Atomic Mass and Formula Mass Atomic Mass and Formula Mass

Atomic mass = mass of an atom Atomic mass = mass of an atom expressed relative to the mass assigned to expressed relative to the mass assigned to carbon-12 (carbon-12 is used as the carbon-12 (carbon-12 is used as the standard)standard)

Formula mass = sum of the atomic Formula mass = sum of the atomic masses of all the atoms in a compoundmasses of all the atoms in a compound

Formula mass calculationFormula mass calculation

HH22OO H x 2 = 1.01 amu x 2 = 2.02 amuH x 2 = 1.01 amu x 2 = 2.02 amu O x 1 = 16.00 amu x 1 = O x 1 = 16.00 amu x 1 = 16.00 amu16.00 amu Sum = Sum = 18.02 amu18.02 amu

CC66HH1212OO66 C x 6 = 12.01 amu x 6 = 72.06 amuC x 6 = 12.01 amu x 6 = 72.06 amu H x 12 = 1.01 amu x 12 = 12.12 amuH x 12 = 1.01 amu x 12 = 12.12 amu O x 6 = 16.00 amu x 6 = O x 6 = 16.00 amu x 6 = 96.00 amu96.00 amu Sum = Sum = 180.18 amu180.18 amu

Measuring MatterMeasuring Matter

Counting UnitsCounting Units12 = dozen12 = dozen2 = pair2 = pair500 = ream500 = ream

This works for objects we can manipulate This works for objects we can manipulate with bare hands.with bare hands.

Chemists need a way to accurately count Chemists need a way to accurately count the number of atoms, molecules, or the number of atoms, molecules, or formula units in a sample. formula units in a sample.

The Mole!!!!!!!The Mole!!!!!!!

SI base unit for measuring the amount of a SI base unit for measuring the amount of a substancesubstance

Mole = number of carbon atoms in exactly Mole = number of carbon atoms in exactly 12 grams of pure carbon-12. 12 grams of pure carbon-12. Carbon-12 used as a standard.Carbon-12 used as a standard.

1 mole anything1 mole anything = 6.02 X 10 = 6.02 X 1023 23 representative particlesrepresentative particles Representative particles can be:Representative particles can be:

AtomsAtomsMolecules (Covalently bonded)Molecules (Covalently bonded)Formula units (Ionically bonded)Formula units (Ionically bonded)

Atoms, molecules, and formula units are Atoms, molecules, and formula units are so small it’s impossible to count them so small it’s impossible to count them individually.individually.

So, chemists need a special counting unit.So, chemists need a special counting unit.

Avogadro’s NumberAvogadro’s Number

Avogadro’s # = 6.02 X 10Avogadro’s # = 6.02 X 102323

602000000000000000000000602000000000000000000000

You don’t have to write this number, it’s just for effect…just know You don’t have to write this number, it’s just for effect…just know it’s a big number and use the scientific notation alwaysit’s a big number and use the scientific notation always

So how big is Avogadro’s # ?So how big is Avogadro’s # ?

If you gave away 1 million dollars to each If you gave away 1 million dollars to each person on Earth every day, it would take person on Earth every day, it would take more than 3000 years to distribute the more than 3000 years to distribute the money.money.

If you spread Avogadro's number of If you spread Avogadro's number of unpopped popcorn kernels across the unpopped popcorn kernels across the USA, the entire country would be covered USA, the entire country would be covered in popcorn to a depth of over 9 miles. in popcorn to a depth of over 9 miles.

