PRACTICAL (2) Acid – based Equilibrium Clinical Analytical Chemistry CLS 231 PRACTICAL (2) Acid – based Equilibrium Lecturer: Amal Abu - Mostafa

Titration Acid base titrations Definition: it is a method for determining the concentration of a substance in solution by adding to it a standard reagent of known concentration using a suitable indicator

Acid base titrations The technique of titration is as follows: Titrant (standard solution) in the burette Unknown concentration solution (analyte) + suitable indicator → in the conical flask

Color in alkaline medium The indicator An indicator is a substance that undergoes a change in colour when the end-point of a titration is reached. The most commonly used indicators during titration are: methyl orange MO and phenolphthalein ph.ph. Indicator Color in acid medium Color in alkaline medium METHYLORANGE RED YELLOW phenolphthalein COLORLESS PINK

Acid base titrations An acid-base reaction is often called a neutralization reaction. This is because when you add just enough strong base to react exactly with a strong acid in a solution, we say the acid has been neutralized. One product of a neutralization reaction is always water. Acid + a base = water and a salt HCl (aq) + KOH (aq)  H20(L) + KCl (aq) The net reaction is: H+ (aq) + OH- (aq)  H20(L)

Acid base titrations 1-Neutralization of strong acid and base: When a strong acid and a strong base solution are mixed, a neutralization reaction occurs, and the products do not have characteristics of either acids or bases. Instead, a neutral salt and water are formed. Look at the reaction below: HCl (aq) + NaOH (aq)  H20(L) + NaCl (aq) . 2-Neutralization of strong base and weak acid: the resulting salt will be basic with PH greater than 7. Example: reaction between sodium hydroxide and acetic acid.

4-Neutralization of weak acid and weak base: 3-Neutralization of strong acid and weak base: The resulting salt will be acidic with PH less than 7. Example: reaction between hydrochloric acid and ammonium hydroxide. 4-Neutralization of weak acid and weak base: The salt formed show no change in PH. Example: reaction between acetic acid and ammonium hydroxide.

Determination of concentration of sodium hydroxide using standard solution of hydrochloric acid: Principle: Reaction between sodium hydroxide and hydrochloric acid according to the following equation: HCl+NaOH → NaCl+ H20 since both acid and base are strong, so we can use any indicator.

Data for experiment 1-Materials used: Burette. Funnel. 10ml pipette. Conical flask. Holder. White paper. 2-Reagents used: Solution of Sodium hydroxide. Standard solution of Hydrochloric acid (0.1M). Phenolphthalein (1-2 drops). Methyl orange (1-2 drops). Distilled water.

3. Shake the flask regularly to mix the content. Procedure: 1. Transfer (10 ml) of NaOH by pipette to a conical flask. 2. Add 1 drop of methyl orange then titrate with HCl till neutralization (indicator change from yellow to orange). 3. Shake the flask regularly to mix the content. 4. Repeat the experiment two times and then tabulate your result. 5. Repeat the experiment using ph.ph indicator, and compare the result.

6. Calculate the concentration of sodium hydroxide (mol/L) as follows: ( M x V) = (M\ x V \) n NaOH n \ HCl

Calculate the strength (g/L): strength= concentration x Molecular weight C = M × M.wt