Question

Out of the following the number of compounds which can be used to remove water from alcohol is \(\mathrm{CaO}, \mathrm{Na}, \mathrm{Mg}, \mathrm{CaCl}_{2},\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O}\right)_{2} \mathrm{Mg}\), conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{PCl}_{5}\)

Short answer

4 compounds can be used to remove water from alcohol.

Step-by-step solution

Understanding the Problem

The task is to identify compounds from the given list that can be used to remove water from alcohol, effectively acting as dehydrating agents.

Consider Alcohols and Dehydrating Agents

Alcohols typically undergo dehydration in the presence of specific dehydrating agents. Common dehydrating agents include chemicals like calcium oxide (CaO), phosphorus pentachloride (PCl₅), concentrated sulfuric acid (H₂SO₄), and calcium chloride (CaCl₂).

Evaluating Each Compound

- **CaO**: A drying agent capable of removing water due to its hygroscopic nature. It can be used for drying alcohol. - **Na**: Reacts with alcohol to form sodium alkoxides and hydrogen gas, but not primarily used for dehydration. - **Mg**: While reactive, it is not typically used for dehydration of alcohol. - **CaCl₂**: Another hygroscopic compound often used to dry alcohol by absorbing water. - **(C₂H₅O)₂Mg**: Also known as a Grignard reagent, not suitable for dehydration. - **Conc. H₂SO₄**: A strong dehydrating agent, frequently used for removing water from alcohol. - **PCl₅**: Able to replace the hydroxide group with chloride, effectively removing water.

Count Suitable Compounds

From the evaluation in Step 3, the compounds suitable for dehydration are: CaO, CaCl₂, conc. H₂SO₄, and PCl₅. This gives us a total of 4 compounds.

Key concepts

Alcohol Dehydration

Alcohol dehydration is a chemical reaction where water is removed from an alcohol molecule. This process often requires a substance known as a dehydrating agent. Dehydrating agents facilitate the reaction either by absorbing water directly or by chemically reacting with the alcohol to remove water.

In alcohol dehydration, concentrated sulfuric acid ext {(H}_{2} ext{SO}_{4}) is commonly used. It works by providing excess hydronium ions ( H₃ ext{O}^+ ) to protonate the alcohol, making it a better leaving group. This helps in removing the water molecule, often resulting in the formation of an alkene. Other effective dehydrating agents include phosphorus pentachloride ( ext{PCl}_{5}) and calcium oxide ( ext{CaO}) .

Remember, the effectiveness of dehydration depends largely on the nature of both the alcohol and the dehydrating agent, as well as reaction conditions like temperature.

Hygroscopic Compounds

Hygroscopic compounds are substances that can absorb moisture from their environment. This property makes them excellent drying agents in various chemical processes, including the dehydration of alcohols.

Calcium chloride ( ext{CaCl}_{2}) is a classic example of a hygroscopic compound. It is often used to remove water from organic solvents and alcohols because it can absorb water in its crystal lattice. Similarly, calcium oxide ( ext{CaO}) , also known as quicklime, is another hygroscopic substance. It not only absorbs moisture but also reacts with it, which enhances its ability to act as a drying agent.

These compounds are crucial in industries where maintaining water-free environments is essential, such as in the production of certain pharmaceuticals and chemical syntheses.

Chemical Reactions with Alcohol

Alcohols are versatile compounds that can undergo a variety of chemical reactions. The presence of the hydroxyl group (-OH) makes them reactive and amenable to several transformations.

For instance, sodium ( ext{Na}) can react with alcohols, yielding sodium alkoxides and hydrogen gas. This is not primarily a dehydration reaction, but it demonstrates the reactive nature of alcohols.

When discussing reactions involving alcohols, one must consider other factors such as the type of alcohol (primary, secondary, or tertiary) and the environmental conditions, as these influence the reaction pathways and the desired products.

In the context of dehydration, chemical reactions often aim to achieve the transformation of alcohols into alkenes, which are used in various applications, from fuel sources to monomers in polymer production.

Drying Agents in Chemistry

Drying agents are crucial in chemistry for removing water from substances. They are particularly important in the preparation and purification of products where moisture can affect the outcomes.

Common drying agents include hygroscopic compounds like calcium chloride ( ext{CaCl}_{2}) and calcium oxide ( ext{CaO}) , which work by absorbing water molecules from their surroundings. These agents are often used in laboratories to dry solvents and gases, ensuring that reactions are carried out under anhydrous conditions.

It's important to select a drying agent that is compatible with the other chemicals involved in the process to prevent unwanted side reactions. Advanced knowledge of the chemical properties and interaction potential of these agents is essential for laboratory and industrial applications alike. By controlling the presence of water in reactions, chemists can ensure the success and purity of chemical transformations.