The Chemistry of Acids and Bases

The Chemistry of The Chemistry of Acids and BasesAcids and Bases Chemistry I – Chapter 19Chemistry I – Chapter 19

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Acids

Have a sour taste. Vinegar is a solution of acetic acid. CitrusHave a sour taste. Vinegar is a solution of acetic acid. Citrusfruits contain citric acid.fruits contain citric acid.

React with certain metals to produce hydrogen gasReact with certain metals to produce hydrogen gas..

React with carbonates and bicarbonates to produce carbon React with carbonates and bicarbonates to produce carbon dioxide gasdioxide gas

Have a bitter taste.Have a bitter taste.

Feel slippery. Many soaps contain basesFeel slippery. Many soaps contain bases..

Bases

ACIDS

• An acid is a compound that increases the number of hydrogen ions when dissolved in water (H+) (present as H3O+ ions)

• An acid solution tastes sour• An acid can change the color of certain

compounds

What is an ion?An ion is an atom that has lost or

gained an electron giving it a positive (+) or negative (-) charge.

Some Properties of Acids

Produce H+ (as H3O+) ions in water (the hydronium ion is a hydrogen ion

attached to a water molecule)

Taste sour

Corrode metals

Electrolytes

React with bases to form a salt and water

pH is less than 7

Turns blue litmus paper to red “Blue to Red A-CID”

USES OF ACIDS

• Citric acid and ascorbic acid (Vitamin C) are found in orange juice

• Carbonic acid and phosphoric acid give a “bite” to soft drinks

• Acids in your stomach aid in digestion• Sulfuric acid is the most widely used

industrial acid in the world. It is used in making metals, paper, paints, and fertilizers.

Acid and BasesAcid and Bases

Acid and BasesAcid and Bases

Acid and BasesAcid and Bases

Some Properties of Bases Produce OHProduce OH-- ions in water ions in water

Taste bitter, chalkyTaste bitter, chalky

Are electrolytesAre electrolytes

Feel soapy, slipperyFeel soapy, slippery

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

pH greater than 7pH greater than 7

Turns red litmus paper to blue “Basic Blue”Turns red litmus paper to blue “Basic Blue”

Uses of Bases• Bases are used in soaps (remember, bases are

slippery)• Bases are used to make paper, in oven cleaners, and

to unclog drains• Ammonia is a base and is used in many household

cleaners

Some Common Bases

NaOHNaOH sodium hydroxidesodium hydroxide lyelye

KOHKOH potassium hydroxide potassium hydroxide liquid soapliquid soap

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

Mg(OH)Mg(OH)22 magnesium hydroxidemagnesium hydroxide “MOM” Milk of magnesia“MOM” Milk of magnesia

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

Acid/Base definitions

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

Bases – produce OH- ions

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

Most acids produce H+ (H3O+) in water

Some bases produce OH- in water

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

ACID BASE

NEUTRAL

The pH Scale

Acid and Base strength is measured ona scale that ranges from 0 to 14.

Let’s get pHunky!

The The pH scalepH scale is a way of is a way of expressing the strength of acids expressing the strength of acids and bases. and bases. Under 7 = acidUnder 7 = acid

7 = neutral 7 = neutralOver 7 = baseOver 7 = base

NoteNote: Stronger acids: Stronger acids have have lower numbers & lower numbers & stronger bases have stronger bases have higher numbershigher numbers

What does “pH” mean?

• pH stands for “power of hydronium ion”

Detecting Acids and Bases

• You can detect an acid using an indicator.

• INDICATOR - A substance that changes color in the presence of an acid or a base.

INDICATORS• Litmus paper is an indicator An acid turns blue litmus paper red A base turns red litmus paper blue

• Cabbage juice can be used as an indicator

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 base)pH meter (7 is neutral, <7 acid, >7 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 Paper tests like litmus paper and

pH paperpH paper– Put a stirring rod into the solution and stir.Put a stirring rod into the solution and stir.– Take the stirring rod out, and place a drop Take the stirring rod out, and place a drop

of the solution from the end of the stirring of the solution from the end of the stirring rod onto a piece of the paperrod onto a piece of the paper

– Read and record the color change. Note Read and record the color change. Note what the color indicates.what the color indicates.

– You should only use a small portion of the You should only use a small portion of the paper. You can use one piece of paper for paper. You can use one piece of paper for several testsseveral tests..

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 Must be calibrated with a

buffer solutionbuffer solution

Neutralization Reaction• When an acid and a base are combined a salt

and water are formed.• Ex. HCl + NaOH → NaCl + H2O(acid) (base) (salt) (water)The pH of the salt should be close to neutral (pH 7)