slide show mole concept

8/6/2019 Slide Show Mole Concept

1/12

The Mole

Q: how long would it take to spend a mole of $1 coins if

they were being spent at a rate of 1 billion per second?


2/12

Background: atomic masses Look at the atomic masses on the periodic

table. What do these represent? E.g. the atomic mass of C is 12 (atomic # is 6) We know there are 6 protons and 6 neutrons P

rotons and neutrons have roughly the samemass. So, C weighs 12 u (atomic mass units). What is the actual mass of a C atom? Answer: approx. 2 x 10-23 grams (protons and

neutrons each weigh about 1.7 x10-24 grams)Two problems1. Atomic masses do not convert easily to grams

2. They cant be weighed (they are too small)


3/12

The MoleWith these problems, why use atomic mass at all?

1. Masses give information about # of p+

, n0

, e

2. It is useful to know relative massE.g. Q - What ratio is needed to make H2O?

A - 2:1 by atoms, but 2:16 by mass

It is useful to associate atomic mass with amass in grams. It has been found that1g H, 12g C, or 23g Na have 6.02x1023 atoms

6.02 x 1023 is a mole or Avogadros number mol is used in equations, mole is used in

writing; one gram = 1 g, one mole = 1 mol. Read 4.3 (167-9). Stop after text beside fig 2. Do Q1-6. Challenge: 1st slide (use reasonable units)


4/12

The Mole: Answers1. A mole is a number (like a dozen). Having

this number of atoms allows us to easilyconvert atomic masses to molar masses.

2. 6.02x1023

3. 602 000 000 000 000 000 000 0004. 3.00 x 6.02x1023 = 18.06x1023 or 1.81x1024

(note: there are 3 moles of atoms in onemole of CO

2

molecules. In other words,there are 5.42x1024 atoms in 3.00 mol CO2)

5. 3.01x1023

6. a) 1.43 kg z 12 = 0.119 kg per orange

b) 1.01 g z 6.02x1023 = 1.68 x 1024 g


5/12

MollionaireQ: how long would it take to spend a mole of

$1 coins if they were being spent at a rate of1 billion per second?

A: $ 6.02 x 1023 / $1 000 000 000

= 6.02 x 1014 payments = 6.02 x 1014 seconds6.02 x 1014 seconds / 60 = 1.003 x 1013 minutes

1.003 x 1013 minutes / 60 = 1.672 x 1011 hours

1.672 x 1011

hours / 24 = 6.968 x 109

days6.968 x 109 days / 365.25 = 1.908 x 107 years

A: It would take 19 million years


6/12

Comparing sugar (C12H22O11) & H2O

No, sugar has

more (45:3 ratio)

Yes (6.02x1023

in each)

Yes.

No, molecules

have dif. masses

No, moleculeshave dif. sizes.

1 mol each

Yes, thats what

grams are.mass?No, they have dif.

molar masses# of moles?

No, they have dif.molar masses

# ofmolecules?

No# of atoms?

No, they have dif.densities.

volume?

1 gram eachSame


7/12

Molar mass The mass of one mole is called molar mass

E.g. 1 mol Li = 6.94 g Li This is expressed as 6.94 g/mol What are the following molar masses?

S SO2Cu3(BO3)232.06 g/mol 64.06 g/mol308.27 g/mol

Calculate molar masses (to 2 decimal places)

CaCl2(NH4)2CO3O2Pb3(PO4)2

C6H12O6

Cu x 3 = 63.55 x 3 = 190.65

B x 2 = 10.81 x 2 = 21.62O x 6 = 16.00 x 6 = 96.00

308.27


8/12

Molar mass The mass of one mole is called molar mass

E.g. 1 mol Li = 6.94 g Li This is expressed as 6.94 g/mol What are the following molar masses?

S SO2Cu3(BO3)232.06 g/mol 64.06 g/mol308.27 g/mol

Calculate molar masses (to 2 decimal places)

CaCl2(NH4)2CO3O2Pb3(PO4)2

C6H12O6

110.98 g/mol (Cax1, Clx2)

96.11 g/mol (Nx2, Hx8, Cx1, Ox3)32.00 g/mol (Ox2)

811.54 g/mol (Pbx3, Px2, Ox8)

180.18 g/mol (Cx6, Hx12, Ox6)


9/12

Converting between grams and moles If we are given the # of grams of a compound

we can determine the # of moles, & vise-versa In order to convert from one to the other you

must first calculate molar massg = mol x g/molmol = g z g/mol

This can be represented in an equation triangle

g

mol g/mol

g= g/mol x mol0.25HCl53.15H2SO4

3.55NaCl

1.27Cu

Equationmol (n)gg/molFormula

9.136.46mol= g z g/mol0.541998.08

g= g/mol x mol20758.44

mol= g z g/mol0.020063.55


10/12

Simplest and molecular formulaeConsider NaCl (ionic) vs. H2O2 (covalent)

Cl Na

Na Cl

Cl

Cl

Na

Na

Chemical formulas are either simplest (a.k.a.empirical) or molecular. Ionic compoundsare always expressed as simplest formulas.

Covalent compounds can either be molecular

formulas (I.e. H2O2) or simplest (e.g. HO)Q - Write simplest formulas for propene (C3H6),C2H2, glucose (C6H12O6), octane (C8H14)

Q - Identify these as simplest formula, molecular

formula, or both H2O, C4H10, CH, NaCl


11/12

AnswersQ - Write simplest formulas for propene (C3H6),

C2H2, glucose (C6H12O6), octane (C8H14)Q - Identify these as simplest formula, molecular

formula, or both H2O, C4H10, CH, NaCl

A - CH2

A - H2O is both simplest and molecular

C4H10 is molecular (C2H5 would be simplest)

CH is simplest (not molecular since CH cantform a molecule - recall Lewis diagrams)

NaCl is simplest (its ionic, thus it doesnt

form molecules; it has no molecular formula)

CH CH2O C4H7

For more lessons, visit

www.chalkbored.com


12/12

Amole is the amount of pure substance containing the same

number of chemical units as there are atoms in exactly 12

grams of carbon-12 (i.e., 6.023 X 1023). This involves the

acceptance of two dictates -- the scale of atomic masses and

the magnitude of the gram. Both have been established byinternational agreement. Formerly, the connotation of "mole"

was "gram molecular weight." Current usage tends to apply the

term "mole" to an amount containingAvogadro's number of

whatever units are being considered. Thus, it is possible tohave a mole of atoms, ions, radicals, electrons, or quanta. This

usage makes unnecessary such terms as "gram-atom," "gram-

formula weight," etc.

Source(s):

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