Acids and Bases (p. 256-261, 264-265). Acids Taste sour

Acids and Bases

(p. 256-261, 264-265)

Acids

• Taste sour

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.

Some Properties of Acids

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

ion attached to a water molecule)

þ Taste sour

þ Corrode metals

þ Electrolytes

þ React with bases to form a salt and water (neutralization reaction)

þ pH is less than 7

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

Acids

• Ionize when dissolved in water (they dissociate (break apart) into their ions; +, -).– This allows the water to conduct electricity (which

means they are electrolytes).

– Ex- HCl is an acid…when placed in water, it becomes H+ and Cl-

Do you remember what an ion is?

An ion is an atom that has lost or gained an electron giving it a positive

(+) or negative (-) charge.

Acids

– Acids produce Hydrogen Cations• Therefore, the formula for an acid must have H

in it (usually it will be at the beginning of the chemical formula only)–Ex. HCl, H2SO4

Acids

• The H+ will attach to H2O to form Hydronium ions (H3O+)

– Acids produce H3O+ in water

Most acids produce H+ (H3O+) in water

Strong vs. Weak AcidsSee Table on p. 258

Strong Acid• Ionize completely

• HNO3+ H2O H3O+ + NO3-

• strong electrolytes– (can conduct

electricity well)

Weak AcidDon’t ionize completely

(don’t produce as many ions)

CH3COOH + H2O H3O+ + CH3COO-

weak electrolytes

BASES

• Taste Bitter and Soapy• Feel Slippery

Some bases contain hydroxide ions, OH- , in their formulas, others don’t.

NaOH sodium hydroxide lye

KOH potassium hydroxide liquid soap

Ba(OH)2 barium hydroxide stabilizer for plastics

Mg(OH)2 magnesium hydroxide “MOM” Milk of magnesia

Al(OH)3 aluminum hydroxide Maalox (antacid)

Bases

– Those that don’t have OH in the formula will react with water to produce OH- ions.

• Base Water ammonium hydroxide

• All produce hydroxide ions, OH- , in water & conduct electricity (electrolytes).

Strong vs. Weak Bases

Strong Bases• Have OH and a metal

atom in their formula– (ex-NaOH)

• Dissociate (break apart) in water to give: OH- & metal ion

• ex. NaOH OH- + Na+

• Strong electrolyte

Weak BasesDon’t have OH in their

formula (ex-NH3)

ionize in water to produce OH- (water gives up an H), but doesn’t ionize completely

ex. NH3 + H2O NH4+ + OH-

Weak electrolyte

Some Properties of BasesProduce OH- ions in water

Taste bitter, chalky

Are electrolytes

Feel soapy, slippery

React with acids to form salts and water

(neutralization reactions)

pH greater than 7

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

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.

*TO BE NEUTRAL THE SUBSTANCE MUST HAVE EQUAL AMOUNTS OF H3O+ AND OH- IONS!!

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

*TO BE NEUTRAL THE SUBSTANCE MUST HAVE EQUAL AMOUNTS OF H3O+ AND OH- IONS!!

Let’s get pHunky!Let’s get pHunky!

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

7 = neutralOver 7 = base

Note: Stronger acids have lower numbers & stronger bases have higher numbers

What does “pH” mean?

• pH stands for “power of hydronium ion”• A strong acid (low pH..2 or 3) has a high

amount of Hydronium ions (H3 O+ )• A weak acid (higher pH…5 or 6) has a low

amount of Hydronium ions (H3 O+ )

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 indicatorAn acid turns blue litmus paper redA base turns red litmus paper blue

pH testing• There are several ways to test pH– Blue litmus paper (red = acid)– Red litmus paper (blue = basic)– pH paper (multi-colored)– pH meter (7 is neutral, <7 acid, >7 base)– Universal indicator (multi-colored)– Indicators like phenolphthalein– Natural indicators like red cabbage,

radishes

Paper testing

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)