1. دکتر امید رجبی دانشیار گروه شیمی دارویی
شیمی عمومی
دکتر امید رجبی دانشیار گروه شیمی دارویی
REACH will present significant challenges to all of us. There’s still much water to flow under the bridge before the detailed requirements of REACH are set in tablets of stone.
However, there is one thing we can anticipate and that is that REACH will demand much greater supply chain co-operation on the use of chemicals.
From the chemical manufacturer, through the formulator, to the product manufacturer to the final retailer we will all have to work together far more, understand each others challenges, languages and contribution to a mutual value chain.
Today we want to share with you some ideas about how such partnerships can work. We don’t offer a panacea, nor do we imagine that our relationship is necessarily representative of those that you in this room may have, but we feel much of the learning from our experience can be interpreted constructively in your supply chains.

2. Chemistry and Calculations for the Hydrolysis of Salts
The last two years has woken the retail sector up to the risks presented by chemicals BUT today we don’t want to dwell on this

3. NaCl is the salt that comes from a strong acid and a strong base.
The ions of salts can have an influence on the pH of a solution.
Ions that come from a strong acid or base do not influence the pH.
WHY?
Since strong acids and bases are 100% ionized in water, the ions are unable to reform the molecular acid or the base in water.
HCl + H2O  H3O+ + Cl- “one way arrow”
NaOH + H2O  Na OH- + H2O “one way arrow”
NaCl is the salt that comes from a strong acid and a strong base.

4. Auto hydrolysis of water.
What would the pH of a sodium chloride solution 25oC)?
pH = 7
What gives rise to this pH?
Auto hydrolysis of water.
H2O + H2O ↔ H3O OH-

5. weak acid: HNO2 KNO2 A basic solution.
Salts that contain ions that come from a weak acid or base.
weak acid: HNO2
A salt containing the anion of the weak acid and the cation from a strong base.
KNO2
Add water: KNO2(s) + H2O  K+ + NO2- + H2O
Hydrolysis: NO2- + H2O ↔ HNO2 + OH-
A basic solution.

6. CHEMISTRY: KNO2(s)  K+ + NO2-
Calculate the pH of a 0.10 M KNO2 solution. Ka(HNO2) =
CHEMISTRY: KNO2(s)  K+ + NO2-
More Chemistry: NO2- + H2O ↔ HNO2 + OH-
Equilibrium: I C E
N/A
-X N/A X X
0.10-X N/A X X
KaKb = 1.0 x 10-14
Try dropping
pOH = -log[OH-] = 5.83
x =1.49 x 10-6 = [OH-]
pH = 14 – 5.83 = 8.17

7. Weak Base: (CH3)3N trimethylamine
Salts that contain ions that come from a weak acid or base.
Weak Base: (CH3)3N trimethylamine
A salt containing the cation of the weak base and the anion from a strong acid.
(CH3)NHCl trimethylammonium chloride
Add water: (CH3)NHCl (s) + H2O  (CH3)NH+ + Cl- + H2O
Hydrolysis: (CH3)NH+ + H2O ↔ (CH3)NHOH + H+
An acidic solution.

8. CHEMISTRY: (CH3)NHCl(s) + H2O  (CH3)NH+ + Cl- + H2O
Calculate the pH of a 0.10 (CH3)NHCl solution. Kb((CH3)NHCl ) =
CHEMISTRY: (CH3)NHCl(s) + H2O  (CH3)NH+ + Cl- + H2O
More Chemistry: (CH3)NH+ + H2O ↔ (CH3)NHOH- + H+ I C E
N/A
Equilibrium:
-x N/A x x
0.10-x N/A x x
KaKb = 1.0 x 10-14
Try dropping
pH = -log[H+] = 5.43
x =3.68 x 10-6 = [H+]

9. NH4CN(aq) Ka(NH4+) = 5.6 x 10-10 Kb(CN-) = 2.04 x 10-5
What if both ions of a salt come from weak acid and a weak base?
Then the Ka and Kb of the acid or base from which the ions come from must be compared.
NH4CN(aq) Ka(NH4+) = 5.6 x Kb(CN-) = 2.04 x 10-5
note: Ka was calculated from Kb(NH3) and Kb from Ka HCN
Since Kb(CN-) is greater than Ka(NH4+), the solution is basic.