Chapter 8
Chemicals in action
An acid and base reaction occurs when a complete exchange of electrons between the proton donor and proton acceptor occurs. In this process a salt if formed. In the definition, a salt is a substance formed from an acid by its replaceable hydrogen either wholly or partially by a metal or an equivalent radicle. Example of salt formation
Mg+H2SO4→MgSO4+H2
Mg+HCl→MgCl2+H2
In the modern ionic theory, a salt is a compound of oppositely charged ions. From this point of view, there is no difference between NaCl and NaOH. Further, anhydrous aluminum chloride is not a salt since the bond is essentially covalent. But hydrated aluminum chloride is a salt since the bond is ionic bond and has both positive and negative charges.
Hydrolysis of salts
Hydrolysis is a term used to describe certain chemical reactions of double decomposition brought about by water. In salt hydrolysis, there is a reaction between the salt and water molecules. When the equilibrium exist between hydrogen and hydroxide ions in water is distorted
Kw = [H+][OH-]
Basicity and acidity
The basicity or acidity of the final solution is due to the tendency of the salt formed by neutralization to react with the water thereby partially reversibility process of neutralization. This partial reversal of neutralization due to the reaction of the water is the hydrolysis. The study of the hydrolytic behavior of various salts can be analyzed using two major approaches. The salts form by the strong acids and strong bases and the salts formed by the weak acids and the weak bases.
The salts of strong acids and strong bases
A strong acid is an acid that completely dissociate to give all their hydrogen ions. A strong base is a base that completely dissociate in water to give all it hydroxyl ions. Consider the hydrolytic behavior of NaCl; a salt formed by the combination of a strong acid (HCl), and a strong base (NaOH). The ions formed do not react with water because NaOH and HCl ionizes completely is solutions. Therefore, the strength of an acid is determined by the number of hydrogen ions present is the solution. The acid is said to the strong acid if it completely ionizes in water to give all the hydrogen ions, while the base is said to be a strong base if it ionizes in water to give all it hydroxyl ions.
Salts of weak acid and strong bases
An acid is said to be a weak acid if it ionizes partially in water to give hydrogen ions, if we consider sodium acetone Na2CO3 and sodium cyanide undergo hydrolysis to for a solution;
Consider the hydrolysis of sodium acetone
CH3cooNa↔CH3coo +Na+
CH3coo-+H2o↔CH3cooH+OH-
The acetone ions will react with water to give a weakly ionized acetic acid and hydroxyl ions hence the Ph. of the titration between a weak acid and a strong base is more than 7 and hence is basic.
The concept of molarity
The molarity of a substance is the number of moles of a substance in a 1000ml of water. To determine the molarity of unknown concentration, the concept of titration is applied. The standard solution is a solution containing a known concentration of a particular chemical species. The process by which the concentration of the species is determined is known as standardization or titration. The primary standard substances are analytically pure and by dissolving a known weight of the primary standard and diluting the definite value a solution of known concentration is really repeated. The standard solutions are, however, prepared form materials that are analytically pure. Such solutions must be standardized against a suitable primary standard.
Creating a solution of known concentration from table 1
Moles of sodium hydrogen carbonate in the sample
The mass of sodium hydrogen carbonate is 5 grams as recorded in table 1 , the molar mass of sodium hydrogen carbonate is 84.
The number of moles in 100ml of solution is = mass molar mass=5g84
= 0.0595moles
The molarity of the solution is usually given by the number of moles in a 1000ml or in 1litre of the solution
Molarity moles solutel solution=mass solutemolar mass solutel solute
= 0.0595x1000ml50ml
= 1.19 molar
Chapter 3
Atoms and periodic table
An atom is said to be the basis from which the matter is made. The atoms are very small particle to be visible by our own eyes. Therefore, scientists have been having an indirect way of determining the evidence that an atom does exist. An atom is composed of small particle called protons, neutrons, and electrons. These particles are described in terms of their physical properties. That is, mass and the charge. The proton and the neutron have equal or approximately the same mass. The charges in proton and electron are equal and in the opposite direction. A neutron as its name sound has no charge, which is it’s electrically not charged. The proton and the neutron are located at the middle of the center of the nucleus. Since the proton is positively charged then, the nucleus is positively charged. The electron usually move around the nucleus is their own orbits. The force of attraction between the positively charged proton and the negatively charged electrons hold the atom together. The number of electron and proton in an atom are equal and hence there net charge of the atom is zero.
Periodic table
Periodic table is formed by organization of the elements. The elements are arranged according to the atomic number. The atomic number is the number of neutron plus the number of proton in an atom. The periodic table is classified in term of the periods and the groups. Each element belonging to an individual group, or period exhibit similar chemical and physical properties. In the current periodic table, that is the figure 1, every horizontal row in the periodic table is called the period. Along the period, a gradual change in the chemical properties occurs from one element to the other (figure 1). This change in the chemical and physical properties occurs due to a change in the number of protons and electrons in an atom. The increase in the electron is important to the atom since the outermost electrons determine the chemical properties of an atom.
Work cited
C. Chen, S. T. Yang, W. S. Ahn, R. Ryoo. Chem. Commun. 3627 (2009).
T. Sakakura, J. C. Choi, H. Yasuda. Chem. Rev. 107, 2365 (2007); (b) L.-N. He, Z.-Z.
Yang,A.-H. Liu, J. Gao
S. Fukuoka, M. Kawamura, K. Komiya, M. Tojo, H. Hachiya, K. Hasegawa, M. Aminaka,H
Okamoto, I. Fukawa, S. Konno. Green Chem. 5, 497 (2003).
Figure 1
