Acids & Bases

So, what are acids?

• The word comes from the Latin word 'acere', which means sour. All acids taste sour
• Acids make a blue vegetable dye, litmus, turn red (indicator)
• Neutralizes bases (destroys the chemical properties of bases
• Produce H+ in aqueous solutions

And bases?

• They taste bitter
• ill restore the original blue color of litmus after having been reddened by an acid.
• Neutralize acids (destroys the chemical properties of acids)
• Produce OH- in aqueous solutions

Measure Acidity

If the substance is less than 7 on the scale, it is an acid.

However, for a base the substance has to have a pH greater than 7

What can we do with pH?

• pH doesn't just tell us if a solution is neutral, an acid, or a base...
• It also tells us the concentration of H+ ions in the solutions in moles/Liter

From this equation, we can find the concentration of H+ given the pH

Example Problem

It is the same structure of equation with pOH and OH- for bases

The Meaning of Acids and Bases

• There are multiple definitions of what it is to be an acid or a base
• One such example is the Arrhenius Definition

Arrhenius Definition

• An Arrhenius acid is a compound that increases the concentration of H+ ions that are present when added to water. These H+ ions form the hydronium ion (H3O+) when they combine with water molecules.
• An Arrhenius base is a compound that increases the concentration of OH- ions that are present when added to water.

The Brønsted-Lowry Definition

• Acids are defined as proton donors, whereas bases are defined as proton acceptors. A compound that acts as both a Brønsted-Lowry acid and base together is called amphoteric.This took the Arrhenius definition one step further, as a substance no longer needed to be composed of hydrogen (H+) or hydroxide (OH-) ions in order to be classified as an acid or base.

Finally, the Lewis Theory

• The Lewis theory of acids and bases states that acids act as electron pair acceptors and bases act as electron pair doners. This definition doesn't mention anything about the hydrogen atom at all, unlike the other definitions. Making it a much more versatile theory.

Neutralization of Acids and Bases

What is Neutralization?

• A special property of acids and bases is their ability to neutralize the other's properties. .

What does it do?

• In an acid-base (or neutralization) reaction, the H+ ions from the acid and the OH- ions from the base react to create water (H2O)
• Another product of a neutralization reaction is an ionic compound called a salt.

Titrations

• Titration helps us determine the concentration of an unknown substance from a known concentration. Typically, the know solution is added a known quantity of the the unknown solution until the reaction is complete. Often, an indicator is used to usually signal the end of the reaction, the endpoint.

Titration Curves

• We can graph the volume of the substance (x-axis) and the pH level (y-axis) in an acid base reactionto determine the titration curve
• The curve's shape is determined by the type of acid and base (ie strong/weak acid with strong/weak base)

A buffer is a solution containing a weak acid and its conjugate base

In the buffered region, the amount of strong base added is still not enough to neutralize completely the weak acid. Thus, the solution will now contain both acid and a significant amount of base. The acidity of buffer solutions changes little when they are diluted or when certain amounts of acids or bases are added.