Can someone help me with this problem?

[Patrick Essio 1H]

Hello!
I am doing one of the practice midterm worksheets and I came across this problem that I am struggling with. Can someone provide some insight?

[Angela Hung 1H]

First you want to find the concentration of OH- in solution, which you get by raising 10 to the -2.94 power, which is the given pOH value. Then, use the equation Kw=Ka x Kb to find Kb. When setting up your ice table, you already know the equilibrium concentration of OH- which is what you got when you raised 10 to the -2.94 power. Since the concentration of OH- in solution before the reaction was 0, you know the change or 'x' will be that value. Instead, your x value which you are trying to find will be the initial concentration of NH3. That gives you x-(whatever value you got for 10^-2.94) as your equilibrium concentration value for NH3.

Hope that helps!

[Erin Haisan 1B]

Hello! First, we have to find the hydroxide concentration (OH) using the pOH value, which we would do by calculating 10^-2.94. This value will be used to calculate x, which is the concentration of NH3. Next, use an ice table, then replace the usual x's with the value of 10^-2.94 since we are solving for NH3, not the hydroxide concentration. Next, find the Kb value since we are solving for a base, not an acid (Ka), using Kw=Ka*Kb. Set your ice table equation equal to the Kb value, then solve for x. Hope this is helpful!