Chemical Quantities Avogadro’s Number

Many words are used to express Many words are used to express a specific quantity.a specific quantity.

–Pair =2Pair =2–Dozen = 12Dozen = 12

• By mass – 1lb of bananasBy mass – 1lb of bananas• By volume – a gallon of milkBy volume – a gallon of milk• By count – 20 calculatorsBy count – 20 calculators

How do we measure matter?How do we measure matter?

How do we measure matter?How do we measure matter?

• What if I wanted to know What if I wanted to know how many ATOMS were how many ATOMS were in this copper penny? in this copper penny? Would you like to count? Would you like to count? Could you?Could you?

• A mole is the most A mole is the most appropriate unit when appropriate unit when dealing with atoms.dealing with atoms.

Avogadro’s NumberAvogadro’s Number

• You can count particles if you introduce a term You can count particles if you introduce a term that represents a specified number of particles.that represents a specified number of particles.

• 1 mole = 6.02 x 101 mole = 6.02 x 1023 23 (Avogadro’s number) (Avogadro’s number) representative particles.representative particles.

• Or 602,000,000,000,000,000,000,000Or 602,000,000,000,000,000,000,000• A very large number!A very large number!

MOLEMOLE

• A mole is the SI unit that measures the A mole is the SI unit that measures the amount of a substance.amount of a substance.

• A mole can be related to: A mole can be related to: • The number of particlesThe number of particles• The massThe mass• The volume of elements and The volume of elements and

compoundscompounds

1 mole of hockey pucks would equal the mass of 1 mole of hockey pucks would equal the mass of the moon!the moon!

1 mole of basketballs would fill a bag the size of 1 mole of basketballs would fill a bag the size of the earth!the earth!

1 mole of pennies would cover the Earth 1/4 mile 1 mole of pennies would cover the Earth 1/4 mile deep!deep!

MOLEMOLE

• Use dimensional analysis to Use dimensional analysis to convert:convert:– moles to moleculesmoles to molecules– moles to atomsmoles to atoms– moles to formula unitsmoles to formula units

• Conversion Factor to Remember:Conversion Factor to Remember:– 1 mol = 6.02 x 101 mol = 6.02 x 102323

• The units for Avogadro’s number The units for Avogadro’s number will be atoms, molecules, or will be atoms, molecules, or formula units.formula units.

• The unit depends on the type of The unit depends on the type of compound or if just a singular compound or if just a singular element.element.

MOLE ExamplesMOLE Examples

• How many moles are in 3.25 X 10How many moles are in 3.25 X 102020 atoms of atoms of lead?lead?

• How many moles are there in 8.3 x 10How many moles are there in 8.3 x 102626 molecules? molecules?

• How many atoms are in 0.425 mol nitrogen?How many atoms are in 0.425 mol nitrogen?• How many formula units are in 8.56 X 10How many formula units are in 8.56 X 10-3-3 mol mol

NaCl?NaCl?

Chemical QuantitiesMolar Mass

Molar MassMolar Mass

• Molar Mass equals 1 mole of an element or compound.Molar Mass equals 1 mole of an element or compound.• To calculate Molar Mass:To calculate Molar Mass:

1.1. Obtain all of the masses of the involved elements Obtain all of the masses of the involved elements from the periodic table.from the periodic table.

2.2. Round mass to 2 decimal places.Round mass to 2 decimal places.3.3. Multiply each element’s mass by the subscript.Multiply each element’s mass by the subscript.4.4. Add these massesAdd these masses5.5. Round the answer to the proper number of Round the answer to the proper number of

significant digits.significant digits.

Terms to Know for Terms to Know for Mass of a CompoundMass of a Compound

• Molecular massMolecular mass - - mass of one mass of one molecule of a covalent compound molecule of a covalent compound (unit = amu)(unit = amu)

• Formula massFormula mass - - mass of one mass of one formula unit of an ionic compound formula unit of an ionic compound (unit = amu)(unit = amu)

• Molar massMolar mass - - mass of one mole of mass of one mole of anything: molecules, formula units, anything: molecules, formula units, atoms, etc. (unit = g/mol).atoms, etc. (unit = g/mol).

Difference between Difference between Molecular Mass & Molar MassMolecular Mass & Molar Mass

• Same numerical value, but different unitsSame numerical value, but different units

Molar Mass of Element ExamplesMolar Mass of Element Examples• Carbon = 12.01 g/molCarbon = 12.01 g/mol

• Aluminum = 26.98 g/molAluminum = 26.98 g/mol

VIDEO to more Discussion on the MOLEVIDEO to more Discussion on the MOLE

The Mole and Avogadro's Number from Khan Academy

Molar Mass of Compounds ExamplesMolar Mass of Compounds Examples

• WaterWaterHH22O = 2 hydrogen & 1 oxygenO = 2 hydrogen & 1 oxygen

2(1.01) + 16.00 = 18.02 g/mol2(1.01) + 16.00 = 18.02 g/mol• SucroseSucrose

CC1212HH2222OO1111 = 12 carbon, 22 hydrogen, 11 oxygen = 12 carbon, 22 hydrogen, 11 oxygen

