ACID-BASE TITRATION
In many situations, we want to get rid of the acidic properties of an acid completely, so we must neutralize the acid with a base. We can also neutralize a base with an acid. This is done cleaning up chemical spills, in disposing of waste industrial chemicals, and even within your own digestive track. There are situations when we may not know exactly how concentrated the acid or base that we are trying to neutralize is, so we may not know what volume we need to use. Remember that H+ makes acids acidic and OH- makes bases basic. In order for something to be completely neutral you need exactly 1 H+ for every OH-, like in water:
H+ (aq) + OH-(aq) à H2O
We can’t see the ions to count them, so chemists have a way of keeping track of the number of ions using a quantity called the mole. They measure concentration is moles per liter. This is called molarity and abbreviated M. Think of it like a percent, or parts per million. The higher the molarity, the more concentrated a substance is. 12M is as concentrated as you can get HCl.
For example, a concentration might be written as 2.0M, which would be said as 2 Molar.
The process of adding measured volumes of acid or base of known concentration to an acid or base of unknown concentration until neutralization occurs is called titration.
The point at which the neutralization has occurred is called the end point.
The end point is usually reached when a color change is noted.
The color change is produced by using an acid base indicator (usually phenolphthalein) that changes color when an acid or base is present.
TITRATION CALCULATIONS
The unknown concentration or volume can be calculated from the known volumes and the known concentration of the standard solution using this equation:
(MA)(VA) = (MB)(VB)
Ex) We have 500mL of 12M hydrochloric acid that have spilled. How many mL of 6M sodium hydroxide would we have to add to it so that it is completely neutralized?
Step 1: List your variables
MA – 12M
VA – 500mL
MB – 6M
VB - x
Step 2: Substitute the terms into the equation
(MA)(VA) = (MB)(VB)
(12M)(500mL) = (6M)(xmL)
Step 3: Solve for the missing variable
6000 = 6x à6000/6 = x à x = 1000mL
In order to exactly neutralize 500mL of 12M acid we need to add 1000mL of 6M base.