When a weak base (B) dissolves in water it reacts with it to produce hydroxyl ions (OH-) and the conjugate acid (BH+). At the same time some amounts of the products of the reaction (OH- ,and BH+ ) react to produce the base (B), this is called the reverse direction. At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction. At this point the concentrations of all species (OH- , BH+ , and B) remain constant in solution (does not change with time).
The ionization constant, Kb, can then be expressed as the following equation:
Thus, Kb is a constant that is equal to the hydroxyl ion concentration, [OH-], multiplied by the conjugate acid concentration, [BH+], and divided by the concentration of the weak base in solution, [B], at equilibrium.
Kb values for weak bases can range from being very small (e.g. urea, Kb = 1.5×10-14 at 25 °C) to being relatively large (e.g. ammonia, Kb = 1.74×10-5 at 25 °C).
Kb gives an insight into the extent at which the base reacts with water to produce an alkaline solution. A larger Kb value means that the base reacts more readily with water. For example, Assuming that we have two solutions with the same concentrations of urea and of ammonia (see above for Kb values), then it is expected that the hydroxyl ion concentration in the ammonia solution is larger than that in the urea solution. Because ammonia has a larger Kb value and would have more potential to produce alkalinity (hydroxyl ions) in solution.
Feel free to write comments, or questions?
The ionization constant, Kb, can then be expressed as the following equation:
Kb values for weak bases can range from being very small (e.g. urea, Kb = 1.5×10-14 at 25 °C) to being relatively large (e.g. ammonia, Kb = 1.74×10-5 at 25 °C).
Kb gives an insight into the extent at which the base reacts with water to produce an alkaline solution. A larger Kb value means that the base reacts more readily with water. For example, Assuming that we have two solutions with the same concentrations of urea and of ammonia (see above for Kb values), then it is expected that the hydroxyl ion concentration in the ammonia solution is larger than that in the urea solution. Because ammonia has a larger Kb value and would have more potential to produce alkalinity (hydroxyl ions) in solution.
Feel free to write comments, or questions?
No comments:
Post a Comment
Thank you for your comment.