Question

Write a balanced chemical equation showing how each metal reacts with \(\mathrm{HCl}\). (a) \(\mathrm{K}\) (b) \(\mathrm{Ca}\) (c) \(\mathrm{Na}\) (d) \(\mathrm{Sr}\)

Short answer

\(\mathrm{K} + \mathrm{HCl} \rightarrow \mathrm{KCl} + \mathrm{H}_2\), \(\mathrm{Ca} + 2\mathrm{HCl} \rightarrow \mathrm{CaCl}_2 + \mathrm{H}_2\), \(\mathrm{Na} + \mathrm{HCl} \rightarrow \mathrm{NaCl} + \mathrm{H}_2\), and \(\mathrm{Sr} + 2\mathrm{HCl} \rightarrow \mathrm{SrCl}_2 + \mathrm{H}_2\).

Step-by-step solution

Writing Reaction for Potassium (K)

For group 1 metals like potassium (K), the general reaction with hydrochloric acid (HCl) is a single-displacement reaction where hydrogen is displaced to form hydrogen gas and a salt. The balanced chemical equation for potassium reacting with hydrochloric acid is: \(2\mathrm{K} + 2\mathrm{HCl} \rightarrow 2\mathrm{KCl} + \mathrm{H}_2\).

Writing Reaction for Calcium (Ca)

Calcium (Ca) is a group 2 metal that reacts with hydrochloric acid (HCl) to form calcium chloride (CaCl2) and hydrogen gas. The balanced chemical equation for the reaction is: \(\mathrm{Ca} + 2\mathrm{HCl} \rightarrow \mathrm{CaCl}_2 + \mathrm{H}_2\).

Writing Reaction for Sodium (Na)

Sodium (Na) is another group 1 metal and reacts similarly to potassium with hydrochloric acid. The balanced equation for sodium reacting with hydrochloric acid is: \(2\mathrm{Na} + 2\mathrm{HCl} \rightarrow 2\mathrm{NaCl} + \mathrm{H}_2\).

Writing Reaction for Strontium (Sr)

Strontium (Sr) is in group 2 like calcium and reacts with hydrochloric acid to form strontium chloride (SrCl2) and hydrogen gas. The balanced chemical equation for the reaction is: \(\mathrm{Sr} + 2\mathrm{HCl} \rightarrow \mathrm{SrCl}_2 + \mathrm{H}_2\).

Key concepts

Chemical Reactions

Understanding chemical reactions is fundamental to the study of chemistry. A chemical reaction occurs when substances, known as reactants, undergo a process that changes them into different substances, called products. This transformation happens through the breaking and forming of chemical bonds.

Every chemical reaction is governed by certain laws, one of which is the conservation of mass. This principle states that in a closed system, mass cannot be created or destroyed in a chemical reaction. Therefore, when writing chemical equations, it is crucial to balance them, ensuring that the number of atoms for each element is the same on both the reactant and product sides.

Types of Chemical Reactions

There are many types of chemical reactions, but the reactions in our exercise are examples of single-displacement reactions, where one element displaces another in a compound. In the displacement reactions between metals and hydrochloric acid (HCl), hydrogen is displaced to form hydrogen gas (H₂) and a metal chloride salt.

In summarizing chemical reactions, knowing how to balance chemical equations is vital because it reflects the conservation of mass, allowing us to predict the amounts of products and reactants involved.

Reactivity of Metals

Metals differ in how readily they undergo chemical reactions, a property known as reactivity. The reactivity of metals is crucial when they react with acids like hydrochloric acid (HCl). Reactivity is often influenced by the metal's position in the Periodic Table.

For example, metals in group 1, known as alkali metals (such as potassium (K) and sodium (Na)), are highly reactive. They will react vigorously with HCl to produce hydrogen gas and metal chlorides, like potassium chloride (KCl) and sodium chloride (NaCl).

Trends in Reactivity

The reactivity of metals typically increases as we move down a group in the Periodic Table. This is because as the atomic size increases, the outermost electrons are further from the nucleus, making them easier to remove. This trend is evident as both potassium and sodium (from group 1) react similarly with HCl, following a quick and straightforward displacement process.

Hydrochloric Acid Metal Reaction

When metals react with hydrochloric acid (HCl), a type of chemical reaction occurs where the acid reacts with the metal to produce a metal chloride and hydrogen gas. This reaction is not only a great example of a chemical reaction but also an excellent illustration of metal reactivity.

The reaction can be written as a balanced chemical equation, which adheres to the law of conservation of mass, where the total mass of the reactants equals the total mass of the products. The general form of the equation for the reaction between metals and HCl is as follows:
\[\text{Metal} + \text{HCl} \rightarrow \text{Metal Chloride} + \text{H}_2\].

The specific balanced equations for the metals in our exercise illustrate the ratio in which the reactants combine to form products, and they highlight the different amounts of HCl needed to react with different metals. Alkali and alkaline earth metals, such as potassium (K), calcium (Ca), sodium (Na), and strontium (Sr), all react to form their respective chlorides and hydrogen gas, showcasing their reactivity with acids.

Practical Implications

These reactions are not just academic exercises; they also have practical implications in industries where metals are exposed to acids, helping us predict and control the outcomes of these chemical interactions.