MEET THE MOLE.

oThe mole is a unit of measurement.oThe unit can be defined in multiple ways.

(We’ll learn 3 today.)oIn its simplest terms, it represents a

specific number. oDozen = what number?oPair = what number?oBaker’s dozen = what number?oMole = 6.02 x 1023

oAtoms are SUBmicroscopic. In order to have an amount large enough with which to really interact, we need quite a few atoms.

MOLES

o6.02x1023

oMy pet mole is named Avogadro.

AVOGADRO’S NUMBER

oCountingoWeighingoAmount

of Space Needed

DEFINING THE MOLE

oSome questions simply test your understanding of the definitions.

oCalculate the molar mass of sulfur dioxide, a gas produced when sulfur-containing fuels are burned.

oSO2oS = 32.07 goO = 2(16.00 g)oTotal = 64.07 g/moloCan also be expressed as 1 mol SO2 = 64.07 g

MOLAR MASS EXAMPLE 6.5

oPolyvinyl chloride, called PVC, which is widely used for floor coverings (“vinyl”) as well as for plastic pipes in plumbing systems, is made form a molecule with the formula C2H3Cl. Calculate the molar mass of this substance.

o62.49 g/mol

MOLAR MASS PRACTICE PROBLEM 6.5

oMost questions will require you to apply the definitions to convert from one unit to another.

oAluminum (Al), a metal with a high strength-to-weight ratio and a high resistance to corrosion, is often used for structures such as high-quality bicycle frames. Compute both the number of moles in a 10.0-g sample of aluminum.

UNIT CONVERSION EXAMPLE 6.3

A silicon chip used in an integrated circuit of a computer has a mass of 5.68 mg. How many silicon (Si) atoms are present in this chip? The average atomic mass for silicon is 28.09 amu.

UNIT CONVERSION EXAMPLE 6.4

During cellular respiration, a cell releases 0.25 mol of O2 gas. What volume is needed to hold this gas?

UNIT CONVERSION EXAMPLE

10-2 Practice Problems (1-3, 12-14, 17, 18, 23-25)

PARTNER PRACTICE

BACK TOGETHER WITH 10 MIN LEFT IN

CLASS.

Exit Questi

on

Calculate the number of formula

units in a 45.0 gram sample of FeO.

Exit Questi

on Groups

PROBLEM-BASED LEARNING ACTIVITY

o Let’s make sure that we all understand how the particle vocabulary can complicate a problem.

o Consider: Calculate the number of oxygen atoms in 3.5 g aluminum sulfate.

o A few examples in your practice packet.

HIGHER LEVEL APPLICATIONS OF MOLE

MOLE THINK

TAC TOE

CHOOSE A PARTNER. WORK IS DUE AT THE END OF

THE PERIOD.

oThe relative amounts of each element in a compound are expressed in percent composition.

oAKA: percent by mass of each elemento% of element = grams of element X

100 grams of compound

PERCENT COMPOSITION

Carvone is a substance that occurs in two forms, both of which have the same molecular formula (C10H14O) and molar mass. One type of carvone give caraway seeds their characteristic smell; the other is responsible for the smell of spearmint oil. Compute the mass percent of each element in carvone.

PERCENT COMPOSITION EXAMPLE 6.9

o Mass % is easily related to chemical formulas

o The relationship of moles to chemical formulas requires a little more thought.

o First, let’s learn two new vocabulary words.

CONNECTING MOLES & MASS % TO CHEMICAL

FORMULAS

o Empirical formula: lowest whole number ratio of the atoms of the elements in a compoundo Ionic compounds are criss-crossed and

then reduced. Ionic compound formulas are nearly always empirical formulas.

o Covalent compounds are not always reduced formulas. (Ex. C6H12O6)

o Therefore, an empirical formula doesn’t have to be the same as the actual molecular formula of the compound.

TYPE OF CHEMICAL FORMULA: EMPIRICAL

FORMULA

CH2OCalculate the mass percent of each element.

C = 40% H = 6.7% O = 53.3%

Isn’t this the reduced formula for: C3H6O3, C4H8O4, C5H10O5, & C6H12O6

The mass percent of each of these compounds is the same.

EMPIRICAL FORMULA

o Molecular formula: actual formula for the compound which gives the composition of the moleculeo Glucose shares an empirical formula

with many compounds, but it has its molecular formula all to itself.

o 6(CH2O) = glucose

TYPE OF CHEMICAL FORMULA: MOLECULAR

FORMULA

o When an unknown compound is found, instruments can tell scientists the mass percent composition of the compound.

o Calculations are required to convert that series of percentages into a chemical formula.

o We start by converting to the empirical formula.

APPLYING THE VOCABULARY

Situation: A white solid has been found on the floor of a government mailroom. Is it dangerous? Step 1: Mass spectrometer analysis• 40.9 % Carbon• 4.58% Hydrogen• 54.5% Oxygen• Molar mass of 180

grams/moleStep 2: Convert % to formula with simple calculations

Use a simple rhyme!o % to gramo Gram to moleo Divide by the

smallesto Multiply ‘til

whole.

CALCULATING EMPIRICAL FORMULA

Situation: A white solid has been found on the floor of a government mailroom. Is it dangerous? Mass spectrometer analysis• 40.9 % Carbon• 4.58% Hydrogen• 54.5% Oxygen• Molar mass of 180

grams/mole

o An oxide of aluminum is formed by the reaction of 4.151 g of aluminum with 3.692 g of oxygen. Calculate the empirical formula for this compound.o % to gram = IS DONE FOR YOUo Gram to mole = dimensional analysiso Let’s carry out the calculation on the board.

EMPIRICAL FORMULA EXAMPLE 6.11

A sample of lead arsenate, an insecticide used against the potato beetle, contains 1.3813 g of lead, 0.00672 g of hydrogen, 0.4995 g of arsenic, and 0.4267 g of oxygen. Calculate the empirical formula for lead arsenate.

EMPIRICAL FORMULA EXAMPLE 6.13

The most common form of nylon is 63.68% carbon, 12.38% nitrogen, 9.80% hydrogen, and 14.4% oxygen. Calculate the empirical formula for nylon.

EMPIRICAL FORMULA EXAMPLE 6.14

Molecular Formula= n(empirical formula)

(Remember 6(CH2O) = glucose)We know how to calculate the empirical formula, but how do we know what number to multiply it by?

n= actual formula mass/molar mass of empirical

CALCULATING MOLECULAR FORMULA

A white powder is analyzed and found to have an empirical formula of P2O5. The compound has a molar mass of 283.88 g/mol. What is the compound’s molecular formula?

MOLECULAR FORMULA EXAMPLE 6.15

o A compound used as an additive for gasoline to help percent engine knock shows the following percentage composition:o 71.65% Clo 24.27% Co 4.07% Ho The molar mass is known to be 98.96 g.

Determine the empirical formula and the molecular formula for this compound.

MOLECULAR FORMULA PRACTICE PROBLEM

6.15

Mole Airlin

es

PROBLEM-BASED

LEARNINGDAY 1: FORENSIC

CHEMISTDAY 2: ASSISTANT

MEDICAL EXAMINER

WARM UP FOR

QUIZ

The final product in protein metabolism is urea. Urea contains 20.00% C, 6.73% H, 46.65% N, and 26.64% O. The molar mass of urea is 60.07g/mol. Calculate the empirical formula and

molecular formula.

Mole Airlin

es

PROBLEM-BASED

LEARNINGDAY 1: FORENSIC

CHEMISTDAY 2: ASSISTANT

MEDICAL EXAMINER