Ch 7

Question 1

Atomic mass unit (amu)

Answer 1

= the unit of mass for atoms

Question 2

Molecular mass

Answer 2

is the sum of the masses of all atoms in a molecule

Question 3

Formula mass

Answer 3

is the sum of the masses of all atoms in a formula unit of an ionic compound (or molecule – used interchangeably)

Question 4

The formula mass is

Answer 4

• The mass in amu of a compound

- The sum of the atomic masses of the elements in a formula

Question 5

Experimentally know conversion

Answer 5

1 amu = 1.66053 x 10^-24 g

Question 6

Avogadro’s Number

Answer 6

6.022 x 10^23

Question 7

Avogadro’s number

Answer 7

• is equal to 1 mole

- Makes working with large numbers easier

Question 8

Molar mass

Answer 8

• is the mass of one mole of molecules, atoms, ions, or formula units
• Numerically equal to the substance’s formula mass

Question 9

Difference between molar mass and formula mass is units:

Answer 9

• Molecular weight: weight of a molecule, in amu

- Molar mass: mass of one mole of a compound, in grams

Question 10

Molar mass conversion factors

Answer 10

• Are written from molar mass

- Relate grams and moles of an element or compound.

Question 11

Percent composition

Answer 11

Is the percent by mass of each element in a formula.

Question 12

Percent composition formula

Answer 12

Mass element in compound / Mass of compound x 100%

Question 13

The molecular formula

Answer 13

Is the true or actual number of the atoms in a molecule

Question 14

The empirical formula

Answer 14

Is the simplest whole number ratio of the atoms (this is the formula for ionic compounds)

Question 15

Empirical Formula Problems

Answer 15

1) . Convert percentages given to grams
2) . Convert grams to moles
3) . Divide by the smallest number in order to ascertain the whole number ratio of atoms of different elements in the compound
4) . Clear any obvious fractions in step 3.

Question 16

Percentages given

Answer 16

• Assume 100 g sample (percentages easily translate into gram quantities)
• Convert grams into moles
• Divide by the smallest number of moles present.
• If you do not have whole numbers at this point, clear the fraction by multiplying every number by the whole number that accomplishes this end.

Question 17

Relating Molecular and Empirical Formulas :A molecular formula

Answer 17

• Is a multiple (or equal) of its empirical formula
• Has a molar mass that is the empirical mass multiplied by a whole number

molar mass = whole number x empirical mass

-Is obtained by multiplying the empirical formula by a whole number