CHM1311 Oxidation States and Redox Reactions

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Questions and Answers

What type of reaction involves the transfer of a proton?

Redox reaction

Acid-base reaction (correct)

Precipitation reaction

Combination reaction

In the reaction Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s), which process occurs?

Precipitation

Reduction

Oxidation (correct)

Acid-base reaction

What does an oxidation state represent?

A theoretical parameter of electron bookkeeping (correct)

The number of protons in an atom

An observable property of a chemical reaction

The actual charge of an atom in a molecule

What is the oxidation state of Cl in HCl?

-1 Signup and view all the answers

When assigning oxidation states, what should you do if two rules contradict each other?

Follow the rule that appears higher on the list Signup and view all the answers

In the reaction NaI (aq) + AgNO3 (aq) → NaNO3 (aq) + AgI (s), what type of reaction is represented?

Precipitation reaction Signup and view all the answers

What does the charge of an atom calculate as?

#protons - #electrons Signup and view all the answers

What is the oxidation state of sodium (Na) when it forms Na+?

+1 Signup and view all the answers

What is the oxidation state of sulfur in S8?

0 Signup and view all the answers

What is the oxidation state of phosphorus in P2O5?

5 Signup and view all the answers

What is the oxidation state of chromium in CrO4^2-?

6 Signup and view all the answers

What is the oxidation state of calcium in CaH2?

2 Signup and view all the answers

In which of the following does hydrogen have an oxidation state of –1?

2 Signup and view all the answers

What is the oxidation state of carbon in CO?

-2 Signup and view all the answers

What is the oxidation state of oxygen in SO2?

-2 Signup and view all the answers

What is the oxidation state of xenon in XeF4?

6 Signup and view all the answers

What is the primary purpose of adding H+ ions during the balancing of half-reactions in acidic solution?

To balance the number of hydrogen atoms Signup and view all the answers

In a basic solution, what modification is made to the balancing procedure involving H+ ions?

For each H+, an OH– is added to both sides Signup and view all the answers

When combining H+ and OH– ions during the balancing process, what compound is formed?

Water (H2O) Signup and view all the answers

What is the function of the electrons in the balancing of half-reactions?

To balance the net charge on each side Signup and view all the answers

Which step may be necessary before combining the two half-reactions in redox reactions?

Multiplying the half-reactions by the least common denominator Signup and view all the answers

What is the process by which a substance loses electrons called?

Oxidation Signup and view all the answers

Which statement correctly describes an oxidizing agent?

It causes oxidation in another reactant. Signup and view all the answers

In the reaction Zn + Cu2+ → Zn2+ + Cu, which species is the reducing agent?

Zn Signup and view all the answers

What happens to the oxidation state of a reducing agent in a redox reaction?

It increases. Signup and view all the answers

Which of the following is a characteristic of reduction in redox reactions?

Gain of electrons Signup and view all the answers

In the half-reaction Zn → Zn2+ + 2 e–, what does the zinc atom do?

It loses electrons. Signup and view all the answers

For the reaction represented as 2Fe + 3CO2 → Fe2O3 + 3C, what is the role of Fe?

It is reduced. Signup and view all the answers

What mnemonic aids in remembering the concepts of oxidation and reduction?

LEO says GER Signup and view all the answers

What is the first step in the half-equation method for balancing redox reactions?

Write out the net ionic form of the reaction Signup and view all the answers

In the oxidation process, what happens to the oxidation state of copper (Cu) when it is transformed from Cu(s) to Cu2+(aq)?

It increases Signup and view all the answers

Which species is being reduced in the reaction where Cu(s) reacts with NO3–(aq) to form Cu2+(aq) and NO(g)?

NO3– Signup and view all the answers

What is the purpose of adding electrons to balance the half-reaction?

To balance the charges on both sides Signup and view all the answers

In an acidic solution, how would you balance the half-reaction ClO2(g) → ClO3–(aq)?

By adding H+ and H2O Signup and view all the answers

What happens to nitrogen (N) in the given redox reaction of Cu(s) with NO3–(aq)?

It is reduced Signup and view all the answers

When balancing the overall redox reaction, how do you ensure that the number of atoms and charges are equal on both sides?

By adjusting the coefficients of the reactants and products Signup and view all the answers

Which step is NOT involved in balancing redox reactions using the half-equation method?

Removing all electrons Signup and view all the answers

Study Notes

Chemical Reactions Categories

Acid-Base Reaction: Involves proton transfer, e.g., HCl + H2O → H3O+ + Cl–.
Precipitation Reaction: Formation of a solid, e.g., NaI + AgNO3 → NaNO3 + AgI(s).
Redox Reaction: Involves transfer of electrons, e.g., Zn + Cu2+ → Zn2+ + Cu.

Oxidation States and Electron Transfer

Oxidation State: A theoretical charge on an atom if electrons were removed from bonds.
Calculated as the difference between the number of protons and electrons.
Common oxidation states: H (+1), O (–2), Na (+1), F (–1).

Determining Oxidation States

Follow specific rules to assign oxidation states, prioritize higher rules if contradictory.
For polyatomic ions, calculate oxidation numbers using the overall charge.

Half-Reaction Method

Separation of Reactions: Redox reactions can be split into oxidation and reduction half-reactions.
Balance elements, then balance oxygen by adding H2O and hydrogen by adding H+.
Charge is balanced by adding electrons.

Examples of Oxidation States Calculation

In S8, S = 0 because it's a pure element.
In P2O5, P = +5 and O = –2.
In CrO42–, Cr = +6 and O = –2.
In CaH2, Ca = +2 and H = –1 (as part of a hydride).

Redox Agents

Oxidizing Agent: Causes oxidation in another species, itself reduced (oxidation state decreases).
Reducing Agent: Causes reduction in another species, itself oxidized (oxidation state increases).

Oxidation and Reduction Terminology

Oxidation: Loss of electrons (OIL - Oxidation Is Loss).
Reduction: Gain of electrons (RIG - Reduction Is Gain).
Example: Zn oxidizes to Zn2+, while Cu2+ reduces to Cu.

Example Redox Reactions

In reaction: Cu + NO3– → Cu2+ + NO, Cu is oxidized, and nitrogen in nitrate is reduced.
Overall reactions, such as those involving manganese (MnO4–), often require balancing steps.

Balancing Redox Reactions

For acidic solution, followed by adding water and H+ ions.
In basic solutions, add OH– for each H+, simplifying when combined.

Lead Oxidation in Environmental Testing

Example reaction: Pb + MnO4– → Pb2+ + Mn2+.
Percent composition calculation involves understanding the stoichiometry of the reaction and the mass of lead oxidized in the soil sample.

Additional Concepts

Monitoring oxidation states helps to identify agents and balance reactions in various mediums.
The practical application of these concepts can be observed in environmental chemistry and industrial practices.

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Description

This quiz focuses on the fundamental concepts of oxidation states and redox reactions as covered in CHM1311. Key chemical reactions such as acid-base, precipitation, and redox are explored through various examples. Test your understanding of electron transfer and reaction mechanisms in chemistry.