ACIDS & BASES…all you need to “get” for the test…

In 20 minutes!

DEFINITIONS

Acid Base

Produces hydronium in aqueous (water) solutions (Arrhenius)

Donates hydrogen ions to another species (Bronsted-Lowry)

Taste sour pH < 7 Turns litmus (and

many other indicators red)

Produces hydroxide in aqueous (water) solutions (Arrhenius)

Receives hydrogen ions from acid (Bronsted-Lowry)

Taste bitter; feel slippery

pH > 7 Turns litmus (and

many other indicators blue)

THE IONIZATION PROCESS…..A compound’s ability to behave as an acid

is that’s compound’s ability to “donate” hydrogen ions (protons).“Strong” acids release those ions VERY

readily and completelyFor example CH4 is NOT an acid—at all!

That donation is represented thusly:H2SO4 + H2O HSO4

1- + H3O1+ (1st ionization)

HSO41- + H2O SO4

2- + H3O1+ (2nd ionization)

IONS IN AQUEOUS SOLUTIONS EXIST IN EQUILIBRIUM… HSO4

1- + H2O SO42- + H3O1+

What you should notice:

HSO41- becomes SO4

2-; therefore, (donates H1+)

in the reverse, SO42- becomes HSO4

1- (receives H+)

H2O becomes H3O1+; therefore, (receives H+)

In the reverse, H3O1+ becomes H2O (donates H+)

Translation: for weak ionizations and/or dilute solutions, that are reversible (in equilibrium), acids become conjugate bases, and, conversely, bases become conjugate acids.

TRY THESE FOR EXAMPLES: HF + H2O H3O+ + F-

NH4+ + OH- NH3 + H2O

CO32- + H2O HCO3

- + OH-

CONSIDER: Hydronium ions in the presence of hydroxide

ions can form water! Of course, the leftovers ions form a “salt”. For example:

HCl(aq) + NaOH(aq) H2O(l) + Na+(aq) Cl-(aq)

Because both the acid and the base are “strong”, the resulting hydronium and hydroxide concentration are equal.

The resulting pH is neutral. The “salt” is sodium chloride.

Another example: HSO4

- + NaOH H2O(l) + Na+ + SO42- +

OH-

The resulting solution is still basic.

PH The actual measurements of

concentration result in the calculation of pH.

Pure water is defined by equal concentrations of hydrogen ions and hydroxide ions. [H3O+] = [OH-] = 1 x 10-7M

[H3O+] x [OH-] = 1 x 10-14 (memorize these

numbers)

THE SCALE Using the logarithmic function of those

concentrations, we get the pH scale:

Water has a pH of 7pH = -log [H3O+]

Higher concentrations of hydronium means a smaller log!2.34 x 10-4 [H3O+] = 3.63

Smaller concentrations mean higher logs!2.34 x 10-10 [H3O+] = 9.63

RELATING [HYDRONIUM] & [HYDROXIDE] Because a species is only an acid or a

base in water, the concentrations of these ions are related:

[H3O+] [OH-] = 1 x 10-14

Which means that as one concentration increases, the other decreases…. (don’t forget the constant.)

One can also take the pOH of the hydroxide concentration.

Interestingly, pH + pOH = 14

PRACTICAL EXAMPLES

MORE…

BUFFERS (A LITTLE EXTRA!)

Buffer- a solution that resists changes in pH when limited amounts of acid OR base are added.

Ions of “weak” acids and bases, by definition, mean ions that are available to receive or to donate hydrogen ions &/or hydroxide ions.

CO2(g) + H2O(l) H2CO3 (aq) H+ (aq) +

HCO3-(aq)

YOUR TURN… Compile 3 questions to

ask/clarify/review:

1.

2.

3.