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? (e) Is \(\mathrm{N}\) oxidized, reduced,or neither, upon the conversion of ammonia to nitrogen trichloride?

Short answer

The oxidation number of chlorine in bleach (NaOCl) is +1, and its oxidation number in chloramine (NH2Cl) is also +1. Therefore, chlorine is neither oxidized nor reduced during the conversion of bleach to chloramine. The oxidation number of nitrogen in nitrogen trichloride (NCl3) is +3, and its oxidation number in ammonia (NH3) is -3. Thus, nitrogen is oxidized during the conversion of ammonia to nitrogen trichloride.

Step-by-step solution

Calculate the oxidation number of Chlorine in bleach

To find the oxidation number of chlorine, let's use the equation Na(+1) + O(-2) + Cl(x) = 0 Solve for x: 1 - 2 + x = 0 x = +1 So, the oxidation number of chlorine in bleach is +1. 2. Identify the oxidation number of chlorine in chloramine (b) It is given that chloramine has the chemical formula, NH2Cl. We can write this as follows: N(-3) + 2H(+1) + Cl(x) = 0. We need to solve for x (the oxidation number of chlorine).

Calculate the oxidation number of Chlorine in chloramine

To find the oxidation number of chlorine, let's use the equation N(-3) + 2H(+1) + Cl(x) = 0 Solve for x: -3 + 2 + x = 0 x = +1 So, the oxidation number of chlorine in chloramine is +1. 3. Identify the transformation of Cl during the conversion of bleach to chloramine (c) To determine if the chlorine is oxidized, reduced, or stays the same, we compare the oxidation numbers of chlorine in bleach and chloramine. As seen in step 1 and step 2, the oxidation number of Cl in bleach is +1, and the oxidation number of Cl in chloramine is also +1.

Transformation of Chlorine

Since the oxidation numbers of chlorine in bleach and chloramine are the same, there is no change in the oxidation state of chlorine. Thus, chlorine is neither oxidized nor reduced during the conversion of bleach to chloramine. 4. Identify the oxidation number of N in nitrogen trichloride (d) It is given that nitrogen trichloride has the chemical formula NCl3. We can write this as follows: N(x) + 3Cl(-1) = 0. We need to solve for x (the oxidation number of nitrogen).

Calculate the oxidation number of Nitrogen in nitrogen trichloride

To find the oxidation number of nitrogen, let's use the equation N(x) + 3Cl(-1) = 0 Solve for x: x - 3 = 0 x = +3 So, the oxidation number of nitrogen in nitrogen trichloride is +3. 5. Identify the transformation of N during the conversion of ammonia to nitrogen trichloride (e) To determine if the nitrogen is oxidized, reduced, or stays the same, we compare the oxidation numbers of nitrogen in ammonia and nitrogen trichloride. As seen in step 2, the oxidation number of N in ammonia (NH3) is -3, and the oxidation number of N in nitrogen trichloride (NCl3) is +3 from step 4.

Transformation of Nitrogen

Since the oxidation number of N in ammonia is -3 and the oxidation number of N in nitrogen trichloride is +3, there is a change in the oxidation state of nitrogen. Thus, nitrogen is oxidized during the conversion of ammonia to nitrogen trichloride.

Key concepts

Chemical Oxidation States

Understanding chemical oxidation states is essential for analyzing redox reactions. Oxidation states, also known as oxidation numbers, are used to describe the degree of oxidation of an atom in a chemical compound. These are hypothetical charges that an atom would have if all bonds to atoms of different elements were fully ionic. Oxidation numbers are assigned based on a set of rules, such as oxygen usually having an oxidation state of -2, and hydrogen typically having a +1 when bonded to non-metals.

For example, in NaOCl (bleach), sodium (Na) has a standard oxidation number of +1, oxygen (O) has an oxidation number of -2, and chlorine (Cl) can be calculated by balancing the equation, resulting in an oxidation number of +1 for chlorine, because the compound is neutral overall. Similarly, in NH2Cl (chloroamine), the oxidation number of chlorine can be deduced by knowing that nitrogen (N) typically has an oxidation number of -3, and hydrogen (H) has an oxidation state of +1. The oxidation states must sum up to zero since chloroamine is a neutral molecule, confirming that chlorine has an oxidation number of +1. Understanding these principles is fundamental to mastering the concept of redox reactions.

Redox Reactions

Redox reactions are a type of chemical reaction that involves a transfer of electrons between two species. Redox is a shorthand for reduction-oxidation. These two processes occur simultaneously; when one substance undergoes oxidation, another undergoes reduction. Oxidation refers to the loss of electrons, while reduction refers to the gain of electrons. In the process, the oxidation numbers of atoms change to reflect the transfer of electrons.

For example, when bleach is mixed with ammonia, one of the by-products can be chloramine (NH2Cl), where no change in oxidation state of chlorine occurs, indicating that no redox reaction involving chlorine has taken place between bleach (NaOCl) and chloramine. However, when ammonia (NH3) is converted to nitrogen trichloride (NCl3), nitrogen's oxidation state changes from -3 to +3, showing that it has lost electrons and has been oxidized. It's important to recognize these changes in oxidation states to understand the redox behavior in chemical reactions.

Balancing Oxidation-Reduction Equations

Balancing oxidation-reduction equations, or redox equations, involves ensuring that both the number of atoms and electric charges are equal on both sides of the equation. This process is crucial because, in accordance with the law of conservation of mass, the number of each type of atom must remain constant, and the net charge must also be the same on both sides of a chemical equation.

To balance a redox equation accurately, one must first separate the two halves of the reaction - the oxidation half and the reduction half - and balance each half-reaction for both mass and charge. Then, the half-reactions are recombined, and the electrons lost and gained are balanced by adjusting the coefficients in the overall equation. This method ensures that the redox reaction, as a whole, remains charge and mass balanced. Remembering to check both atom counts and charge balance is crucial when finalizing a balanced equation. By following these steps, students can accurately and confidently balance complex redox equations, enhancing their understanding of the conservation principles underlying chemical reactions.