Lab Activity 1: Total Acidity

Acidity depends on: Acid strength in solution (measured by the degree of hydrogen ion (H+) dissociation 1. Strong acids: almost totally dissociates, releasing their hydrogen ions for bonding to other ions (HCl) 2. Weak acids: Have their H ions strong bonded (only few released) CH3COOH

Concentration of acidic compounds in solution. (expressed in: %w/w, %v/v, ppm, M (moles/l), N (Equivalent Weight (EW/Volume) - EW = MW/Valency - Meq (milliequivalents) = Actual weight (W)/ EW - Number of equivalents of an acid or base: eq = N x Volume

Total Acidity A measure of all the H+ of both dissociated and undissociated acids in solution. Titratable acidity is used to approximate total acidity. Titratable acidity can be measured by: 1- reacting the acid present with a base such as NaOH to the end point (equivalence point or neutrality point( at which H+ are equal to OH- in solution) indicated by a color change of an indicator. 2. By a pH-meter

Titrations SA/SB –equivalence point is neutral. WA/SB –equivalence point is basic. WB/SA –equivalence point is acidic.

Titration Titration Titration – A standard solution with a known [ ] (the titrant) is used to determine the [ ] of an unknown solution. – The reaction that occurs is a neutralization reaction. standard solution (in buret) unknown solution

Equivalence point Equivalence point – Point in the rxn which equal amounts of H 3 O + and OH - exist. dramatic change in pH End Point – Point at which a color change is observed. The equivalence point and end point are not necessarily concurrent. Titration

equivalence point pH Volume of M NaOH added (mL) Titration of a Strong Acid With a Strong Base Solution of NaOH Solution of NaOH Solution of HCl H+H+ H+H+ H+H+ H+H+ Cl Cl - Na + OH - Titration Curve

Features of the Strong Acid-Strong Base Titration Curve 1.The pH starts out low, reflecting the high [H 3 O + ] of the strong acid and increases gradually as acid is neutralized by the added base. 2.Suddenly the pH rises steeply. This occurs in the immediate vicinity of the equivalence point. For this type of titration the pH is 7.0 at the equivalence point. 3.Beyond this steep portion, the pH increases slowly as more base is added.

The four Major Differences Between a Strong Acid- Strong Base Titration Curve and a Weak Acid- Strong Base Titration Curve 1.The initial pH is higher. 2.A gradually rising portion of the curve, called the buffer region, appears before the steep rise to the equivalence point. 3.The pH at the equivalence point is greater than The steep rise interval is less pronounced.

For Experiments follow the lab manual !!