Ephedrine sulfate is a salt of a weak base (ephedrine, Kb = 2.3 × 10-5 ). We can determine that it is a salt of a weak base from the counter ion (sulfate, SO4-2, is negatively charged). Because sulfate has two negative charges then it associates with two protonated ephedrine ions (BH+) to form a 2:1 salt ( (BH+)2SO4-2). When 1 mole of the salt dissolves in water it completely dissociates into 2 moles BH+ and 1 mole SO4-2. Protonated ephedrine acts as an acid and its Ka value can be calculated from Kb of ephedrine:
Lets say we have a solution containing 0.05 M ephedrine sulfate then its pH can be calculated using the pH equations for monoprotic weak acids as the following:
Note here that C = 0.05 × 2 = 0.1 M because this is a 2:1 salt. Thus, by having Ka = 4.35 × 10-10, and C = 0.1 M in the above equations we get pH = 5.18. Or an online pH calculator can be used to make this calculation.
Lets say we have a solution containing 0.05 M ephedrine sulfate then its pH can be calculated using the pH equations for monoprotic weak acids as the following:
Note here that C = 0.05 × 2 = 0.1 M because this is a 2:1 salt. Thus, by having Ka = 4.35 × 10-10, and C = 0.1 M in the above equations we get pH = 5.18. Or an online pH calculator can be used to make this calculation.
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