assigning oxidation numbers quiz

Assigning Oxidation Numbers

What is the oxidation number on N in Li 3 N?

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What is the oxidation number on N in N 2 O 5 ?

What is the oxidation number on hydrogen, what is the oxidation number on n in hno 3 , what is the oxidation number for cu in cuso 4 , what is the oxidation number for i 2 , what is the oxidation number for mn in mncl 2 , what is the oxidation number on cr 4+ , what is the oxidation number on f in if 7 , the sum of all oxidation numbers must equal.

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Chemical Reactions : Oxidation Numbers Quiz

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AP®︎/College Chemistry

Course: ap®︎/college chemistry   >   unit 4.

• Oxidation–reduction (redox) reactions

Worked example: Using oxidation numbers to identify oxidation and reduction

• Balancing redox equations
• Worked example: Balancing a simple redox equation
• Worked example: Balancing a redox equation in acidic solution
• Worked example: Balancing a redox equation in basic solution

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22.6: Assigning Oxidation Numbers

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Moving from studying the element iron to iron compounds, we need to be able to clearly designate the form of the iron ion. An example of this is iron that has been oxidized to form iron oxide during the process of rusting. Although Antoine Lavoisier first began the idea of oxidation as a concept, it was Wendell Latimer (1893-1955) who gave us the modern concept of oxidation numbers. His 1938 book The Oxidation States of the Elements and Their Potentials in Aqueous Solution laid out the concept in detail. Latimer was a well-known chemist who later became a member of the National Academy of Sciences. Not bad for a gentleman who started college planning on being a lawyer.

Assigning Oxidation Numbers

The oxidation number is a positive or negative number that is assigned to an atom to indicate its degree of oxidation or reduction. In oxidation-reduction processes, the driving force for chemical change is in the exchange of electrons between chemical species. A series of rules have been developed to determine oxidation numbers:

• For free elements (uncombined state), each atom has an oxidation number of zero. \(\ce{H_2}\), \(\ce{Br_2}\), \(\ce{Na}\), \(\ce{Be}\), \(\ce{K}\), \(\ce{O_2}\), \(\ce{P_4}\), all have an oxidation number of 0.
• Monatomic ions have oxidation numbers equal to their charge. \(\ce{Li^+} = +1\), \(\ce{Ba^{2+}} = +2\), \(\ce{Fe^{3+}} = +3\), \(\ce{I^-} = -1\), \(\ce{O^{2-}} = -2\), etc. Alkali metal oxidation numbers \(= +1\). Alkaline earth oxidation numbers \(= +2\). Aluminum \(= +3\) in all of its compounds. Oxygen's oxidation number \(= -2\) except when in hydrogen peroxide \(\left( \ce{H_2O_2} \right)\), or a peroxide ion \(\left( \ce{O_2^{2-}} \right)\) where it is \(-1\).
• Hydrogen's oxidation number is \(+1\), except for when bonded to metals as the hydride ion forming binary compounds. In \(\ce{LiH}\), \(\ce{NaH}\), and \(\ce{CaH_2}\), the oxidation number is \(-1\).
• Fluorine has an oxidation number of \(-1\) in all of its compounds.
• Halogens (\(\ce{Cl}\), \(\ce{Br}\), \(\ce{I}\)) have negative oxidation numbers when they form halide compounds. When combined with oxygen, they have positive numbers. In the chlorate ion \(\left( \ce{ClO_3^-} \right)\), the oxidation number of \(\ce{Cl}\) is \(+5\), and the oxidation number of \(\ce{O}\) is \(-2\).
• In a neutral atom or molecule, the sum of the oxidation numbers must be 0. In a polyatomic ion, the sum of the oxidation numbers of all the atoms in the ion must be equal to the charge on the ion.

Example \(\PageIndex{1}\)

What is the oxidation number for manganese in the compound potassium permanganate \(\left( \ce{KMnO_4} \right)\)?

The oxidation number for \(\ce{K}\) is \(+1\) (rule 2).

The oxidation number for \(\ce{O}\) is \(-2\) (rule 2).

Since this is a compound (there is no charge indicated on the molecule), the net charge on the molecule is zero (rule 6).

So we have:

\[\begin{align*} +1 + \ce{Mn} + 4 \left( -2 \right) &= 0 \\ \ce{Mn} - 7 &= 0 \\ \ce{Mn} &= +7 \end{align*}\nonumber \]

When dealing with oxidation numbers, we must always include the charge on the atom.

Another way to determine the oxidation number of \(\ce{Mn}\) in this compound is to recall that the permanganate anion \(\left( \ce{MnO_4^-} \right)\) has a charge of \(-1\). In this case:

\[\begin{align*} \ce{Mn} + 4 \left( -2 \right) &= -1 \\ \ce{Mn} - 8 &= -1 \\ \ce{Mn} &= +7 \end{align*}\nonumber \]

Example \(\PageIndex{2}\)

What is the oxidation number for iron in \(\ce{Fe_2O_3}\)?

\[\begin{align*} &\ce{O} \: \text{is} \: -2 \: \left( \text{rule 2} \right) \\ &2 \ce{Fe} + 3 \left( -2 \right) = 0 \\ &2 \ce{Fe} = 6 \\ &\ce{Fe} = 3 \end{align*}\nonumber \]

If we have the compound \(\ce{FeO}\), then \(\ce{Fe} + \left( -2 \right) = 0\) and \(\ce{Fe} = 2\). Iron is one of those materials that can have more than one oxidation number.

