Finding Oxidation Numbers Practice Problems and Answers

Wayne Breslyn
28 Dec 201810:01
EducationalLearning
32 Likes 10 Comments

TLDRThis video tutorial walks viewers through the process of determining oxidation numbers for various elements in nine different compounds. By following general rules and applying them to each compound, the video encourages practice to master the skill. It covers neutral compounds, ions, and special cases like peroxides and highlights the importance of prioritizing rules to resolve conflicts. The strategy involves using known oxidation numbers to solve for the unknowns, ultimately aiming for a sum of zero in neutral compounds and matching the charge in ions.

Takeaways
  • 📚 The video explains how to find oxidation numbers for elements in compounds.
  • 🎯 Start by identifying the oxidation number of known elements to find the unknown.
  • 🌐 In neutral compounds, all oxidation numbers add up to zero.
  • ⚖️ For ions, oxidation numbers sum to the charge of the ion.
  • 🔢 Oxygen typically has an oxidation number of -2, except with fluorine and in peroxides.
  • 🤔 Nitrogen usually has a -3 oxidation number, but exceptions apply based on the compound.
  • 🌟 In compounds like O2, the oxidation number for the single element is zero.
  • 🧪 Peroxides, such as hydrogen peroxide (H2O2), are an exception for oxygen's oxidation number.
  • 🔄 When multiple rules apply, prioritize rules higher in the list if there's a conflict.
  • 🔢 In the cyanide ion (CN-), carbon has an oxidation number of +2, and nitrogen has -3.
  • 🍷 In asymmetrical molecules like ethanol (C2H5OH), different carbons may have different oxidation numbers.
Q & A

  • What is the main topic of the video?

    -The main topic of the video is how to find the oxidation numbers for each element in various compounds.

  • How does the video guide the viewer in practicing oxidation number calculations?

    -The video guides the viewer by providing a list of nine compounds, encouraging the viewer to find the oxidation numbers for one compound, then checking their work against the video, and progressively trying more challenging compounds.

  • What is the first compound discussed in the video and what is its significance?

    -The first compound discussed is nitrogen oxide (NO). It is significant because it introduces the concept of a neutral compound where all oxidation numbers add up to zero.

  • How does the video handle conflicting rules for oxidation numbers?

    -The video prioritizes the most important general rules at the top and sometimes ignores rules lower in the list if they conflict with the higher priority rules.

  • What is the oxidation number of nitrogen in nitrogen monoxide (N2O)?

    -The oxidation number of nitrogen in N2O is +1.

  • How does the video approach calculating oxidation numbers for ions?

    -For ions, the oxidation numbers of all elements add up to the charge on the ion. The known oxidation numbers are used to set up an equation to solve for the unknown oxidation number.

  • What is the oxidation number of chlorine in chlorine trifluoride (ClF3)?

    -The oxidation number of chlorine in ClF3 is +3.

  • How is the oxidation number of oxygen determined in compounds like O2, where it is a pure element?

    -In pure elements like O2, the oxidation number is zero since it is not combined with any other different element.

  • What is the oxidation number of manganese in the ion MnO4^-?

    -The oxidation number of manganese in MnO4^- is +7.

  • How does the video address the calculation of oxidation numbers for compounds with multiple carbon atoms, like ethanol (C2H5OH)?

    -The video explains that each carbon atom may have a different oxidation number if attached to different groups. For ethanol, one carbon has an oxidation number of -3, and the other has an oxidation number of -1.

  • What is a key takeaway from the video for calculating oxidation numbers?

    -A key takeaway is to use the general rules as a guide, but also to be flexible and adjust based on the specific compound, whether it's neutral or an ion, and to consider the unique circumstances of each element within the compound.

Outlines
00:00
📚 Understanding Oxidation Numbers

This paragraph introduces the concept of oxidation numbers and explains the process of determining them for various elements in nine given compounds. It emphasizes the importance of practice in mastering the calculation of oxidation numbers. The speaker provides general rules for calculating oxidation numbers, starting with the example of nitrogen oxide (NO), a neutral compound where all oxidation numbers add up to zero. The speaker also explains the strategy of using known oxidation numbers to find the unknown ones and highlights exceptions to the general rules, such as the case of dinitrogen monoxide (N2O).

05:02
🧪 Applying Rules to Determine Oxidation Numbers

The second paragraph delves into the application of oxidation number rules for different compounds, including ions. It covers the calculation for compounds like NO3- (the nitrate ion), O2 (oxygen gas), ClF3 (chlorine trifluoride), and others. The speaker explains how to handle exceptions, such as the peroxide ion (O2^2-), and provides strategies for dealing with compounds that contain only one type of element. The paragraph also discusses the oxidation numbers of elements in ions, like MnO4^-2 (permanganate ion) and CN^- (cyanide ion), emphasizing the need to add up oxidation numbers to the charge on the ion. The paragraph concludes with the example of Cr2O7^2- ( dichromate ion) and the challenges of determining oxidation numbers in asymmetrical molecules like ethanol (C2H5OH).

