Question

Assign oxidation numbers to all the atoms in each of the following. a. \(\mathrm{SrCr}_{2} \mathrm{O}_{7}\) b. \(\mathrm{CuCl}_{2}\) c. \(\mathrm{O}_{2}\) d. \(\mathrm{H}_{2} \mathrm{O}_{2}\) e. \(\mathrm{MgCO}_{3}\) f. \(\mathrm{Ag}\) g. \(\mathrm{PbSO}_{3}\) h. \(\mathrm{PbO}_{2}\) i. \(\mathrm{Na}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\) j. \(\mathrm{CO}_{2}\) k. \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Ce}\left(\mathrm{SO}_{4}\right)_{3}\) l. \(\mathrm{Cr}_{2} \mathrm{O}_{3}\)

Short answer

The oxidation numbers for the given compounds are: a. SrCr₂O₇: Sr(+2), Cr(+6), O(-2) b. CuCl₂: Cu(+2), Cl(-1) c. O₂: O(0) d. H₂O₂: H(+1), O(-1) e. MgCO₃: Mg(+2), C(+4), O(-2) f. Ag: Ag(0) g. PbSO₃: Pb(+2), S(+4), O(-2) h. PbO₂: Pb(+4), O(-2) i. Na₂C₂O₄: Na(+1), C(+3), O(-2) j. CO₂: C(+4), O(-2) k. (NH₄)₂Ce(SO₄)₃: N(-3), H(+1), Ce(+3), S(+6), O(-2) l. Cr₂O₃: Cr(+3), O(-2)

Step-by-step solution

Oxidation numbers for SrCr₂O₇

The oxidation numbers are: Sr(+2), Cr(+6), O(-2) b. CuCl₂

Oxidation numbers for CuCl₂

The oxidation numbers are: Cu(+2), Cl(-1) c. O₂

Oxidation numbers for O₂

The oxidation number is: O(0) d. H₂O₂

Oxidation numbers for H₂O₂

The oxidation numbers are: H(+1), O(-1) e. MgCO₃

Oxidation numbers for MgCO₃

The oxidation numbers are: Mg(+2), C(+4), O(-2) f. Ag

Oxidation numbers for Ag

The oxidation number is: Ag(0) g. PbSO₃

Oxidation numbers for PbSO₃

The oxidation numbers are: Pb(+2), S(+4), O(-2) h. PbO₂

Oxidation numbers for PbO₂

The oxidation numbers are: Pb(+4), O(-2) i. Na₂C₂O₄

Oxidation numbers for Na₂C₂O₄

The oxidation numbers are: Na(+1), C(+3), O(-2) j. CO₂

Oxidation numbers for CO₂

The oxidation numbers are: C(+4), O(-2) k. (NH₄)₂Ce(SO₄)₃

Oxidation numbers for (NH₄)₂Ce(SO₄)₃

The oxidation numbers are: N(-3), H(+1), Ce(+3), S(+6), O(-2) l. Cr₂O₃

Oxidation numbers for Cr₂O₃

The oxidation numbers are: Cr(+3), O(-2)

Key concepts

Introduction to Redox Reactions

Redox reactions are a fascinating part of chemistry that involve the transfer of electrons between two substances. Although they might seem complex, understanding them is crucial for comprehending many natural and industrial processes. These reactions can either be oxidation, where a substance loses electrons, or reduction, where a substance gains electrons. Looking at examples can simplify the concept: when iron rusts, it undergoes an oxidation process by losing electrons to oxygen. In this reaction, oxygen is reduced. Redox reactions play an essential role in various chemical phenomena, such as combustion, photosynthesis, and battery operations. They are always characterized by changes in oxidation states of the involved compounds. Mastering redox reactions is foundational for advancing in fields like biochemistry, pharmacology, and energy sciences. When approaching this topic, one has to focus on the concept of electron transfer, balance the overall electron gain and loss, and accurately assign oxidation numbers for each atom involved. This will help determine which atoms are oxidized or reduced.

Understanding Oxidation States

Oxidation states, sometimes referred to as oxidation numbers, are an essential part of redox reactions. They indicate how many electrons an atom can gain, lose, or share. Understanding them can seem tough, but a simple method involves following a set of rules. These rules help systematically assign oxidation numbers to atoms in a molecule.

• Elements in their natural form always have an oxidation number of zero. For example, in O₂, each oxygen atom has an oxidation number of 0.
• Fluorine, being the most electronegative element, always has an oxidation number of -1 in its compounds.
• Oxygen usually has an oxidation number of -2, except in peroxides like H₂O₂, where it is -1.
• Hydrogen has an oxidation number of +1, except in metal hydrides where it is -1.
• The sum of oxidation numbers in a neutral compound is zero, while in polyatomic ions, it equals the ion's charge.

By using these rules, you can assign oxidation states for molecules, as done in the exercise. Remember, the calculated values help track the transfer of electrons in redox reactions, so practice with different compounds will strengthen this skill.

Effective Chemistry Education Practices

Chemistry education can sometimes feel overwhelming due to the numerous concepts and technical details involved. However, utilizing effective study strategies can enhance understanding and make learning more engaging. Here are some educational tips tailored to chemistry students:

• Visual Learning: Use diagrams, visual aids, and molecular models to grasp the structure of molecules and visualize processes such as redox reactions.
• Practice Problems: Regularly solve exercises similar to the oxidation number assignments, as repetition is key to mastering chemical concepts.
• Group Study: Engage in study groups to discuss and solve complex problems collaboratively, which can lead to a better understanding through peer discussion.
• Interactive Tools: Leverage online simulations and virtual labs, which can provide hands-on experience with chemical reactions and their analysis without requiring physical materials.
• Connecting to Real Life: Relate chemical principles to everyday life scenarios to see their applications, making the learning process more relatable and memorable.

By incorporating these methods, students can find a balance between theoretical knowledge and practical application, ultimately demystifying intricate chemistry topics like oxidation states and redox reactions. With the right approach, each concept builds a strong foundation for further chemistry exploration.