which chemical applied on copper starts reacting with iron?

There is no single chemical that is typically applied to copper that will react with iron. Copper and iron are not highly reactive with each other, and do not typically undergo significant chemical reactions in most circumstances.

However, if copper and iron are in contact with each other in the presence of an electrolyte, such as saltwater or an acidic solution, then a galvanic reaction may occur. In a galvanic reaction, the more reactive metal (in this case, iron) will corrode and lose electrons, while the less reactive metal (copper) will gain electrons and remain relatively stable.

If copper and iron are in contact in the presence of an electrolyte and a voltage is applied, such as in a battery or electroplating process, then the reaction between the two metals may be more significant.

In general, the use of chemicals on copper and iron should be done with caution and only with a clear understanding of the potential reactions that may occur. Mixing different chemicals together can be dangerous and should only be done by trained professionals in appropriate facilities, using proper safety equipment and procedures.

There are many chemicals or mixtures of chemicals that can react with iron metal, depending on the specific conditions and intended application. Some common examples include:

Acids: Many acids can react with iron to form iron salts and hydrogen gas. For example, hydrochloric acid (HCl) and sulfuric acid (H2SO4) are commonly used to clean or etch iron surfaces.

Alkaline solutions: Strong alkaline solutions, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), can also react with iron, often resulting in the formation of iron oxides or hydroxides.

Oxidizers: Oxidizing agents, such as nitric acid (HNO3) or hydrogen peroxide (H2O2), can react with iron to form iron oxides or hydroxides.

Chlorine compounds: Chlorine-based compounds, such as bleach or chlorine gas, can react with iron to form iron chlorides or iron oxides.

Organic solvents: Some organic solvents, such as acetone or ethanol, can dissolve iron or react with iron oxides.

It’s worth noting that the use of chemicals to react with iron should be done with caution and only with a clear understanding of the potential reactions and hazards involved. Mixing different chemicals together can be dangerous and should only be done by trained professionals in appropriate facilities, using proper safety equipment and procedures.