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

2. 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

3. 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

4. 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

5. 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)

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

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

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