 # A compound will have the same composition by mass.

## Presentation on theme: "A compound will have the same composition by mass."— Presentation transcript:

A compound will have the same composition by mass.

Calculate the following percentage by mass: percent = portion/total x 100 If two samples are the same substance, they should have the same percent composition by mass.

A compound will have the same physical and chemical characteristics.

Do the have the same percent composition? Are they the same compound?

Mass Ratio Percent Composition of compounds was used to determine the MASS RATIO between elements. Regardless of number of atoms, the MASS RATIO is the same.

carbon-12 The standard for mass was arbitrarily chosen to be one atom of carbon-12 the MASS RATIO between elements was then used to calculate others. The mass of one carbon-12 atom was set at 12 (exactly) “amu”. “amu” is an arbitrarily chosen amount.

ATOMIC MASS UNIT “amu” is an arbitrarily chosen amount. It is so small, it is not practical for actual use….. A person named Avogardo, invented a multiple that would allow the MASS RATIO to be preserved but to be measured in grams. He called it : a mole P310-317

The Mole A mole of any element is defined to be the same number of atoms of that element equal to the number of atoms in 12.0 g of carbon-12 P310-317

The mass of 1 mole (in grams) Equal to the numerical value of the average atomic mass (get from periodic table) 1 mole of C atoms= 12.01 g 1 mole of Mg atoms =24.31 g 1 mole of Cu atoms =63.55 g Where are these numbers from? PERIODIC TABLE Molar Mass

Other Names Related to Molar Mass Atomic Mass Single atom, mass is measured in amu’s instead of grams. Only the units are different: Atomic/Individual/ MICROSCOPIC = amu Molar/A lot of/VISIBLE/ MACROSCOPIC = g

Find the molar mass (usually we round to the hundreds place) Learning Check! a.1 mole of Br atoms b.1 mole of Sn atoms =79.90 g/mole = 118.71 g/mole

Mass in grams of 1 mole equal numerically to the sum of the atomic masses 1 mole of CaCl 2 = 110.98 g/mol (1 mole Ca x 40.08 g/mol ) + (2 moles Cl x 35.45 g/mol) = 110.98 g/mol CaCl 2 Molar Mass of Molecules and Compounds

Mass in grams of 1 mole equal numerically to the sum of the atomic masses 1 mole of N 2 O 4 Molar Mass of Molecules and Compounds = 92.02 g/mol

A.Molar Mass of K 2 O = B. Molar Mass of antacid Al(OH) 3 = K 2 O = 94.20 g/molAl(OH) 3 = 78.03 g/mol Learning Check!

Other Names Related to Molar Mass Molecular Mass/Molecular Weight: Single molecule, mass is measured in amu’s instead of grams. same numerical value as 1 mole of molecules. Only the units are different: Individual/MICROSCOPIC= amu A lot of/VISIBLE/MACROSCOPIC= g

Other Names Related to Molar Mass Molecular Mass/Molecular Weight: Single molecule, mass is measured in amu’s instead of grams. But, the molecular mass/weight is the same numerical value as 1 mole of molecules. Only the units are different Formula Mass/Formula Weight: Same goes for compounds. But again, the numerical value is the same. Only the units are different.

Other Names Related to Molar Mass THE POINT: You may hear all of these terms which mean the SAME NUMBER… just different units Molar Mass = Gram Formula Weight in our textbook With Avogadro’s #, you may also hear the terms: molecules, atoms, formula units, ions, particles, “things” IT DEPENDS ON WHAT YOU’RE TALKING ABOUT: example: 1 dozen eggs versus 1 dozen roses 1 mole of H 2 O molecules vs. 1 mole of NaCl formula units

Prozac, C 17 H 18 F 3 NO, is a widely used antidepressant that inhibits the uptake of serotonin by the brain. Find its molar mass. 309.38 grams Learning Check

molar mass Grams Moles Calculations with Molar Mass Do you multiply or divide by molar mass? It depends on which way you’re going. Use conversion factors.

Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al? 3.00 moles Al ? g Al Converting Moles and Grams

1.Molar mass of 1 mole Al = 26.98 g Al 2. Conversion factors for Al 26.98 g Al or 1 mol Al 1 mol Al 26.98g Al 3. Setup3.00 moles Al x 26.98 g Al = 1 mole Al Answer = 81.0 g Al

Iron (III) oxide is often called rust, it forms when iron metal reacts with moisture. How many moles of Fe 2 O 3 are in 3.00 grams of Fe 2 O 3 ? 3.00 grams of Fe 2 O 3 ? moles Fe 2 O 3 Converting Moles and Grams

1. Molar mass of Fe 2 O 3 YOU MUST CALCULATE IT! 2. Conversion factors for Fe 2 O 3 ? g Fe 2 O 3 or 1 mol Fe 2 O 3 1 mol Fe 2 O 3 ? g Fe 2 O 3 3. Setup3.00 grams Fe 2 O 3 x 1 moleFe 2 O 3 ? grams Fe 2 O 3 Answer = 0.0188 mol Fe 2 O 3

1. Molar mass of Fe 2 O 3 159.70 grams 2. Conversion factors for Fe 2 O 3 159.70 g Fe 2 O 3 or 1 mol Fe 2 O 3 1 mol Fe 2 O 3 159.70 g Fe 2 O 3 3. Setup3.00 grams Fe 2 O 3 x 1 moleFe 2 O 3 159.70 g Fe 2 O 3 Answer = 0.0 188 mole Fe 2 O 3

The artificial sweetener aspartame (Nutra-Sweet) formula C 14 H 18 N 2 O 5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame? Learning Check!

225 g C 14 H 18 N 2 O 5 = ? mol C 14 H 18 N 2 O 5 225g x _?__mol__ = mol ? g Setting it up: Do you know a relationship between moles and grams for C 14 H 18 N 2 O 5 ?

225 g C 14 H 18 N 2 O 5 = ? mol C 14 H 18 N 2 O 5 The relationship is: MOLAR MASS! 1 mol = the sum of the atomic masses from the periodic table in grams! 225g x _1__mol__ = ? mol ? g Setting it up:

225 g C 14 H 18 N 2 O 5 = ? mol C 14 H 18 N 2 O 5 225g x _1__mol__ = ? mol 294.34 g How do you enter this in your calculator? Setting it up: Enter first number first, multiply numerators, divide by denominators. 225 x 1 / 294.35 =