Part 1

Some Properties of Acids

Taste sour

Corrode metals

pH is less than 7

React with bases to form a salt and water

Produce H+ (as H3O+) ions in water

Some Properties of Bases

Taste bitter, chalkyTaste bitter, chalky

Feel soapy, slipperyFeel soapy, slippery

pH greater than 7pH greater than 7

Produce OHProduce OH-- ions in water ions in water

React with acids to form salts and waterReact with acids to form salts and water

Some Common Bases

NaOHNaOH sodium hydroxidesodium hydroxide lyelye

KOHKOH potassium hydroxidepotassium hydroxide liquid soapliquid soap

Ba(OH)Ba(OH)22 barium hydroxidebarium hydroxide stabilizer for stabilizer for

plasticsplastics

Mg(OH)Mg(OH)22 magnesium hydroxidemagnesium hydroxide Milk of magnesia Milk of magnesia

Al(OH)Al(OH)33 aluminum hydroxidealuminum hydroxide Maalox (antacid)Maalox (antacid)

Acid/Base definitions

• Definition #1: Arrhenius (traditional)

Acids – produce H+ ions (or hydronium ions H3O+)

Bases – produce OH- ions

(problem: some bases don’t have hydroxide ions!)

HCl + H 2O H3O+ + Cl-

Arrhenius acid is a substance that produces H+ (H3O+) in water

Arrhenius base is a substance that produces OH- in water

Acid - a substance Acid - a substance that accepts an that accepts an electron pairelectron pair

Base - a substance Base - a substance that donates an that donates an electron pairelectron pair

Definition #2 – Lewis Definition #2 – Lewis

TheThe pH scalepH scale is ais a way way

of expressing the strength of acids and of expressing the strength of acids and bases. bases.

Instead of using very small numbers, Instead of using very small numbers, we just use the NEGATIVE power of we just use the NEGATIVE power of 10 on the Molarity of the H10 on the Molarity of the H++ (or OH (or OH--) ) ion.ion.

Under 7 = acidUnder 7 = acid7 = neutral7 = neutral

Over 7 = baseOver 7 = base

pH of Common pH of Common SubstancesSubstances

pH testing• There are several ways to test pHThere are several ways to test pH

– Blue litmus paper (red = acid)Blue litmus paper (red = acid)– Red litmus paper (blue = basic)Red litmus paper (blue = basic)– pH paper (multi-colored)pH paper (multi-colored)– pH meter (7 is neutral, <7 acid, >7 pH meter (7 is neutral, <7 acid, >7

base)base)– Universal indicator (multi-colored)Universal indicator (multi-colored)– Indicators like phenolphthaleinIndicators like phenolphthalein– Natural indicators like red cabbage, Natural indicators like red cabbage,

radishesradishes

Paper testing• Paper tests like litmus paper and pH Paper tests like litmus paper and pH

paperpaper

pH meter

• Tests the voltage of the Tests the voltage of the electrolyteelectrolyte

• Converts the voltage to pHConverts the voltage to pH• Very cheap, accurateVery cheap, accurate• Must be calibrated with a buffer Must be calibrated with a buffer

solutionsolution

pH indicators• Indicators are dyes that can be

added that will change color in the presence of an acid or base.

• Some indicators only work in a specific range of pH

• Once the drops are added, the sample is ruined

• Some dyes are natural, like radish skin or red cabbage

Acid or base?

• HF

• NaOH

• HBr

• KOH

• NH4OH

• HCl

• HI

• Ca(OH)2

• Mg(OH)2

• Ba(OH)2

• H2S

• Al(OH)3