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Chapter 5: Problem 108

Calculate the oxidation number of manganese in the following compounds. Group compounds with the same oxidation number and describe any trends. (a) \(\mathrm{MnO}\) (b) \(\mathrm{Mn}_{2} \mathrm{O}_{3}\) (c) \(\mathrm{MnO}_{2}\) (d) \(\mathrm{MnO}_{3}\) (e) \(\mathrm{Mn}_{2} \mathrm{O}_{7}\) (f) \(\mathrm{Mn}(\mathrm{OH})_{2}\) (g) \(\mathrm{Mn}(\mathrm{OH})_{3}\) (h) \(\mathrm{H}_{2} \mathrm{MnO}_{4}\) (i) \(\mathrm{HMnO}_{4}\) (j) \(\mathrm{CaMnO}_{3}\) (k) \(\mathrm{MnSO}_{4}\)

Short Answer

Expert verified
The oxidation states of manganese range from +2 to +7, often increasing with more oxygen atoms.

Step by step solution

01

Identifying Oxidation Rules

Before calculating, recall that the oxidation number of oxygen is typically -2, and hydrogen is +1. We'll apply these rules to find the oxidation number of manganese in each compound.
02

Calculate Oxidation Number for Each Compound

Start with the formula: the sum of oxidation numbers in a neutral compound is zero and in an ion is the charge of the ion.
03

Step 2a: Compound (a) \( \mathrm{MnO} \)

In \( \mathrm{MnO} \): \( x + (-2) = 0 \), so \( x = +2 \). Therefore, the oxidation number of Mn is +2.
04

Step 2b: Compound (b) \( \mathrm{Mn}_{2} \mathrm{O}_{3} \)

In \( \mathrm{Mn}_{2} \mathrm{O}_{3} \): \( 2x + 3(-2) = 0 \), \( 2x - 6 = 0 \), \( 2x = 6 \), so \( x = +3 \). The oxidation number of Mn is +3.
05

Step 2c: Compound (c) \( \mathrm{MnO}_{2} \)

In \( \mathrm{MnO}_{2} \): \( x + 2(-2) = 0 \), \( x - 4 = 0 \), \( x = +4 \). The oxidation number of Mn is +4.
06

Step 2d: Compound (d) \( \mathrm{MnO}_{3} \)

In \( \mathrm{MnO}_{3} \): \( x + 3(-2) = 0 \), \( x - 6 = 0 \), \( x = +6 \). The oxidation number of Mn is +6.
07

Step 2e: Compound (e) \( \mathrm{Mn}_{2} \mathrm{O}_{7} \)

In \( \mathrm{Mn}_{2} \mathrm{O}_{7} \): \( 2x + 7(-2) = 0 \), \( 2x - 14 = 0 \), \( 2x = 14 \), \( x = +7 \).The oxidation number of Mn is +7.
08

Step 2f: Compound (f) \( \mathrm{Mn(OH)}_{2} \)

In \( \mathrm{Mn(OH)}_{2} \): Oxygen is -2, hydrogen is +1. Therefore, \( x + 2(-2+1) = 0 \), \( x + 2(1) = 0 \), \( x = +2 \). The oxidation number of Mn is +2.
09

Step 2g: Compound (g) \( \mathrm{Mn(OH)}_{3} \)

In \( \mathrm{Mn(OH)}_{3} \): \( x + 3(-2+1) = 0 \), \( x + 3(1) = 0 \), \( x = +3 \). The oxidation number of Mn is +3.
10

Step 2h: Compound (h) \( \mathrm{H}_{2} \mathrm{MnO}_{4} \)

In \( \mathrm{H}_{2} \mathrm{MnO}_{4} \): \( 2(+1) + x + 4(-2) = 0 \), \( 2 + x - 8 = 0 \), \( x = +6 \). The oxidation number of Mn is +6.
11

Step 2i: Compound (i) \( \mathrm{HMnO}_{4} \)

In \( \mathrm{HMnO}_{4} \): \( +1 + x + 4(-2) = 0 \), \( 1 + x - 8 = 0 \), \( x = +7 \). The oxidation number of Mn is +7.
12

Step 2j: Compound (j) \( \mathrm{CaMnO}_{3} \)

In \( \mathrm{CaMnO}_{3} \): \( +2 + x + 3(-2) = 0 \), \( 2 + x - 6 = 0 \), \( x = +4 \). The oxidation number of Mn is +4.
13

Step 2k: Compound (k) \( \mathrm{MnSO}_{4} \)

The sulfate ion \( \mathrm{SO}_{4}^{2-} \) has a total charge of -2. Therefore, \( x - 2 = 0 \), \( x = +2 \). The oxidation number of Mn is +2.
14

Group Compounds by Oxidation Number

Now, group the compounds:- Oxidation number +2: \( \mathrm{MnO}, \mathrm{Mn(OH)}_{2}, \mathrm{MnSO}_{4} \)- Oxidation number +3: \( \mathrm{Mn}_{2} \mathrm{O}_{3}, \mathrm{Mn(OH)}_{3} \)- Oxidation number +4: \( \mathrm{MnO}_{2}, \mathrm{CaMnO}_{3} \)- Oxidation number +6: \( \mathrm{MnO}_{3}, \mathrm{H}_{2} \mathrm{MnO}_{4} \)- Oxidation number +7: \( \mathrm{Mn}_{2} \mathrm{O}_{7}, \mathrm{HMnO}_{4} \)
15

