pH and Titration Notes Honors Chemistry

pH measure of the strength of acids and bases pH = power of hydrogen pH = -log [H+] logarithmic scale – so when you change a number on the scale, you change by a factor of 10 pH 3 is 10 times less acidic than pH 2 pH 1 is 100 times more acidic as pH 3

pH of Common Substances

pOH measures strength of the hydroxide ion pOH = -log [OH-] highest value of pH or pOH = 14 lower value of pOH = stronger base pH + pOH = 14 if find one of the values, then subtract from 14 to find the other example: if pH is 3, then pOH is 11 (14-3 = 11)

Example pH Calculations [H+] = 1 x 10-5 M pH = -log (1 x 10-5) pH = 5 Calculate the pH for the following: [H+] = 1 x 10-2 [H+] = 3.0 x 10-6 [H+] = 8.2 x 10-8 [H+] = 9.5 x 10-11

Converting pH to [H+] use: 10-pH = [H+] example: pH = 5.3, so 10-5.3 = 5.01 x 10-6 M Calculate the [H+] for the following: pH = 2.37 pH = 7.25 pH = 11.05 pH = 6.50

Example pOH Calculations [OH-] = 4 x 10-3 M pOH = - log (4 x 10-3) = 2.40 Calculate the pOH for the following: [OH-] = 2.3 x 10-12 [OH-] = 5.8 x 10-5 [OH-] = 9.0 x 10-8 [OH-] = 7.45 x 10-3

Converting pOH to [OH-] use: 10-pOH = [OH-] example: pOH = 2.8, so 10-2.8 = 1.58 x 10-3 Calculate the [OH-] for the following: pOH = 11.2 pOH = 3.46 pOH = 8.77 pOH = 7.0

More pH/pOH Calculations A/B/N 3.2 x 10-3 1.26 x 10-5 10.3 7.89

Neutralization reaction between an acid and a base in which their acidic and basic properties disappear Acid + Base  Salt + Water salt = metal and a non-metal ex. HCl + NaOH  NaCl + H2O ex. HCl + Ca(OH)2  CaCl2 + H2O

Titration technique used by chemists to determine the unknown concentration of a substance using a neutralization reaction uses an indicator to tell when reaction has reached neutralization indicator – chemical that is one color in an acid and another color in a base end point – the point in the reaction when neutralization has occurred and the indicator changes color

Acid-Base Indicators   An acid – base indicator changes color when it is in a solution of a certain pH. Red litmus paper turns blue and is used as an indicator of a basic solution that would have a pH above 7. Blue litmus paper turns red and is used as an indicator of an acidic solution that would have a pH below 7. Phenolphthalein is also a common kind of acid – base indicator. It turns clear in an acid and pink in a base. http://www.middleschoolchemistry.com/multimedia/chapter6/lesson8#proton_transfer_illustration

Titration Equation when reaction in titration is neutral, moles of acid = moles of base moles = molarity (M) x volume (V) so use the equation: Moles Acid = Moles Base M1V1 = M2 V2

Titration Example 1 What is the molarity of a CsOH solution if 30.0 mL of the solution is neutralized by 26.4 mL of a 0.250 M HBr solution?

Titration Example 2 What is the molarity of a nitric acid solution if 43.33 mL of a 0.100 M KOH solution is needed to neutralize 20.0 mL of HNO3?

Titration Example 3 What is the concentration of a household ammonia cleaning solution if 49.9 mL of a 0.59 M HCl solution is required to neutralize 25.0 mL of ammonia solution?

Titration Example 4 A titration of 50 mL of an unknown concentration of NaOH solution uses a 0.5 M HCl solution. The buret containing HCl initially reads 49.8 mL and reads 22.5 mL after the end point is reached. What is the molarity of the NaOH solution?