Question

Formaldehyde is warmed with \(50 \% \mathrm{NaOH}\). The order of reaction that takes place is

Short answer

The reaction is first-order.

Step-by-step solution

Understanding the Reaction

This exercise involves identifying the order of a reaction where formaldehyde is warmed with 50% NaOH. In this scenario, formaldehyde undergoes a Cannizzaro reaction, which is common in aldehydes without alpha-hydrogens when reacted with concentrated alkali like NaOH.

Identifying the Reaction Type

The key reaction involved here is the Cannizzaro reaction. Formaldehyde ( ext{HCHO}), as an aldehyde without alpha-hydrogens, will disproportionate into a carboxylate salt and an alcohol when reacted with concentrated NaOH.

Determining the Order of Reaction

In a Cannizzaro reaction, the rate depends only on the concentration of the aldehyde. This means the reaction is a first-order reaction with respect to the aldehyde, despite it being a bimolecular disproportionation.

Finalizing the Order

The overall order of the reaction is determined by its slowest step, which is dependent on the concentration of formaldehyde, making the reaction first-order overall.

Key concepts

Formaldehyde

Formaldehyde (HCHO) is a simple aldehyde and one of the most important compounds in the study of organic chemistry. It consists of a carbon atom doubly bonded to an oxygen atom and singly bonded to two hydrogen atoms. This structure makes formaldehyde quite reactive and allows it to participate in a variety of chemical reactions. Generally, aldehydes like formaldehyde are susceptible to oxidation and reduction reactions.

The Cannizzaro reaction, where formaldehyde is involved when mixed with a strong base like NaOH, leverages the lack of alpha-hydrogens in this molecule. This results in a unique disproportionation reaction that converts the aldehyde into a mixture of alcohols and carboxylate acids or salts.

Reaction Order

The concept of reaction order is crucial in understanding how the concentration of reactants affects the rate of a chemical reaction. Reaction order defines the power to which the concentration of a reactant is raised in the rate law. In other words, it indicates how the speed of the reaction varies with changes in reactant concentration.

In the Cannizzaro reaction of formaldehyde with NaOH, the rate of reaction is determined to be first-order with respect to formaldehyde. This implies that doubling the concentration of formaldehyde will, in turn, double the rate of the reaction. The order of the reaction informs us about the stoichiometry of the rate-determining step and helps predict the behavior of the reaction under different conditions.

Aldehyde Reactions

Aldehydes are versatile compounds with a variety of reactions. One noteworthy reaction is the Cannizzaro reaction, which occurs in aldehydes devoid of alpha-hydrogens when exposed to strong bases. During this reaction, two molecules of an aldehyde are transformed: one is reduced to an alcohol, and the other is oxidized to a carboxylate ion.

This unique disproportionation process showcases the reactivity of aldehydes in different environments and illustrates their significant roles in organic chemistry. The Cannizzaro reaction specifically is an excellent example of how structural characteristics influence chemical behavior. It is essential for students to grasp these fundamental concepts to appreciate the wide range of transformations possible with aldehydes.

NaOH Concentration

The concentration of NaOH used in reactions plays a vital role in determining the reaction mechanism and outcome. In the Cannizzaro reaction, a high concentration of NaOH acts as the base necessary for the simultaneous oxidation-reduction process that occurs with aldehydes like formaldehyde.

Using a 50% NaOH solution provides not only the alkaline environment needed for the reaction to take place but also ensures that the reaction rate is sufficient for practical observation and analysis. This further highlights how varying the concentration of a reactant, such as NaOH, can significantly affect the course of chemical reactions by altering rates or even the pathway taken during the reaction.