Question

The number of moles of \(\mathrm{AgCl}\) precipitated when excess \(\mathrm{AgNO}_{3}\) is mixed with one mole of \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{4}\right.\) \(\left.\mathrm{Cl}_{2}\right] \mathrm{Cl}\) is (a) 4 (b) 3 (c) 2 (d) 1

Short answer

The number of moles of \\(\mathrm{AgCl}\\) precipitated is 1.

Step-by-step solution

Understanding the compound

The compound \([ \text{Cr}\left(\text{NH}_3\right)_4\text{Cl}_2\right]\text{Cl}\) is a coordination complex. It consists of a chromium central metal atom, four ammonia ligands, two chloride ions inside the coordination sphere, and one chloride ion outside the sphere, which is the ionizable chloride.

Identify ionic chloride

In the compound \([ \text{Cr}\left(\text{NH}_3\right)_4\text{Cl}_2\right]\text{Cl}\), the chloride ion outside the coordination sphere is the one that is free to react with \(\text{AgNO}_3\) to form \(\text{AgCl}\) precipitate.

Determine reaction with AgNO₃

When \(\text{AgNO}_3\) is added to the solution, the free chloride ion reacts with silver nitrate to form \(\text{AgCl}\) precipitate. Only one chloride ion is available outside the complex which can react.

Calculate moles of AgCl formed

Since there is only one chloride ion available to react with each mole of \([ \text{Cr}\left(\text{NH}_3\right)_4\right. \ \left.\text{Cl}_2\right]\text{Cl}\), when excess \(\text{AgNO}_3\) is mixed with one mole of the compound, the moles of \(\text{AgCl}\) precipitated will also be 1.

Key concepts

Coordination Complexes in Chemistry

A coordination complex is a fascinating entity found within the realm of chemistry. It consists of a central metal atom or ion, such as chromium in our example, surrounded by molecules or ions referred to as ligands. The central atom and the ligands form a coordination sphere, which gives these complexes unique properties.
Coordination complexes have various applications and are pivotal in many natural processes, including photosynthesis and the transport of oxygen in the blood. They can exist in different geometries, such as octahedral, tetrahedral, and square planar, depending on the coordination number and type of ligands present. Understanding the structure of a coordination complex is crucial because it influences reactivity and stability. These complexes often have interesting colors and magnetic properties, which can be used to identify or characterize them.

The Science of Precipitation Reactions

Precipitation reactions are a type of reaction in which solutes react in solution to form an insoluble solid known as a precipitate. In the case of our exercise, when silver nitrate ( AgNO₃) is mixed with a coordination complex, a precipitation reaction occurs that results in the formation of silver chloride ( AgCl).
Precipitates are often visualized as a solid forming in the solution, signaling a chemical change. This reaction type is used in various applications like water treatment, extraction of metals, and the formation of pigments. To predict whether a precipitate will form, chemists use solubility rules which help identify insoluble compounds formed by combining different ionic solutions. The insolvable material then can be removed from the mixture through filtration.

Understanding Ligands

Ligands are a core component of coordination complexes. They are ions or molecules that bind to a central metal atom to form the complex. In the compound ext[Cr(NH₃)₄Cl₂] , ammonia ( NH₃) acts as a neutral ligand by donating a lone pair of electrons to the metal center. This donation forms a coordinate bond, sometimes referred to as a dative covalent bond.
Ligands can vary widely in their size, charge, and mode of binding. They are often categorized as monodentate, bidentate, or polydentate based on how many donor atoms interact with the central metal. Altering the ligands in a coordination complex can affect properties like solubility, geometric configuration, and even the color of the complex. For students exploring this topic, it's essential to see how ligand types influence the overall behavior of their complexes.

Exploring Ionic Compounds

Ionic compounds are chemical compounds composed of cations and anions that are held together by strong electrostatic forces in an ionic bond. These compounds typically consist of metals and nonmetals—like sodium chloride ( NaCl), in which sodium (a metal) and chloride (a nonmetal) form a stable ionic bond.
In the context of the coordination complex ext[Cr(NH₃)₄Cl₂]Cl, the chloride ions outside the coordination sphere exemplify this ionic aspect. When introduced to silver nitrate ( AgNO₃), a chemical change occurs as the chloride ions react with silver ions to form an insoluble AgCl precipitate. Understanding ionic compounds and the principles behind ionic interactions helps in predicting the behavior of substances in various chemical reactions, making it a fundamental concept in chemistry.