Acids Bases MCQ-Questions Answers
Acids Bases questions answers in online learning chemistry contain 10 MCQ-questions for school college classes. Before participating in this quiz chemistry test, study carefully the acid base properties and concepts like Arrhenius theory in aqueous solution, Bronsted Lewary concepts, Lewis valence shell electronic theory, Hard soft acid base, or SHAB principle and pH scale of acids and bases in chemistry.
Arrhenius Theory in Aqueous Solution
In this domain page, we discuss briefly the modern ides about acids and bases for chemistry or chemical science. Our general ideas regarding acid and alkali based on Arrhenius concepts in which an acid is a compound molecule that yield H+ ion in water solution and the base is a compound molecule yields OH– in water solution and utilization readily form solvent or water. Hence Arrhenius’s theory very useful for explaining acid and bases in water solution but can’t explain the strength in glacial acetic acid or ammonia solution.
For example, in aqueous solution nitric and sulfuric acid (the main component of acid rain) completely dissociates and is almost equally strong. But when these acids are taken in glacial acid medium nitric acid much stronger than the other two acids. Hence solvent plays an important role in explaining acid base redox reactions. Boric acid is a weak acid but when boric acid mixed with sulfuric acid behaves as a strong acid with strong oxidizing properties. Arrhenius theory explaining the acid and bases neutralization reaction in liquid water solution only but it does not explain the properties in gas or solid-phase acid base reaction.
Oxoacids of Phosphorus in Chemistry
The oxidation number of the phosphorus atom in the oxoacids of phosphorus, hypophosphorous, phosphorus, phosphoric acid = +1, +3, and +5 respectively. With the increasing oxidation number acidic character also increases. Therefore, the acidic character of these acids should be in the order, H3PO4 < H3PO3 < H3PO2. But experimental observation is the reverse order
H3PO2 ≥ H3PO3〉H3PO4. The experimental order explained when we consider the structures of these phosphorus acids.
In the H3PO2 structural dimensions, one hydrogen atom attaches phosphorus through oxygen and another hydrogen bonding directly with phosphorus. Therefore, proton attached to oxygen has a far greater chance of dissociation than any direct chemical bond. Hence H3PO2 dissociates one proton in the solution. In a similar way, H3PO3 and H3PO4 dissociate two and tree protons respectively. In this series, the number of unprotonated oxygen, which is responsible for the enhancement of acidity. Dissociable protons increase from H3PO2 to H3PO4. Therefore, the overall inductive effect of the unprotonated oxygen decreases from H3PO2 to H3PO4. Hence the acidity slightly falls off in the order, H3PO2 ≥ H3PO3〉H3PO4.
Difference Between Bases and Alkalis
Alkalis are the substances of our environment dissolved in water to produce bases but all the bases are not dissolved in water. Hence all the alkalies are bases but all the bases are not alkalies. For example, Na2O is alkalis and base properties because it dissolved in water to produce NaOH. But metal hydroxide like Al(OH)3, Fe(OH)3, Zn(OH)2, etc does not dissolve in water but reacts with acids to produce salt and water. Therefore, these are bases but not alkalis.
Acid and Bases and Periodic Table
Acidic oxides react with water to give respective oxoacids. With the increasing oxidation number, electronegativity, electron affinity acidity increases but shielding electron of the central atom decreases the acidity of the substances. Therefore, the central chemical element plays an impotent role in the acidity of the substances.
- Generally, electronegativity and ionization energy increase left to right in the period of the periodic table with the increasing of atomic number. Hence the acidic character generally increases left to right in the periodic table.
- But electronegativity decreases top to bottom in the group of the periodic table. Hence the acidic character generally decreases top to bottom in the periodic table.
Among Na2O, MgO, As2O3, and N2O5, nitrogen has the highest oxidation number and electronegativity. Therefore, the order of acidic nature of these oxides, Na2O < MgO < As2O3 < N2O5.
pH Scale of Acids and Alkali
In acid solutions, the concentration of hydrogen ion is high and in alkaline solution low. Sorensen suggested the new way of expressing the concentration of hydrogen ion in logarithm form. The negative of the logarithm of H+ ion concentration or activity defined as pH scale. Therefore, pH = – log CH+. Now for the solution pH = 3, CH+ = 10-3 and pH = 8, CH+ = 10-8. Hence the neutral solution has pH =7. Any polar solution having pH less than seven will be acid and the solution having pH above seven will be alkaline.
Conjugate Acids and Bases in Chemistry
In 1923, Lowry and Bronsted introduces the new concepts of acids and bases. According to these new concepts, an acid is defined as a substance that has the tendency to lose a proton but a base is a substance that has the tendency to gain a proton. The free proton is not likely to occur in the solution and combine with solvents molecule. For example, in water, glacial acetic acid, ammonia, and ethyl alcohol solvents, the proton combines to form H3O+, CH3COOH2+, NH4+, and CH3CH2OH2+ respectively. The beauty of Bronsted-Lewary concepts reflects the fact that it contains all effects of Arrhenius concepts and further extended to explaining acid-base equilibrium in non-aqueous media.
Lewis Theory of Acids and Bases
A more here general theory for acids was proposed on the basis of the electronic configuration of valence orbital. According to Lewis, an acid is a substance (molecule, ion, or radical) which readily accept a lone pair of electron particles from the dinner substances, which would be the base. Acid is thus an electron pair acceptors and the base is a dinner of electron pair. For example, Et3N + BCl3 → Et2N : BCl3. It is an acid base neutralization reaction that can be followed with an indicator in chloro-benzene solution. There are no protons or OH groups involved. Therefore, the neutralization reaction means the formation of coordinate linkage to form an adduct complex. Hard soft acid base or HSAB-principle also based on lewis theory. This theory explains the stability of the complex in terms of electric polarization of soft and hard acids and bases.