Question

The oxidation number of oxygen in \(\mathrm{KO}_{3}, \mathrm{Na}_{2} \mathrm{O}_{2}\) is : (a) 3,2 (b) 1,0 (c) 0,1 (d) \(-0.33,-1\)

Short answer

The oxidation number of oxygen in KO3 is -0.33, and in Na2O2 is -1. The correct answer is (d) -0.33, -1.

Step-by-step solution

Identify Oxidation Numbers for Elements in K+ Ion

The potassium ion (K+) in potassium superoxide (KO3) carries a +1 charge since group 1 elements typically have an oxidation number of +1.

Calculate Oxygen's Oxidation Number in KO3

Let x be the oxidation number of oxygen in KO3. We know that the sum of oxidation numbers in a compound is zero. The formula KO3 implies there are three oxygen atoms. Thus, the equation is 1(+1) + 3(x) = 0. Solving for x gives x = -1/3.

Identify Oxidation Numbers for Elements in Na+ Ion

The sodium ion (Na+) in sodium peroxide (Na2O2) carries a +1 charge, which is characteristic of group 1 elements.

Calculate Oxygen's Oxidation Number in Na2O2

Let x be the oxidation number of oxygen in Na2O2. Applying the rule that the sum of oxidation numbers in a compound is zero, with two sodium ions and two oxygen atoms, we have the equation 2(+1) + 2(x) = 0. Solving for x gives x = -1.

Key concepts

Understanding Chemical Oxidation States

Chemical oxidation states, also known as oxidation numbers, are theoretical charges that an atom would have if the compound was composed of ions. They are essential for understanding redox reactions, which involve the transfer of electrons between species. An atom's oxidation state can vary depending on the chemical environment.

In our example with potassium superoxide (\textbf{KO}\(_3\)) and sodium peroxide (\textbf{Na}\(_2\)\textbf{O}\(_2\)), we attribute oxidation states to identify how electrons are distributed among the atoms in each compound. For alkali metals like potassium (K\(^+\)) and sodium (Na\(^+\)), the oxidation state is typically +1. Since potassium and sodium are in Group 1 of the periodic table, they tend to lose one electron, giving them a +1 charge.

Oxygen, however, typically has an oxidation number of -2, but in compounds like potassium superoxide and sodium peroxide, the presence of additional oxygen atoms and the overall charge neutrality requirement result in oxygen having non-typical oxidation numbers. It can be counterintuitive, and hence, identifying the correct oxidation numbers requires understanding both the general rules and the exceptions that apply to chemical compounds.

Balancing Redox Equations

Balancing redox equations is a crucial skill in chemistry that ensures the conservation of mass and charge during chemical reactions. Redox (reduction-oxidation) reactions are characterized by the change in oxidation numbers of atoms through the transfer of electrons. One substance gets oxidized (loses electrons) while another is reduced (gains electrons).

The process of balancing redox equations can be complex and often involves several steps: determining oxidation states, separating the reaction into half-reactions (oxidation half and reduction half), balancing the number of atoms and charges in each half-reaction, and finally combining the half-reactions. An important point when balancing redox equations is the need to add electrons to one side of a half-reaction to balance the charge, which are then canceled out when the two half-reactions are combined.

In electrochemical cells, for example, balancing redox equations is fundamental for understanding how batteries operate or how metals undergo corrosion. With the correct balancing of redox equations, students gain the power to predict reaction products and their quantities, a vital skill for both laboratory work and industry applications.

Physical Chemistry for JEE

Physical Chemistry is a significant portion of the Joint Entrance Examination (JEE) syllabus, which is a standardized test for admission to various engineering colleges in India. It involves the application of physical principles to understand the behavior of molecules and predict chemical reactions. Mastering topics such as chemical thermodynamics, electrochemistry, and kinetic theory is critical for success in JEE.

Questions on topics like oxidation numbers and balancing redox equations not only test a student’s understanding of the concepts but also their ability to apply this knowledge to solve complex problems. For JEE preparation, it’s important to have a thorough grasp of these physical chemistry topics through practice and understanding their practical applications.

Moreover, knowing how to approach problems systematically, as shown in the step by step solutions for finding oxidation states, prepares students to tackle the Physical Chemistry section confidently. JEE often includes questions that challenge a student's ability to interconnect different concepts, demonstrating the need for a solid understanding of fundamental principles like chemical oxidation states and the balancing of redox reactions.