Chromium(III) nitrate

Chromium(III) nitrate is an inorganic compound with the formula Cr(NO₃)₃. It is one of the many nitrate salts of chromium. Chromium(III) nitrate usually refers to the nonahydrate, Cr(NO₃)₃·9H₂O, a violet or purple solid that is highly soluble in water.

Properties

Chromium(III) nitrate nonahydrate is a deliquescent solid, which means it can absorb moisture from the air and dissolve in it. This property makes it necessary to store the compound in airtight containers to prevent it from becoming a liquid. When dissolved in water, it forms a violet solution, due to the presence of the [Cr(H₂O)₆]³⁺ ion. Upon heating, chromium(III) nitrate can decompose, releasing nitrogen dioxide (NO₂), a toxic and corrosive gas.

Synthesis

Chromium(III) nitrate can be synthesized by dissolving chromium, chromium(III) oxide, or chromium(III) hydroxide in nitric acid. The reaction with chromium metal is slow and can take several days, while using chromium(III) oxide or hydroxide speeds up the process.

\[ \text{Cr} + 4\text{HNO}_3 \rightarrow \text{Cr(NO}_3)_3 + 2\text{H}_2\text{O} + \text{NO}_2 \]

\[ \text{Cr}_2\text{O}_3 + 6\text{HNO}_3 \rightarrow 2\text{Cr(NO}_3)_3 + 3\text{H}_2\text{O} \]

\[ \text{Cr(OH)}_3 + 3\text{HNO}_3 \rightarrow \text{Cr(NO}_3)_3 + 3\text{H}_2\text{O} \]

Uses

Chromium(III) nitrate is used in the preparation of other chromium compounds. It is a starting material for the synthesis of chromium coordination complexes, which have applications in dyeing, tanning leather, and in the ceramic industry as a pigment. Its ability to form colored complexes with various organic compounds makes it useful in analytical chemistry for detecting certain molecules.

Safety

Chromium(III) nitrate is considered to be of low toxicity, but it is still a strong oxidizer and can cause fires if it comes into contact with combustible materials. The compound should be handled with care, avoiding ingestion, inhalation, or skin contact. Safety equipment such as gloves and goggles should be used when handling the chemical.

Environmental Impact

While chromium(III) compounds are generally less harmful than chromium(VI) compounds, they can still pose risks to the environment. Chromium(III) can accumulate in the water and soil, potentially leading to chromium contamination. Proper disposal methods should be followed to minimize environmental impact.