # of moles?

Answer 4

Avogadro’s number

Question 5

Do you use Avogadro’s number directly to convert from grams?

Answer 5

No

Question 6

What do you use to convert from grams if you don’t use Avogadro’s number?

Answer 6

The Mole Island chart

Question 7

The molar mass of the compound is equal to what?

Answer 7

The molar mass of a compound is equal to the molar mass of the all the elements that it is composed of

Question 8

What does the chemical formula tell you?

Answer 8

It tells you how many/much of each element is in the compound

Question 9

What are the units for molar mass?

Answer 9

The units are g/mol

Question 10

What is the formula unit?

Answer 10

The simplest ratio of cations to anions

Question 11

What can molar mass be used for?

Answer 11

Can be used to convert the amount of a substance from moles to mass, or mass to moles

Question 12

Why is percent composition useful for scientists?

Answer 12

Percent composition helps them determine the specific elements in a compound and the ratios of the elements in the compound

Question 13

What is percent composition?

Answer 13

Percent composition is the percentage by mass of each element in a compound

Question 14

If you know the composition of a compound, then what else can you do?

Answer 14

Then you can determine the percentage composition of the elements that make up the entire compound

Question 15

What do you do first when finding percent composition?

Answer 15

You determine the mass of each element (by the amount of elements present x the atomic mass)

Question 16

What is the second step for finding percent composition?

Answer 16

Calculate the molar mass of the compound (add all the masses of each element together)

Question 17

What is the third step for finding percent composition?

Answer 17

Divide the mass of each element by the molar mass them multiply by 100 to get a percentage

Question 18

What is the fourth and last step for finding percent composition?

Answer 18

Verify your answers and the percentages should add up to 100%

Question 19

What is the empirical formula?

Answer 19

It is the simplest ratio of elements in a compound

Question 20

It is okay if the empirical formula my not always be the right formula for the compound?

Answer 20

Yes

Question 21

What is the empirical formula calculated from?

Answer 21

The percent composition

Question 22

What is the first step in finding the empirical formula?

Answer 22

Convert the percent composition to mass in grams (assume in a 100 g sample)

Question 23

What is the second step in finding the empirical formula?

Answer 23

You need to convert the mass to moles by using the atomic mass (divide each element by their own atomic mass)

Question 24

What is the third step in finding the empirical formula?

Answer 24

Determine which element has the lowest number of moles

Question 25

What is the fourth step in finding the empirical formula?

Answer 25

Set up ratios by dividing all each element by the least amount of moles

Question 26

What do you need to do if each element does not have a full number after you divided by the least amount of moles?

Answer 26

You need to multiply all elements by a common number to get the smallest whole number ratio

Question 27

If the number is/ends in .33 what do you multiply by?

Answer 27

Multiply by 3

Question 28

If the number is/ends in .25 what do you multiply by?

Answer 28

Multiply by 4

Question 29

If the number is/ends in .66 what do you multiply by?

Answer 29

Multiply by 3

Question 30

If the number is/ends in .75 what do you multiply by?

Answer 30

Multiply by 4

Question 31

If the number is/ends in.5 what do you multiply by?

Answer 31

Multiply by 2

Question 32

What is the fifth step in finding the empirical formula?

Answer 32

Place the numbers from the ratios as the subscripts of that element in the empirical formula

Question 33

What can empirical formulas be used to determine (in regards to the molecular formula)?

Answer 33

Can be used to determine the molecular formula if the molar mass of the compound is known

Question 34

What is the first step in finding the molecular formula?

Answer 34

Make sure the empirical formula and the molar mass of the compound is given

Question 35

What is the second step in finding the molecular formula?

Answer 35

Calculate the molar mass of the empirical formula

Question 36

What is the third step in finding the molecular formula?

Answer 36

Divide the molar mass of the compound by the molar mass of the empirical formula

Question 37

What is the fourth and final step in finding the molecular formula?

Answer 37

Multiply all of the subscripts by the ratio (answer) found in the previous step