# Determining Buffer Systems: NH3/NH4NO3

• eku_girl83
In summary, the conversation revolved around determining whether certain solutions were buffer systems or not. The first solution, KH2PO4/H3PO4, was determined to be a buffer system because H3PO4 is a weak acid and H2PO4- is its conjugate base. The second solution, NaClO4/HClO4, was determined to not be a buffer system because HClO4 is a strong acid. The third solution, NH3/NH4NO3, was determined to be a buffer system as the pKb for ammonia is 4.75 and the pKa for NH4NO3 is 9.25, indicating that it can act as a buffer solution. The conversation also
eku_girl83
Here's my question:

State whether each of the following solutions is a buffer system or not.

a) KH2PO4/H3PO4
H3PO4 is a weak acid
H2PO4- is the conjugate base derived from the salt
thus, this is a buffer system

b) NaClO4/HClO4
not a buffer system b/c HClO4 is a strong acid

c) NH3/NH4N03
NH3 is the base and NH4NO3 is the acid, i suppose
but I'm not sure how to determine the relative strength/weakness of these.

Could someone tell me whether these are correct or not? And please help me with part c?

a, b OK.

c - it is a buffer. pKb for ammonia is 4.75 IIRC so the pKa is 9.25 - for the reaction

NH4+ <-> NH3 + H+

Last edited by a moderator:
eku_girl83 said:
NH3 is the base and NH4NO3 is the acid, i suppose
NH4NO3, by itself, is a salt and NH3 (or NH4OH) is the conjugate base derived from it.

Edit : Oops ! Didn't see Borek's post. Nevermind.

NH4N03 is weakly acidic and partially dissociates because NH4 itself is a weak electrolyte, remembering that NH3 is a weak base. Therefor [c] is also a buffer system.

You need to use the Henderson Hasselbalch equation to find the pH of a buffer solution. There are two similar forms of the equation for acidic and basic buffers. Thats how you can determine the strength (if you call it so) of a particular solution.

If you have an acid and its conjugate base, the buffer solution is called an acidic buffer. If you have a base and its conjugate acid, the buffer solution is called a basic buffer. As a base and its conjugate acid bear conjugate relationship, this is not really a great way to say it. However, buffers like ammonia/ammonium salt (nitrate, chloride etc) are basic buffers as ammonia for all practical purposes is an extremely weak acid and a strong base.

Cheers
Vivek

## 1. What is a buffer system?

A buffer system is a solution that resists changes in pH when small amounts of acid or base are added. It consists of a weak acid and its conjugate base, or a weak base and its conjugate acid.

## 2. How do you determine the buffer system for NH3/NH4NO3?

To determine the buffer system for NH3/NH4NO3, you need to identify the weak acid and its conjugate base. In this case, NH3 is the weak base and NH4NO3 is the conjugate acid. This makes NH3/NH4NO3 a buffer system.

## 3. What is the pH range of the NH3/NH4NO3 buffer system?

The pH range of the NH3/NH4NO3 buffer system is between 9.25 and 10.75. This range is determined by the pKa of NH3, which is 9.25.

## 4. How does the concentration of NH3 and NH4NO3 affect the buffer capacity?

The buffer capacity of the NH3/NH4NO3 system is directly proportional to the concentration of the weak base (NH3) and its conjugate acid (NH4NO3). A higher concentration of these components will result in a higher buffer capacity, meaning the solution can resist larger changes in pH.

## 5. Can the NH3/NH4NO3 buffer system be used in biological systems?

Yes, the NH3/NH4NO3 buffer system can be used in biological systems. It is commonly found in the human body, where it helps maintain a stable pH in bodily fluids such as blood and urine.

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