Corrosion & pH: Explaining Observations of Iron Nail

In summary, the data table contained information on how iron nails submerged in different aqueous solutions would corrode. NaCl, NaSCN, HCl, H2SO4, and KNO3 all had no corrosion observed, while Na3PO4 and NaOH produced corrosion. The Attempt at a Solution proposes that the lack of corrosion observed on basic environments may be due to the presence of strong electrolytes, while the corrosion observed on acidic environments may be due to the presence of H+ and HSCN. Black solids were observed on all solutions, and hematite was the solid formed.
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Homework Statement


Hello guys. We are given a hypothetical data table and this is pretty much what it contains. It tells that when an iron nail is submerged in various aqueous solutions, the following observations were made. We are to give explanations to each why these things were observed. There is a supply of oxygen in all of those. So, corrosion would occur whenever it can.

Solution pH Observations

NaCl Neutral corrosion was observed, red-brown solids are seen

NaSCN Acidic corrosion observed, red brown solids observed

HCl Acidic corrosion observed, black solids, gas evolved(H2)

H2SO4 Acidic corrosion was observed, black solids, gas evolved(H2)

KNO3 Neutral corrosion observed, red-brown solids

Na3PO4 Basic no corrosion observed

NaOH Basic no corrosion observed

Homework Equations





The Attempt at a Solution



The first thing I noticed were the bases. No corrosion was observed. I don't really know why. I saw on some source(http://www.corrosion-doctors.org/Electrochemistry-of-Corrosion/Cathodic-processes.htm[/URL]) [Broken] that reduction of oxygen would still occur at basic environment. Fe would still oxidize as usual, and that further oxidation of the Fe2+ ions that were to form would still occur to form rust. Or does Fe metal do not oxidize at pH>7 solutions? So my question here is that why were there no corrosion observed on basic environment?

On the acids, observations are should be what it is. H2 gas were observed since the strong acids would react with the pure metal to that would reduce the hydrogen ions on HCl and produce H2 gas. The black solids are particularly interesting. Black means that it would be a "magnetite" that was formed right? How can this be? Is this because of the presence of a very strong acids (thus more H+) and that's why it was a magnetite and not a hematite?

On the neutral solutions, corrosions were still observed. But now, solids formed are reddish brown, like what they usually seen are. This means that they're hematite. Corrosion happens on neutral solutions because they contain (in the given table's case) strong electrolytes which dissociates completely and acts as a pathway for e- to walk through so that it can react to Oxygen (O2) without actually being too close to the metal. Is that right? And why were the solids hematite and not magnetite?

On the other note, one acidic solution produced the result of a neutral solution. How can this happen? Is this because the salt solution of NaSCN has SCN- ions that hydrolyzes, giving a small amount of H+ and HSCN?? And that it is just weak acid, giving a result as if it was a neutral solution? Is my 'hypothesis' correct?

Please help me. I'm really confused on how pH level affect corrosion.
 
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What is the significance of red-brown solids and black solids, as opposed to the absence of these?
 

1. What is corrosion?

Corrosion is a natural process that occurs when metal is exposed to oxygen and moisture, causing it to deteriorate and lose its strength. It is often referred to as rust in the case of iron.

2. How does pH affect corrosion?

pH is a measure of the acidity or basicity of a substance. In the case of iron nails, a low pH (acidic) environment can accelerate the corrosion process, while a high pH (basic) environment can slow it down.

3. Why do iron nails corrode faster in saltwater?

Saltwater contains chloride ions which are more reactive and can speed up the corrosion process of iron. This is because the chloride ions can break down the protective oxide layer on the surface of the nail, exposing it to further corrosion.

4. How can we prevent corrosion?

There are several ways to prevent corrosion, such as using corrosion-resistant materials, applying protective coatings, or using sacrificial anodes. In the case of iron nails, applying a coat of paint or using galvanized nails (coated with zinc) can help prevent corrosion.

5. Can corrosion be reversed?

Corrosion cannot be reversed, but it can be slowed down or prevented. Once metal has corroded, the damage is irreversible. Therefore, it is important to take preventative measures to avoid corrosion in the first place.

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