# What are better acids for removing rust from an iron nail than phosphoric, or oxalic acid?

I'm planning to conduct an experiment in which I test how fast rusting occurs with changes to the concentration of NaCl in the solution.

I want to measure that by finding the change in mass of an iron nail over time, but in order to do that I need to clean off all the rust on the nail before weighing. I have a relatively short time to conduct the experiments.

I've heard acids like phosphoric acid, oxalic acid, or citric acid will work. I'm looking for the best acid to separate the rust from the nail preferably without using steel wool or any abrasive method. I can, however, spray down the nail with distilled water if necessary. Any suggestions?

In the automotive industry, pickling of steel plates is done with a diluted solution of sulphuric acid. You might use hydrochloric acid, too, but be sure to use pure (for lab purposes) $\ce{HCl}$. Commercial $\ce{HCl}$ (also known as muriatic acid) quite often contains traces of other metals (iron included, and $\ce{Fe^2+}$ and $\ce{Fe^3+}$ ions give muriatic acid its yellowish colour, that may turn your nail inert to some extent.