Acids

Examples:

HC2H3O2 vinegar

H2C6H6O6 ascorbic acid (Vitamin C)

H2CO3 carbonic acid (in sodas)

HCl hydrochloric acid (stomach acid)

H3PO4 phosphoric acid (in colas)

H2SO4 sulfuric acid (battery acid)

The hydrogens that appear first in the formula are called ACIDIC PROTONS, or just PROTONS for short.

When acids dissolve in water they lose their acidic proton to a water molecule

HCl + H2O H3O+1 + Cl-1

The H3O+1 ion that’s formed is called the HYDRONIUM ION

Strong acids: an acid that dissociates completely into hydronium ions. None of the original acid is left over.

Weak acids: an acid that only partially dissociates into hydronium ions. Some of the original acid is left over.

pH scale

0 7 14acidic basic

If pH = 7.0, the solution is neutral

As the hydronium concentration ([H3O+1]) increases, the solution becomes more acidic and the pH drops.

Bases

Examples:

Al(OH)3 Aluminum hydroxide (antacids)

Ca(OH)2 Calcium hydroxide (soil additive)

Mg(OH)2 Magnesium hydroxide (antacid)

NaOH Sodium hydroxide (lye)

NH3 Ammonia (cleaning solution)

Bases are usually ionic compounds that contain the hydroxide (OH-) group. Ammonia is an exception.

When bases dissolve in water, they increase the concentration of hydroxide ions (OH-1) in the solution. They can do this in one of two ways:

NaOH (s) Na+1 + OH-1

NH3 + H2O NH4+1 + OH-1

While ammonia does not have a hydroxide group, it increases the [OH-1] by reacting with water.

Strong bases: a base that ionizes completely when dissolved in water. None of the original compound remains. Example: NaOH

Weak bases: A base that only partially ionizes when dissolved in water. Some of the original compound is left over. Example: NH3

Acid and Base characteristics

Both are corrosive and will react with indicators

Acids have a sour taste.

Bases have a bitter taste and feel slippery.

Acid-Base reactions

The H+1 from the acid reacts with the OH-1 from the base to form water.

H+ + OH- H2O

This is called a reaction

Examples:

What would the products be if HCl and NaOH reacted?

HCl + NaOH H2O + NaCl

If HCl and KOH reacted?

HCl + KOH H2O + KCl

If HCl and Mg(OH)2 reacted?

HCl + Mg(OH)2 H2O + MgCl222

In general...

*A salt is any ionic compound that is NOT an acid or a base.

Titrations

Titrations allow the concentration of an acid or base to be determined using an acid-base reaction and an indicator.

1. Measure out a volume of the acid or base that has the unknown concentration.

2. Add small volumes of the other reactant until the indicator changes color.

3. Use the ‘magic equation’ to calculate the unknown concentration.

C1V1 = C2V2

C1 = unknown concentration

V1 = volume used for unknown

C2 = known concentration

V2 = total volume added of known concentration

Examples:

25 mL of HCl are titrated with 12.5 mL of 1.0 M NaOH. What is the concentration of the HCl?

C1(25 mL) = (1.0 M)(12.5 mL)

C1V1 = C2V2

C1 = 12.5/25

C1 = 0.5 M

The concentration of the HCl is 0.5 M

10 mL of NaOH are titrated with 10 mL of 1.0 M H2SO4. What is the concentration of the NaOH?

C1(10 mL) = 2(1.0 M)(10 mL)

C1V1 = C2V2

C1 = 20/10

C1 = 2.0 M

The concentration of the NaOH is 2.0 M

There are TWO acidic protons in H2SO4. The [H3O+] will be two times more concentrated than the original acid.