Ch 7 Sec 3 Using Chemical Formulas pages 237-244 1 Modern Chemistry Chapter 7 Chemical Formulas and...

Ch 7 Sec 3 Using Chemical Formulas pages 237-244

1

Modern ChemistryModern ChemistryChapter 7Chapter 7

Chemical Formulas and Chemical Formulas and Chemical CompoundsChemical Compounds

Sections 1, 3 & 4Chemical Names and Formulas

Using Chemical FormulasDetermining Chemical Formulas


2

Ch

ap

ter

Vocab

ula

ryMonatomic ionBinary compoundNomenclatureOxyanionSaltFormula Mass Percent CompositionEmpirical Formula


3

Section 3

Using Chemical Formulas


4

Ato

mic

Mass A

nim

ati

on


5

• Formula Mass – – the mass of any molecule, formula

unit or ion.– The sum of all the average atomic

masses of all the atoms represented by the formula

– Unit: a.m.u.

• Molecular mass– Mass of a molecule – in a.m.u.

Definitions


6

• Molar mass – – the mass of one mole of atoms of an

element – The mass of one mole of molecules

or formula units of a compound– Numerically equal to formula mass– Unit: grams/mole (g/mol)

Definitions


7

• List the elements in the compound.• List the number of atoms of each

element.• Multiply each number of atoms by

the – Relative atomic mass (for formula

mass)– Molar mass (for molar mass)

• Add the products.

Calculating Formula Mass or Molar Mass


8

List the elements in the compound.


(NH4)2SO4

N

H

S

O

2

8

1

4

x 14.01 = 28.02

x 1.008 = 8.064

x 32.06 = 32.06

x 16.00 = 64.00

+

132.144List the number of atoms of each

element.

• Multiply each number of atoms by the – Relative atomic mass (for formula mass)– Molar mass (for molar mass)

Add the products…


9


(NH4)2SO4

N

H

S

O

2

8

1

4

x 14.01 = 28.02

x 1.008 = 8.064

x 32.06 = 32.06

x 16.00 = 64.00

132.144From the periodic table4 sig figs

The unit is amu for formula mass. The unit is g/mol for molar mass


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Pra

cti

ce P

ag

e 2

38

1. Find the formula mass of each of the following:

a. H2SO4

b. Ca(NO3)2

c. PO4 3−

d. MgCl2


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Pra

cti

ce P

ag

e 2

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2. Find the formula mass of each of the following:

a. Al2S3

b. NaNO3

c. Ba(OH)2


12

One mole of …

Nitrogen (balloon)

CdS (yellow)

Water (cylinder)

NaCl (white)

p. 239


13

Mole

An

imati

on


14

The formula could stand for 1 molecule of water with 2 hydrogen atoms and 1 oxygen atom… or …

The formula could stand for 1 mole of water molecule which contain 2 moles of hydrogen atoms and 1 mole of oxygen atoms.

Chemical Formulas & Moles


15

Conversions with Compounds

MASSgrams

AMOUNT

moles

PARTICLESmolecules

MOLAR MASS 6.022 x 10 23

xx


16

Conversions with Compounds

MASSgrams

AMOUNT

moles

PARTICLESatoms

MOLAR MASS 6.022 x 10 23

xx


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Grams-Moles-Molecules Conversions

p. 240


18

g

mol C

on

vers

ion

An

imati

on

p. 240


19

Dimensional Analysis

# & unit given unit wantedunit givenx

Fill in units first; then numbers !

=unit given

Put in numbers to make the numerator equal to

the denominator


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Dimensional Analysis

x x x x =

Arrange the units so that all cancel out except the last one, which should be the one you want.


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Pra

cti

ce P

ag

e 2

42

1. How many moles of compound are there in the following?

a. 6.60 g (NH4)2SO4

b. 4.5 kg Ca(OH)2

2. How many molecules are there in the following?

a. 25.0 g H2SO4

b. 125 g of sugar, C12H22O11

3. What is the mass in grams of 6.25 mol of copper(II) nitrate?


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% C

om

posit

ion

An

imati

on


24

Find the molar mass of the compound.

Percent Composition(NH4)2SO4

N

H

S

O

2

8

1

4

x 14.01 = 28.02

x 1.008 = 8.064

x 32.06 = 32.06

x 16.00 = 64.00

132.144Divide the subtotal for each element

by the molar mass

132.14 = .2120

132.14 = .06103

132.14 = .2426

132.14 = .4843


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Multiply each by 100 to get a percent.

Percent Composition(NH4)2SO4

N

H

S

O

28.02

8.064

32.06

64.00

132.144

132.14 = .2120

132.14 = .06103

132.14 = .2426

132.14 = .4843

x100 = 21.20%

x100 = 6.103%

x100 = 24.26%

x100 = 48.43%


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HydratesSalt which have the ability to bind

water molecules within their crystal lattice.

Anhydrous - salts without waterExamples

CuSO4 5H2O

copper(II) sulfate pentahydrateCoCl2 6H2O

cobalt (II) chloride hexahydrate


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CuSO4 5H2O

Hydrates

CoCl2 6H2O


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What percentage of sodium carbonate decahydrate, Na2CO3 10H2O, is sodium

carbonate?1. Find the molar mass of Na2CO3 (the anhydrous compound).

2. Find the mass Na2CO3 10H2O (the hydrate).

3. Divide mass of compound (anhydrous) by mass of the hydrate and multiply by 100.


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Percent Composition of a HydrateCuSO4 5H2O

Cu

S

O

H

O

1

1

4

10

5

x 63.55 = 63.55

x 32.06 = 32.06

x 16.00 = 64.00

x 1.008 = 10.08

x 16.00 = 80.00

249.69

159.61

90.08

249.69

249.69

x 100 =

63.92%

x 100 =

36.08%


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What is the percentage of MnCl2 in MnCl2 2H2O?

77.73%

How much water could 100g of anhydrous MnCl2 absorb if the hydrated form is MnCl2 2H2O?

28.64g


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Pra

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1. Find the percentage compositions of the following:

a. PbCl2 b. Ba(NO3)2

2. Find the mass percentage of water in ZnSO4•7H2O.

3. Magnesium hydroxide is 54.87% oxygen by mass. How many grams of oxygen are in 175 g of the compound? How many moles of oxygen is this?


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Section 3 Homework

Ch 7 Sec 3 Using Chemical Formulas pages 237-244 1 Modern Chemistry Chapter 7 Chemical Formulas and...

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