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Chapter 4: Problem 50

Determine the oxidation number for the indicated element (b) \(\mathrm{Al}\) in each of the following compounds: (a) \(\mathrm{Co}\) in \(\mathrm{LiCoO}_{2}\), in \(\mathrm{NaAlH}_{4}\), (c) \(\mathrm{C}\) in \(\mathrm{CH}_{3} \mathrm{OH}\) (methanol), \((\mathrm{d}) \mathrm{N}\) in \(\mathrm{GaN},\) (e) Cl in \(\mathrm{HClO}_{2},\) (f) \(\mathrm{Cr}\) in \(\mathrm{BaCrO}_{4}\)

Short Answer

Expert verified
The oxidation numbers for the indicated elements in the given compounds are: (a) Co in LiCoO₂: +3 (b) Al in NaAlH₄: +3 (c) C in CH₃OH (methanol): -2 (d) N in GaN: -3 (e) Cl in HClO₂: +3 (f) Cr in BaCrO₄: +6

Step by step solution

01

Assign known oxidation numbers

Assign the oxidation number to lithium (Li) and oxygen (O) in LiCoO₂: Li is a monoatomic ion, so its oxidation number is equal to its charge: Li⁺, oxidation number is +1. Oxygen (O) has an oxidation number of -2 in this compound (no indication of a peroxide).
02

Calculate the oxidation number of Co.

Since the compound is neutral, the sum of the oxidation numbers equals 0: (+1) + Co + [2 × (-2)] = 0 Now, solve for Co's oxidation number: Co - 3 = 0 Co = +3 The oxidation number of Co in LiCoO₂ is +3. #b) Al in NaAlH4#
03

Assign known oxidation numbers

Assign the oxidation number to sodium (Na) and hydrogen (H) in NaAlH₄: Na is a monoatomic ion, so its oxidation number is equal to its charge: Na⁺, oxidation number is +1. Since H is part of a metal hydride (AlH₄⁻), its oxidation number is -1.
04

Calculate the oxidation number of Al

Since NaAlH₄ is neutral, the sum of the oxidation numbers equals 0: (+1) + Al + [4 × (-1)] = 0 Now, solve for Al's oxidation number: Al - 3 = 0 Al = +3 The oxidation number of Al in NaAlH₄ is +3. #c) C in CH3OH (methanol)#
05

Assign known oxidation numbers

Assign the oxidation number to hydrogen (H) and oxygen (O) in CH₃OH: H in organic compounds usually has an oxidation number of +1. Oxygen (O) has an oxidation number of -2.
06

Calculate the oxidation number of C

Since CH₃OH is neutral, the sum of the oxidation numbers equals 0: C + [(3 × +1) + (-2) + (+1)] = 0 Now, solve for C's oxidation number: C + 2 = 0 C = -2 The oxidation number of C in CH₃OH is -2. #d) N in GaN#
07

Identify the charges of the ions

GaN is an ionic compound formed by Ga³⁺ and N³⁻ ions.
08

Determine the oxidation number

The oxidation numbers are equal to the charges of the ions: For Ga, the oxidation number is +3. For N, the oxidation number is -3. #e) Cl in HClO2#
09

Assign known oxidation numbers

Assign the oxidation number to hydrogen (H) and oxygen (O) in HClO₂: H in compounds usually has an oxidation number of +1. Oxygen (O) has an oxidation number of -2.
10

Calculate the oxidation number of Cl

Since HClO₂ is neutral, the sum of the oxidation numbers equals 0: (+1) + Cl + [2 × (-2)] = 0 Now, solve for Cl's oxidation number: Cl - 3 = 0 Cl = +3 The oxidation number of Cl in HClO₂ is +3. #f) Cr in BaCrO4#
11

Assign known oxidation numbers

Assign the oxidation number to barium (Ba) and oxygen (O) in BaCrO₄: Ba is a monoatomic ion, so its oxidation number is equal to its charge: Ba²⁺, oxidation number is +2. Oxygen (O) has an oxidation number of -2.
12

Calculate the oxidation number of Cr

Since BaCrO₄ is neutral, the sum of the oxidation numbers equals 0: (+2) + Cr + [4 × (-2)] = 0 Now, solve for Cr's oxidation number: Cr - 6 = 0 Cr = +6 The oxidation number of Cr in BaCrO₄ is +6.

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Most popular questions from this chapter

Suppose you have \(5.00 \mathrm{~g}\) of powdered magnesium metal, \(1.00 \mathrm{~L}\) of \(2.00 \mathrm{M}\) potassium nitrate solution, and \(1.00 \mathrm{~L}\) of \(2.00 \mathrm{M}\) silver nitrate solution. (a) Which one of the solutions will react with the magnesium powder? (b) What is the net ionic equation that describes this reaction? (c) What volume of solution is needed to completely react with the magnesium? (d) What is the molarity of the \(\mathrm{Mg}^{2+}\) ions in the resulting solution?

Classify each of the following substances as a nonelectrolyte, weak electrolyte, or strong electrolyte in water: (a) \(\mathrm{H}_{2} \mathrm{SO}_{3}\), (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (ethanol), (c) \(\mathrm{NH}_{3}\), (d) \(\mathrm{KClO}_{3}\), (e) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\)

We have learned in this chapter that many ionic solids dissolve in water as strong electrolytes, that is, as separated ions in solution. What properties of water facilitate this process? Would you expect ionic compounds to be soluble in elemental liquids like bromine or mercury, just as they are in water? Explain.

A solution is made by mixing \(15.0 \mathrm{~g}\) of \(\mathrm{Sr}(\mathrm{OH})_{2}\) and \(55.0 \mathrm{~mL}\) of \(0.200 \mathrm{MHNO}_{3}\). (a) Write a balanced equation for the reaction that occurs between the solutes. (b) Calculate the concentration of each ion remaining in solution. (c) Is the resultant solution acidic or basic?

Hard water contains \(\mathrm{Ca}^{2+}, \mathrm{Mg}^{2+},\) and \(\mathrm{Fe}^{2+},\) which interfere with the action of soap and leave an insoluble coating on the insides of containers and pipes when heated. Water softeners replace these ions with \(\mathrm{Na}^{+}\). (a) If \(1500 \mathrm{~L}\) of hard water contains \(0.020 \mathrm{M} \mathrm{Ca}^{2+}\) and \(0.0040 \mathrm{M} \mathrm{Mg}^{2+}\), how many moles of \(\mathrm{Na}^{+}\) are needed to replace these ions? (b) If the sodium is added to the water softener in the form of \(\mathrm{NaCl}\), how many grams of sodium chloride are needed?
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