It matters how much matter matters.

Review

• Matter is made up of either elements or compounds.• Elements are pure substances made of one kind of atom.

They cannot be broken down into simpler chemical substances.

• Compounds are two or more elements chemically combined into an unchangeable proportion. They can be broken down into simpler substances.

• A Chemical formula indicates how many of each element is in the compound

• The amount of matter is often measured in 3 ways• Mass in grams (100 grams of potato chips)• Volume in liters (2-liter bottle of soda)• By count (12 eggs)

Chemical Quantities• Measuring by Count:

• Atoms in a sugar molecule

• Demonstration: Sugar & Sulfuric Acid(draw in your notes & make 3 observations)

• Sugar is made from carbon, hydrogen and oxygen.• The addition of sulfuric acid causes bonds to break

(absorb energy), form new bonds (release energy) and produces carbon and water

• Formula for sugar: C12H22O11

• 12 Carbon• 22 Hydrogen• 11 Oxygen

Elements & Compounds

Which element is most abundant in a sugar molecule; carbon, hydrogen, or oxygen?• Hydrogen has the most atoms in the molecule, but only makes up 6.49%

in terms of mass• Oxygen has the fewest but makes up 51.41% of the mass of sugar.

How is that possible?•Oxygen is much more massive. In fact, it has 16 times the mass of hydrogen.

Elements & Compounds• Atomic Mass: The weighted average of the masses of all the

isotopes of an element.• Found on the Periodic Table• Measured in amu (atomic mass units)• Atomic masses on the P.T. are not exact masses but are

averages of all the isotopes multiplied by their abundance in real life.

Examples: Atomic mass of carbonhydrogenoxygen = 16.00 amu

= 12.01 amu= 1.01 amu

Elements & Compounds• Formula Mass: the sum of the atomic masses of all the atoms

in a chemical formula.

• Examples: C12H22O11 carbon: 12.01amu x 12 atoms =hydrogen: 1.01amu x 22 atoms =oxygen: 16.00amu x 11 atoms =

• For sig. figs, assume the atomic masses in the P.T. are measurements

144.12amu 22.22amu+ 176.00amu 342.34amu

• Find the formula masses for:• H2O• CO2

• Na2SO4

• CH2O• Fe2O3

• C6H12O6

Percent Composition Percent composition: percent by mass of a element that is

contained in a compound total mass of the element divided by the total mass of the

compound, multiplied by 100.

Example: What percent does hydrogen make up in Sucrose, C12H22O11?

Carbon: 12 atoms x 12.01amu =Hydrogen: 22 atoms x 1.01amu =Oxygen: 11 atoms x 16.00amu =

+144.12amu + 22.22amu+176.00amu 342.34amu

% comp = 22.22amu 342.34amu

x100

% comp = 6.49%

} the part

} the whole

Percent Composition % composition formula works with mass in grams too

Example: 200.grams of sugar was decomposed into 84.5grams of carbon. What percent is carbon in the sucrose?

84.5g carbon 200.g sucrose% mass of carbon = x 100

% mass of carbon = 42.25%

Hydrates• Hydrate – a substance that has a specific number of water

molecules bonded to each of its formula units.• Most often a salt• Example: sodium carbonate decahydrate: Na2CO3∙10H2O

• The dot represents a loose bond between Na2CO3 and H2O• Coefficient shows how many water molecules are in the

formula

• What percent of water (H2O) is in the hydrate Na2CO3∙10H2O?• Use % composition formula

Na: 22.99amu x 2 atoms : C: 12.01amu x 1 atom :O: 16.00amu x 3 atoms :H: 1.008amu x 20 atoms:O: 16.00amu x 10 atoms:

45.98amu 12.01amu 48.00amu 20.16amu+160.00amu 286.15amu

} the part } the whole

% comp = (20.16amu + 160.00amu) x 100 286.15amu% comp = 62.960%

Empirical Formula

● Chemical (molecular) formula tells us the precise number of atoms in a compound● Empirical formula – the simplest ratio of atoms in a compound

●Ex. glucose: C6H

12O

6●ratio is 6:12:6, which can be reduced to 1:2:1●therefore, the empirical formula for glucose is CH

2O

●Ex: N2H

4→

C3H

6→

Na2CO

3→

NH2

CH2

Na2CO

3

Empirical FormulaMolecular Formula from Empirical Formula

· Determine the molecular formula for hydrazine if the empirical formula is NH2 and the formula mass is 32.06amu.

Step 1: Find the empirical formula mass.nitrogen: 1 atom x 14.01amu =hydrogen: 2 atoms x 1.01amu =

Step 2: Divide the formula mass given by the empirical formula mass.

Step 3: Take the result and multiply it the number of atoms in the empirical formula

14.01amu+2.02amu16.03amu

formula mass: 32.06amuempirical formula mass: 16.03amu

= 2

N(1x2)H(2x2) = N2H4