In order to understand what a buffer solution is, it’s firstly helpful to understand that many natural chemical reactions and biological processes require a specific pH range – from 0-14 – in order to take place. For example, the ideal soil pH to grow rice is 6. If the pH level becomes too basic or too acidic, the rice will either not grow properly or it will die.
A buffer solution is a type of solution that barely changes its pH even if a small amount of acid or base is added to it. It acts as a neutraliser for both acid and base. It is a combination of weak acid and conjugate base or vice-versa.
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Why is pH balance important?
Many synthetic and biological or natural processes require pH balance. A buffer solution is often necessary to maintain this balance. For example, an important natural buffer solution can be found in the blood. This buffer solution involves carbonic acid and bicarbonate ions:
H2CO3 + H2O <==> HCO3– + H3O+
The left side of the chemical equation represents the weak acid while the right side represents the conjugate base. Blood pH must be maintained between 6.8 and 7.8. If the pH level goes outside this range, a person may become seriously ill or die because many enzymes in the body necessary for various functions may stop working.
Microorganisms, including pathogens, optimally grow within the pH range of between 6.0 and 7.5. Most microorganisms die in environments with acidic pH of 4.6 and below, or a basic pH of 11 and above. This fact is important for the food processing industry.
What are buffer solutions used for?
Acid-base balance is crucial in many commercial and industrial processes. Among the processes that require maintaining a specific range of pH are:
- Drinks manufacturing (wine, beers, spirits, etc.)
- Food processing and preservation
- Aquaculture, aquariums, and fish tanks
- Agriculture, including hydroponics
- Drinking water treatment
- Sewerage treatment
- Swimming pool maintenance
- Renewable energy production
- Electroplating of mechanical components
- Manufacturing chemicals like fertilisers and colouring dyes for fabrics
- Manufacturing medicines
These various processes are sensitive to change in the pH levels. Hence, many of them require buffer solutions and controlled environments. For example, bicarbonate is commonly used as a buffer to maintain the pH level of swimming pools.
What is the pH of a buffer solution?
The pH levels of buffer solutions vary widely depending on the type of solution and specific acidity or alkalinity required by reactants, systems or processes. For example, during the fermentation process of making wine, the vat mixture must be maintained at an acidic level. The fermentation agent, yeast, prefers a pH range of between 4 and 6.
The ideal pH level range for fermenting red wine is between 3.5 and 3.8. The relatively high acidity is needed to counteract the tendency of potassium ions leaching from grape skins. Potassium leaching causes a rise in the pH level of the mixture.
To maintain the ideal acidity range of the wine fermentation mixture, a simple solution of saturated potassium bitartrate is used at 1% or 10 g/L concentration. This can give a pH level of 3.56. Meanwhile, an acetic acid solution of 0.1M concentration can provide a pH of 2.9.
The role of buffers in biochemical reactions
Buffer solutions are needed to maintain the efficient functions of organic substances in experimental settings. This is particularly true for some enzymes that act as catalysts for biochemical reactions. These classes of enzymes require slightly acidic to alkaline conditions to function:
- Transferases – these enzymes are responsible for transferring or moving functional groups from one molecule to another. One example is alanine aminotransferase which shuffles the alpha‐amino group between alanine and aspartate. These enzymes require a pH range of between 6.5 and 7.5. Phosphate buffers are commonly used to maintain this range.
- Hydrolases – these enzymes help cleave the molecular bonds of organic molecules through hydrolysis. Ideally, a pH of 8.0 is needed. You can use barbital buffers, Tris buffers, and phosphate buffers.
- Lyases – in terms of function, these enzymes are similar to hydrolases but they leave a double bond in one of the molecules. You can use the same buffers as the ones used in hydrolases to maintain a pH range of between 7.0 and 8.5.
- Isomerases – these enzymes transfer functional groups from one molecule to another, forming isomers (same formula but different molecular arrangement) of the molecules involved. The ideal pH range of 7.0 to 8.5 can be maintained using Tris buffers, phosphate buffers, and barbital buffers.
- Ligases – these enzymes help catalyse the formation of new molecular bonds. They condense and hydrolyse molecules that have high energy. They need a pH range of between 7.0 and 8.0. Tris buffers and phosphate buffers are most suited for these enzymes.
How do buffer solutions work?
To illustrate how buffer solutions work, here is a typical example of an acidic buffer solution – a mixture of ethanoic acid and sodium ethanoate. Ethanoic acid is a weak type of acid, which has a chemical equilibrium in an aqueous solution that can be written as follows:
CH3COOH (aq) <==> CH3COOH–(aq) + H+(aq)
When you add sodium ethanoate, more ethanoate ions will tip the balance further to the left. This means that this solution is acidic and has a lot of hydrogen ions but also has a lot of ethanoate ions. When you add an acid, the extra hydrogen ions will react with ethanoate ions to form ethanoic acid, removing the excess hydrogen ions.
When you add an alkali into the buffer solution, the excess hydroxide molecules will react with the ethanoic acid to form ethanoate ions and water. The hydroxide ions can also react with the hydrogen ions to form water.
Examples of buffer solutions
Buffer solutions are either acidic or alkaline solutions. These solutions remove excess hydrogen ions or excess hydroxide ions through chemical reactions. The exact by-product may vary depending on the type of buffers. Examples of common buffers are:
- Citrate additives – help reduce the discolouration of fruit
- Potassium citrate – an antioxidant and buffering additive commonly found in cakes, biscuits, and jam
- Sodium citrate – a versatile food additive that resists change in acidity. It is commonly added to jams and jellies
- Calcium citrates – typically used in carbonated drinks to regulate acidity
- Potassium tartrate – used as a buffer in wine making and bread production
Buffering agents and their pH range
Buffer solutions are combinations of weak acid and conjugate base or vice-versa. They are named depending on the buffering agents.
These are some simple buffering agents with corresponding useful pH range:
- Citric acid 2.1–7.4
- Acetic acid 3.8–5.8
- Monopotassium phosphate 6.2–8.2
- Borate 8.25–10.25
How to store buffer solutions
Different types of buffer solutions need specific environmental conditions for longer storage time. Typically, you can store a commercial grade technical buffer for up to two years if it remains in an unopened container. However, if you open it, it may only last between three and six months.
Conversely, alkali buffer solutions do not last very long when opened. The typical shelf life of these solutions is one month. The exposure to air shortens its shelf life.
Whether you have an acidic or basic buffer solution, it should be stored in closed plastic containers or within Stoppard flasks/bottles. It is also crucial to maintain the temperature of the storage room between 15 and 25°C. You may need to refrigerate it.
Where to buy buffer solutions
Depending on the type of buffer solutions and your purpose, you have a wide range of options. For instance, you can purchase a buffer solution for hydroponics gardening from a gardening store. You can also order online or from a chemical store.
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