Arrhenius acid - any HA, H2A, H3A, or RCOOH substance

with an H+ to donate

Examples include HCl, H2SO4, H3PO4, and CH3COOH

Arrhenius base - any MOH, M(OH)2, or M(OH)3 substance

with an OH- to donate

Examples include NaOH, Ca(OH)2, and Fe(OH)3

Acids and bases react with one another in

NEUTRALIZATION reactions which produce water and a

salt.

HA + MOH --> HOH + MA

What volume of 0.25 M phosphoric acid is needed to

titrate 50 mL of 0.35 M barium hydroxide?

First, let’s write a balanced equation to relate the two

chemicals that are involved.

2H3PO4 + 3Ba(OH)2 --> 6H2O + Ba3(PO4)2

We know more about the barium hydroxide so we’ll begin with the

volume and molarity for the stoichiometry.

0.05 L Ba(OH)2(0.35 mol Ba(OH)2)(2 mol H3PO4)(1 L H3PO4) 1 L Ba(OH)2 3 mol Ba(OH)2 0.25 mol H3PO4

= 0.47 L H3PO4

Titration is a lab technique that involves reacting one substance of a known molarity with one of unknown concentration in order to determine

the unknown.

This problem is EXACTLY the solution stoichiometry from the previous unit. The only thing

that’s new is the word TITRATE.

Some acids are STRONG. This means that they

dissociate completely to give H+ ions and anions.

HCl ---> H+ + Cl-

There are 6 strong acids. They are HCl, HBr, HI, HNO3,

HClO4, and H2SO4.

Because STRONG species ionize completely, we can

easily find pH for them.

There are certain bases which are STRONG. They are the alkali metal hydroxides AND

Ca(OH)2, Sr(OH)2, and Ba(OH)2. Being STRONG

means they dissociate 100%.

You will see [ ] used in this unit. The [ ] mean equilibrium concentration (molarity). For

a strong species, the [ ] will be easy to discern.

pH is a measure of the acidity or basicity of a solution. Note

the H is capitalized. Why?

Mathematically, we can find pH = - log [H+]

Your calculator will do this for you easily.

What is the pH of a 0.3 M solution of HNO3?

HNO3 is a strong acid so we can find the pH readily.

[HNO3] = [H+]because HNO3 --> H+ + NO3

-

pH = - log [H+]pH = - log (0.3 M)

pH = 0.52

pH does not have units but what does it mean?

If pH < 7, then you have an ACIDIC solution.

When pH = 7, your solution is NEUTRAL.

If pH >7, then your solution is BASIC.

Acids are substances that:react with metals to produce H2

cause blue litmus to turn redtaste sour

have H+ ions

Bases are substances that:cause red litmus to turn blue

taste bitterfeel slippery

have OH- ions

There are 4 equations that work together to solve

problems.

pH = - log [H+]pOH = -log [OH-]pH + pOH = 14

[H+][OH-] = 1 x 10-14 = Kw

What is the pH, the pOH, the [H+], and the [OH-] of a

solution of 0.25 M Ca(OH)2?

Since Ca(OH)2 is a STRONG base, it dissociates

completely.

Ca(OH)2 --> Ca2+ + 2 OH-

What will the [OH-] be?Since there are 2 hydroxides for every one Ca(OH)2, the hydroxide molarity is 0.5 M.

pOH = -log [OH-]pOH = -log (0.5M)

pOH = 0.3pH + pOH = 14pH = 14 - pOHpH = 14 - 0.3

pH = 13.7 > 7 therefore basic

[H+][OH-] = 1 x 10-14

[H+](0.5M) = 1 x 10-14

[H+](0.5M) = 1 x 10-14

0.5 M 0.5 M

[H+] = 2 x 10-14 M

Every other acid is a weak acid and ionizes partially to produce

H+ ions in solution.

HC2H3O2 <--> H+ + C2H3O2-

Notice the double-headed set of arrows? This means the

reaction is at equilibrium. The forward equation occurs at the same time and same rate of

speed as the reverse reaction.

Weak acids and weak bases do not dissociate completely. They exist in equilibrium with their ions. This means that finding pH becomes more

challenging for weak species.