Question

You are given two solutions containing \(\mathrm{FeCl}_{2}\) and \(\mathrm{FeCl}_{3}\) at the same concentration. One solution is light yellow, and the other one is brown. Identify these solutions based only on color.

Short answer

Light yellow is FeCl₂; brown is FeCl₃.

Step-by-step solution

Understand the Compounds

FeCl₂, also known as Iron(II) chloride, typically forms a light green color when in solution. However, in some cases, it can appear light yellow, especially when the concentration is low. FeCl₃, known as Iron(III) chloride, forms a yellow to brown solution depending on its concentration.

Analyze Color Descriptions

The exercise describes one solution as light yellow and the other one as brown. Given the potential color characteristics of FeCl₂ and FeCl₃ solutions, light yellow would be more closely associated with FeCl₂, and brown would correspond to FeCl₃.

Match Colors to Compounds

Match the described colors of the solutions to the compounds: Light yellow corresponds to FeCl₂, as it matches the potential lighter color variations of FeCl₂. Brown corresponds to FeCl₃, as it matches the possible darker color variations of FeCl₃.

Key concepts

FeCl₂ color

Iron(II) chloride, chemically represented as FeCl₂, is known for its color variations when dissolved in water. Although FeCl₂ solutions are commonly associated with a light green tint, they can appear light yellow in certain conditions. The change to a yellowish color often occurs when the solution is diluted or at lower concentrations.

Understanding this color change is critical in identifying different iron chloride solutions. Students should also be aware of the context of the solution's environment, such as concentration and impurities that might affect its appearance. So when you see a light yellow iron solution, FeCl₂ might be the compound you are looking at.

FeCl₃ color

Iron(III) chloride, or FeCl₃, displays a distinctive color range in aqueous solutions but prominently features yellow to brown hues based on concentration. At lower concentrations, FeCl₃ solutions appear yellow; as the concentration increases, the color deepens to brown.

This color gradient is linked to the amount of FeCl₃ present. In more concentrated forms, the brown color becomes prominent due to increased absorption of light. This concept is vital for effective chemical analysis and identification of unknown solutions. If faced with a brown iron solution, it is likely that you're dealing with FeCl₃, especially when other distinguishing factors align with this observation.

Iron oxidation states

Iron can exist in multiple oxidation states, with Fe²⁺ and Fe³⁺ being the most common in iron chloride compounds. The oxidation state directly impacts the compound's chemical behavior and its appearance when dissolved in water.

• Fe²⁺ is the oxidation state in FeCl₂, known as iron(II) chloride. This state is more reducing and can show colors from light green to light yellow in solution.
• Fe³⁺ is present in FeCl₃, termed iron(III) chloride. It is more oxidizing and can exhibit colors ranging from yellow to brown.

These differences in oxidation states and associated colors are crucial for distinguishing between iron chloride solutions. Being able to identify based on oxidation state reinforces understanding of basic chemical principles and aids in more accurate laboratory analyses.

Solution color identification

Identifying the color of a chemical solution is a fundamental yet powerful technique in chemistry. It involves observing the visible characteristics of a solution to gain insights into its composition. With iron chloride solutions, color becomes an excellent indicator of specific compounds present.

• Light yellow colors often suggest the presence of FeCl₂, or iron(II) chloride, especially in dilute solutions due to its characteristically lighter hue.
• Brown shades mostly point towards FeCl₃, or iron(III) chloride, indicative of higher concentrations where the color turns darker.

Color observations require careful consideration of other conditions, such as solution concentration and environmental factors. Therefore, while color provides a significant clue, always corroborate with additional tests for a comprehensive analysis.