ACIDS AND BASESUNIT 10General ChemistrySpring 2010

The Importance

Of acids… Blood is controlled by buffers Citrus fruits (citric acid) Vinegar (acetic acid) Vitamin C (ascorbic acid) Aspirin (acetyl salicylic acid) Car batteries (sulfuric acid)

The Importance

Of bases… Baking soda Milk of magnesia Antacids have carbonates, bicarbonates

and hydroxides to neutralize acids Ammonia (cleaning products) Sodium hydroxide, aka: lye (oven and drain

cleaner)

How do you know you have… An acid?

Produces H+ in water Blue litmus paper turns red Sour taste Reacts on metal pH less than 7

Metal etched using acid

How do you know you have… A base?

Produces OH- ions in water (hydroxide ions) Red litmus paper turns blue Slippery feel Bitter taste (taste shampoo tomorrow

morning) pH higher than 7

pH

Means “potency of hydrogen” Refers to pondus hydrogenii (potential

hydrogen)

The pH Scale

Arrhenius Acids

Substance that ionizes in water to produce hydrogen ions (H+)

“ionization”- process by which covalent compounds form cations and anions Ex) HCl H+ + Cl-

Arrhenius Base

Substance that dissociates in water to release hydroxide ions (OH-)

“dissociation”- process by which ionic compounds separate into ions Ex) NaOH Na+ + OH-

Neutralization Reactions

An acid neutralizes a base to yield a salt and water.

Example A) Hydrochloric acid reacts with sodium hydroxide to give the salt sodium chloride and water.HCl + NaOH NaCl + H2O

Different acids yield different salts, but water is always a product

Neutralization Reactions

Example B)H2SO4 + 2 NaOH Na2SO4 + 2 H2O

The hydrogen ion (H+) from the acid is neutralized by the hydroxide (OH-) ion from the base.

These two ions combine to form water.

Identifying an Acid and Base

Each salt is composed of the cation (+) from the reacting base and the anion (-) from the acid.

Predict the acid and base that produce the following salts:

a) Potassium acetate, KC2H3O2

Let’s see some steps first.

Predicting Acids and Bases

1) Split the salt formula into ions2) Which ion gets H+? Write the formula3) Which ion gets OH-? Write the formula

A) Potassium acetate, KC2H3O2

KOH + HC2H3O2 KC2H3O2 + HOH

OPPOSITES ATTRACT!

Predicting Acids and Bases

Lithium fluoride, LiFHF + LiOH Li F + H2O

The pH Scale Revisited

What is pH again? It expresses the acidity of a solution; the

concentration of hydrogen ions Ranges from…

0 14 As pH decreases, the concentration of hydrogen ions

increases, and the concentration of hydroxide ions decreases.

In a neutral solution, the concentration of hydroxide ions and hydrogen ions are equal.

Acid-Base Indicators

Methyl Red Color change ~pH 5 Below pH 5: red Above pH 5: yellow At 5? Orange (only a portion has been

converted from yellow to red)

Acid-Base Indicators

Bromthymol blue Color change ~pH 7 Below pH 7: yellow Above pH 7: blue At 7: greenish

Acid-Base Indicators

Phenolphthalein Color change ~ pH 9 Below pH 9: colorless Above pH 9: pink At pH 9: very light pink