Chemistry Unit 5B
Representative Particle
- an atom - avogadro's number (6.02 x 10 ²³)
Why do we use 6.02 X 10²³?
- because atoms are so small, Avogardo's Number has to be pretty big - scientists use this number because it is the number of particle in 12 grams of Carbon-12
STP
- often used to measure gas density and volume - at STP, 1 mole of any gas occupies 22.4 L - 0° C (273.15 K) - 1 atm - 1 mole = 22.4 L
Avogadro's Number
-6.02 x 10²³ - number of units in one mole of any substance
What is the molar mass of NaCl?
58.44 g/mol
Finding Grams from Percent
1. convert, if given, percent into decimal - if not given, first find the percent composition of the element 2. multiply decimal by the total mass of the compound
Determining Percent Composition
1. divide by the mass of the element by the total mass of the compound 2. multiply by 100
Finding the Formula of Hydrates: Similar to Finding an Empirical Formula
1. find the mass of the water by subtraction 2. grams → moles - mass of water → moles - mass of salt → moles 3. divide by the smallest mole value 4. round to a whole # if necessary
Finding Molecular Formulas from the Empirical Formula
1. find the molar mas of the empirical formula 2. divide the molar mass of the compound by the molar mass of the empirical formula 3. multiply they empirical formula by that number
Finding the Empirical Formula
1. grams → moles 2. divide by the smallest 3. round 'til whole
What is the molar mass of hydrogen?
1.01 g/mol
How many formula units are there in 24 grams of FeF₃?
1.3 x 10²³ formula units
How many ions are in NaOH?
2
What is the molar mass of water?
2 Hydrogen = 2 X 1.01 = 2.02 g/mol 1 Oxygen = 1 X 16.00 = 16.00 g/mol 2.02 + 16.00 = 18.02 g/mol
Find the number of atoms of phosphorus (P) in 3.44 moles of phosphorus.
2.07 x 10²⁴ atoms
What is the molar mass of lead?
207.20 g/mol
Use 2-STEP dimensional analysis (grams to mole using the molar mass THEN moles to volume) to determine what volume the gas occupies at STP 28.0 g N₂
22.4 L
What is the molar mass of aluminum?
26.98 g/mol
What is the mass of 4.56 moles of sulfur dioxide?
292 grams
How many oxygen atoms are in CaCO₃? *look at subscripts
3
Find the number of atoms in 36 grams of germanium (Ge).
3.0 x 10²³ atoms
Use dimensional analysis (1 mol = 22.4 L) to convert from volume to moles 71.7 L O₂
3.02 moles
Convert 987 grams of Ra(OH)₂ to moles.
3.80 grams
What are some ways you can measure pieces of matter?
by dozens, reams, grosses, moles, etc. *when we count things, we often group them into a large unit
What does ions stand for?
charged atoms
Molecular Formula
chemical formula that shows the ACTUAL number of atoms in a compound
What does molecules stand for?
covalent bonds
Gram Atomic Mass
elements
What does atoms stand for?
elements of the periodic table
What type of representative particle would CaCl₂ be?
formula
How do you measure matter?
in grams
How do you measure volume?
in liters/milliliters
How are atoms counted?
in moles
What type of representative particle would OH⁻ be?
ion
What does formula units stand for?
ionic bonds
Gram Formula Mass
ionic compounds
What is a representative particle?
it is whatever you are counting
How do you find the molar mass of a compound?
just add up its atomic masses
How is mole abbreviated?
mol
What type of representative particle would CO₂ be?
molecule
Gram Molecular Mass
molecules
Anhydrates
salt WITHOUT the water molecules attached
Hydrates
salts WITH water molecules attached
What type of representative particle would Fe be?
atom
How many molecules are in 44.99 grams of water?
1.503 x 10 ²⁴ molecules
How many oxygen atoms are in Al₂(SO₄)₃
12 *this is because you multiple the subscripts (4 X 3)
What is the molar mass of carbon?
12.01 g/mol
What is the molar mass of (NH₄)₂SO₄?
132.17 g/mol
Use dimensional analysis (1 mol = 22.4 L) to convert from moles to volume 0.750 mol N₂
16.8 L
Use 2-STEP dimensional analysis (grams to mole using the molar mass THEN moles to volume) to determine what volume the gas occupies at STP 65 g CO₂
33 L
What is the molar mass of F₂?
38.00 g/mol
How many grams are there in 2.3 x 10²⁴ atoms of silver (Ag)?
410 grams
Use dimensional analysis (1 mol = 22.4 L) to convert from moles to volume 2.05 mol H₂
45.9 L
How many ions are in Al₂(SO₄)₃
5
Change 8.35 mole to CO₂ molecules.
5.03 x 10 ²⁴ molecules
Convert 6.6 moles of ZnO to grams.
540 grams
How many formula units are in 67.69 grams of salt (NaCl)?
6.973 x 10 ²³ formula units
How many molecules of nickel (Ni) is 3.88 x 10²⁵ atoms of nickel?
64.5 moles
What is the molar mass of Ge?
72.61 g/mol
Use 2-STEP dimensional analysis (grams to mole using the molar mass THEN moles to volume) to determine what volume the gas occupies at STP 105 g O₂
73.5 L
What is the molar mass of Ca(OH)₂?
74.10 g/mol
What is the molar mass of BeCl₂?
79.91 g/mol
How many moles of water is 5.87 x 10²³ molecules?
9.75 x 10 ⁻² moles
What is 6.02 X 10²³ also known as?
Avogardo's Number * it is an equivalency- a conversion factor ** just like 1 dozen = 12 pieces
TRUE or FALSE? Each mole has the same number of particles (6.02 X 10²³), just different masses.
TRUE
Molar Mass
also known as the decimal number on the periodic table, the average atomic mass (grams/mole)
Empirical Formula
the LOWEST whole-number ratio of the atoms of the elements in a compound
Mole
the amount of a substance that contains 6.02 X 10²³ representative particles
What is molar mass the generic term for?
the mass of one mole of any substance
Percent Composition
the percentage by mass of each element in a compound
Molar Volume
the volume occupied by one mole of a substance at a given pressure and volume
Why can the appearance of the same amount of multiple materials seem way different in size?
this is because, although you have the same amount of that material, the particles can be vastly different sizes
When do we use moles?
to count very small things, such as, water molecules
