Acids and Bases

Arrhenius acid – any HA, H2A, H3A, or R-COOH compound

where A- is any anionExamples: HCl, H2CO3, H3PO3, CH3COOH

Arrhenius base – any MOH, M(OH)2, or M(OH)3 compound where M+ is either a

metallic cation or the ammonium ionExamples: KOH, Mg(OH)2, Al(OH)3

Bronsted-Lowry acid – a proton donor Bronsted-Lowry base – a proton acceptor

In acids and bases, to what proton are they referring? Right, the H+ ion is the proton.

Substances that can behave as either an acid or a base are amphoteric or amphiprotic.

Bronsted-Lowry definition

Acid and Base Characteristics

Acids Have pH < 7 Cause blue litmus

paper to turn red Taste sour React with metals to

produce H2 gas

Bases Have pH > 7 Cause red litmus

paper to turn blue Taste bitter Feel slippery

Acids and bases react together to form water and a salt. A salt is a chemical compound created from the combination of an acid and a base.

HA + MOH HOH + MA acid base water salt

Neutralization Reactions

Titration is a lab procedure used to determine the concentration of an unknown solution. Titration problems look no different from the solution stoichiometry problems with which you are already familiar. The only difference is the use of the word titrate. Read “titrate” as “reacts with.”

Titration Problems

What mass of phosphoric acid is needed to titrate 150 ml of 0.4 M solution of potassium hydroxide?

First, since there are two chemicals reacting, a balanced equation is in order

H3PO4 + 3KOH K3PO4 + 3 H2O

Solving a Titration Problem

Next, you have the volume and the molarity of the KOH solution. You are looking for the mass of the phosphoric acid.

0.150 L KOH ( 0.4 mol KOH) (1 mol H3PO4)(98 g H3PO4) 1 L KOH 3 mol KOH 1 mol H3PO4

= 1.96 g of H3PO4 needed for reaction

Continuation of Titration Problem

pH is a measure of the acidity or basicity of a solution. Mathematically, it is expressed as

pH = - log [H+] where the brackets mean molarity

You may see H3O+ referred to as you are reading. H3O+ is the hydronium ion and simply means a hydrogen ion has attached to the water molecule.

For all intents and purposes, H3O+= H+ .

pH, pOH, [H+ ], [OH-]

You don’t have to understand logarithms to find pH.

It’s as easy as pushing a button on your calculator!

Ex: Find the pH of a solution with an [ H+ ] = 4.2 x 10-5 M.In your calculator: (-) log 4.2 x 10-5 and enter/ =. The pH = 4.38. Note that pH and pOH values do not have units on them. H+ and OH- have units of molarity as they are concentrations.

pH, pOH, [H+ ], [OH-]

A p function always means to take the negative logarithm of the term.

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

pH and pOH are relatedpH + pOH = 14

If you know one value, you can find the other by subtracting from 14.

pH, pOH, [H+ ], [OH-]

Water exists in equilibrium with its ions. H2O (l) H+ (aq) + OH- (aq)

We can write a relationship of the two ions called Kw.

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

This means that if you know one ion concentration, the other can easily be found by substitution into the equality to solve.

pH, pOH, [H+ ], [OH-]

If you are given pH, you can work backwards to find the hydrogen ion concentration.

Ex: The pH of a solution is 10.8. What is the [ H+ ] pH = - log [H+] 10.8 = - log [H+] divide through by -1 -10.8 = log [H+] On your calculator, push 2nd/shift log (-) 10.8. You

are raising 10 to the power of -10.8. You find the [ H+ ] = 1.58 x 10-11 M.

Finding [ H+ ] given pH