Home

Home
Common Compounds
Exam Guide
FAQ
Features
Glossary
Construction Kits
Companion Notes
Just Ask Antoine!
Simulations
Slide Index
Toolbox
Tutorial Index

FAQ
Introduction
Measurement
Matter
Atoms & ions
Compounds
Chemical change
The mole
Gases
Energy & change
The quantum theory
Electrons in atoms
The periodic table
Chemical bonds
Solids
Liquids
Solutions
Acids & bases
Redox reactions
Reaction rates
Organic chemistry
Everyday chemistry
Inorganic chemistry
Environmental chemistry
Laboratory
History of chemistry
Miscellaneous


Home :FAQ :Redox reactionsPrint | Comment
Previous Question Next Question

Why won't iron dissolve as easily in HNO3 as it does in HCl?

I just completed a method development lab in which we looked further into the determination of iron using the dichromate method. Instead of using HCl (which we used in a previous iron determination), I used HNO3. The problem I encountered was that the iron did not dissolve well in the nitric acid. We also observed that the solution turned slightly black when adding 0.5 M stannous chloride. Could the nitrate ion have an effect on the oxidation/reduction of the iron and could it also oxidize the tin (II) to tin (IV)?
Jared Anderson

When you dissolve the iron in HCl, you'll get Fe2+ (at least, until the O2 in air starts to work on it). It should dissolve in dilute HNO3, but some of the iron will go over to iron(III). If you put iron in concentrated HNO3, it becomes resistant to corrosion or dissolution. This process is called passivation. is some disagreement about how passivation works, but it probably involves laying down an oxide film of some kind.

As for the tin, probably. If the concentration of the nitric acid was high enough it shouldn't have any problem oxidizing tin(II) to tin(IV).

Author: Fred Senese senese@antoine.frostburg.edu



General Chemistry Online! Why won't iron dissolve as easily in HNO_3_ as it does in HCl?

Copyright © 1997-2010 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/redox/faq/passivation.shtml