Observe and Explain Trends

Manganese exhibits multiple oxidation states, from +2 to +7, often increasing with the number of oxygen atoms in the compound due to its higher valency with more electronegative elements like oxygen.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Chemical Compounds
Chemical compounds consist of atoms of different elements bonded together, forming a unique substance with its own properties. The compounds we are examining all involve manganese (Mn) bonded with elements like oxygen (O), hydrogen (H), calcium (Ca), and sulfur (S). Each of these elements contributes to the overall characteristics of the compound, including its reactivity and stability.
  • For instance, oxygen is highly electronegative and tends to pull electrons towards itself, creating polar bonds.
  • In \(\mathrm{MnO}\) and \(\mathrm{MnO}_2\), manganese forms strong bonds with oxygen, affecting its oxidation state.
  • Compounds like \(\mathrm{Mn(OH)}_2\) also involve hydrogen, impacting the compound's acidity or basicity.
Understanding the basic constituents of these compounds helps in calculating the oxidation numbers and predicting reactions.
Oxidation Number Calculation
Calculating oxidation numbers involves determining how many electrons an atom gains or loses when forming a compound. This requires understanding the specific rules that dictate how oxidation numbers are assigned. The general rule is that the sum of oxidation numbers in any compound should equal the total charge of that compound.
  • For example, in \(\mathrm{MnO}\), oxygen typically has an oxidation number of -2, so manganese must be +2 to balance it out to zero.
  • In polyatomic ions like \(\mathrm{SO}_4^{2-}\), the total charge must be considered. This means balancing the known oxidation states (oxygen at -2) with the total charge to find manganese's state.
By following these rules, one can systematically find the oxidation states of manganese in various compounds.
Trends in Oxidation States
Manganese exhibits a wide range of oxidation states, from +2 to +7, each correlating with the number of bonds it forms with oxygen atoms. These states are crucial for understanding manganese's diverse chemical behavior.
  • In lower oxidation states like +2 or +3, manganese usually forms with fewer oxygen atoms, as seen in \(\mathrm{MnO}\) and \(\mathrm{Mn_2O_3}\).
  • As the number of oxygen atoms increases, manganese takes on higher oxidation states, such as +6 or +7, seen in compounds like \(\mathrm{HMnO_4}\).
Recognizing these trends is important for predicting the reactivity and properties of manganese compounds in different oxidation states.
Oxidation Rules
There are standard rules to follow when calculating oxidation numbers, which serve as a guide for determining the state of each element within a compound.
  • Oxygen almost always has an oxidation number of -2, except in peroxides or when bonded to fluorine.
  • Hydrogen, when bonded with non-metals, generally has an oxidation number of +1.
  • For elements like manganese within a neutral compound, the sum of all oxidation numbers should equal zero.
Applying these rules ensures consistency and accuracy in identifying oxidation states, aiding in chemical analysis and reactions.
Manganese Chemistry
Manganese is an element that plays a vital role in various chemical processes due to its diverse oxidation states. These states allow manganese to participate in a multitude of reactions and compounds.
  • In its lower oxidation states, manganese functions more like a metal, favoring ionic bonds and forming less reactive compounds.
  • At higher oxidation states, as seen in \(\mathrm{Mn_2O_7}\), manganese behaves more as a non-metal, forming covalent bonds and highly reactive compounds.
The ability to transition between these states makes manganese an important component in many chemical and industrial applications, like catalysts or pigments.

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Most popular questions from this chapter

The common oxidation numbers for iron are +2 and +3 . Iron reacts with \(\mathrm{O}_{2}(g)\) and \(\mathrm{Cl}_{2}(g)\) to form two different oxides and two different chlorides. What would be the formula of the four compounds formed? Classify the compounds according to bond type. Explain your answer.

What are the characteristics of atoms that tend to enter into metallic bonding?

Decide whether each of the following reactions involves oxidation-reduction. If it does, identify what is oxidized and what is reduced. (a) \(\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{H}_{2} \mathrm{CO}_{3}(a q)\) (b) \(\mathrm{Fe}_{2} \mathrm{O}_{3}(s)+3 \mathrm{CO}(g) \longrightarrow 2 \mathrm{Fe}(s)+3 \mathrm{CO}_{2}(g)\) (c) \(\mathrm{CO}_{2}(g)+\mathrm{H}_{2}(g) \longrightarrow \mathrm{CO}(g)+\mathrm{H}_{2} \mathrm{O}(g)\) (d) \(\mathrm{CO}(g)+2 \mathrm{H}_{2}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{OH}(l)\)

Which of the following compounds are best described as metallic? (a) \(\mathrm{CaH}_{2}\) (b) \(\mathrm{BrF}_{3}\) (c) \(\mathrm{NF}_{3}\) (d) \(\mathrm{SiCl}_{4}\) (e) \(\mathrm{AsH}_{3}\) (f) \(\mathrm{MgZn}_{2}\)

Two characteristics of an atom are reflected in the AVEE that favor metallic bonding. What are they?
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