3.3b The Mole

POINT > Explain the concept of the mole POINT > Define Avagadro’s number POINT > Perform conversions using the mole POINT > Define molar mass

POINT > Explain the concept of the mole Recall that each element has an atomic mass. For example, the atomic mass of C is U What is the mass of a C atom in grams? Answer: approx. 2 x grams; g

POINT > Explain the concept of the mole g Masses on this scale are not very useful, so chemists invented the mole (mol) Just like a “dozen” represents a specific number, so does a mole A mole is the number of atoms in g of carbon = 6.02 × 10 23

POINT > Define Avagadro’s number A mole is 6.02 × This is Avagadro’s number Avagadro’s work with gas particles helped inspire the development of the mole How large is this number….?

POINT > Define Avagadro’s number If you had $6.02 x … and spent $1,000,000,000 per second = 6.02 x seconds 6.02 x seconds / 60 = x minutes x minutes / 60 = x hours x hours / 24 = x 10 9 days x 10 9 days / = x 10 7 years It would take 19 million years

WB CHECK: What is Avagadro’s number? A mole is what number?

POINT > Explain the concept of the mole 1 dozen cookies = 12 cookies 1 mole of cookies = 6.02 x cookies 1 dozen cars = 12 cars 1 mole of cars = 6.02 x cars 1 dozen Al atoms = 12 Al atoms 1 mole of Al atoms = 6.02 x Al atoms Note that the number is always the same, but the mass is very different!

We use the mole (mol) as a unit of measure for an amount of a chemical substance We use the mole to convert between the number of particles and the mass of a substance: Recall that 6.02 x atoms of carbon = 1.0 mol carbon Also: 12.01g carbon = 1.0 mol carbon We can now convert between number of atoms, grams, and moles

POINT > Perform conversions using the mole We can now convert between number of atoms, grams, and moles using these conversion factors: 1 mol C 12.0g C 12.0g C 1 mol C 1 mol C 6.02 x atoms C 6.02 x atoms C 1 mol C

POINT > Perform conversions using the mole Ex. How many carbon atoms are in mol C? Step 1: we want the number of atoms of C Step 2: we are given mol C Step 3: conversion - 1 mole C = 6.02 × atoms C = mol C × 1 mol C 6.02 × atoms C 7.22 × atoms C

POINT > Perform conversions using the mole Ex. How many moles of carbon are in 1.25 × atoms C? Step 1: we want the number of moles of C Step 2: we are given 1.25 × atoms C Step 3: conversion - 1 mole C = 6.02 × atoms C 1.25 × atoms C × 1 mol C 6.02 × atoms C = 2.08 × mol C

WB CHECK: How many atoms in mol C? 3.0 x C atoms How many moles is 7.63 x C atoms? 12.7 moles carbon

POINT > Perform conversions using the mole How many atoms in 2.7 g carbon? 2.7g C x mol C x = 1.4 x C atoms 1 mol C 12.0g C 6.02 x atoms C 1 mol C = mol C = 1.35 x atoms C

POINT > Perform conversions using the mole How many grams is 4.9 x carbon atoms? 4.9 x atoms C x 8.14 x 10 2 mol C x = 9.8 x 10 3 g C 1 mol C 6.02 x atoms C 12.0g C 1 mol C = 8.14 x 10 2 mol C = 9.77 x 10 3 g C

How many atoms in 10.0g carbon? 10.0g C x mol C x = 5.01 x C atoms 1 mol C 6.02 x atoms C 12.0g C 1 mol C = mol C = 5.02 x C atoms WB CHECK:

POINT > Define molar mass 12.01g carbon = 1.0 mol carbon 12.01g is the molar mass of carbon The atomic mass of any element in grams = molar mass of the element Ex. the molar mass of sulfur is 32.06g 32.06g sulfur has 6.02 x sulfur atoms and is one mole of sulfur

WB CHECK: What is the molar mass of calcium (Ca)? What is the mass of 2.0 mol helium (He)? How many zinc atoms are in 65.4g of zinc (Zn)?

Homework: Finish reading Ch 3.3 pages Practice #1-4 page 81 #1-3 page 81 #1-3 page 82 #1-3 page 83 F.A. #1-7 page 83