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Chapter 4: Problem 88

Give the oxidation number of arsenic in each of the following: (a) \(\mathrm{AsH}_{3}\) (b) \(\mathrm{H}_{2} \mathrm{~A} \mathrm{~s} \mathrm{O}_{4}^{-}\) (c) \(\mathrm{AsCl}_{3}\)

Short Answer

Expert verified
(a) -3, (b) +5, (c) +3

Step by step solution

01

Title - Determine the oxidation number of arsenic in \( \mathrm{AsH}_{3} \)

To determine the oxidation number of arsenic (As) in \(\mathrm{AsH}_{3}\), first recognize that hydrogen (H) usually has an oxidation state of +1. The total charge of \(\mathrm{AsH}_{3}\) is 0. Therefore, set up the following equation for the sum of oxidation numbers: \[ \mathrm{Oxidation \ state \ of \ As} + 3 \( +1 \) = 0 \] Solving for the oxidation state of As, \[ \mathrm{Oxidation \ state \ of \ As} = -3 \]
02

Title - Determine the oxidation number of arsenic in \( \mathrm{H}_{2}\mathrm{As}\mathrm{O}_{4}^{-} \)

To find the oxidation number of arsenic (As) in \(\mathrm{H}_{2} \mathrm{As} \mathrm{O}_{4}^{-}\), recognize that hydrogen (H) has an oxidation state of +1 and oxygen (O) has an oxidation state of -2. The total charge of the ion is -1. Set up the equation: \[ 2 \( +1 \) + \mathrm{Oxidation \ state \ of \ As} + 4 \( -2 \) = -1 \] Solving for the oxidation state of As, \[ 2 + \mathrm{Oxidation \ state \ of \ As} - 8 = -1 \] \[ \mathrm{Oxidation \ state \ of \ As} = +5 \]
03

Title - Determine the oxidation number of arsenic in \( \mathrm{AsCl}_{3} \)

To calculate the oxidation number of arsenic (As) in \(\mathrm{AsCl}_{3}\), recognize that chlorine (Cl) usually has an oxidation state of -1. The molecule is neutral, so the total charge is 0. Set up the equation: \[ \mathrm{Oxidation number of As} + 3 \( -1 \) = 0 \] Solving for the oxidation state of As, \[ \mathrm{Oxidation state of As} - 3 = 0 \] \[ \mathrm{Oxidation state of As} = +3 \]

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Key Concepts

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

oxidation state
The oxidation state, also known as the oxidation number, is an essential concept in chemistry that helps to track how electrons are transferred during chemical reactions. It is a hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Understanding oxidation states is crucial because:

  • It helps balance redox (reduction-oxidation) reactions.
  • It aids in determining electron flow in reactions.
  • It assists in naming chemical compounds systematically.

To assign oxidation states, follow these simple rules:
  • The oxidation state of an atom in its elemental form is 0.
  • For a monoatomic ion, the oxidation state is equal to its charge.
  • Hydrogen generally has an oxidation state of +1, while oxygen usually has an oxidation state of -2.
  • The sum of the oxidation states in a neutral molecule must be 0. For polyatomic ions, the total should equal the ion's charge.
Using these rules, you can determine the oxidation state of elements in compounds. For example, in \(\text{AsH}_{3}\), arsenic has an oxidation state of -3 because hydrogen is typically +1, and the overall charge is 0.
chemical formulas
Chemical formulas represent the types and number of atoms in a molecule, using symbols from the periodic table and numerical subscripts. Proper understanding of chemical formulas is essential because:

  • They provide a concise way of describing chemical entities.
  • They convey the proportions of atoms necessary to form a substance.
  • They are crucial for stoichiometry, which involves calculations of reactants and products in chemical reactions.

Molecular formulas like \(\text{AsH}_{3}\), \(\text{H}_{2}\text{As}\text{O}_{4}^{-}\), and \(\text{AsCl}_{3}\) convey important information about the compounds. For instance, \(\text{H}_{2}\text{As}\text{O}_{4}^{-}\) tells us that the ion consists of two hydrogen atoms, one arsenic atom, and four oxygen atoms, with an overall charge of -1. By interpreting chemical formulas, you can determine how elements combine and how they interact in various chemical processes.
redox reactions
Redox reactions (short for reduction-oxidation reactions) are a type of chemical reaction where electrons are transferred between two species. Redox reactions are essential in numerous chemical and biological processes and can be identified by changes in oxidation states.
Here’s why understanding redox reactions is important:

  • They play a crucial role in energy production, such as in cellular respiration.
  • They are fundamental in industrial processes, such as metal extraction and electroplating.
  • They help in the understanding of corrosion and its prevention.

