Question

Which one of the following compounds in aqueous solution gives a white precipitate with perchloric acid? (a) \(\mathrm{NaCl}\) (b) \(\mathrm{MgCl}_{2}\) (c) \(\mathrm{KCl}\) (d) \(\mathrm{FeCl}_{3}\)

Short answer

None of the given compounds typically form a white precipitate with perchloric acid.

Step-by-step solution

Understand the Problem

The problem asks which compound forms a white precipitate when reacting with perchloric acid in an aqueous solution. Given options are different chlorides of sodium, magnesium, potassium, and iron.

Identify Potential Reactions

Perchloric acid is a strong acid. Generally, it reacts with metal salts to form either soluble products or a precipitate, depending on the solubility of the resulting compound.

Apply Solubility Rules

Use solubility rules to determine if the chloride of each metal forms an insoluble compound with perchloric acid. Generally, perchlorates are soluble, but some metal perchlorates are not. Magnesium perchlorate (Mg(ClO_4)_2), for example, is soluble, while equipoised iron and potassium perchlorates have different reactivity.

Check the Reaction of Each Compound

Assess the reaction between each given chloride and perchloric acid: - NaCl and KCl do not form a precipitate. - MgCl_2 does not form a precipitate as Mg(ClO_4)_2 is soluble. - FeCl_3 can potentially form a complex precipitate with perchlorates, but it depends on temperature and concentration.

Determine the Most Likely Precipitate Formation

Based on the typical behavior, none of the common chloride compounds listed forms a distinct "white" precipitate under usual conditions, but historically, iron and some complex metals might demonstrate unusual reactions resulting in precipitates.

Conclude Based on Chemical Knowledge

Consider practical laboratory conditions; iron chloride FeCl_3 can form complexes with ligands but Mg(ClO_4)_2 and others usually remain soluble in typical conditions.

Key concepts

Solubility Rules

Solubility rules are guidelines used to predict whether a substance will dissolve in a solvent, like water, to form a solution. These rules help chemists determine whether a chemical reaction will yield a soluble product or form a precipitate.

• Most nitrate \(\text{NO}_3^-\) salts are soluble.
• Most salts containing alkali metal ions \(\text{Li}^+, \text{Na}^+, \text{K}^+, \text{Rb}^+, \text{Cs}^+\) and the ammonium ion \(\text{NH}_4^+\) are soluble.
• Most chloride, bromide, and iodide salts are soluble, except for those containing silver \(\text{Ag}^+\), lead \(\text{Pb}^{2+}\), and mercury \(\text{Hg}_2^{2+}\).
• Most sulfate \(\text{SO}_4^{2-}\) salts are soluble, except for barium sulfate \(\text{BaSO}_4\), lead sulfate, mercury sulfate, and calcium sulfate.
• Carbonates \(\text{CO}_3^{2-}\), phosphates \(\text{PO}_4^{3-}\), chromates \(\text{CrO}_4^{2-}\), sulfides, and hydroxides are generally insoluble, with some exceptions.

By applying these rules, the compounds can be examined. Most perchlorates \(\text{ClO}_4^-\) are soluble, yet empirical exceptions exist such as certain rare or complex metal perchlorates that might demonstrate insolubility under specific conditions.

Precipitate Formation

Precipitate formation occurs when an insoluble solid forms from a solution during a chemical reaction. This process typically happens when two soluble salts react in an aqueous solution to form one or more insoluble products. When the conditions are right, the solid precipitate forms and separates from the remaining liquid.To predict when a precipitate will form, chemists use solubility rules and chemical equations to evaluate interactions between ions. For example:

• If two reactant ions form a compound that is deemed insoluble by solubility rules, a precipitate is likely to form.
• Precipitation reactions are commonly seen in reactions involving exchange of ions, where the product may include an insoluble compound.
• The color and texture of the precipitate can vary depending on the substances involved. For instance, common precipitates include white zinc sulfate \(\text{ZnSO}_4\) or yellow lead iodide \(\text{PbI}_2\).

In the scenario given, none of the common chloride compounds listed directly forms a definitive white precipitate under standard conditions, showcasing the importance of empirical evaluation in some cases.

Aqueous Solution Chemistry

Aqueous solution chemistry involves studying the properties and behaviors of substances dissolved in water. Water is an excellent solvent because of its polarity, which attracts and dissolves various ionic and molecular compounds. Understanding these interactions is crucial when analyzing reactions in a solution. In a typical aqueous solution:

• Dissolved ions allow electrical conductance, which is a key property in solutions.
• Reactions in aqueous solutions often involve changes in ion arrangements, leading to different phases such as solids (precipitates).
• Factors like temperature and concentration can influence the outcomes of reactions, including whether products remain dissolved or form precipitates.

The given exercise revolves around how different chlorides behave when exposed to perchloric acid in an aqueous environment. Knowledge of aqueous solution behavior assists in predicting if any combination leads to solid formation, as solutions offer a medium for potential interactions and reactions to occur.