Concentration of ammonia in a solution

In summary, the conversation is about finding the concentration of ammonia in a solution with a pH of 8.3 and a given Kb value. The equation used is Kb=[OH-][NH4+]/[NH3] and the concentration of OH- and NH4 is found by calculating pOH = 14 - pH. The final answer is 2,21 \times 10^{-6}.
  • #1
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Hello all,

I had chemistry a long time ago, but now I am very rusty at it :frown: so I am hoping you can get me started with this problem I have;

A particular solution of ammonia (Kb = 1.8 x 10-5) has a pH of 8.3.
What is the concentration of ammonia in this solution?

Is it the concentration of NH3 I have to find? I know I can find [OH-] since I know the pH, but what does the final equation look like? Something like [tex]Kb=[OH-][NH4+]/[NH3][/tex]?

Thank you for any help!
 
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  • #2
NH4 and OH- is going to have same amount of equilibrium concentration gained from the NH3. So If you know the pH, then how do you find the pOH, and what is the concentration of OH-? Multiply both sides by NH3 and divide bothsides by Kb. What happens?
 
  • #3
Ok, so pOH = 14 - pH = 14 - 8,3 = 5,7. Concentration of OH- and NH4 is therefore [tex]1,995 \times 10^{-6}[/tex]? And then [tex] [NH3] = \frac{[OH^-][NH4^+]}{K_b}[/tex]?
 
  • #4
So plug the values and see what you get, I hope this answer agree with the true answer, does it?? If not tell me.
 
  • #5
I got [tex]2,21 \times 10^{-7}[/tex], which seems reasonable I guess. Maybe a bit low?!
 
  • #6
You don't have the answer? It should be reasonable right? because its the equilibrum concentration right?
 
  • #7
Nope don't have answer (yet) :(, but it seems kinda right.. Probably is equilibrum concentration..
 
  • #8
sveioen said:
I got [tex]2,21 \times 10^{-7}[/tex], which seems reasonable I guess. Maybe a bit low?!
I got [tex]2,21 \times 10^{-6}[/tex] instead.
 

1. What is the concentration of ammonia in a solution?

The concentration of ammonia in a solution refers to the amount of ammonia molecules present in a given volume of the solution. It is typically expressed in units of molarity (moles of ammonia per liter of solution) or parts per million (ppm).

2. How is the concentration of ammonia in a solution measured?

The concentration of ammonia in a solution can be measured using various techniques, such as titration, spectrophotometry, or ion-selective electrode methods. These methods involve reacting ammonia with a known reagent or using instruments to detect the amount of ammonia present in the solution.

3. What factors can affect the concentration of ammonia in a solution?

The concentration of ammonia in a solution can be affected by factors such as temperature, pressure, pH, and the presence of other chemicals. For example, increasing the temperature of a solution can cause more ammonia molecules to dissociate, increasing its concentration.

4. Why is it important to know the concentration of ammonia in a solution?

Knowing the concentration of ammonia in a solution is important for many reasons. Ammonia is a toxic gas and can be harmful to human health and the environment at high concentrations. Additionally, ammonia is commonly used in industries such as agriculture and manufacturing, so knowing its concentration is crucial for proper handling and safety measures.

5. How can the concentration of ammonia in a solution be controlled?

The concentration of ammonia in a solution can be controlled by adjusting the amount of ammonia added to the solution, as well as by controlling factors such as temperature, pressure, and pH. Diluting the solution with water can also decrease the concentration of ammonia. Additionally, proper storage and handling procedures can prevent the escape of ammonia gas, thereby controlling its concentration in a solution.

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