Hydrazine is somewhat toxic. Use the following...

Hydrazine is somewhat toxic. Use the following half-reactions to explain why household bleach (highly alkaline solution of sodium hypochlorite) should not be mixed with household ammonia or glass cleansers that contain ammonia. $\mathrm{ClO}^{-}+\mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{OH}^{-}+\mathrm{Cl}^{-} \quad \mathscr{E}^{\circ}=0.90 \mathrm{~V}$ $\mathrm{N}_{2} \mathrm{H}_{4}+2 \mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{NH}_{3}+2 \mathrm{OH}^{-} \quad \mathscr{E}^{\circ}=-0.10 \mathrm{~V}$

Hydrazine is somewhat toxic. Use the following half-reactions to explain why household bleach (highly alkaline solution of sodium hypochlorite) should not be mixed with household ammonia or glass cleansers that contain ammonia.
$\mathrm{ClO}^{-}+\mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{OH}^{-}+\mathrm{Cl}^{-} \quad \mathscr{E}^{\circ}=0.90 \mathrm{~V}$
$\mathrm{N}_{2} \mathrm{H}_{4}+2 \mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{NH}_{3}+2 \mathrm{OH}^{-} \quad \mathscr{E}^{\circ}=-0.10 \mathrm{~V}$

Key Concepts

Reaction Spontaneity and Hazard

When combining species with significantly different standard electrode potentials, the overall reaction can be both spontaneous and vigorous. In the context of mixing household bleach (a strong oxidizer) with ammonia-containing products, the potential difference can drive a rapid and uncontrolled redox reaction. This may lead to the formation of toxic or otherwise hazardous products, which is why such mixtures are dangerous.

Standard Electrode Potentials

Standard electrode potentials quantify the tendency of a chemical species to be reduced. They are measured under standard conditions and provide a scale to compare oxidizing and reducing strengths. A high positive potential indicates a strong oxidizing agent, while a low or negative potential indicates a weak oxidizing agent (or strong reducing agent). The difference in these potentials between two half-reactions determines the spontaneity and driving force of the overall reaction.

Redox Reactions

Redox reactions involve the transfer of electrons between chemical species. In these processes, one substance is oxidized (loses electrons) while another is reduced (gains electrons). When considering household chemicals, understanding redox reactions explains how a strong oxidizer (like the hypochlorite ion in bleach) can react with a reducing agent (such as ammonia or related compounds) to produce potentially hazardous materials.

Half-Reaction Method

The half-reaction method breaks the overall redox process into two parts: one showing oxidation and the other showing reduction. By writing separate equations for each process, one can analyze the electron transfer, balance equations, and combine the reactions to predict the overall reaction. This approach is essential for understanding how two different chemical species interact in a redox event.

Transcript

00:01 So in this video we're going to work through question 86 from chapter 20, which says hydrozine is somewhat toxic.

00:09 Use the following half reactions to explain my household bleach, a highly alkaline solution of sodium hypochlorite, should not be mixed with household ammonia or glass pleaders so that it contain ammonia.

00:22 And the two half reactions we have are clo minus plus h2o plus two electrons yields 2 -oh minus plus dl -9us, and the reduction potential.

00:31 For that half reaction is positive 0 .9 volts.

00:34 And then our second half reaction is into h4, which is hydrazine, plus 2h2o, plus 2 electron yields, 2nh3, which is ammonia, plus 2 .0h minus.

00:45 And the reduction potential for that half reaction is negative 0 .10 volts.

00:51 So what can we learn from these half reactions? so these half reactions together tell us how ammonia reacts.

01:01 With hypochlorite.

01:03 We just need to write them in a way that we can add them together so that our electrons cancel from both sides.

01:11 And then our two half reactions will together be a redox reaction.

01:15 So the way these are both written right now is as reduction half reactions where we're gaining electrons on the reactant side of thing.

01:24 So we want to write one of them as an oxidation half reaction.

01:28 Since we're having a redox reaction, we need both reduction and oxidation to occur.

01:33 So which one are we going to flip the direction of? well, we're going to flip the direction of the second one, and that's because the reduction potential for that half reaction is negative.

01:42 So a redox reaction occurs spontaneously when the standard potential for that cell is positive.

01:52 So we're going to flip the half reaction that will give us a positive standard cell potential when we add these together...

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