Alkaline Buffers

A buffer solution can be defined as a mixture formed by combining a weak base with its conjugate acid or a weak acid with its conjugate base. When you add either an acid or a base to a buffer solution, it doesn’t modify its pH.

A buffer solution can be of two types—acidic buffer solution (having pH less than 7) and alkaline buffer solution (having pH more than 7). The buffer solution serves as just a reference sample for pH measurement tools & electrodes and a reference for adjusting the ph of many other solutions. 

Alkaline buffers are made up of a weak base and the salt of that base. An alkali buffer solution is a combination of ammonium hydroxide & ammonium chloride in a specific proportion. These buffers are used in planted aquariums or extremely hard water, wherein phosphate buffers may cause algae or fog. 

Solutions with alkaline buffers 

The pH of an alkaline buffer solution is higher than 7. This weak base and one of its salts are widely used to make alkaline buffer solutions. 

A blend of ammonia solution & ammonium chloride solution is indeed a prominent example. The pH of the solution would’ve been 9.25 if they were blended in equal molar amounts. It makes no difference whatever concentrations you use, as much as they are all the same. 

Buffer solutions and their working 

A buffer solution must have components that will eliminate any hydrogen and hydroxide ions added to it; alternatively, its pH will alter. This is accomplished in various ways by acidic or alkaline buffer solutions. 

As is customary, we’ll use a blend of ammonia & ammonium chloride solutions.

Because ammonia is indeed a weak base, the equilibrium point will be much to the left: 

NH3[aq] + H20[l] ⇌ NH4+[aq] + OH–[aq] 

Ammonium chloride provides a bunch of additional ammonia to this. According to Le Chatelier’s Principle, this will shift the equilibrium position to the left even more. 

As a result, the solution will include the following key elements: 

• A quantity of ammonia that hasn’t been decomposed. 

• Ammonium ions in abundance from ammonium chloride. 

• There are already enough hydroxide ions in the fluid to make it alkaline. 

The presence of other molecules (such as water and chloride ions) has no bearing on the reasoning. 

Incorporating acid into the buffer solution 

There seem to be two ways to get rid of the hydrogen ions you’re putting in. 

Ammonia is used to remove it. 

An ammonium molecule is perhaps the most probable basic material that a hydroxyl group will target. Ammonium ions will be generated as a result of their reaction. 

NH3[aq] + H+[aq] ⇌ NH4+[aq] 

The hydrogen ions would be eliminated in large part, but not entirely. Because the ammonium ion is mildly acidic, several hydrogen ions would be liberated once again. 

Hydrogen ions are removed by reacting with hydroxide ions. 

Keep in mind that the interaction between ammonia and water had produced some hydroxide ions. 

 NH3[aq] + H20[l] ⇌ NH4+[aq] + OH–[aq] 

Water is formed when hydrogen ions mix with all these hydroxide ions. The balance shifts to substitute the hydroxide ions as quickly as this occurs. This continues again until the majority of the hydrogen atoms have been eliminated.

Due to the obvious equilibrium, not many hydrogen ions are eliminated, only the majority of them.

An alkali is added to this buffer solution. 

A simple reaction involving ammonium ions removes the hydroxide ions from the alkali. 

NH4+[aq] + OH–[aq] ⇌ NH3[aq] + H2O[l] 

Because the produced ammonia seems to be a weak base, it may react with water, making the process reversible. That indicates that the majority (though not all) of the hydroxide ions present in the solution have been eliminated.

Conclusion:

An alkaline buffer is a non-phosphate buffer that works with an acid buffer to increase pH and alkalinity (KH). Those buffers are used in planted aquariums or extremely hard water, where phosphate buffers may cause algae or cloud cover. Alkaline buffer solutions elevate pH and maintain a buffering range of 7.2 to 8.5. It is mild, harmless, and beneficial to the freshwater ecosystem. Alkaline buffers are distinguished from other buffers by the absence of phosphates. That makes it suitable for planted aquariums, where excess phosphate can promote algae development.