biological chemistry

How to Calculate pH and pKa of a Buffer Using Henderson-Hasselbalch Equation?

Henderson Hasselbalch Equation Sample Problems

How to Calculate pH and pKa of a Buffer using Henderson-Hasselbalch Equation?

Henderson-Hasselbalch equation is a numerical expression which relates the pH, pKa and Buffer Action of a buffer. A buffer is a solution which can resist the change in pH. Chemically, a buffer is a solution of equimolar concentration of a weak acid (such as acetic acid – CH3COOH) and its conjugate base (such as acetate ion – CH3COO¯). In the previous post, we have discussed the Titration Curve of a weak acid and the Derivation of Henderson-Hasselbalch Equation. The characteristic shape of the titration curve of a weak acid is also described by the Henderson-Hasselbalch equation. In this chapter we will discuss the methods to calculate the pH or pKa of a buffer using Henderson-Hasselbalch equation using sample problems.

Learn more: Titration Curve of a Weak Acid (Acetic Acid)

Lean more: How to Derive Henderson-Hasselbalch Equation?

Henderson-Hasselbalch Equation is given as:

Hasselbalch equation


pH – the negative logarithm of H⁺ ion concentration in the medium.

pKa – the negative logarithm of Ka of the acid (Ka is the dissociation constant)

Proton acceptor – the ionized or deprotonated acid (example – CH3COO¯).

Proton donor – intact (non-ionized) weak acid (example – CH3COOH).

Let’s see some sample problems and solutions.

Problem-1: A mixture of 0.20M acetic acid and 0.30M sodium acetate is given. Calculate the pH of the medium if the pKa of the acetic acid is 4.76.

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biological chemistry

pH and pKa – Henderson-Hasselbalch Equation Deriving

ph and pKa Relationship

Henderson–Hasselbalch Equation
How to Derive Henderson Hasselbalch Equation?

Henderson-Hasselbalch equation is a simple expression which relates the pH, pKa and the buffer action of a weak acid and its conjugate base. The Henderson-Hasselbalch equation also describes the characteristic shape of the titration curve of any weak acid such as acetic acid, phosphoric acid, or any amino acid. The titration curve of a weak acid helps to determine the buffering pH which is exhibited around the pKa of that acid. For example, in the case of acetate buffer, the pKa is 4.76. This is the best buffering pH of acetic acid. Besides, at this pH the acetic acid (CH3COOH) and acetate ions (CH3COO¯) will be at equimolar concentration in the solution. This equimolar solution of a weak acid and its conjugate base will resist the change in pH by donating or taking up the H⁺ ions. (pH is the negative logarithm of hydrogen ion concentration in a medium.The pKa is the negative logarithm of Ka. The Ka is the dissociation constant (similar to the equilibrium constant) for the ionization reaction of an acid.)

Learn more: Titration Curve of a Weak Acid (Acetic Acid)

In the present post, we will see the derivation of Henderson-Hasselbalch equation from the ionization reaction of a weak acid. We also discuss the significance of Henderson-Hasselbalch equation.

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biological chemistry

Disaccharides: Properties, Structure, Formation and Examples (Short Lecture Notes)

Disaccharides Lecture Notes

(Carbohydrates Part 3: Properties, Structure and Examples of Disaccharides)

What are Disaccharides?

Disaccharides are carbohydrates which contain two covalently linked monosaccharide units. Sucrose, Maltose, Lactose, Trehalose and Cellobiose are naturally occurring disaccharides. The individual monosaccharide units in a disaccharide are called ‘residues’. All disaccharides are soluble in water

Glycosidic bonds links monosaccharide units

The monosaccharide units in disaccharides (and also in polysaccharides) are linked through a special type of covalent bond called Glycosidic bond (specifically O-glycosidic bond). O-glycosidic bond is formed by the reaction between the hydroxyl group of one monosaccharide with the anomeric carbon atom of the other. During the glycosidic bond formation, one molecule of water is eliminated as given in the diagram. Glycosidic bonds are strong covalent bonds and they can be hydrolyzed by treating with mild acids. The hydrolysis of the glycosidic bond of a disaccharide releases its corresponding monosaccharide units.

Structure of Glycosidic Bond

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biological chemistry

Monosaccharides: Definition, Structure, Characteristics, Classification, Examples and Functions

Biochemistry of Monosaccharides

Chemical Structure, Characteristics, Examples & Classification

Monosaccharides are Simplest Sugars

Monosaccharides are the simplest carbohydrates. They are polyhydroxy aldehydes or ketones with a carbon backbone. The carbon backbone in monosaccharides usually consists of 3 – 6 carbon atoms. The simplest monosaccharides are glyceraldehyde and dihydroxyacetone (with 3 carbons). The most abundant monosaccharide in nature is a 6 carbon sugar called glucose. Majority of the monosaccharides follow the empirical formula C(H2O)n. Monosaccharide with five or more carbon can predominantly exist as cyclic structures in the aqueous condition. All monosaccharides are colourless, crystalline solids and that are readily soluble in water but insoluble in nonpolar solvents. Most of the monosaccharides are sweet in taste.

More in Biochemistry: Lecture Notes, MCQ, PPTs, Videos

Polyhydroxy aldehydes

Chemical Structure of Monosaccharides

Ø  All monosaccharides are polyhydroxy (contain many hydroxyl groups) aldehydes or ketones.

Ø  The hydroxyl groups are attached to the carbon backbone.

Ø  The number of carbon atoms in the backbone of monosaccharides varies from 3 to 6.

Ø  The carbon backbone of monosaccharides is unbranched and individual carbon atoms are connected by single bonds.

Ø  Monosaccharides are broadly classified into Aldoses and Ketoses.

Ø  In the open chain conformation of a monosaccharide, one of the carbon atoms of the backbone is double bonded to an oxygen atom to form the carbonyl group (C=O).

Ø  If the carbonyl group is at the end of the carbon chain it will be an aldehyde group (R – COH) and thus the sugar formed will be an Aldose sugar.

Ø  Similarly, if the carbonyl group is inner to the carbon chain, it will be a keto group (C=O) and the sugar formed will be a Ketose sugar.

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biological chemistry

Carbohydrates Simple Lecture Notes: Definition, Types, Classification, Examples and Functions

Simple notes on carbohydrates

(Biochemistry of Carbohydrates: Introduction, Properties, Classification and Biological Significance)

Carbohydrates are polyhydroxy aldehydes or ketones

significance of carbohydratesCarbohydrates are the most abundant bio-macro-molecules on the earth. They are commonly known as sugars because most of them have a sweet taste. Chemically all carbohydrates are polyhydroxy (contain many hydroxyl, – OH, groups) aldehydes or ketones. All carbohydrates are hydrates of carbon and they contain C, H and O. The ratio of hydrogen and oxygen in the majority of carbohydrates will be in 2:1 as in water. Some carbohydrates also contain nitrogen, phosphorous and sulfur. Majority of carbohydrates, not all, have the empirical formula (CH2O)n. In biochemistry, carbohydrates are denoted as saccharides. The term saccharide is derived from a Greek word ‘sakkharon’ meaning sugar.

Green plants fix the energy of sunlight by photosynthesis. In photosynthesis, the light energy is converted into the chemical energy and it is stored in some carbohydrates such as glucose, fructose, sucrose, starch etc. The oxidative breakdown of these carbohydrates by respiration release the energy stored in them and this energy is utilized for the various metabolic activities of the cells.

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