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