Problem 54 - Chemistry: The Central Science

Question

Write balanced molecular and net ionic equations for the reactions of (a) hydrochloric acid with nickel, (b) dilute sulfuric acid with iron, (c) hydrobromic acid with magnesium, (d) acetic acid, \(\mathrm{CH}_{3} \mathrm{COOH}\), with zinc.

Step-by-Step Solution

Answer

(a) Molecular: Ni + 2HCl -> NiCl2 + H2 ; Net ionic: Ni + 2H+ -> Ni2+ + H2 (b) Molecular: Fe + H2SO4 -> FeSO4 + H2 ; Net ionic: Fe + 2H+ -> Fe2+ + H2 (c) Molecular: Mg + 2HBr -> MgBr2 + H2 ; Net ionic: Mg + 2H+ -> Mg2+ + H2 (d) Molecular: Zn + 2CH3COOH -> Zn(CH3COO)2 + H2 ; Net ionic: Zn + 2H+ -> Zn2+ + H2

Step 1: Reaction (a) - Hydrochloric acid with nickel

The molecular equation for the reaction between hydrochloric acid (HCl) and nickel (Ni) is given by: Ni + 2HCl -> NiCl2 + H2 Now, let's break it down into its ions and write the net ionic equation.

Step 2: Net ionic equation for reaction (a)

In this reaction, we have: Ni + 2H+ + 2Cl- -> Ni2+ + 2Cl- + H2 As 2Cl- appears on both sides of the equation, we can cancel it out. The net ionic equation for reaction (a) is: Ni + 2H+ -> Ni2+ + H2

Step 3: Reaction (b) - Dilute sulfuric acid with iron

The molecular equation for the reaction between dilute sulfuric acid (H2SO4) and iron (Fe) is given by: Fe + H2SO4 -> FeSO4 + H2 Now, let's break it down into its ions and write the net ionic equation.

Step 4: Net ionic equation for reaction (b)

In this reaction, we have: Fe + 2H+ + SO4^2- -> Fe2+ + SO4^2- + H2 As SO4^2- appears on both sides of the equation, we can cancel it out. The net ionic equation for reaction (b) is: Fe + 2H+ -> Fe2+ + H2

Step 5: Reaction (c) - Hydrobromic acid with magnesium

The molecular equation for the reaction between hydrobromic acid (HBr) and magnesium (Mg) is given by: Mg + 2HBr -> MgBr2 + H2 Now, let's break it down into its ions and write the net ionic equation.

Step 6: Net ionic equation for reaction (c)

In this reaction, we have: Mg + 2H+ + 2Br- -> Mg2+ + 2Br- + H2 As 2Br- appears on both sides of the equation, we can cancel it out. The net ionic equation for reaction (c) is: Mg + 2H+ -> Mg2+ + H2

Step 7: Reaction (d) - Acetic acid with zinc

The molecular equation for the reaction between acetic acid (CH3COOH) and zinc (Zn) is given by: Zn + 2CH3COOH -> Zn(CH3COO)2 + H2 Now let's break it down into its ions and write the net ionic equation.

Step 8: Net ionic equation for reaction (d)

In this reaction, we have: Zn + 2CH3COO- + 2H+ -> Zn2+ + 2CH3COO- + H2 As 2CH3COO- appears on both sides of the equation, we can cancel it out. The net ionic equation for reaction (d) is: Zn + 2H+ -> Zn2+ + H2

Key Concepts

Molecular Equations

Molecular equations play a vital role in depicting chemical reactions by representing all reactants and products as compounds. For instance, when hydrochloric acid reacts with nickel, the molecular version of the equation is simple: \( \text{Ni} + 2\text{HCl} \rightarrow \text{NiCl}_2 + \text{H}_2 \).
This equation indicates that nickel and hydrochloric acid combine to form nickel chloride and hydrogen gas.

• Key Elements: Molecular equations list the complete neutral formulas for each compound involved in a chemical reaction.
• Purpose: These equations provide a general outline of the chemical reaction process, showing the compounds before and after the reaction.

Molecular equations are often the starting point for writing net ionic equations, which involve breaking these compounds into their ion forms. They help us reach a more precise picture of the actual chemical changes. Understanding both molecular and net ionic equations is essential for a comprehensive understanding of chemical reactions.

Acid-Metal Reactions

Acid-metal reactions are fascinating chemical processes where an acid reacts with a metal to produce a salt and hydrogen gas. These reactions are typically characterized by the formation of hydrogen gas bubbles as a visible sign. For example, when sulfuric acid reacts with iron, hydrogen gas forms, and iron sulfate is produced: \( \text{Fe} + \text{H}_2\text{SO}_4 \rightarrow \text{FeSO}_4 + \text{H}_2 \).
Here are some features of these reactions:

• Common Acids: Hydrochloric acid, sulfuric acid, and acetic acid are typical reactants with metals.
• Common Metals: Iron, magnesium, zinc, and nickel frequently react with acids efficiently.
• Observable Effects: The reaction is often accompanied by the evolution of gas bubbles (hydrogen gas) and sometimes heat.

These reactions are not just important in scientific contexts, but they are also utilized in various industrial processes and laboratory practices to extract pure metals or generate hydrogen gas.

Chemical Equations Balancing

Balancing chemical equations is a crucial skill in chemistry. It ensures that a chemical equation complies with the law of conservation of mass, which states that mass in a closed system must remain constant. When balancing, you adjust the coefficients, which are the numbers placed before compounds, to ensure that there are equal numbers of each type of atom on both sides of the equation.
For example, to balance the chemical reaction involving magnesium and hydrobromic acid, \( \text{Mg} + 2\text{HBr} \rightarrow \text{MgBr}_2 + \text{H}_2 \), you place a '2' before \(\text{HBr}\) to balance the hydrobromic acid's hydrogen and bromine atoms.
Key steps include:

• Count the number of each type of atom on the reactant and product sides.
• Adjust the coefficients to get an equal number of atoms on both sides.
• Check your work to ensure both sides match.

Balancing equations can initially seem challenging, but practice is key to mastering this fundamental chemical skill. Balanced equations are essential for calculating reactants' and products' quantities, which is crucial for laboratory and industrial applications.