Problem 26 - Chemistry and Chemical Reactivity

Question

Balance each of the following equations, and then write the net ionic equation. Show states for all reactants and products \((\mathrm{s}, \ell, \mathrm{g}, \mathrm{aq})\) (a) the reaction of sodium hydroxide and iron (II) chloride to give iron(II) hydroxide and sodium chloride (b) the reaction of barium chloride with sodium carbonate to give barium carbonate and sodium chloride

Step-by-Step Solution

Answer

(a) Net ionic: \( \text{Fe}^{2+} \text{(aq) + 2OH}^- \text{(aq)} \rightarrow \text{Fe(OH)}_2 \text{(s)} \). (b) Net ionic: \( \text{Ba}^{2+} \text{(aq) + CO}_3^{2-} \text{(aq)} \rightarrow \text{BaCO}_3 \text{(s)} \).

Step 1: Write the Unbalanced Equation for Reaction (a)

Begin with the unbalanced chemical equation for the reaction: \[ \text{NaOH (aq) + FeCl}_2 \text{ (aq)} \rightarrow \text{Fe(OH)}_2 \text{ (s) + NaCl (aq)} \]

Step 2: Balance the Equation for Reaction (a)

Count and balance the number of atoms for each element. The balanced equation is: \[ 2\text{NaOH (aq) + FeCl}_2 \text{ (aq)} \rightarrow \text{Fe(OH)}_2 \text{ (s) + 2NaCl (aq)} \] Now each element has a balanced number of atoms on both sides.

Step 3: Write the Net Ionic Equation for Reaction (a)

Identify the ions in the aqueous solutions: - NaOH dissociates into \( \text{Na}^+ \) and \( \text{OH}^- \)- FeCl ext{2} dissociates into \( \text{Fe}^{2+} \) and \( \text{Cl}^- \)- Fe(OH) ext{2} is a solid and does not dissociate.The net ionic equation is: \[ \text{Fe}^{2+} \text{(aq) + 2OH}^- \text{(aq)} \rightarrow \text{Fe(OH)}_2 \text{(s)} \]

Step 4: Write the Unbalanced Equation for Reaction (b)

Start with the unbalanced chemical equation for the reaction: \[ \text{BaCl}_2 \text{ (aq) + Na}_2\text{CO}_3 \text{ (aq)} \rightarrow \text{BaCO}_3 \text{ (s) + NaCl (aq)} \]

Step 5: Balance the Equation for Reaction (b)

Count and balance the number of atoms for each element. The balanced equation is: \[ \text{BaCl}_2 \text{ (aq) + Na}_2\text{CO}_3 \text{ (aq)} \rightarrow \text{BaCO}_3 \text{ (s) + 2NaCl (aq)} \] Each element now has an equal number of atoms on both sides.

Step 6: Write the Net Ionic Equation for Reaction (b)

Identify the ions in the aqueous solutions: - BaCl ext{2} dissociates into \( \text{Ba}^{2+} \) and \( \text{Cl}^- \)- Na ext{2}CO ext{3} dissociates into \( \text{Na}^+ \) and \( \text{CO}_3^{2-} \)- BaCO ext{3} is a solid and does not dissociate.The net ionic equation is: \[ \text{Ba}^{2+} \text{(aq) + CO}_3^{2-} \text{(aq)} \rightarrow \text{BaCO}_3 \text{(s)} \]

Key Concepts

Balancing Chemical Equations

Balancing chemical equations is crucial to understand the stoichiometry of a reaction. Balancing ensures that the number of each type of atom is the same on both sides of the equation, respecting the law of conservation of mass. To balance a chemical equation:

• Write down the unbalanced equation.
• Count the number of atoms of each element on both sides.
• Adjust coefficients (the numbers in front of substances) to balance the atoms.
• Repeat this process until all elements are balanced.

This process can seem challenging at first, but it becomes intuitive with practice. Remember, only the coefficients can be changed to balance equations, not the subscripts in chemical formulas. This distinction is important as changing subscripts alters the substances and therefore the reaction itself.

Net Ionic Equations

Net ionic equations highlight the chemical species that participate directly in a chemical reaction. These are helpful when dealing only with the components that change during the reaction, particularly in aqueous solutions. To derive a net ionic equation:

• Write the balanced chemical equation including states of matter.
• Dissociate strong electrolytes (compounds that are completely dissolved) into their ions.
• Identify and cancel out the spectator ions, which appear unchanged on both sides.
• Write the remaining ions and compounds to construct the net ionic equation.

Net ionic equations simplify complex reactions by omitting the inactive components, resulting in a clearer picture of the chemical changes occurring.

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions combine to form an insoluble solid, known as a precipitate. These are key reactions in chemistry often used to separate substances. Recognizing precipitation reactions involves:

• Mixing two ionic compounds in solution.
• Observing the formation of a solid product out of the liquid solution.
• Using solubility rules to predict whether a precipitation reaction will occur.

For example, when barium chloride ( BaCl_2) mixes with sodium carbonate ( Na_2CO_3), insoluble barium carbonate ( BaCO_3) precipitates out of the solution. Understanding precipitation reactions is particularly useful in laboratory settings, waste treatment, and in the production of various industrial chemicals.