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Question Video: Identifying Which Method Is Not Used to Lower Rusting Rates Chemistry • 10th Grade

Which of the following is not a method for lowering the rate of rusting? [A] Alloying [B] Greasing [C] Welding [D] Galvanizing [E] Electroplating


Video Transcript

Which of the following is not a method for lowering the rate of rusting? (A) Alloying, (B) greasing, (C) welding, (D) galvanizing, or (E) electroplating.

First, let’s define what we mean by rusting and how it happens. Rusting is a reaction between water or oxygen in metal parts that contain a high proportion of iron. Rusting is a form of corrosion. Corrosion is an irreversible, destructive process where a metal reacts with other substances to form more stable compounds. To protect a metal from rusting, something must be done to slow down or stop the other substances from coming into contact with the iron. Let’s look at our answer choices to see if they are likely to lower the rate of rusting.

Answer choice (A), alloying, is the process of mixing a metal with other elements to produce a new material with unique properties. The other elements are often metals. Some alloys of iron are more resistant to rusting than pure iron. For example, stainless steel is an alloy containing iron and chromium and other elements. The chromium helps the alloy form a protective passivation layer that blocks oxygen and water from getting to the iron. Passivation is the process of chemically treating a metal part to form a protective barrier on its surface. This question asks us which method would not be used to slow down rusting. Since alloying could be used to slow the rusting of iron, we can eliminate answer choice (A).

Answer choice (B), greasing, is when we add a layer of grease to a metal part. The grease provides a physical barrier against oxygen and water, slowing the rate of rusting. So, we can eliminate answer choice (B).

Answer choice (C), welding, is a process for connecting metal parts. It usually involves melting metals in a small area so that the metal parts can be connected to each other. Since the composition of a weld is usually the same as the original metal parts, welding is unlikely to affect the rate of rusting. Answer choice (C) is the most likely answer, but let’s rule out answer choices (D) and (E) just to be sure.

Answer choice (D), galvanization, is the process of coating an iron-containing metal part with zinc. This is usually done by dipping the iron part into molten zinc. This coating stops rusting, even if it is scratched. A scratched coating will act as a sacrificial anode, corroding in place of the iron. Therefore, galvanization can prevent rusting.

Electroplating can produce the same effects as galvanization. Electrolysis is used when electroplating to deposit one metal onto another. This, like galvanization, can prevent rusting.

Therefore, the answer choice that is not a method for lowering the rate of rusting is answer choice (C), welding.

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