MOLECULAR FORMULAS

ACIDSACIDS

BASES

BASES

SALTS

SALTS

Objectives2.3 To differentiate among acids,

bases, and salts based on their formulas.

2.4 To justify the need to produce various acids, bases, and salts based on their uses/properties.

Molecular Formulas

Allows one to determine the nature of the compound

Deals with letters/symbols from the periodic table to describe substances instead of words

EXAMPLE:

Acids, bases and salts all have their own rules to follow when constructing their molecular formulas

Molecular formulas

Words

Molecular Formulas

**sometimes hydrogen is found at the end……ex. CH3COOH- H at the end of formula are called “organic acids”

Usually begins with the letter “H” (hydrogen)

Usually combines with a nonmetal or a group of atoms (ex. SO4, ClO4)

ACIDS

Exception

The Rules…..

HCl

HS

HF

HNO3

H2SO4

CH3

CH4

C & H only –

are NOT acids!!!

C8H18

C3H8

CH3

CH4

C3H8

ACIDS EXCEPTIONS(misleading solutions)

HNO3

H3PO4

HCl

Examples

NOTE: any “H” combined with carbon by itself is usually an exception and not considered an acid

(called hydrocarbons or“false acids”)

TESTERS: Where do you think these solutions belong? CLICK ENTER FOR THE CORRECT ANSWER

ACIDS “FALSE ACIDS”

1. HNO3

6. H2SO4

2. C4H8

3. HBr

4. CH3

5. C3H8

Usually ends with an OH Usually combines with a metal or a

NH4 group

BASESThe Rules…..

NaOH

KOH

Mg(OH)2

LiOH

NH3

CH3OH

C2H4(OH)2

Alcohols –

are NOT bases!!!

C2H5OH

**When OH is found at the end of the formula but attached to a carbon and

hydrogen it is considered to be a “false base”

- these are called alcohols

C2H5OH

CH3OH

CH3COOH

BASES EXCEPTIONS(misleading solutions)

NaOH

LiOH

Mg(OH)2

NOTE: any “OH” combined with a carbon and a hydrogen together is usually a “false base”.

-called alcohols

Examples

***salts are formed during the neutralization of an acid with a base***

SALTSThe Rules…..

NaClKI

K3PO4

LiBr

Salt formulas neither start with H nor end with OH

Generally begin with a metal and end with a nonmetal or a group of atoms

PCl3

2 non-metals

are NOT salts!!!

CCl4

CF4CO2

PCl3

CCl4

SALTS EXCEPTIONS(misleading solutions)

MgCl2NH4Cl

KI

NOTE: these exceptions just have to be memorized

Examples

TESTERS: Where do you think these solutions belong?

ACIDS BASES SALTS

1. H3PO4

6. KOH

2. C8H18

3. Ca(OH)2

4. HI

5. MgCl2

Which of the following substances is a base? a. LiCl

b. CH3OH

c. KOH

d. HNO3

Be careful – CH3OH is an alcohol

Which of the following substances is a salt? a. HCl

b. Mg(OH)2

c. CF4

d. CaF2Be careful – CF4 is made from 2

non-metals, so it is NOT a salt

Which of the following substances is are acids?

1. HCl

2. CH3COOH

3. KOH

4. H2CO3

5. C2H6

6. Na2SO4

7. NH3

8. HF

Be careful! This is

vinegar or acetic acid!

You are given three substances & asked to classify their nature in the table below.

Which table correctly identifies the nature of each substance?

Nature Substance

? MgCl2? HBr

? NaOH

Nature Substance

Acid MgCl2Salt HBr

Base NaOH

Nature Substance

Salt MgCl2Base HBr

Acid NaOH

Nature Substance

Salt MgCl2Acid HBr

Base NaOH

ACIDS:-common in foods (enhance flavors and preserve food)-medications

BASES:-used in fertilizers, pulp and paper, plastics and food industry-processing of chemical products-common in household cleaning products-extremely important in soaps and detergents as it dissolves grease

SALTS:-used in dyes-changes physical properties by lowering freezing or melting point (ex. salt on our roads to melt ice)

Roles of Acids, Bases & Salts

Acids usually begin with H Bases usually end with OH Salts begin with a metal & end with either a

non-metal or group Exceptions:

CH3COOH is an acid (vinegar) A formula with only C & H are not acids, bases or

salts (hydrocarbons) A formula with only C & H, ending with OH are not

bases (alcohols) NH3 is a base (ammonia) A formula with 2 non-metals are not salts (ex.

PCl3)

Worksheet #2 Study guide Module 3, page 4-5 Text Book

-page 323 #1, #2, #6-page 331 #3 (under exercises)

-page 346 #1, #2, #3

Activities

References

Science Quest, Grenier,Daigle & Rheaume, 1998

Physical Science Student Study Guide 416-436

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