Molar MassMolar Mass

We don’t deal with “amu” balances in We don’t deal with “amu” balances in Chemistry…we deal with balances which Chemistry…we deal with balances which measure mass in grams…so we need a measure mass in grams…so we need a way to measure the mass of 1 mole of a way to measure the mass of 1 mole of a substance…substance…

The molar mass is just like the atomic The molar mass is just like the atomic mass and formula mass…just a different mass and formula mass…just a different unit. (g/mol instead of amu)unit. (g/mol instead of amu)

Molar mass Calculation exampleMolar mass Calculation example

CaCa22CCCa x 2 = 40.08 g/mol x 2 = 80.16 g/molCa x 2 = 40.08 g/mol x 2 = 80.16 g/molC x 1 = 12.01 g/mol x 1 = C x 1 = 12.01 g/mol x 1 = 12.01 g/mol12.01 g/mol Sum = 92.17 g/molSum = 92.17 g/mol

NN22HH44

N x 2 = 14.01 g/mol x 2 = 28.02 g/molN x 2 = 14.01 g/mol x 2 = 28.02 g/molH x 4 = 1.01 g/mol x 4 = H x 4 = 1.01 g/mol x 4 = 4.04 g/mol4.04 g/mol Sum = 32.06 g/molSum = 32.06 g/mol

Watch out for these…Watch out for these…

Let’s say you have 1 mole of CaClLet’s say you have 1 mole of CaCl22 … …How many moles of CaHow many moles of Ca2+2+ do you have? do you have?

How many moles of ClHow many moles of Cl1-1- do you have? do you have?

How many formula units of CaClHow many formula units of CaCl22 do you do you

have?have?

Mass and the MoleMass and the Mole

1 mole of Fe has the same number of 1 mole of Fe has the same number of atoms as 1 mole of Neatoms as 1 mole of Ne6.02 X 10 6.02 X 10 2323 atoms of each atoms of each

1 mole of Fe 1 mole of Fe does notdoes not have the same have the same mass as 1 mole of Nemass as 1 mole of Ne1 atom of Fe 1 atom of Fe does notdoes not have the same mass have the same mass

as 1 atom of Neas 1 atom of Ne

Mass to Mole ExampleMass to Mole Example

How many moles are present in 4.395 How many moles are present in 4.395 grams of sodium chloride?grams of sodium chloride?

Mole to Mass ExampleMole to Mass Example

Suppose you have a 0.548 mole sample of Suppose you have a 0.548 mole sample of dinitrogen triiodide. What is the mass (in dinitrogen triiodide. What is the mass (in grams) of this sample? grams) of this sample?

Moles to Particles ExampleMoles to Particles Example

A sample of potassium chloride contains A sample of potassium chloride contains 2.57 moles. How many formula units of 2.57 moles. How many formula units of potassium chloride are present in this potassium chloride are present in this sample?sample?

Particles to Moles ExampleParticles to Moles Example

A sample of chlorine gas contains A sample of chlorine gas contains 5.48 X 105.48 X 102424 molecules of chlorine gas. molecules of chlorine gas. How many moles of chlorine gas does this How many moles of chlorine gas does this sample contain?sample contain?

Multistep ConversionsMultistep Conversions

The mole is the key here. It is the thing The mole is the key here. It is the thing which chemists use the most when dealing which chemists use the most when dealing with calculations involving chemical with calculations involving chemical reactions.reactions.

There are two main types of multipstep There are two main types of multipstep conversions:conversions:Mass to particleMass to particleParticle to massParticle to mass

Mass to Particle ExampleMass to Particle Example

A baker needs 758 grams of sucrose A baker needs 758 grams of sucrose (C(C1212HH2222OO1111) to bake a cake. How many ) to bake a cake. How many

sucrose molecules will be in the unbaked sucrose molecules will be in the unbaked cake? cake?

Particles to Mass ExampleParticles to Mass Example

8.0 X 108.0 X 102020 atoms of calcium are present in atoms of calcium are present in a multivitamin. How many grams of a multivitamin. How many grams of calcium does a person consume when calcium does a person consume when they take the vitamin?they take the vitamin?

Moles and GasesMoles and Gases

At the same temperature and pressure, At the same temperature and pressure, equal volumes of gases contain the same equal volumes of gases contain the same number of gas particles.number of gas particles.

STP = Standard Temperature and STP = Standard Temperature and Pressure (0 Pressure (0 ooC and 1 atmosphere)C and 1 atmosphere)

At STP, it was found experimentally that At STP, it was found experimentally that 1 mole of any gas had a volume of 22.4L.1 mole of any gas had a volume of 22.4L.

