Ampholyte vs Amphoteric
We come across molecules, which we categorize as basic, acidic or neutral. Basic solutions show pH values higher than 7 and the acidic solutions show pH values, which are lower than 7. Solutions having pH value 7 are said to be neutral. There are some molecules, which differ from this normal categorization. Ampholytes are one such molecule.
What is Amphoteric?
Amphoteric is the ability of a molecule, ion or a species like that to act as a base and an acid. There are some molecules, which have both these properties under certain circumstances. There are some metal oxides and hydroxides, which are amphoteric. As example, zinc oxide, aluminum oxide, aluminum hydroxide, and lead oxides can be taken. In acidic mediums, they act as bases, and in basic mediums, they act as acids. The most common and well known amphoteric molecule is the amino acid, which can be seen in all the biological systems.
What is Ampholyte?
An ampholyte is a molecule having both basic and acidic groups. The best and most widely occurring common example for ampholyte is amino acids. We know that all the amino acids have a –COOH, -NH2 groups and a –H bonded to a carbon. The carboxylic group is the acidic group in the amino acid and the amino group acts as the basic group. Other than these, there is a –R group in every amino acid. The R group differs from amino acid, to amino acid. The simplest amino acid with R group being H is glycine. However, the R group in some amino acids contains additional carboxylic groups or amino groups. For example, lysine, histidine and arginine amino acids have additional amine groups. And aspartic acids, glutamic acids contain additional carboxylic groups. Further, some of them contain –OH groups, which can act as a base or acid under certain circumstances (tyrosine). Due to both acidic and basic groups, they generally have at least two pKa values (if there is more than one –NH2 group or –COOH group, then there will be more than two pKa values). Therefore, the titration curves of ampholytes are complex than the normal titration curves. In various systems, ampholytes can be present in various charged forms depending on the pH. For example, in an acidic solution, the amino group of the amino acids will be in the positively charged from, and the carboxyl group will be present as –COOH. In a basic pH solution, the carboxyl group will present in the form of an anion (-COO-), and the amino group will be present as –NH2. In human bodies, pH is close to 7.4. In this pH, amino acids present as zwitterions. In this case, the amino group is protonated and has a positive charge, whereas the carboxyl group is negatively charged. Therefore, the net charge of the molecule is zero. At this point, the molecule has reached its isoelectric point.
What is the difference between Ampholyte and Amphoteric?
• Amphoteric is the ability of a molecule to act as an acid or a base. Ampholytes are molecules which are amphoteric. Therefore, ampholytes have both acidic and basic groups.
• Zinc oxide, aluminum oxide, aluminum hydroxide, and lead oxides are amphoteric, which have different behaviors in acidic and basic solutions. However, these are not ampholytes. Amino acid is an ampholyte, which has both acidic and basic groups present in one molecule. Hence, it is amphoteric.