Problem 113 - Chemistry: The Central Science in SI Units, Global Edition

Question

Aqueous solutions of ammonia \(\left(\mathrm{NH}_{3}\right)\) and bleach (active ingredient \(\mathrm{NaOCl}\) ) are sold as cleaning fluids, but bottles of both of them warn: "Never mix ammonia and bleach, as toxic gases may be produced." One of the toxic gases that can be produced is chloroamine, \(\mathrm{NH}_{2} \mathrm{Cl}\). (a) What is the oxidation number of chlorine in bleach? (b) What is the oxidation number of chlorine in chloramine? (c) Is Cl oxidized, reduced, or neither, upon the conversion of bleach to chloramine? (d) Another toxic gas that can be produced is nitrogen trichloride, \(\mathrm{NCl}_{3}\). What is the oxidation number of \(\mathrm{N}\) in nitrogen trichloride? \((\mathbf{e})\) Is \(\mathrm{N}\) oxidized, reduced, or neither, upon the conversion of ammonia to nitrogen trichloride?

Step-by-Step Solution

Answer

(a) The oxidation number of Cl in bleach (NaOCl) is +1. (b) The oxidation number of Cl in chloroamine (NH2Cl) is +1. (c) Cl is neither oxidized nor reduced upon the conversion of bleach to chloroamine. (d) The oxidation number of N in nitrogen trichloride (NCl3) is +3. (e) N is oxidized upon the conversion of ammonia to nitrogen trichloride.

Step 1: (a) Oxidation number of Cl in NaOCl (bleach)

To find the oxidation number of Cl in NaOCl (bleach), we will first look at the oxidation numbers of the other elements in the compound. Na is an alkali metal and has an oxidation number of +1, while O generally has an oxidation number of -2. Now we can create an equation to represent the total oxidation numbers of the compound: \[+1 + (-2) + x = 0\] \[x = +1\] Therefore, the oxidation number of Cl in bleach (NaOCl) is +1.

Step 2: (b) Oxidation number of Cl in NH2Cl (chloroamine)

To find the oxidation number of Cl in NH2Cl (chloroamine), we first look at the oxidation numbers of the other elements in the compound. N usually has an oxidation number of -3, while H has an oxidation number of +1. Since there are two H atoms in the compound, we can create an equation to represent the total oxidation numbers of the compound: \[(-3) + 2(+1) + x = 0\] \[-3 + 2 + x = 0\] \[x = +1\] Therefore, the oxidation number of Cl in chloroamine (NH2Cl) is +1.

Step 3: (c) Cl's oxidation state during conversion from NaOCl to NH2Cl

Comparing the oxidation numbers of Cl in NaOCl (bleach) and NH2Cl (chloroamine), which are both +1, we can determine that during the conversion of bleach to chloroamine, the oxidation number of Cl remains the same. Thus, Cl is neither oxidized nor reduced in this process.

Step 4: (d) Oxidation number of N in NCl3 (nitrogen trichloride)

To find the oxidation number of N in NCl3 (nitrogen trichloride), we first look at the oxidation number of Cl, which is typically -1. Since there are three Cl atoms in the compound, we can create an equation to represent the total oxidation numbers of the compound: \[x + 3(-1) = 0\] \[x - 3 = 0\] \[x = +3\] Therefore, the oxidation number of N in nitrogen trichloride (NCl3) is +3.

Step 5: (e) N's oxidation state during conversion from NH3 to NCl3

Comparing the oxidation numbers of N in NH3 (ammonia) and NCl3 (nitrogen trichloride), which are -3 and +3 respectively, we can determine that during the conversion of ammonia to nitrogen trichloride, the oxidation number of N increases from -3 to +3. Thus, N is oxidized in this process.

Key Concepts

Oxidation State

Oxidation state, or oxidation number, is a concept used to keep track of electrons in molecules and ions, especially during chemical reactions. It indicates the hypothetical charge of an atom if all bonds to atoms of different elements were 100% ionic. Understanding oxidation states is crucial because they help us identify changes in electron distribution during chemical reactions.

For instance, in the compound NaOCl (bleach), the oxidation state of chlorine (Cl) is +1. This is calculated by knowing that sodium (Na) typically has an oxidation state of +1 and oxygen (O) is -2. The sum of these oxidation states must equal zero in a neutral compound. We set up the equation: \[+1 + (-2) + x = 0\] This simplifies to \(x = +1\), making chlorine's oxidation state in NaOCl +1.

Reduction and Oxidation Reactions

Reduction and oxidation reactions, often abbreviated as redox reactions, represent a type of chemical reaction where the oxidation numbers of atoms are altered. In these reactions, the substance that gains electrons is said to be reduced, whereas the one losing electrons is oxidized.

With the conversion of bleach (NaOCl) to chloroamine (NH2Cl), the oxidation state of chlorine remains unchanged at +1, indicating that chlorine is neither oxidized nor reduced in this process. However, in another reaction involving ammonia converting to nitrogen trichloride \( (NCl_3) \), nitrogen experiences a change in oxidation state from -3 to +3, signifying that nitrogen is oxidized.

Redox reactions are fundamental to many biological processes and chemical industry applications. They are crucial for energy production, whether in photosynthesis or cellular respiration.

Chemical Reactions Safety

Chemical reactions can sometimes result in hazardous conditions if not performed safely. Understanding the components and products involved in chemical reactions can prevent dangerous situations.

A classic example of a chemical safety warning is the mixture of ammonia \((NH_3)\) and bleach \((NaOCl)\). These two common household cleaners, when mixed, can produce toxic gases, including chloramine \((NH_2Cl)\) and nitrogen trichloride \((NCl_3)\).

• The primary recommendation for safe chemical handling is to always read and follow label warnings and instructions on all products.
• Ensure proper ventilation, use protective gear such as gloves and goggles, and avoid mixing unknown chemicals.

These precautions can minimize risks and protect against exposure to toxic materials.

Toxic Gas Production

When ammonia and bleach are mixed, one of the dangerous outcomes is toxic gas production. These gases can pose serious health dangers if inhaled or contacted.

Chloramine \((NH_2Cl)\) is one such toxic gas that is produced when the two chemicals interact. It can cause respiratory issues and irritation to the eyes and skin. Another dangerous compound that might form is nitrogen trichloride \( (NCl_3) \). Nitrogen trichloride is even more hazardous, with potential to cause severe health problems on exposure.

• The best prevention is to avoid mixing cleaning agents unless sure of the absence of harmful reactions.
• If exposure occurs, it's crucial to move to fresh air immediately and seek medical attention if symptoms persist.

Understanding how these gases are produced can help prevent accidental exposure and safeguard health.