Question

A chemist attempts to protect two pieces of iron by placing them in contact with other substances. The chemist attaches a strip of strontium to one piece of iron and some sulfur to the other. After some time outdoors, one of the iron pieces has rusted while the other has not. Which one rusted? Why? (Hint: Use what you know about metals and nonmetals.)

Short answer

The piece of iron attached to sulfur rusted because sulfur does not offer sacrificial protection like strontium does.

Step-by-step solution

Understand the concept of reactivity series

The reactivity series is a list of metals arranged in order of their reactivity from highest to lowest. It is used to determine which metals can displace others from their compounds. Metals higher in the series can displace metals lower down in the series from their compounds.

Determine the position of iron, strontium, and sulfur in the reactivity series

In the reactivity series, strontium is above iron, meaning it is more reactive, while sulfur, being a nonmetal, is not usually included in the metallic reactivity series. Therefore, we can imply that strontium can protect iron through sacrificial protection but sulfur cannot.

Apply sacrificial protection principles

Strontium, being more reactive, will oxidize in preference to the iron when it is in contact with water and oxygen, providing sacrificial protection to the iron. The iron attached to sulfur does not have such protection since sulfur does not react in the same way as a more reactive metal would.

Determine which piece of iron rusted

Based on the principles of sacrificial protection, the piece of iron attached to strontium would be protected from rusting due to the higher reactivity of strontium. Consequently, the piece of iron attached to sulfur is the one that rusted.

Key concepts

Reactivity Series

The reactivity series is a crucial concept in chemistry, particularly when discussing metals. It acts like a leaderboard, ranking metals from the one that throws the biggest reactivity 'tantrum' to the one that is the most 'chill.' In other words, it organizes metals by their willingness to partake in chemical reactions.

• At the top, we have the 'life of the party' metals that react even if you just say the word 'water.'
• Moving down, you find metals that need a bit more coaxing to react.
• Then there are the metals at the bottom, the 'introverts,' that prefer not to react at all.

This list isn't just for show; it gives scientists and engineers a game plan when they're mixing metals or trying to prevent a reaction. For example, if you want to protect a less reactive metal, you'd sacrifice a more reactive one—think of it as the reactive metal taking one for the team.

In the context of our textbook exercise, strontium is the life of the party, ready to react before the iron even gets a chance. This character trait of strontium makes it an excellent bodyguard against rust.

Metal and Nonmetal Reactivity

When talking about the social lives of elements—yes, elements have social lives too—metals and nonmetals have different ways of interacting with others. Metals, such as iron, are like people who are eager to lend you money; we say they are 'reducing agents.' They readily lose electrons, which is essentially chemical currency.

• Some metals, like our party-animal strontium, are very generous, giving away electrons left and right.
• Others, like gold, are more like misers, very reluctant to part with their electrons.

Nonmetals, on the other hand, would rather take your money, or in chemical terms, gain electrons. Sulfur, from our example, is more of a 'taker.' But when it comes to protecting metal from corrosion, sulfur doesn't offer much help. It's not willing to jump in front of iron and take the hit from oxygen and water the way strontium is.

Corrosion and Rusting

Imagine metal as a superhero with one weakness: rust. Rusting is the Achilles' heel, especially for iron. Technically, it's just iron reacting with oxygen in a slow burn romance called oxidation. If this love affair gets any encouragement from water, rusting happens faster, much like gossip can speed up the development of a real-life romance.

• Corrosion is the general term we use for metals deteriorating because of these reactions.
• Rusting, specifically, is corrosion gone wild, attacking our iron hero.

However, just like in any good superhero story, there's a way to save the day. Enter sacrificial protection! It's the equivalent of a sidekick jumping in to take the villainous blow. By attaching a more reactive metal, like strontium, to iron, strontium faces the brunt of the attack, slowly deteriorating while keeping the iron safe and sound.

So, in the case of the chemist's dilemma in our exercise, the piece of iron that had sulfur as an ally was left exposed to the elements and rusted away. The piece with strong, reactive strontium stood rust-free, proving that when it comes to protection, metal's reactivity steals the show.