Chapter 10.1 and 10.2 Calculating atoms

Molar Mass Is the same as the atomic weight on the periodic table Element Examples  g C = 1 mol C  1.01 g H = 1 mol H  g Fe = 1 mol Fe

Molar Mass To find the molar mass of a compound –Count the number of each element –Multiply that number by the Average Atomic mass for that element –Add all the elements total masses together

Calculate molar mass of magnesium carbonate 24.3 g g + 3 x (16.00 g) = 84.3 g/mole So, 84.3 g/mole = molar mass for magnesium carbonate

Examples  Calculate the molar mass of : Na 2 S N2O4N2O4 C Ca(NO 3 ) 2 = g/mol = g/mol = g/mol = g/mol

What is the mole? Not this kind of mole!

Mole - a word used to represent a large number of objects. Moldy

Avogadro’s Number: the number of particles in one mole of particles. 1 mole particles = 602,000,000,000,000,000,000,000 particles 1 mole particles = 6.02 X representative particles **Memorize this number for the test** **Memorize this number for the test**

The Mole 12 donuts = 1 dozen donuts12 donuts = 1 dozen donuts 12 ears of corn = 1 dozen ears of corn12 ears of corn = 1 dozen ears of corn 6.02 X particles = 1 mole particles.6.02 X particles = 1 mole particles. Molar mass is the mass listed on the periodic table in red rounded to closest whole numberMolar mass is the mass listed on the periodic table in red rounded to closest whole number Molar mass = 1 mole atoms = 6.02 X atomsMolar mass = 1 mole atoms = 6.02 X atoms 12 donuts = 1 dozen donuts12 donuts = 1 dozen donuts 12 ears of corn = 1 dozen ears of corn12 ears of corn = 1 dozen ears of corn 6.02 X particles = 1 mole particles.6.02 X particles = 1 mole particles. Molar mass is the mass listed on the periodic table in red rounded to closest whole numberMolar mass is the mass listed on the periodic table in red rounded to closest whole number Molar mass = 1 mole atoms = 6.02 X atomsMolar mass = 1 mole atoms = 6.02 X atoms

What are Representative Particles?  The smallest pieces of a substance: 1)molecular compound - molecule 2)ionic compound - formula unit (made of ions) 3)element: is the Remember the 7 diatomic elements? (made of molecules) H2H2 N2N2 O2O2 F2F2 Cl 2 I2I2 Br 2 atom

Solving Problems in Chemistry

Required Work for Solving Problems in Chemistry List given List conversions Start with given information including proper units Determine the units for your answer. Put in conversions until the last unit is what you are solving for.

Solving Problems in Chemistry 1. How many sulfur atoms are equivalent to 3 moles of sulfur atoms? Given: 3 moles of sulfur atoms = ? Sulfur atoms Conversion: 1 mole of sulfur atoms = 6.02 X sulfur atoms x atoms S 3 moles S 6.02 x atoms S 1 mole S X = x atoms S 1

2. How many atoms are present in 3.7 moles of sodium? 3.7 moles Na = ? atoms Na 1 mole Na = 6.02 X atoms Na 3.7 moles Na6.02 X atoms Na 1 mole Na X = = 2.22 X atoms Na 1 List given: List conversions: Set Up:

3. How many atoms are present in 155 moles of Arsenic? 155 moles As = ? atoms As 1 mole As = 6.02 X atoms As 155 moles As6.02 X atoms As 1 mole As X = = 9.33 X atoms As 1 List given: List conversions: Set Up:

Atoms to Moles

1. How many moles of Xenon are e quivalent to 5.66 X atoms Xe ? 5.66 X atoms Xe = ? moles Xe 1 mole Xe = 6.02 X atoms Xe 5.66 X atoms Xe 1 mole Xe 6.02 X atoms Xe X = = moles Xe 6.02 X X moles Xe List given: List conversions: Set Up:

2. How many moles of Silver are e quivalent to X atoms Ag ? X atoms Ag = ? moles Ag 1 mole Ag = 6.02 X atoms Ag X atoms Ag 1 mole Ag 6.02 X atoms Ag X = = 4.8 X moles Ag X moles Ag 6.02 X List given: List conversions: Set Up:

Moles To Grams

1. moles of sulfur atoms equals how many grams of sulfur? Given: 3 moles S = ? Grams S Conversion: 1 mole S = 32 grams S 96 grams S 3 moles S X= 96 grams S 1 32 grams S 1 mole S

2. Find the mass in grams of 8.6 moles bromine 8.6 moles Br = ? grams Br 1 mole Br = 80 grams Br 8.6 moles Br 80 grams Br 1 mole Br X = = 688 grams Br 1 List given: List conversions: Set Up:

3. Find the mass in grams of 7.55 moles silicon 7.55 moles Si = ? grams Si 1 mole Si = 28 grams Si 7.55 moles Si 28 grams Si 1 mole Si X = = grams Si 1 List given: List conversions: Set Up:

Grams to Moles

1. How many moles are in 38 grams of Carbon? 38 grams C = ? moles C 1 mole C = 12 grams C 38 grams C 1 mole C 12 grams C X = = 3.17 moles C 38 moles C 1212 List given: List conversions: Set Up:

2. How many moles are in 2 grams of Hydrogen? 2 grams H = ? moles H 1 mole H = 1 grams H 2 grams H 1 mole H 1 grams H X = = 2 moles H 1 List given: List conversions: Set Up:

Grams to Particles

Solving Problems in Chemistry grams sulfur is equal to how many atoms of sulfur? Given: 57 grams S = ? atoms S Conversion: 1 mole S = 32 grams S 1 mole S = 6.02 X atoms S 1.07 X atoms S 57 grams S XX= 3.43 X atoms S X atoms S 1 mole S 32 grams S

2. How many atoms of Sulfur are in 100 grams of Sulfur? 100 grams S = ? atoms S 1 mole S = 32 grams S 1 mole S = 6.02 X atoms S 100 grams S 1 mole S 32 grams S X = =1.88 X atoms S 6.02 X atoms S 1 mole S X 6.02 X atoms S 32 List given: List conversions: Set Up:

The Mole-Volume Relationship  gases - hard to determine mass  how many moles of gas?  2 things affect gas Volume:  a) Temp & b) Pressure  compare all gases at = temp & pressure

Standard Temperature and Pressure  0ºC & 1 atm pressure - abbreviated “STP” any  At STP, 1 mol of any gas has V of 22.4 L - Called molar volume  1 mol of any gas at STP = 22.4 L

Density of a gas  D = m / V (density = mass/volume) - for gas units are: g / L  find density of a gas at STP if formula known  You need: 1) mass and 2) volume  Assume 1 mol, so mass is molar mass (from periodic table)  At STP, V = 22.4 L

 If given density  If given density, find molar mass of gas  Assume 1 mol at STP, so V = 22.4 L modify: D = m/V to show:  “m” will be mass of 1 mol, given 22.4 L m = D x V

 What is molar mass of a gas with density of g/L?  How about a density of 2.86 g/L? = 44.0 g/mol 64.0 g/mol

Notice all conversions must go through the MOLE! Copy this conversion map into your notes!

That’s all Folks !