acids and bases describing acids and bases. history of theory for acids and bases arrhenius, svante...

Acids and Bases

Describing Acids and Bases

History of theory for Acids and Bases

• Arrhenius, Svante   – Swedish physical chemist (1859-1927) – one of the

first who attempted to scientifically describe acids and bases

• Arrhenius acid– substance that, when dissolved in water, produces

hydrogen ions (proton) • H+

• Arrhenius base– substance that, when dissolved in water, produces

hydroxide ions• OH-

Examples of Arrhenius Acid and Base

Arrhenius acid

Arrhenius base

Chapter 14: Acids and Bases-- Describing Acids and Bases --

Acids- Properties

• Aqueous solutions of acids are called electrolytes• Have a sour taste• Conduct electricity -- some well, some poorly• Cause some indicators, or chemical dyes, to change color• React with many metals to produce hydrogen gas• React with bases containing hydroxide ions to form salt and water• pH < 7

Bases- Properties

• Conduct electricity -- some well, some poorly• Taste bitter and feel slippery• Cause some indicators, or chemical dyes, to change color• React with acids containing hydroxide ions to form salt and water• pH >7

Chapter 14: Acids and Bases-- Describing Acids and Bases --

Names and Formulas of Acids• Acid takes the form of HX, where H is the hydrogen ion and X is a

monatomic or polyatomic ion

• Rules for naming– When the name of the anion (X) ends in “–ide”

- the acid name begins with hydro-- then, replace “-ide” with “ –ic” and add the word

“acid” to the end.

• Examples– HCl: hydrochloric acid– HBr: hydrobromic acid

Chapter 14: Acids and Bases-- Describing Acids and Bases --

Names and Formulas of Acids

– When the anion name ends in “-ate”• the acid is named by replacing “-ate” with “–ic” and adding the

word “acid” to the end.

• Examples– H2SO4: sulfuric acid (since it contains the sulfate ion)– HNO3: nitric acid (since it contains the nitrate ion)

Chapter 14: Acids and Bases-- Describing Acids and Bases --

Names and Formulas of Acids

– When the anion name ends in ”-ite”• the acid is named by replacing “-ite” with “-ous” , and

adding the word “acid” to the end.

• Examples:

– -H2SO3: sulfurous acid (since it contains the sulfite ion)

- HNO2: nitrous acid (since it contains the nitrite ion)

Chapter 14: Acids and Bases-- Describing Acids and Bases --

Names and Formulas of Bases

• Bases are named the same way as other ionic compounds – Example: NaOH= Sodium Hydroxide

- The cation is left the same

- The anion is found on our list of common polyatomic ions from the back of your periodic table

• ***One to know: NH3 = Ammonia

• Now, let’s practice!

Strengths of Acids and Bases

• Acids and bases are classified into one of two categories depending on their strength– The strength depends on the amount of ions

formed• The more ions formed = strong acid • Fewer ions formed = weak acid

Strong Bases

• The strength of a base is determined by the percent of units dissociated, NOT the number of OH- ions produced.

• This can be determined by seeing how well the substance dissociates (or separates) in solution

• Example– NaOH Na+ + OH-

– This is a strong base because it completely dissociates into ions when you put it in water

Strong Acids

• Completely dissociate, or separate into ions, when mixed with water

• Common strong acids and bases

Strong Acids Strong Bases

Hydroiodic acid HI Sodium Hydroxide NaOH

Hydrochloric acid HCl Potassium Hydroxide KOH

Hyrdrobromic acid HBr Lithium Hydroxide LiOH

Nitric acid HNO3 Calcium Hydroxide Ca(OH)2

Weak Acids and Bases

• Most acids and bases are weak• Weak acids and bases only partially dissociate

(or separate) when put into water• Examples

– Carbonic acid is a weak acid found in soft drinks– Ammonia is a weak base found in household

cleaning products

The pH Scale

• The pH scale measures the concentration of hydrogen ions in solution– Ranges from 0-14– Neutral solutions have a pH of 7– 0 is strongly acidic– 14 is strongly basic

• The pH scale is like the Richter scale, which measures earthquakes. The change of 1 unit is a tenfold

• Meaning- an earthquake with a tremor measuring 4.0 is 10x greater than one measuring 3.0.