Problem 38 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is produced, when copper reacts with chlorine? (a) \(\mathrm{CuCl}_{4}\) (b) \(\mathrm{Cu}_{2} \mathrm{Cl}\) (c) \(\mathrm{Cu}_{2} \mathrm{Cl}_{2}\) (d) \(\mathrm{CuCl}_{2}\)

Step-by-Step Solution

Answer

Copper reacts with chlorine to produce \(\mathrm{CuCl}_2\).

Step 1: Understand the Reactants

Copper (Cu) is a metal that can form two common oxidation states: +1 and +2. Chlorine (Cl) is a non-metal that typically forms a -1 oxidation state in compounds.

Step 2: Consider Possible Compounds of Copper and Chlorine

Copper and chlorine can react to form different compounds depending on the oxidation state of copper. Common compounds include copper(I) chloride ( \(\mathrm{Cu}_2\mathrm{Cl}_2\)) and copper(II) chloride (\(\mathrm{CuCl}_2\)).

Step 3: Formula Validation

Evaluate each given option:- (a) \(\mathrm{CuCl}_4\): This implies the presence of Cu(IV), which is not stable.- (b) \(\mathrm{Cu}_2\mathrm{Cl}\): This implies one chlorine with oxidation state -1 bonding with two copper atoms, which is uncommon.- (c) \(\mathrm{Cu}_2\mathrm{Cl}_2\): This represents copper(I) chloride, formed with copper having +1 oxidation state.- (d) \(\mathrm{CuCl}_2\): This represents copper(II) chloride, formed when copper has a +2 oxidation state.

Step 4: Determine Common Product

Copper generally reacts with chlorine to form \(\mathrm{CuCl}_2\) because it is more stable for copper to exist as \(\mathrm{Cu}^{2+}\) in cupric chloride.

Key Concepts

Oxidation States

In chemistry, oxidation states, also known as oxidation numbers, describe the degree of oxidation of an atom in a chemical compound. They are essential for understanding how elements combine and react with one another. Copper, for instance, is a versatile element that can exist in more than one oxidation state. The most common oxidation states for copper are +1 and +2.

When copper forms compounds, it can either lose one electron to achieve a +1 oxidation state, known as copper(I), or lose two electrons to achieve a +2 oxidation state, known as copper(II). The oxidation state helps predict the kind of compounds copper can form. For chlorine, its oxidation state in compounds is usually -1, as it gains one electron to fill its outer shell. Evaluating these oxidation states is crucial for understanding and predicting chemical reactions, such as those involving copper and chlorine.

Copper Reactions

Copper is a transition metal known for its ability to participate in a variety of chemical reactions. When copper reacts with other elements, its oxidation state determines the type of compounds formed. For instance, when copper reacts with chlorine, it forms either copper(I) chloride or copper(II) chloride, depending on the oxidation state of copper at the time of reaction.

- **Copper(I) Chloride (\(\mathrm{Cu}_2\mathrm{Cl}_2\))**: Formed when copper is in the +1 oxidation state. This occurs when each copper atom loses one electron while each chlorine atom gains an electron.- **Copper(II) Chloride (\(\mathrm{CuCl}_2\))**: Formed when copper is in a more stable +2 oxidation state, which involves the loss of two electrons from copper. Each chlorine atom still gains one electron, making copper(II) chloride a more common and stable reaction product between copper and chlorine.

Understanding these reactions not only helps identify the products formed but also illustrates the broader principles of how elements with differing properties react to form stable compounds.

Chemical Compounds of Copper

Copper forms various chemical compounds, depending on its oxidation state and reaction conditions. Two prominent compounds include copper(I) chloride and copper(II) chloride, each with distinct chemical and physical properties.

- **Copper(I) Chloride \(\mathrm{Cu}_2\mathrm{Cl}_2\)**: This compound appears as a white crystalline solid but can darken when exposed to light due to decomposition.- **Copper(II) Chloride \(\mathrm{CuCl}_2\)**: A greener or yellowish-brown compound, typically more stable than copper(I) chloride. It is often seen in its dihydrate form \(\mathrm{CuCl}_2\cdot2\mathrm{H}_2\mathrm{O}\), which is blue-green in color and more commonly used in laboratories and industry.

These characteristics of copper compounds highlight the diversity and applications they have, from laboratory synthesis to practical applications such as catalysis and pigment production.