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Question Video: Determining the Order That Rusting Will Occur In an Experiment Chemistry • 10th Grade

Put the following tubes in the order in which rusting will occur, starting with the slowest.

02:31

Video Transcript

Put the following tubes in the order in which rusting will occur, starting with the slowest.

Each tube contains a nail with different conditions. Rusting is a type of corrosion affecting iron. Rusting occurs when iron is exposed to oxygen and water, which forms hydrated iron(III) oxide. This means that any measure we take to protect iron from oxygen or water will slow down the process of rusting. The process of rusting is also accelerated when iron is exposed to salts or a low pH.

Tube (E) is the only one where the nail is exposed to salt water. Since rusting occurs more quickly when iron is exposed to salts, rusting will occur the fastest in tube (E). In test tubes (A), (B), and (D), measures have been taken to protect the nail from oxygen or water. But in test tube (C), the nail is exposed to tap water and oxygen from the air, so rusting will occur more quickly in test tube (C) than in test tubes (A), (B), or (D).

If we look at test tube (D), the nail has been protected from water by a stopper and the addition of anhydrous calcium chloride. Anhydrous calcium chloride is a desiccant, which means that it can absorb any water that enters the tube. This will protect the nail from water for a long time, meaning that rusting will occur the slowest in this tube.

Now we just need to determine whether rusting will occur more quickly in tube (A) or in tube (B). In tube (A), there’s no water, but the nail is exposed to the air. Air has some amount of water vapor in it, meaning that water will eventually make its way into the tube.

In tube (B), measures have been taken to protect the tube from oxygen in the air. The tube is stoppered, and there’s a layer of oil. However, this tube is full of tap water. There’s always some amount of oxygen gas that’s dissolved in tap water. This means there’s already both oxygen and water in the tube. So rusting will occur more slowly in tube (A) than in tube (B) because it will take some time for water vapor from the air to enter the tube.

So putting the tubes in the order that rusting will occur starting with the slowest is (D), then (A), then (B), then (C), then (E).

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