Molar Mass

Sections 4-4 to 4-6

Carbon

• Atomic # is 6

• Atomic mass is 12.01 u

• Molar mass (mass per mole) is 12.01 g/mole

Molar Mass

• Molar mass for an element is found by taking the atomic mass for that element in the periodic table and changing the units to grams/mole.

• Molar mass for a compound is found by adding the atomic masses (in grams) for ALL the elements in the compound.

H2O

- Molar mass of hydrogen is 1.01g/mole

- There are two atoms of hydrogen in water

- Molar mass of oxygen is 16.0 g/mole

2(1.01 g/mole) H + 16.0 g/mole O = 18.02 g/mole

H2O

NaCl

• Molar mass of sodium is 22.99 g/mole

• Molar mass of chlorine is 35.45 g/mole

22.99 g/mole Na + 35.45 g/mole Cl

= 58.44 g/mole NaCl

What is the mass of 1.31 mol of silver nitrate?

1. Find the correct chemical formula for silver nitrate.

silver = Ag+

nitrate = NO3-

Silver nitrate is AgNO3

2. Find the molar mass of AgNO3.

molar mass Ag = 107.87 g/mole

molar mass N = 14.01 g/mole

molar mass O = 16.00 g/mole

there are three atoms of O

107.87 g/mole Ag + 14.01 g/mole N

+ 3(16.00 g/mole O) = 169.88 g/mole AgNO3

3. Find the mass of 1.31 mole of AgNO3.

X g AgNO3 169.88 g AgNO3

______________ = ______________

1.31 mole AgNO3 1 mole AgNO3

X = 222.54 g AgNO3

How many moles are in a 124 g sample of C8H18?

1. Find the molar mass of C8H18.molar mass C = 12.01 g/molethere are 8 atoms of Cmolar mass H = 1.01 g/molethere are 18 atoms of H

8(12.01 g/mole C) + 18(1.01 g/mole H)

= 114.26 g/mole C8H18

2. Find how many moles of C8H18 are in 124.0 grams.

x moles C8H18 1 mole C8H18

_____________ = ____________

124.0 g C8H18 114.26 g/mole C8H18

x = 1.09 moles C8H18

Copy the Molar Calculator from either the poster on the wall, or from page 108 in the text book.

Do practice questions on page 109 # 4-8,

10-11, 13-16.

These practice questions will be corrected in class on Thursday.