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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