Amphetamine (c9h13n) is a weak base with a pkb of 4.2. calculate the ph of a solution containing an amphetamine concentration of 225 mg>l

pH = 10.505

Explanation:

Molar mass of Amphetamine ( C9H13N) = 135 g/mol

Given that the concentration of Amphetamine = 225 mg/L

mass of Amphetamine in one Liter = = 0.225 g

Number of moles of Amphetamine in one liter =

= 0.001667 mol

∴ molarity = 0.0017 M

              C₉H₁₃N          +        H₂O -------->       C₉H₁₃NH⁺  +      OH⁻

I(M)         0.001667   M                                                  0                 0

C(M)            -x                                                                  x                 x

E(M)         0.001667 - x                                                   x                 x

Pkb = -log Kb = 4.2

∴ Kb = 6.309 x 10⁻⁵

Kb = 6.309 x 10⁻⁵

Equilibrium constant  = [C₉H₁₃NH⁺][OH⁻]/ [C₉H₁₃N]

6.309 x 10⁻⁵  = x² / 0.001667-x

where 0.001667 -x ≅ 0.001667

Then;

x² = 6.309 x 10⁻⁵  × 0.001667

x² =  1.0517103 × 10⁻⁷

x =

x = 0.00032 M

x = [OH-] = 0.00032 M

∴ pOH = -log [OH-]

pOH = -log (0.00032)

pOH =3.495

pH = 14 - 3.495

= 10.505

h let me think

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."