The halogens (except for fluorine) can also have more than one number. In the compound \(\ce{NaCl}\), we know that \(\ce{Na}\) is \(+1\), so \(\ce{Cl}\) must be \(-1\). But what about \(\ce{Cl}\) in \(\ce{NaClO_3}\)?

\[\begin{align*} \ce{Na} &= 1 \\ \ce{O} &= -2 \\ 1 + \ce{Cl} + 3 \left( -2 \right) &= 0 \\ 1 + \ce{Cl} - 6 &= 0 \\ \ce{Cl} - 5 &= 0 \\ \ce{Cl} &= +5 \end{align*}\nonumber \]

Not quite what we expected, but \(\ce{Cl}\), \(\ce{Br}\), and \(\ce{I}\) will exhibit multiple oxidation numbers in compounds.

• The oxidation number is a positive or negative number that is assigned to an atom to indicate its degree of oxidation or reduction.
• In oxidation-reduction processes, the driving force for chemical change is in the exchange of electrons between chemical species.
• Six rules for determining oxidation numbers are listed.
• Examples of oxidation number determinations are provided.

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15 questions, what is the oxidation state of the iron ion fe3+, which ion has an oxidation state of -2, what does the oxidation number represent, why is it important to assign oxidation numbers in chemical reactions, what does a positive oxidation number indicate, how do oxidation numbers help in balancing chemical equations, what is the purpose of systematic nomenclature of chemical compounds, what is the oxidation number of sulfur in s8, in the compound uf6, what is the oxidation number of uranium, what is the oxidation number of fluorine in uranium hexafluoride (uf6), which statement about the oxidation state of hydrogen is correct, what is the oxidation state of chlorine in the chlorate ion (clo3-), when assigning oxidation numbers, what does the sum of all oxidation states in a neutral compound equal to, if sulfur is oxidized in a reaction from -2 to 0, what is its change in oxidation number, in a redox reaction, which element typically has a -1 oxidation state when found in a molecule, description.

Learn about oxidation numbers and how atoms gain or lose electrons to form attractions with other atoms. Explore examples such as the iron ion Fe3+ with an oxidation state of +3 and the oxygen ion O2- with an oxidation state of -2.

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What Are the Rules for Assigning Oxidation Numbers?

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Electrochemical reactions involve the transfer of electrons . Mass and charge are conserved when balancing these reactions, but you need to know which atoms are oxidized and which atoms are reduced during the reaction. Oxidation numbers are used to keep track of how many electrons are lost or gained by each atom. These oxidation numbers are assigned using the following rules.

Rules for Assigning Oxidation Numbers

• The convention is that the cation is written first in a formula, followed by the anion . For example, in NaH, the H is H-; in HCl, the H is H+.
• The oxidation number of a free element is always 0. The atoms in He and N 2 , for example, have oxidation numbers of 0.
• The oxidation number of a monatomic ion equals the charge of the ion. For example, the oxidation number of Na + is +1; the oxidation number of N 3- is -3.
• The usual oxidation number of hydrogen is +1. The oxidation number of hydrogen is -1 in compounds containing elements that are less ​ electronegative than hydrogen, as in CaH 2 .
• The oxidation number of oxygen in compounds is usually -2. Exceptions include OF 2 because F is more electronegative than O, and BaO 2 , due to the structure of the peroxide ion, which is [O-O] 2- .
• The oxidation number of a Group IA element in a compound is +1.
• The oxidation number of a Group IIA element in a compound is +2.
• The oxidation number of a Group VIIA element in a compound is -1, except when that element is combined with one having a higher electronegativity. The oxidation number of Cl is -1 in HCl, but the oxidation number of Cl is +1 in HOCl.
• The sum of the oxidation numbers of all of the atoms in a neutral compound is 0.
• The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion. For example, the sum of the oxidation numbers for SO 4 2- is -2.
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Quiz Oxidation Numbers

Take this quiz after watching the video on assigning oxidation numbers to atoms in molecules and ions. Once this is done this will help you practice the rules. Oxidation numbers can be used to balance equations using oxidation number and ion electron method.

A quiz to test your knowledge on oxidation number determination

1. Which of the following is a False statement?

2. Which substance is being oxidized in the following reaction? 2 HCl (aq) + Zn (s) → ZnCl 2(aq) + H 2(g)

3. What is the oxidation number of Cr in K 2 Cr 2 O 7 ?

4. What is the oxidation number of Cl in HClO2?

5. What is the oxidation number of Mn in MnO 4 –

6. What is the oxidation number of O in O 2 F 2

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