Question

Write a balanced net ionic equation for the reaction of each of the following metals with dilute sulfuric acid in the absence of air. If no reaction occurs, indicate N.R. (a) \(\mathrm{Mn}\) (b) \(\mathrm{Ag}\) (c) \(\mathrm{Sc}\) (d) \(\mathrm{Ni}\)

Short answer

Net ionic equations: (a) Mn(s) + 2H⁺ → Mn²⁺ + H₂↑; (c) 2Sc(s) + 6H⁺ → 2Sc³⁺ + 3H₂↑; (d) Ni(s) + 2H⁺ → Ni²⁺ + H₂↑. Ag: N.R.

Step-by-step solution

Understand the reaction environment

The problem asks for a reaction of each metal with dilute sulfuric acid ( H_2SO_4) under the absence of air. In such a scenario, we typically have metal replacement reactions where the metal reacts with the acid to produce hydrogen gas and a metal sulfate.

Determine possible reactions and identify reactivity

Identify whether each metal will react with dilute sulfuric acid by checking its position on the activity series of metals. Metals above hydrogen in the series will react, while those below may not.

Write chemical equations for reactive metals

For each reactive metal (Mn, Sc, and Ni), write the general reaction format: \[ ext{Metal} + ext{Sulfuric acid} ightarrow ext{Metal sulfate} + ext{Hydrogen gas} \] These become: (a) \( \text{Mn} + \text{H}_2\text{SO}_4 \rightarrow \text{MnSO}_4 + \text{H}_2 \uparrow \)(c) \( \text{Sc} + \text{H}_2\text{SO}_4 \rightarrow \text{Sc}_2\text{(SO}_4\text{)}_3 + \text{H}_2 \uparrow \)(d) \( \text{Ni} + \text{H}_2\text{SO}_4 \rightarrow \text{NiSO}_4 + \text{H}_2 \uparrow \)

Balance the equations

Ensure that each of the above reaction equations is balanced:(a) Balanced equation: \( \text{Mn} + \text{H}_2\text{SO}_4 \rightarrow \text{MnSO}_4 + \text{H}_2 \uparrow \)(c) Balance Sc equation considering charges and stoichiometry: \( 2\text{Sc} + 3\text{H}_2\text{SO}_4 \rightarrow \text{Sc}_2\text{(SO}_4\text{)}_3 + 3\text{H}_2 \uparrow \)(d) Balanced equation: \( \text{Ni} + \text{H}_2\text{SO}_4 \rightarrow \text{NiSO}_4 + \text{H}_2 \uparrow \)

Write net ionic equations

Rewrite the balanced molecular equations as net ionic equations:(a) \( \text{Mn (s)} + 2\text{H}^+ \rightarrow \text{Mn}^{2+} + \text{H}_2 \uparrow \)(c) \( 2\text{Sc (s)} + 6\text{H}^+ \rightarrow 2\text{Sc}^{3+} + 3\text{H}_2 \uparrow \)(d) \( \text{Ni (s)} + 2\text{H}^+ \rightarrow \text{Ni}^{2+} + \text{H}_2 \uparrow \)

Identify non-reactive metal

Silver (Ag) does not react with dilute sulfuric acid because it is below hydrogen in the activity series. Therefore, for Ag, indicate as N.R. (No Reaction).

Key concepts

Activity Series of Metals

The activity series of metals is an essential tool for predicting the likelihood of a metal reacting with an acid or another substance. It is a list of metals arranged in order of decreasing reactivity. This means that metals at the top of the series are more reactive, and those at the bottom are less reactive.
When considering a reaction with dilute sulfuric acid ( H_2SO_4), only metals that are above hydrogen in the activity series will typically react. Metals below hydrogen do not react under normal conditions because they are less reactive than hydrogen, so they cannot displace it.
Here's a simple way to remember:

• More reactive metals can displace hydrogen from acids.
• Less reactive metals cannot displace hydrogen in the activity series.

For example, in the provided exercise, manganese (Mn), scandium (Sc), and nickel (Ni) are above hydrogen in the activity series, so they can react with dilute sulfuric acid. However, silver (Ag) is below hydrogen, indicating no reaction will occur.

Metal Replacement Reactions

Metal replacement reactions occur when a more reactive metal displaces a less reactive metal or hydrogen in a compound. In reactions with dilute sulfuric acid, these are single displacement reactions.
In the presence of sulfuric acid, a more reactive metal will replace the hydrogen ions (H^+) and form hydrogen gas (H_2). The general reaction format is:
\[\text{Metal} + \text{H}_2\text{SO}_4 \rightarrow \text{Metal sulfate} + \text{H}_2 \uparrow\]
The metals that do react, such as Mn, Sc, and Ni, react with the hydrogen ions from sulfuric acid to release hydrogen gas and form metal sulfate. Here’s what happens with manganese:

• Mn displaces H from H_2SO_4, forming MnSO_4 and H_2 gas.
• For Ag, no reaction occurs as it cannot displace H from H_2SO_4.

Balancing Chemical Equations

Balancing chemical equations ensures the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction. This means that the atoms of each element should have the same number on both sides of the equation.
It involves adjusting coefficients, which are numbers placed in front of compounds or elements in the reaction. Each type of atom on the reactant side must equal the same on the product side.
For instance, in balancing the equation for scandium reacting with sulfuric acid:
\[2\text{Sc} + 3\text{H}_2\text{SO}_4 \rightarrow \text{Sc}_2\text{(SO}_4)_3 + 3\text{H}_2 \uparrow\]

• Two Sc atoms on the left balance with two Sc atoms in Sc_2(SO_4)_3 on the right.
• Six hydrogen atoms (from 3H_2) balance with six hydrogen ions on the left.

Balancing keeps the equation consistent and respects ionic charges as needed.

Dilute Sulfuric Acid Reactions

Dilute sulfuric acid is a common reactant in chemical reactions due to its strong acidic nature and reactivity. When dealing with metals, the main reaction occurs with hydrogen ions ( H^+ ) in the acid.
Here’s what happens with metals like Mn, Sc, and Ni:

• The metal reacts with hydrogen ions, reducing them and releasing hydrogen gas ( H_2 ) as a by-product.
• The remaining sulfate ( SO_4^{2-} ) combines with metal ions to form metal sulfates (e.g., MnSO _4 , Sc _2 (SO _4 ) _3 , NiSO _4 ).

Specific reactions, depending on the metal and its position in the activity series, will predict if hydrogen gas will form. Silver, being below hydrogen in the activity series, does not react with dilute sulfuric acid, highlighting the importance of understanding each element's reactivity.