Dilutions
Adding water to an acid or a base dilutes the solution, making it less acidic or less basic.
- Water added to acid: The [H+] concentration of a solution decreases, and the pH increases towards 7.
- Each time the H+ concentration is diluted tenfold, the pH number goes up 1 unit.
- Water added to base: The [OH –] concentration of a solution decreases, which increases [H+] concentration, and the pH decreases towards 7.
***An acid can never be turned into a base by diluting it with water, and a base can never be turned into an acid by diluting it with water.
Diluting a solution reduces the number of moles of solute per unit volume, but the total number of moles of solute in solution does not change
The total number of moles of solute remains unchanged upon dilution, so you can use this equation:
M₁ x V₁ = M₂ x V₂
M₁ and V₁ are the molarity and volume of the initial solution, and M₂ and V₂ are the molarity and volume of the diluted solution.
Dilute solutions are less acidic and less basic than
more concentrated solutions.
• Dilution of an acid or a base results in a solution that
is increasingly neutral.
• It is not possible to go past a pH of 7 when diluting an
acid or a base.
Neutralization Reactions and Titrations
Neutralization:
A neutralization reaction between an acid and a base in aqueous solution produces an ionic compound (generically referred to as a salt) and water. It can be described as a double exchange reaction in which the two compounds exchange cations. The pH of the product approaches 7. This is because the H⁺ and OH⁻ ions are being converted into water molecules. As their concentrations decrease, the pH will move closer to 7.
Titrations:
A titration is a procedure in which a neutralization reaction is monitored with an indicator (such as phenolphthalein) allowing you to calculate the unknown concentration of an acid or base
If the solution is acidic, a standard base solution is added until it is neutralized and vice versa.
The end point is indicated by a color change and is when the number of H⁺ ions is equivalent to the number of OH⁻ ions. Calculations are based off of the following formula
(Volume of acid)(Molarity of H⁺) = (volume of base)(Molarity of OH⁻)
