There are several criteria to consider when choosing a suitable buffer. However, a good buffer is often selected based on the pKa (which measures acidic strength) or dissociation constant of the weak acid in a system. Factors such as temperature fluctuations and concentration can directly affect the pKa of a buffer solution.
Chemical buffers exist naturally as part of biological systems. For example, carbonic acid and bicarbonate anion help to keep the pH of human blood at between 6.8 and 7.8. Without buffers, many biological and physiological functions will not work properly. If blood becomes too acidic (metabolic acidosis) or too basic, for instance, it may lead to shock or even death.
Buffers also play a vital role in many industries as they help to maintain the product quality and maximise shelf life. For instance, most medicines require buffers for specific pH ranges to remain effective.
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What is a Buffer Solution in Chemistry?
Many chemical systems only work well within certain parameters. This is true for enzymes and other biological molecules, which can only function at a certain temperature, pH, and pressure range.
Beyond these range limits, the molecules will either break down or become unreactive. For example, most microorganisms cannot survive temperatures above 100°C. Likewise, bacterial growth is inhibited if the temperature drops to -20 ºC or less.
Adding buffer solutions to a system will ensure the pH level of that system stays within a desirable range. It may inhibit microbial growth or encourage sustained growth, such as in the case of fermented drinks.
Buffers are in dynamic equilibrium. This means the reactions go in opposite directions, as shown in the chemical equations below.
Good chemical buffers have the following properties:
- Dissociation constant – the ideal pKa (acidic strength) range is between 6 and 8. Most experiments involving biochemical reactions require this range to achieve optimal results.
- Solubility – as most acids and many bases are soluble in water, a buffer should also be water-soluble. This is especially important for systems that require biological buffers for biochemical reactions.
- Biological membranes – some biological experiments, for example medicine absorption by target tissues, require the exclusion of biological membranes. In other words, the buffer must not be able to pass through certain tissue or cellular barriers.
- Minimal ion interactions – ideally, buffers should not interfere with other ions in a system. If they do interact, the reaction should be negligible and reversible. Zwitterionic buffers are a good example of this. Also known as Good’s buffers, they have positive and negative charges on different constituent atoms of the same molecule.
- Change resistance – a good buffer must be able to resist pH changes when exposed to fluctuations in concentration (dilution vs. saturation), temperature, and chemical reactions.
- Chemical stability – a buffer must not react with the system in which it’s being used. Otherwise, it would not serve its intended purpose.
- UV absorption – an ideal buffer should not absorb UV rays at wavelengths that may be used for photometric readings.
Examples of Buffer Solutions
Buffer solutions always contain two components – a weak acid or base and its conjugate. Buffers are therefore considered conjugate acid-base pairs.
This means one acts as a proton (H+) donor and the other as a proton acceptor. However, not all conjugate acid-base pairs make useful buffers.
Some examples of common buffers used in chemistry are listed below.
Acetic acid and its conjugate base
Acetic acid (CH3COOH) and its conjugate base (CH3COO–) are mainly used in biochemical studies of enzymes.
Formic acid and its conjugate base
Formic acid (HCHO2) and its conjugate base (CHO2–) have antibacterial properties that hinder the growth of microorganisms.
Pyridine and its conjugate acid
Pyridine (C5H5N) and its conjugate acid (C5H5H+) play a role in the industrial synthesis of fungicides, herbicides, and antiseptics.
Ammonia and its conjugate acid
Methylamine and its conjugate acid
Methylamine (CH3NH2) and its conjugate acid (CH3NH3+) is an amine that can maintain the pH balance of some organic reagents.
What is the Purpose of a Buffer in Chemistry?
The main purpose of a buffer in chemistry is to maintain chemicals’ pH range and extend their shelf life.
This is helpful because chemicals are usually stored in a laboratory for a set period of time. Some are more stable than others, although most chemicals will deteriorate over time. This may be due to various reasons such as dilution or reaction.
The Application of Buffer Solutions in Pharmacy
Many biochemicals, including medicines, are unstable at certain temperatures and pH levels. Others are vulnerable to UV rays from sunlight. There’s also a chance biochemicals may react with gastrointestinal acids and enzymes, thereby reducing their effectiveness.
Buffers are therefore added to medicines to prevent them degrading before they’re absorbed into the bloodstream.
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