Greater Minds Tutors

Introduction Before they are introduced to acids and bases, young chemistry students always think that sodium chloride (common salt) is everything there is to know about salts. However, from their knowledge of acids and bases, they also get to know about other substances, such as copper (II) tetraoxosulphate (VI), potassium trioxocarbonate (IV), ammonium chloride, calcium trioxonitrate (V) etc, which are classified as salts. These substances are the outcomes of the Arrhenius acid-base reactions. So, what is a salt? Definitions We will define a salt in terms of basicity (replaceable hydrogen ions) and neutralization. I) A salt is a substance formed when all or part of the replaceable hydrogen ions in an acid, are replaced by metallic ions (Na+, K+, Mg2+, Ca2+, Cu2+ etc) or ammonium ions (NH4+). This implies that every acid has its corresponding salts. The list below shows examples of some salts and their parent acids. 1. Acid : Hydrochloric acid (HCl) Salts : Sodium chloride...

p H & pH Scale The pH (hydrogen ions potential) is a measure of the acidity or alkalinity of a solution. The concept of pH was introduced by Sörensén in 1909 to bring about the convenience of working with very dilute solutions. To this effect, he developed a scale consisting of fifteen numbers (0 - 14), which is used in pH meter, for measuring the relative acidity or alkalinity in solutions. This scale is known as the pH scale. The numbers in the pH scale are the values of the negative logarithms of the hydrogen ions concentrations in such solutions. From the above, we can define pH as the negative logarithm of the hydrogen ions concentration [H+] to base 10. Mathematically, this is given as: pH = - log [H+] ..........................(i) Alternatively, the above equation can be expressed as pH = log 1/[H+] .........................(ii) From equation (ii), we can also define pH as the logarithm of the reciprocal of the hydrogen ions concentration to base 10. The...

In a layman's term, a base is the opposite of an acid. In other words, a base is everything an acid is not. Recall that in the Part I of this series, we looked at the definition of an acid using three different concepts. Similarly, we are going to define a base using the same concepts. Definition Lewis Bases According to G. N. Lewis, a base is any species that can readily donate a pair of electrons. The availability of lone pair(s) of electrons increases a substance's ability to behave as a base. Examples include H2Ö, ÑH3, Cl-, F- etc. They are also considered to be nucleophiles. Any species with an electron-rich centre is said to be a nucleophile. Brønsted-Lowry Bases According to Brønsted and Lowry, an acid is a proton donor, while a base is a proton acceptor. In other words, any substance that has the ability to accept a proton (hydrogen ion, H+) by donating a pair of electrons to it, is said to be a base. Examples are H2Ö, ÑH3, Br- etc. H2Ö(l) + H+(aq) <----...

Introduction Growing up, we used to think that any substance that burns is an acid, until we learnt about acids, bases and salts in our foundational chemistry class. It was then clear to us that there is more to acids than corrosivity, and not every substance that is corrosive, is an acid. Definition The definitions of an acid is based on three different concepts of acid-base reactions, namely the Lewis, Brønsted-Lowry and Arrhenius concepts. Lewis Acids According to G. N. Lewis, in acid-base reactions, the reactants undergo co-ordinate covalent bonding, in which one reacting species has the ability to accept a lone pair of electrons, while the other can readily donate a lone pair of electrons. A Lewis acid is an electron pair acceptor, because it has an empty orbital. Examples are H+, H3O+, Cu2+, Fe3+. Brønsted -Lowry Acids According to J. H. Brønsted and M. Lowry, an acid-base reaction involves the transfer of proton from one of the reactants to the other. A Brønsted-Low...

Half-life of a Reaction The half-life, t1/2, of a reaction is the amount of time it will take the concentration, [A], of a reactant to reduce to half its initial concentration, [Ao]. That is to say,               @ t1/2, [A] = [Ao]/2 ...……(i) The half-life of the various orders of reaction can be calculated by substituting the above equation into the respective integrated rate laws. ( a) Half-life of a Zeroth-Order Reaction Recall that the zeroth-order integrated rate law is given by:                  [A] = [Ao] - kt …………(ii)                  [Ao] - [A] = kt @ t1/2, [A] = [Ao]/2                  kt1/2 = [Ao] - ([Ao]/2)          ...

In our previous post, we looked at the overview of the rates of chemical reactions, where we studied the concepts and factors that affect the rates of reactions. In this post, we will be studying the rate law and the different orders of reaction, and how to determine them. Rate Law Consider the reaction:             mA + nB ----> Products The rate law states that the rate of a reaction is directly proportional to the active masses of the reactants. This implies that the concentration of the reacting species will determine how fast and how far a reaction can go. Using the above equation, the rate law can be expressed as:             rate & [A]^m[B]^n ..........(i)             rate = k[A]^m[B]^n ..........(ii) where, [A] = concentration of reactant A [B] = concentration of reactant B    & = sign ...