Zinc coats Iron and prevents it from rusting. However Iron cannot be used to coat zinc and prevent it from corroding.Explain this phenomenon.HELP PLEASE URGENT!!
Zinc is higher on the Metal Activity Series than iron. That means zinc metal oxidizes more easily than iron. The metal that oxidizes more easily can protect another metal that oxidizes less easily but not the other way around.
But then copper and tin can also be used to plate iron even if they're less reactive than iron.
Another way to look at this is that the zinc coats the iron. Before iron can corrode, the zinc coating must be removed. One reason this reaction is slow is because zinc forms a thin layer of zinc oxide which remains relatively stable on the surface of the metal (see passivity of metals). More zinc doesn't readily react because the zinc oxide coating resists further oxidation. Tin and copper also form protective coatings on iron. They are less reactive than iron; hence, the coating protects the iron.
From DrBob's and my answer, I hope you can see that a metal surface can be protected in two ways:
1. Coat the active metal with the less active metal. This works well if coating stays in place and does not allow oxidizing agents through it. Cu and Sn on iron fit that description. If there is a breach in such a coating, the exposed area oxidizes even faster than if the coating was absent.
2. Coat the metal to be protected with a more active metal (i.e. zinc over iron). Protection is provided by "sacrificing" the coating to oxidizing agents. This electrochemical protection works even if the coating is partly damaged.
The phenomenon you are referring to is known as sacrificial protection or galvanic protection. It is commonly used to prevent the corrosion of metals.
In this case, zinc is more reactive (or more easily oxidized) than iron. When zinc is in contact with iron, it undergoes a process called galvanic corrosion, which means that it oxidizes instead of the iron. Essentially, the zinc "sacrifices" itself by corroding instead of the iron.
To prevent the corrosion of iron, a thin layer of zinc is applied to its surface, known as zinc coating or galvanizing. This coating acts as a sacrificial anode, meaning that it corrodes first before the iron does. This sacrificial protection is effective because zinc corrodes more readily than iron.
On the other hand, if you were to coat zinc with iron, it would not be able to provide sacrificial protection. Iron is less reactive than zinc, so it does not corrode as readily. Therefore, it cannot effectively sacrifice itself to protect the zinc from corrosion.
In conclusion, zinc coating is effective in preventing the corrosion of iron because zinc is more reactive and readily corrodes, acting as a sacrificial anode. However, iron coating on zinc would not provide the same sacrificial protection mechanism.