In any redox reaction:
  • Reduction refers to the gain of electrons, resulting in a decrease in oxidation state.
  • Oxidation is the loss of electrons, resulting in an increase in oxidation state.
For instance, in the context of the exercises, calculating the oxidation number of arsenic in \(\text{H}_{2}\text{As}\text{O}_{4}^{-}\) involves understanding its role in a possible redox reaction. Knowing whether arsenic is reduced or oxidized helps determine the chemical behavior and reactivity of the compound.

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Most popular questions from this chapter

Do either of the following reactions go to completion? If \(\mathrm{so}\) what factor(s) cause(s) cach to do so? (a) \(\mathrm{MgSO}_{3}(s)+2 \mathrm{HCl}(a q) \longrightarrow \mathrm{MgCl}_{2}(a q)+\mathrm{SO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l)\) (b) \(3 \mathrm{Ba}(\mathrm{OH})_{2}(a q)+2 \mathrm{H}_{3} \mathrm{PO}_{4}(a q) \longrightarrow \mathrm{Ba}_{3}\left(\mathrm{PO}_{4}\right)_{2}(s)+6 \mathrm{H}_{2} \mathrm{O}(I)\)

The active compound in Pepto-Bismol contains \(\mathrm{C}, \mathrm{H}, \mathrm{O},\) and \(\mathrm{Bi} .\) (a) When \(0.22105 \mathrm{~g}\) of the compound was burned in excess \(\mathrm{O}_{2}\), \(0.1422 \mathrm{~g}\) of bismuth(III) oxide, \(0.1880 \mathrm{~g}\) of carbon dioxide, and \(0.02750 \mathrm{~g}\) of water were formed. What is the empirical formula of the compound? (b) Given a molar mass of \(1086 \mathrm{~g} / \mathrm{mol}\), determine the molecular formula. (c) Complete and balance the acid-base reaction between bismuth(III) hydroxide and salicylic acid \(\left(\mathrm{HC}_{7} \mathrm{H}_{5} \mathrm{O}_{3}\right),\) which is used to form this compound. (d) A dose of Pepto-Bismol contains \(0.600 \mathrm{mg}\) of active ingredient. If the yield of the reaction in part (c) is \(88.0 \%,\) what mass (in \(\mathrm{mg}\) ) of bismuth(III) hydroxide is required to prepare one dose?

A mathematical equation useful for dilution calculations is \(M_{\text {dil }} \times V_{\text {dil }}=M_{\text {cunc }} \times V_{\text {cvac }}\). (a) What does each symbol mean, and why does the equation work? (b) Given the volume and molarity of a \(\mathrm{CaCl}_{2}\) solution, how do you determine the amount (mol) and the mass (g) of solute?

Sodium peroxide \(\left(\mathrm{Na}_{2} \mathrm{O}_{2}\right)\) is often used in self-contained breathing devices, such as those used in fire emergencies, because it reacts with exhaled \(\mathrm{CO}_{2}\) to form \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(\mathrm{O}_{2}\). How many liters of respired air can react with \(80.0 \mathrm{~g}\) of \(\mathrm{Na}_{2} \mathrm{O}_{2}\) if each liter of respired air contains \(0.0720 \mathrm{~g}\) of \(\mathrm{CO}_{2} ?\)

Identify the oxidizing and reducing agents in the following reactions: $$ \begin{array}{l} \text { (a) } 5 \mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(a q)+2 \mathrm{MnO}_{4}^{-}(a q)+6 \mathrm{H}^{*}(a q) \longrightarrow \\ 2 \mathrm{Mn}^{2+}(a q)+10 \mathrm{CO}_{2}(g)+8 \mathrm{H}_{2} \mathrm{O}(l) \end{array} $$ (b) \(3 \mathrm{Cu}(s)+8 \mathrm{H}^{+}(a q)+2 \mathrm{NO}_{3}^{-}(a q) \longrightarrow\) $$ 3 \mathrm{Cu}^{2+}(a q)+2 \mathrm{NO}(g)+4 \mathrm{H}_{2} \mathrm{O}(l) $$
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