Problem 26 - Chemistry and Chemical Reactivity

Question

Balance the equation for the following precipitation reaction, and then write the net ionic equation. Indicate the state of each species \((\mathrm{s}, \ell, \mathrm{aq}\) or g). $$\mathrm{Ni}\left(\mathrm{NO}_{3}\right)_{2}+\mathrm{Na}_{2} \mathrm{CO}_{3} \rightarrow \mathrm{NiCO}_{3}+\mathrm{NaNO}_{3}$$

Step-by-Step Solution

Answer

Net ionic equation: \( \mathrm{Ni^{2+}(aq) + CO_3^{2-}(aq) \rightarrow NiCO_3(s)} \)

Step 1: Identify the States of Reactants and Products

Start by assigning states to each compound in the reaction. Typically, nitrates like \( \mathrm{Ni(NO_3)_2} \) and \( \mathrm{NaNO_3} \) are soluble in water, so they are in the aqueous state \((\mathrm{aq})\). Carbonates like \( \mathrm{NiCO_3} \) often form precipitates, making it a solid \((\mathrm{s})\). Sodium carbonate \( \mathrm{Na_2CO_3} \) is generally soluble, thus in the aqueous state \((\mathrm{aq})\).

Step 2: Write the Complete Ionic Equation

Split the aqueous compounds into their constituent ions. The complete ionic equation is:\[ \mathrm{Ni^{2+}(aq) + 2NO_3^-(aq) + 2Na^+(aq) + CO_3^{2-}(aq) \rightarrow NiCO_3(s) + 2Na^+(aq) + 2NO_3^-(aq)} \]

Step 3: Cancel Spectator Ions to Write the Net Ionic Equation

Identify and remove the spectator ions, which are ions that appear unchanged on both sides of the equation. Here, the spectator ions are \( \mathrm{2Na^+} \) and \( \mathrm{2NO_3^-} \). Removing these gives the net ionic equation:\[ \mathrm{Ni^{2+}(aq) + CO_3^{2-}(aq) \rightarrow NiCO_3(s)} \]

Step 4: Check the Equation Balance

Verify that the number of atoms for each element and the charge is balanced on both sides of the net ionic equation. For this equation, one nickel ion \( \mathrm{Ni^{2+}} \) and one carbonate ion \( \mathrm{CO_3^{2-}} \) combine to form one formula unit of \( \mathrm{NiCO_3} \), confirming that both the atoms and charges are balanced.

Key Concepts

Net Ionic Equation

In chemical reactions, particularly in solutions, it's essential to understand the net ionic equation. This equation represents only the components that participate in the reaction. It excludes any ions that do not directly contribute to the formation of the product. When a solid precipitate forms from a solution, we focus on the ions involved in creating that solid.
The net ionic equation simplifies our understanding of the reaction by stripping away non-essential parts, which are known as spectator ions. For example, in a precipitation reaction, if nickel carbonate (\( \mathrm{NiCO_3} \)) forms as a solid, the net ionic equation only includes the ions \( \mathrm{Ni^{2+}(aq)} \) and \( \mathrm{CO_3^{2-}(aq)} \) that come together to form it.

• It highlights the actual chemical change.
• Helps identify the driving force of the reaction.
• Simplifies complex reactions for better comprehension.

Balancing Chemical Equations

Balancing chemical equations is crucial to ensure the conservation of mass and charge. Each side of the equation must have the same number of atoms for each element and an equal charge.
In a precipitation reaction like the one we’re examining, you'll start by checking that the number of atoms for elements like nickel and carbonate are the same on both the reactant and product sides. This ensures that matter is neither created nor destroyed.

• List all reactants and products, determining their states: solid \((s)\), liquid \((\ell)\), aqueous \((aq)\), or gas \((g)\).
• Split the soluble compounds into ions for the complete ionic equation.
• Ensure that each side of the equation has the same number of each type of ion.

Balancing may seem intricate, but once each side mirrors the other in terms of atoms and charge, you’ve achieved a balanced equation.

Spectator Ions

Spectator ions are ions that do not participate in the chemical change of a reaction. They remain in solution, unchanged, and appear in both the reactants and products.
In writing net ionic equations, identifying and removing these ions is crucial. In our example, sodium \( \mathrm{Na^+} \) and nitrate \( \mathrm{NO_3^-} \) ions are spectators.

• They help maintain charge neutrality in the solution.
• Appear unchanged on both sides of the equation.
• Not involved in forming the precipitate or main product.

Their presence is important for maintaining stability in the solution, but they are not highlighted in net ionic equations because they do not influence the main reaction outcome. This practice helps simplify equations, bringing clarity to the chemical change occurring.