Identify the metal which reacts with concentrated \(\mathrm{H}_{2} \mathrm{SO}_{4}\) or \(\mathrm{HNO}_{3}\), but not with concentrated \(\mathrm{HCl}\). (a) \(\mathrm{Fe}\) (b) \(\mathrm{Zn}\) (c) \(\mathrm{Cu}\) (d) Al

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation. For instance, when metals react with acids, a chemical reaction takes place that often produces hydrogen gas and a salt.

Different metals will react with different acids at different rates. This rate of reaction is influenced by the metal's activity level, which is a measure of how easily a metal can lose electrons, becoming positively charged ions or cations. This is also tied to the concept of the reactivity series of metals, which is a list that ranks metals from most reactive to least reactive. A more reactive metal will displace a less reactive metal from its compounds and is more likely to react with an acid.

When metals react with acids, they typically undergo a single displacement reaction, forming a salt and releasing hydrogen gas. This process can be represented by the general equation: \(\text{Acid} + \text{Metal} \rightarrow \text{Salt} + \text{Hydrogen gas}\). The specific type of salt formed depends on the acid and the metal involved in the reaction.

For example, when zinc (Zn) reacts with hydrochloric acid (HCl), the reaction produces zinc chloride (ZnCl2) and hydrogen gas (H2). However, not all metals react with acids. Typically, metals at the top of the reactivity series, such as potassium (K) and sodium (Na), will vigorously react with acids, while metals lower on the series, like copper (Cu), will not react with certain acids, such as concentrated hydrochloric acid (HCl). This specific behavior is crucial for understanding different outcomes when metals are exposed to various types of acids.

The concentration of an acid plays a significant role in the reactivity of metals. Concentrated acids are more likely to react with metals compared to their diluted counterparts. However, not all concentrated acids react the same way with a given metal.

Concentrated hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3) are common examples used in reactivity studies. While some metals like magnesium (Mg) and zinc (Zn) react with all three concentrated acids, copper (Cu) reacts with concentrated sulfuric acid and nitric acid, but not with concentrated hydrochloric acid due to its lower position in the reactivity series. The reactivity of concentrated acids also manifests in different forms; for example, concentrated nitric acid is known to be a powerful oxidizing agent, which can lead to additional reactions beyond the typical acid-metal reaction, such as the production of nitrogen oxides.