(c) maam Queen

1. Chapter 2:
pH and Hydronium-ion
Concentration in Aqueous System

2. pH and Hydronium Ion
• Involves in parenteral admixture programs in
the hospital pharmacies

3. pH of admixed solution
• pH values below or above certain limits may
cause physical-chemical incompatibilities as
well as untoward side effects in patients who
receive them.

4. Instrument/s used to check the pH of
admixed solution
• Standardized pH meter equipped with glass
and calomel electrodes
• pH indicator paper or by calculation

5. Theory about acid/base
Theory Acid Base
Bronsted-lowry Proton donor Proton acceptor
Arrhenius H+ -OH
Lewis Electron pair Acceptor Electron pair
donor

6. Basic principles of Analysis
• pH
– Number of gram equivalent of H per liter of solution.
– Protolysis
• A process whereby a proton is transferred from one
molecule to another
– Autoprotolysis
• Process whereby there is a transfer of a proton from one
molecule to another identical molecule
– Amphoteric
• Property where a substance can act as acid or base.

7. • Henderson-hasselbalch equation
• pH= pKa + log [salt]/[acid]
• pH = pKa + log [conjugate base]/[base]

8. Computation ….
1. Calculate the pH of a solution which contains
3.7 x 10 -2 mole of HAc and 4.8 x 10 -2 mole
of Na Ac in a liter of solution. pKa = 9.26
2. A buffer solution containing 0.1 M each of
HAc and NaAc, is present with Ka of
1.8 x 10 -5 at 25 C. Find the pH of the
solution.

9. 3. What is the ratio of salt and acid conc. If the
solution has a pH of 4.5 and pKa of 4.76

10. Buffer capacity
• Ability of a buffer solution to resist changes in pH
upon addition of acid/alkali.
β = mole of SA or SB/ pH
Compute:
1. Determine the buffer capacity of the following
data:
Initial pH of 0.01 M of NaAc = 4.76
pH after adding NaOH = 4.85

11. Van slyke
• Was responsible for the quantitative
expression expression
• Amount of g/L of strong acid or strong base
required to be added to a solution to change
its pH by 1 unit
• Higher buffer capacity , lower change in pH