Mindmap
Keywords
💡Oxidation Numbers
Oxidation numbers, also known as oxidation states, are a system used in chemistry to keep track of electrons in reactions. They represent the hypothetical charge that an atom would have if all bonds were ionic. In the context of the video, the main theme revolves around calculating these numbers for various elements within compounds, which is essential for understanding redox reactions and the behavior of elements in chemical processes.
💡Neutral Compound
A neutral compound is a substance in which the sum of the oxidation numbers of all the atoms equals zero, indicating that there is no overall charge. This concept is crucial in the video as it is used to determine the oxidation numbers of elements in compounds like NO and N2O, where the sum of the oxidation states must balance out to zero.
💡Ion
An ion is an atom or molecule that has a net electric charge due to the loss or gain of one or more electrons. The video discusses how the oxidation numbers in ions add up to the charge of the ion, which is different from neutral compounds. This understanding is key to calculating the oxidation states in ions like the nitrate ion (NO3-) and the cyanide ion (CN-).
💡Redox Reactions
Redox reactions, short for reduction-oxidation reactions, involve the transfer of electrons between two species. Oxidation states are fundamental in identifying and analyzing redox reactions, as they help to track the changes in the oxidation numbers of elements. The video's focus on calculating oxidation numbers is directly related to understanding these types of chemical reactions.
💡Group 15 Elements
Group 15 elements, also known as the pnictogens, include nitrogen, phosphorus, arsenic, antimony, and bismuth. These elements typically have a -3 oxidation state when bonded to nonmetals, but their oxidation states can vary. In the video, nitrogen, a group 15 element, is highlighted as having an oxidation number of -3 in its compounds, which is important for calculating the oxidation numbers of other elements in the compound.
💡Peroxides
Peroxides are a class of compounds that contain a peroxide ion (O2^2−) in which two oxygen atoms are linked by a single bond and have a -1 oxidation state. The video points out that peroxides, such as hydrogen peroxide (H2O2), are an exception to the general rules for oxygen's oxidation state, which is typically -2 in most compounds.
💡Halogens
Halogens are the elements in group 17 of the periodic table, including fluorine, chlorine, bromine, iodine, and astatine. They are known for their high electronegativity and typically have an oxidation state of -1 when bonded to nonmetals. The video emphasizes that fluorine, a halogen, always has an oxidation state of -1, even in compounds like chlorine trifluoride (ClF3).
💡Transition Metals
Transition metals are elements in the d-block of the periodic table, known for their ability to form compounds with multiple oxidation states. The video briefly mentions transition metals, like manganese (Mn) in permanganate ion (MnO4^-), and explains how their oxidation states can be determined by the charge of the ion and the oxidation states of other elements in the compound.
💡Ethanol
Ethanol (C2H5OH) is an organic compound and a simple alcohol, commonly used as a beverage and in various industrial applications. In the video, ethanol is used as an example of a molecule where the oxidation numbers of carbon can vary depending on their bonding environment, highlighting the complexity of calculating oxidation states in organic molecules.
💡Practice
The video script emphasizes the importance of practice in mastering the skill of calculating oxidation numbers. By working through a series of examples with increasing difficulty, viewers are encouraged to apply the rules and strategies discussed, which is essential for becoming proficient in understanding and using oxidation numbers in chemistry.
💡Exceptions
Exceptions in the context of the video refer to special cases where the general rules for oxidation numbers do not apply. For instance, peroxides and the cyanide ion are exceptions where the oxidation states of oxygen and carbon differ from their usual values. Understanding these exceptions is crucial for accurately calculating oxidation numbers in a variety of compounds.
Highlights

The video explains how to find oxidation numbers for elements in compounds.

There are nine compounds covered in the video for practice.

Oxidation numbers in a neutral compound add up to zero.

Oxygen typically has an oxidation number of -2, except with fluorine and peroxides.

Nitrogen in nitrogen oxide (NO) has an oxidation number of +2.

For N2O (dinitrogen monoxide), each nitrogen has an oxidation number of +1.

In ions, oxidation numbers add up to the charge of the ion.

Nitrogen in the nitrate ion (NO3-) has an oxidation number of +5.

Oxygen gas (O2) has an oxidation number of 0.

In chlorine trifluoride (ClF3), chlorine has an oxidation number of +3.

Manganese in permanganate ion (MnO4-) has an oxidation number of +7.

Hydrogen peroxide (H2O2) is an exception for oxygen's oxidation number, which is -1.

In the cyanide ion (CN-), carbon has an oxidation number of +2, and nitrogen has an oxidation number of -3.

In the dichromate ion (Cr2O7-), each chromium atom has an oxidation number of +6.

Ethanol (C2H5OH) presents a challenge with different oxidation numbers for each carbon due to asymmetric bonding.

The video serves as a practical guide for mastering the calculation of oxidation numbers.

Transcripts

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Chemistry EducationOxidation NumbersNeutral CompoundsIons and ChargesChemical AnalysisElemental ValencyChemical PracticeTeaching VideoChemical BondingChemistry Rules