Question

Write a balanced equation for each of the following single-replacement reactions: (a) Magnesium metal is added to nitric acid. (b) Manganese metal is added to hydrochloric acid.

Short answer

(a) \( \text{Mg} + 2\text{HNO}_3 \rightarrow \text{Mg(NO}_3\text{)}_2 + \text{H}_2 \) (b) \( \text{Mn} + 2\text{HCl} \rightarrow \text{MnCl}_2 + \text{H}_2 \)

Step-by-step solution

Understanding the Problem

We need to write balanced chemical equations for the described single-replacement reactions: (a) magnesium with nitric acid, and (b) manganese with hydrochloric acid.

Identify the Reactants

For part (a), the reactants are magnesium (Mg) and nitric acid (HNO₃). For part (b), the reactants are manganese (Mn) and hydrochloric acid (HCl).

Predict the Products

In single-replacement reactions, a metal replaces the hydrogen in the acid, forming a salt and hydrogen gas. Therefore, for (a), the products are magnesium nitrate (Mg(NO₃)₂) and hydrogen gas (H₂). For (b), the products are manganese chloride (MnCl₂) and hydrogen gas (H₂).

Write Unbalanced Chemical Equations

For part (a): \( \text{Mg} + \text{HNO}_3 \rightarrow \text{Mg(NO}_3\text{)}_2 + \text{H}_2 \) For part (b): \( \text{Mn} + \text{HCl} \rightarrow \text{MnCl}_2 + \text{H}_2 \)

Balance the Chemical Equations

(a) Balance the magnesium and nitrate:- Equation: \( \text{Mg} + 2\text{HNO}_3 \rightarrow \text{Mg(NO}_3\text{)}_2 + \text{H}_2 \)(b) Balance the manganese and chlorine:- Equation: \( \text{Mn} + 2\text{HCl} \rightarrow \text{MnCl}_2 + \text{H}_2 \)

Verify the Balanced Equations

Check that each equation has equal numbers of each type of atom on both sides. (a) Mg: 1, H: 2, N: 2, O: 6 (b) Mn: 1, Cl: 2, H: 2 are balanced.

Key concepts

Single-Replacement Reactions

A single-replacement reaction is a fascinating type of chemical reaction where one element replaces another in a compound. This process can often be seen in reactions involving metals and acids or water.

During a single-replacement reaction:

• One element swaps places with another element that is part of a compound.
• Typically, a metal replaces an element in an acid or salt.
• The general formula is: \( A + BC \rightarrow AC + B \) where \( A \) is the element that replaces \( B \).

In the context of the exercise, a metal (like magnesium or manganese) reacts with an acid, leading to the formation of different products. Understanding which elements can replace others involves knowing the reactivity series of metals, which predicts the tendency of a metal to lose electrons and form positive ions. This knowledge is crucial in predicting whether a single-replacement reaction will occur and helps chemists write balanced chemical equations accurately.

Chemical Reactants

In every chemical reaction, the starting substances are known as reactants. These reactants undergo changes to form new substances. In single-replacement reactions, reactants include a part from which a single element switches with another.

For the exercise provided, the chemical reactants are:

• In part (a): Magnesium (\( \text{Mg} \)) and Nitric Acid (\( \text{HNO}_3 \)).
• In part (b): Manganese (\( \text{Mn} \)) and Hydrochloric Acid (\( \text{HCl} \)).

The behavior of these reactants is determined by their intrinsic properties:

• Metal reactivity, which helps to predict whether the metal can displace hydrogen from the acid.
• Acidity, which is the ability of acids to donate protons (\( \text{H}^+ \)).

Thus, understanding the properties of magnesium, manganese, and acids help us predict the chemical products emanating from these reactants.

Chemical Products

After reactants undergo a chemical reaction, they form chemical products. The type and amount of products depend on the reactants and the nature of the chemical reaction. In single-replacement reactions, one product is typically a salt, while another might be a gas.

In the specified exercise:

• Part (a) results in Magnesium Nitrate (\( \text{Mg(NO}_3)_2 \)) and Hydrogen Gas (\( \text{H}_2 \)).
• Part (b) results in Manganese Chloride (\( \text{MnCl}_2 \)) and Hydrogen Gas (\( \text{H}_2 \)).

Balancing the resulting equations involves ensuring that the number of atoms of each element on the reactant side equals the number on the product side. This is a critical step in chemistry because it adheres to the Law of Conservation of Mass, which states that matter cannot be created or destroyed in a chemical reaction.

By understanding how to find products in single-replacement reactions, chemists can predict the outcomes of mixing particular reactants and prepare balanced chemical equations with confidence.