Acid/Base: pH and pOH

What is the pH scale? The pH scale measures how acidic or how basic a solution is. It is a way to measure the concentration of hydrogen ions in solution. The pH of a solution can be measured using pH paper, litmus paper, indicators, or pH meters. The pH range of a solution is b/w 0 and 14.

The pH of water is 7.0. Any solution with a pH of 7 contains equal concentrations of H+ and OH- and is considered a neutral solution. The pH of an acid solution is less than 7.0. It contains more H+ than OH-. A lower number indicates more hydrogen ions. The pH of a base solution is greater than 7.0. It contains less H+ than OH-. A higher number indicates more OH- ions.

Calculating pH and pOH pH = -log[H+] pOH = -log[OH-] pH + pOH = 14.0 Use the formulas: pH = -log[H+] pOH = -log[OH-] pH + pOH = 14.0 [H+] = 10-pH [OH-] = 10-pOH

Guided Problem What is the [H+] of an NaOH solution if the pOH is measured to be 6.5? What is the pH of a solution that has a [OH-] of 5.8 x 10-9 ?

Neutralization and Buffers Neutralization Reaction - Acids react with bases to form water and a salt. In forming water, both hydrogen ions and hydroxide ions are equal in solution, therefore it is neutral Buffers – solutions containing ions that react with additional acids and bases to minimize their effects on pH. Blood plasma acts as a buffer to keep your blood pH to be about 7.4

Titrations Lab technique where an acid/base of known molarity (titrant) is added to a known volume of acid/base with unknown molarity At point of neutralization, the indicator will change color You can use the now known volume and molarity of titrant to calculate molarity of unknown solution (using MaVa = MbVb

Titration Setup

Guided Practice 3. Neutralization occurs when 35 mL of KOH is titrated into 25 mL of HNO3. If the molarity of KOH is 0.75 M, what is the molarity of the HNO3? 4. Mg(OH)2 + HCl