12(12.01) + 22(1.01) + 11(16.00) = 342.34 g/mol12(12.01) + 22(1.01) + 11(16.00) = 342.34 g/mol

Molar Mass of Compounds Molar Mass of Compounds ExamplesExamples

Sodium ChlorideSodium Chloride– Find the formulaFind the formula

– How many of eachHow many of each

– Multiply masses by subscripts and add the massesMultiply masses by subscripts and add the masses

NaCl

1 sodium, 1 chlorine

1(22.99) + 1(35.45) = 58.44 g/mol

• Use dimensional analysis to Use dimensional analysis to convert convert – moles to mass or mass to moles to mass or mass to

moles.moles.• Mass unit = gramsMass unit = grams• Conversion Factor to Remember:Conversion Factor to Remember:

– 1 mol = molar mass of the element 1 mol = molar mass of the element or compoundor compound

Moles to Mass ExamplesMoles to Mass Examples

• How many moles of carbon are in 26 g of How many moles of carbon are in 26 g of carbon? carbon?

• How many grams are there in 2.37 moles of How many grams are there in 2.37 moles of COCO22??

Moles to Mass ExamplesMoles to Mass Examples

• How many moles are present in 142.1 How many moles are present in 142.1 grams of NaCl?grams of NaCl?

• How many grams are in 3.34 moles of How many grams are in 3.34 moles of potassium bromide?potassium bromide?

Mole Calculations LearnedMole Calculations Learned

MASS

IN

GRAMS

MOLES

NUMBER

OF

PARTICLES/

ATOMS

LITERS

GAS

Chemical QuantitiesPercent Composition

Percent CompositionPercent Composition

• Percent composition is the percent of that Percent composition is the percent of that element in the compound….the total percent for element in the compound….the total percent for the compound will equal 100%.the compound will equal 100%.

• Formula for Percent Composition:Formula for Percent Composition:

100mass total

element of massncompositio %

Percent Composition ExamplesPercent Composition Examples• Example: 9.03 g Mg combined completely with 3.48 g Example: 9.03 g Mg combined completely with 3.48 g

N to form a compound. N to form a compound. • What is the percent composition of the compound?What is the percent composition of the compound?

– 9.03g + 3.48g = 12.51 g (total mass)9.03g + 3.48g = 12.51 g (total mass)– 9.03/12.51 x 100 = 72.2 % of Mg9.03/12.51 x 100 = 72.2 % of Mg– 3.48g/12.51 x 100 = 27.8% of N3.48g/12.51 x 100 = 27.8% of N

• Check: Add % Composition of each element to see if adds up to 100%Check: Add % Composition of each element to see if adds up to 100%– 72.2 % of Mg + 27.8% of N = 100%72.2 % of Mg + 27.8% of N = 100%

Percent Composition ExamplesPercent Composition Examples• When the mass of each element is not given, When the mass of each element is not given,

calculate the molar mass of each element in the calculate the molar mass of each element in the compound before calculating the % composition.compound before calculating the % composition.

• Example: Calculate the percent composition of CExample: Calculate the percent composition of C22HH66..

– Mass of 1 mol of Carbon = 12.0g x 2 = 24gMass of 1 mol of Carbon = 12.0g x 2 = 24g– Mass of 1 mol of Hydrogen = 1.0g x 6 = 6gMass of 1 mol of Hydrogen = 1.0g x 6 = 6g– 24g/30g x 100 = 80%24g/30g x 100 = 80%– 6g/30g x 100 = 20 %6g/30g x 100 = 20 %

• Be sure to check your work.Be sure to check your work.

More Percent Composition More Percent Composition ExamplesExamples

• Calculate the % Composition of these Calculate the % Composition of these compounds:compounds:– NaHSONaHSO44

– NHNH44ClCl

Chemical QuantitiesEmpirical Formulas

Empirical FormulasEmpirical Formulas

• The empirical formula gives the lowest whole The empirical formula gives the lowest whole number ratio of the elements in a compound. number ratio of the elements in a compound. – Reduces the subscripts.Reduces the subscripts.

• The empirical is sometimes and sometimes The empirical is sometimes and sometimes notnot the same as the molecular or “actual” formula.the same as the molecular or “actual” formula.– For ionic compounds, the formula unit is the empirical For ionic compounds, the formula unit is the empirical

formula.formula.• Example when Example when NOTNOT::

– The empirical formula for HThe empirical formula for H22OO22 is HO. is HO.

Empirical FormulasEmpirical Formulas

• The molecular formula for vitamin C is The molecular formula for vitamin C is CC66HH88OO66. What is the empirical formula?. What is the empirical formula?

–A. CHOA. CHO–B. CB. C33HH44OO33

–C. CHC. CH22OO

–D. CD. C22HH44OO22

Empirical FormulasEmpirical Formulas

• Which of the following is an empirical Which of the following is an empirical formula?formula?–A. CA. C33HH66

–B. NaClB. NaCl

–C. CHC. CH44

–D. CD. C44HH1010

VIDEO to more Discussion on the MOLEVIDEO to more Discussion on the MOLE

Emp and Mol formulas from Percent composition