Identifying acids, bases and salts from their molecular formulas

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: Molecular formulas Words Acids, bases and salts all have their own rules to follow when constructing their molecular formulas CO2 = carbon dioxide O2 = oxygen NaCl = sodium chloride

The Rules….. Ex. HS HNO3 HCl HF H2SO4 ACIDS The Rules….. Usually begins with the letter “H” (hydrogen) Usually combines with a nonmetal or a group of atoms (ex. SO4, ClO4) Ex. HS HNO3 HCl HF H2SO4 Exception **If formula ends in “COOH”……ex. CH3COOH it is also an acid - COOH at the end of formula are called “organic acids”

Exceptions!!! C3H8 CH3 C8H18 CH4 C & H only – are NOT acids!!!

(misleading solutions) Examples ACIDS EXCEPTIONS (misleading solutions) HNO3 H3PO4 HCl CH3 CH4 C3H8 NOTE: any “H” combined with carbon by itself is usually an exception and not considered an acid (called hydrocarbons)

ACIDS hydrocarbons TESTERS: Where do you think these solutions belong? CLICK ENTER FOR THE CORRECT ANSWER 1. HNO3 4. CH3 5. C3H8 2. C4H8 6. H2SO4 3. HBr

The Rules….. Ex. KOH LiOH NaOH Mg(OH)2 NH3 Usually ends with an OH BASES The Rules….. Usually ends with an OH Usually combines with a metal or a NH4 group Ex. KOH LiOH NaOH Mg(OH)2 NH3

Exceptions!!! C2H5OH CH3OH C2H4(OH)2 Alcohols – are NOT bases!!! **When OH is found at the end of the formula but attached to a carbon and hydrogen it is an alcohol Alcohols – are NOT bases!!!

Examples BASES EXCEPTIONS NaOH LiOH Mg(OH)2 C2H5OH CH3OH CH3COOH (misleading solutions) NaOH LiOH Mg(OH)2 C2H5OH CH3OH CH3COOH NOTE: any “OH” combined with a carbon and a hydrogen together is an alcohol

The Rules….. Ex. KI LiBr NaCl K3PO4 SALTS The Rules….. 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 Ex. KI LiBr NaCl K3PO4 ***salts are formed during the neutralization of an acid with a base***

Covalently Bonded Compounds CCl4 PCl3 CF4 CO2 2 non-metals are NOT salts!!!

Examples SALTS EXCEPTIONS MgCl2 NH4Cl KI PCl3 CCl4 (misleading solutions) MgCl2 NH4Cl KI PCl3 CCl4 NOTE: these exceptions just have to be memorized

TESTERS: Where do you think these solutions belong? ACIDS BASES SALTS TESTERS: Where do you think these solutions belong? 1. H3PO4 4. HI 2. C8H18 5. MgCl2 3. Ca(OH)2 6. KOH

Ex. Which of the following substances is a base? a. LiCl b. CH3OH c. KOH d. HNO3 Be careful – CH3OH is an alcohol

Ex. Which of the following substances is a salt? a. HCl b. Mg(OH)2 c. CF4 d. CaF2 Be careful – CF4 is made from 2 non-metals, so it is NOT a salt

Be careful! This is vinegar or acetic acid! Ex. 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!

Ex. You are given three substances & asked to classify their nature in the table below. Nature Substance ? MgCl2 HBr NaOH Which table correctly identifies the nature of each substance? B. A. Nature Substance Acid MgCl2 Salt HBr Base NaOH Nature Substance Salt MgCl2 Base HBr Acid NaOH C. Nature Substance Salt MgCl2 Acid HBr Base NaOH

Roles of Acids, Bases & Salts -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)

KEY POINTS 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)

Activities Worksheet #2 Study guide Module 3, page 4-5 Text Book -page 331 #3 (under exercises) -page 346 #1, #2, #3