Question

A metal \((M)\) produces a gas \((N)\) on reaction with alkalies like \(\mathrm{NaOH}\) and \(\mathrm{KOH}\). Same gas is produced when the metal reacts with dilute sulphuric acid Gas \((N)\) reacts with another toxic gas \((P)\) to form methanol at high temperature and pressure. ( \(N\) ) also reacts with metals like \((Q)\) to form electrovalent hydrides. \(M, N, P\) and \(Q\) respectively are (a) \(\mathrm{Zn}, \mathrm{H}_{2}, \mathrm{CO}, \mathrm{Na}\) (b) \(\mathrm{Na}, \mathrm{H}_{2}, \mathrm{Cl}_{2}, \mathrm{Ca}\) (c) \(\mathrm{Al}, \mathrm{H}_{2}, \mathrm{H}_{2} \mathrm{~S}, \mathrm{~B}\) (d) \(\mathrm{Mg}, \mathrm{H}_{2}, \mathrm{NO}_{2}, \mathrm{Al}\)

Short answer

The correct option is (a) Zn, H2, CO, Na. Zinc reacts with alkalies and dilute sulphuric acid to form hydrogen gas, which then reacts with carbon monoxide to form methanol and with sodium to form an electrovalent hydride.

Step-by-step solution

- Analyze Reaction with Alkalies

Determine the metal that reacts with alkalies like NaOH and KOH to produce a gas. Common metals that react in such a way include aluminum and zinc.

- Identify Gas Produced with Sulphuric Acid

The same gas is produced when the metal reacts with dilute sulphuric acid. Typically, hydrogen gas (H2) is generated in these types of reactions.

- Determine Methanol Formation

Methanol is formed when hydrogen gas (H2) reacts with carbon monoxide (CO) at high temperature and pressure. So, the toxic gas (P) is likely to be CO.

- Identify Metal Making Electrovalent Hydrides

The metals that commonly react with hydrogen to form electrovalent hydrides are those that are more reactive, such as Group 1 and 2 metals like Na and Ca.

- Match the Options with Deduced Information

Based on the deductions, we can match each component. The metal (M) reacts with NaOH/KOH and H2SO4 to give H2, the gas (N). Gas (N) forms methanol with CO, the gas (P), and reacts with metals (Q) like Na to form hydrides. Given these criteria, the correct match is Zn for (M), H2 for (N), CO for (P), and Na for (Q). Option (a) fits the description.

Key concepts

Electrovalent Hydrides

Electrovalent hydrides are compounds formed when hydrogen reacts with more electropositive metals such as those from Group 1 (alkali metals) and Group 2 (alkaline earth metals) of the periodic table. The metal donates its valence electron(s) to hydrogen, resulting in the formation of ionic bonds between the two. As a result, the overall structure is characterized by a metal cation (M⁺ or M²⁺) and a hydride anion (H^-).

For instance, if we consider sodium (Na), it can react with hydrogen (H₂) to form sodium hydride (NaH) through the reaction: \[ 2 \text{Na} + \text{H}_2 \rightarrow 2 \text{NaH} \] This reaction is highly exothermic and sodium hydride is commonly used as a strong base in various chemical syntheses. Due to their high reactivity, electrovalent hydrides are typically stored under inert conditions to prevent them from reacting violently with atmospheric moisture or oxygen.

Reaction with Alkalies

Some metals react with alkalies, like sodium hydroxide (NaOH) and potassium hydroxide (KOH), producing a gas. This type of reaction involves a metal reacting with an aqueous solution of the alkali to release hydrogen gas (\text{H}_2). A classic example of such a reaction involves metals like zinc (Zn) and aluminum (Al) which can react with alkalies in a displacement reaction.

The general equation for the reaction of metal M with an alkali NH is: \[ \text{M} + 2 \text{NH} (aq) \rightarrow 2 \text{M} (\text{OH})_n + \text{H}_2 (g) \] Such reactions are utilized in various analytical techniques to identify certain metals based on the gas evolved, and also to produce hydrogen gas for industrial applications. The reactiveness of the metal and the conditions of the reaction, such as concentration and temperature, can greatly affect the rate and extent of the gas production.

Methanol Formation

Methanol (\text{CH}_3\text{OH}) formation is an essential industrial process often achieved through the reaction of hydrogen gas with carbon monoxide (\text{CO}) under high temperature and pressure. This process, known as the hydrogenation of CO, is a form of chemical synthesis where the mixture is exposed to a catalyst like copper, zinc oxide, or chromia to facilitate the reaction.

The chemical equation representing the formation of methanol is: \[ \text{CO} + 2 \text{H}_2 \rightarrow \text{CH}_3\text{OH} \] This reaction is not only significant for the production of methanol, which is widely used as a solvent, a fuel, and in the manufacture of formaldehyde and other chemicals, but also as a method of reducing toxic carbon monoxide from various industrial emission streams, thus indirectly contributing to environmental protection. The high-pressure conditions ensure the reactants come into closer proximity and the high temperature provides the necessary energy to overcome the activation barrier for the reaction to proceed effectively.