Chemistry Notes: Acids and BasesChemistry 2014-2015

Properties of Acids and Bases

Acids taste sour (vinegar,

lemons) aqueous solutions of acids

are electrolytes cause indicators to change

colors many metals react with

acids to produce H2 gas react with bases to form a

salt and water most formulas begin with

H

Bases bitter taste (soap,

unsweetened chocolate) bases are electrolytes in

aqueous solution cause indicators to

change colors feel slippery react with acids to form a

salt and water often contain OH- , or

ammonia NH3

ExamplesThe bolded formulas below to STRONG acids and

bases

Common acids HCl HNO3

H2SO4

H3PO4

HC2H3O2

H2CO3

Common bases NaOH KOH Ca(OH)2

LiOH NH3

Aqua regia is a concentrated mixture of hydrochloric and nitric acid. It creates toxic fumes of chlorine gas and is capable of dissolving gold. It is represented by a fire-breathing dragon in old alchemy works.

Trivia: Aqua Regia

The pH of a substance can tell us if it’s an acid, a base, or neutral. pH is a measurement of the concentration of hydrogen ions (H+) in a solution. The more hydrogen ions present, the more acidic a substance is.

Acids have large amounts of hydrogen ions, and low pH (pH < 7).

Bases have small amounts of hydrogen ions, and high pH (pH > 7).

Measuring pH

Another measurement, pOH, tells use the concentration of hydroxide (OH-) ions in a solution. The more hydroxide ions present, the more basic a substance is.

Acids have small amounts of hydroxide ions, and high pOH (pOH > 7).

Bases have large amounts of hydroxide ions, and low pOH (pOH < 7).

Neutral substances have equal amounts of hydrogen and hydrogen ions (pH = 7, pOH = 7).

The pH and pOH of a substance always add up to 14.

 pH = 5.6 NH3

 Large concentration of OH- ions   Small concentration of H+ ions

pOH = 3.2 pH = pOH H2SO4 NaOH

 Large concentration of H+ ions HCl

Practice: Are these solutions acidic, basic, or neutral?

If the pH of a solution is 6, what is its pOH? Is it an acid or base? 

If the pH of a solution is 4, what is its pOH? Is it an acid or base? 

If the pOH of a solution is 3, what is its pH? Is it an acid or base?

Practice: Are these solutions acidic, basic, or neutral?

Indicators are substances that change color in solutions of different pH

Help determine approximate pH

Indicators

Colorless in acid

Pink in base

Phenolphthalein

Mixture of indicators Changes into

different colors at each pH (rainbow)

Red/orange in acid, blue/purple in base, green around pH = 7

Universal indicator

Blue litmus turns red in acid

Red litmus turns blue in base

Litmus paper

Well, what is H2SO4? Why is Johnny no more?

Acids generally begin with H, so their formulas are easy to recognize. The name of an acid depends on everything after the H in the formula (the anion).

Writing Names and Formulas for Acids and Bases—Acids

Common acids HCl hydrochloric

acid HNO3 nitric acid

H2SO4 sulfuric acid

H3PO4 phosphoric acid

HC2H3O2 acetic acid

H2CO3 carbonic acid

Determine the name of the anion in the acid. For example, HI contains iodide, I-. H2SO3 contains sulfite, SO3

2-. H2Cr2O7 contains dichromate, Cr2O72-.

The last three letters of the anion determine the rules you will use to name the acid. You will take the root of the acid’s name from the anion it contains. -ide hydro ________ ic acid -ite ____________ ous acid (no prefix) -ate ___________ ic acid (no prefix)

Writing Names and Formulas for Acids and Bases—Acids

Therefore, HI is hydroiodic acid, H2SO3 is sulfurous acid, and H2Cr2O7 is dichromic acid. Note that acid names do not contain the word “hydrogen”. To determine the name of an acid from its

formula, you need to swap and drop the anion with hydrogen ions. For example, nitric acid must contain nitrate, NO3

-. If you swap and drop hydrogen (H+) with NO3

-, you get HNO3.

Writing Names and Formulas for Acids and Bases—Acids

Bases are relatively easy to name, since many contain the hydroxide ion, OH-. Ex. Ba(OH)2 is barium hydroxide, NaOH is sodium hydroxide, Al(OH)3 is aluminum hydroxide, Fe(OH)2 is iron (II) hyroxide.

One exception to the rule above is the weak base NH3, ammonia.

Except for ammonia (NH3, a formula you “just need to know”), you usually need to swap and drop to determine the formula of a base. Most will contain hydroxide.

Writing Names and Formulas for Acids and Bases—Bases

Write the names for the following acids and bases. 

LiOH H2SO4 NH3

 

Names and Formulas Practice

Write the names for the following acids and bases. 

Mg(OH)2 HNO2 HCN 

Names and Formulas Practice

Write the names for the following acids and bases.

 HBr Sr(OH)2 HClO4

 

Names and Formulas Practice

Write the formulas for the following acids and bases. 

Ammonia Nitric acid Hydrochloric acid 

Write the formulas for the following acids and bases. 

Calcium hydroxide Chromic acid Chlorous acid