We call this volume the We call this volume the molar volumemolar volume

Moles to VolumeMoles to Volume

A chemical reaction produces 0.82 moles A chemical reaction produces 0.82 moles of oxygen gas. What volume will that gas of oxygen gas. What volume will that gas occupy assuming the chemical reaction occupy assuming the chemical reaction occurred at STP?occurred at STP?

Volume to MolesVolume to Moles

A huge latex balloon with a volume of A huge latex balloon with a volume of 3675 L contains how many moles of 3675 L contains how many moles of helium at STP? helium at STP?

Multistep Conversions using Molar Multistep Conversions using Molar VolumeVolume

How many grams of oxygen gas are How many grams of oxygen gas are present in a sample of oxygen gas with a present in a sample of oxygen gas with a volume of 58.4 L at STP?volume of 58.4 L at STP?

A sample of neon gas has a volume of A sample of neon gas has a volume of 5.2 L at STP. How many grams of neon 5.2 L at STP. How many grams of neon are present in the sample? How many are present in the sample? How many atoms of neon are present in the sample?atoms of neon are present in the sample?

Percent CompositionPercent Composition

The mass of each element in a compound The mass of each element in a compound compared to the entire mass of the compared to the entire mass of the compound, and multiplied by 100%.compound, and multiplied by 100%.

(Part/Whole) X 100%(Part/Whole) X 100%This needs to be done for This needs to be done for eacheach element! element!

Two ways to determine percent Two ways to determine percent compositioncompositionGiven a chemical formulaGiven a chemical formulaGiven experimental mass dataGiven experimental mass data

% Composition Given % Composition Given Chemical FormulaChemical Formula

Determine the percent composition for the Determine the percent composition for the following chemical compounds:following chemical compounds:

CC66HH1212OO66

(NH(NH44))22SS

% Composition Given Mass Data% Composition Given Mass Data

If a compound has a total mass of 4.50 If a compound has a total mass of 4.50 grams, and contains 1.25 grams of carbon grams, and contains 1.25 grams of carbon and 3.25 grams of oxygen, what is its and 3.25 grams of oxygen, what is its percent composition?percent composition?

If a compound contains only 3.10 grams of If a compound contains only 3.10 grams of iron and 1.25 grams of oxygen, what is its iron and 1.25 grams of oxygen, what is its percent composition?percent composition?

Empirical FormulasEmpirical Formulas

Formulas that give the simplest-whole Formulas that give the simplest-whole number ratio of the atoms of the elements number ratio of the atoms of the elements in a compound.in a compound.

These cannot be reduced any further!These cannot be reduced any further!Example: CaClExample: CaCl22 cannot be reduced. cannot be reduced.

Example: CHExample: CH22O cannot be reduced. O cannot be reduced.

Example: Ba(OH)Example: Ba(OH)22 cannot be reduced. cannot be reduced.

Molecular FormulasMolecular Formulas

The formula that gives the actual number The formula that gives the actual number of atoms of each element in a molecular of atoms of each element in a molecular compound.compound.

This formula is always a whole-number This formula is always a whole-number multiple of the empirical formula.multiple of the empirical formula.

This formula can be reduced to yield the This formula can be reduced to yield the empirical formula.empirical formula.

Example: CExample: C66HH1212OO66 can be reduced to can be reduced to CHCH22OO

Determining Molecular Formula Determining Molecular Formula From Empirical FormulaFrom Empirical Formula

Beta carotene can be broken down to form Beta carotene can be broken down to form vitamin A. The empirical formula for beta vitamin A. The empirical formula for beta carotene is Ccarotene is C55HH77. The molar mass of beta . The molar mass of beta

carotene is 536 g/mol. What is the carotene is 536 g/mol. What is the molecular formula?molecular formula?

The molar mass of TNT is 227.0 g/mole. If The molar mass of TNT is 227.0 g/mole. If its empirical formula was determined to be its empirical formula was determined to be CC77HH55NN33OO66 What is its molecular formula? What is its molecular formula?