Calculating molar mass comp.ppt

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Chemical Reactions and Quantities

Molar Mass

The molar mass

• _{is the mass of one mole}

of an element or compound.

• _{is the atomic mass}

Molar Mass from Periodic Table

Molar mass is

the atomic mass

Give the molar mass for each (to the tenths decimal place).

A. 1 mole K atoms = ________

B. 1 mol Sn atoms = ________

Give the molar mass for each (to the tenths decimal place).

A. 1 mole K atoms = 39.1 g

B. 1 mole Sn atoms =118.7 g

Molar Mass of a Compound

The molar mass of a compound is the sum of the molar masses of the elements in the formula.

Example: Calculate the molar mass of CaCl₂.

Element Number of Moles

Atomic Mass Total Mass

Ca 1 40.1 g/mole 40.1 g

Cl 2 35.5 g/mole 71.0 g

Molar Mass of K

PO

Calculate the molar mass of K₃PO₄.

Element Number of Moles

Atomic Mass Total Mass

in K₃PO₄

K 3 39.1 g/mole 117.3 g

P 1 31.0 g/mole 31.0 g

O 4 16.0 g/mole 64.0 g

Some One-mole Quantities

What is the molar mass of each of the following?

A. K₂O

B. Al(OH)₃

A. K₂O 94.2 g/mole

2 mole K (39.1 g/mole) + 1 mole O (16.0 g/mole) 78.2 g + 16.0 g = 94.2 g

B. Al(OH)₃ 78.0 g/mole

1 mole Al (27.0 g/mole) + 3 mol O (16.0 g/mole) + 3 mol H (1.01 g/mole)

27.0 g + 48.0 g + 3.03 g = 78.0 g

Prozac, C₁₇H₁₈F₃NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac?

1) 40.1 g/mole 2) 262 g/mole 3) 309 g/mole

Prozac, C₁₇H₁₈F₃NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac?

3) 309 g/mole

17 C (12.0) + 18 H (1.01) + 3 F (19.0) + 1 N (14.0) + 1 O (16.0) =

204 + 18.2 + 57.0 + 14.0 + 16.0 = 309 g/mole

Molar mass conversion factors

• _{are written from molar mass.}

• _{relate grams and moles of an element or compound.}

Example: Write molar mass factors for methane, CH₄,

used in gas stoves and gas heaters. Molar mass:

1 mol CH₄ = 16.0 g

Acetic acid C₂H₄O₂ gives the sour taste to vinegar. Write two molar mass conversion factors for acetic acid.

Calculating Percent Composition



The formula is found on table T of the

reference table.



Mass of the part

Mass of the Whole X100

NaCl

Claculating Percent Composition



To determine the % composition of

sodium in NaCl



Mass of sodium in formula 22.99



Mass of entire formula 58.44 X100



39.34 %

Determining Percent

Composition



What is the percent composition of

Chlorine in NaCl?



Total mass of Cl in formula 35.45



Total mass of formula 58.44

Determining % Composition



What is the % composition of oxygen in

CuSO4?



Cu = 1 X 63.55 = 63.55

S = 1 X 32.07 = 32.07

O = 4 X 15.99 = 63.96

Total mass 159.58

Mass of Oxygen 63.96

Acetic acid C₂H₄O₂ gives the sour taste to vinegar. Write two molar mass factors for acetic acid.

Calculate molar mass:

24.0 + 4.04 + 32.0 = 60.0 g/mole

1 mole of acetic acid = 60.0 g acetic acid Molar mass factors

1 mole acetic acid and 60.0 g acetic acid

Molar mass factors are used to convert between the grams of a substance and the number of moles.

Calculations Using Molar Mass

Aluminum is often used to build lightweight bicycle frames. How many grams of Al are in 3.00 mole Al?

Molar mass equality: 1 mole Al = 27.0 g Al

Setup with molar mass as a factor:

3.00 mole Al x 27.0 g Al = 81.0 g Al 1 mole Al

Learning Check

Allyl sulfide C₆H₁₀S is a

Calculate the molar mass of C₆H₁₀S.

(6 x 12.0) + (10 x 1.01) + (1 x 32.1) = 114.2 g/mole

Set up the calculation using a mole factor.

225 g C₆H₁₀S x 1 mole C₆H₁₀S

114.2 g C₆H₁₀S

molar mass factor (inverted)

Grams, Moles, and Particles

A molar mass factor and Avogadro’s number convert

• _{grams to particles.}

molar mass Avogadro’s number

g mole particles

• _{particles to grams.}

Avogadro’s molar mass number

Learning Check

How many H₂O molecules are in 24.0 g H₂O?

1) 4.52 x 1023

2) 1.44 x 1025

Solution

How many H₂O molecules are in 24.0 g H₂O?

3) 8.02 x 1023

24.0 g H₂O x 1 mole H₂O x 6.02 x 1023 H

2O molecules

18.0 g H₂O 1 mole H₂O

= 8.03 x 1023 H

Learning Check

If the odor of C₆H₁₀S can be detected from 2 x 10-13 g

Solution

If the odor of C₆H₁₀S can be detected from 2 x 10-13 g

in one liter of air, how many molecules of C₆H₁₀S are present?

2 x 10-13 g x 1 mole x 6.02 x 1023 molecules

114.2 g 1 mole = 1 x 109 molecules C