Problem 65 - Chemistry: An Atoms-Focused Approach

Question

Complete and balance the chemical equations for the precipitation reactions, if any, between the following pairs of reactants, and write the net ionic equations: a. \(\operatorname{Pb}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{Na}_{2} \mathrm{SO}_{4}(a q) \rightarrow\) b. \(\mathrm{NiCl}_{2}(a q)+\mathrm{NH}_{4} \mathrm{NO}_{3}(a q) \rightarrow\) c. \(\operatorname{Fe} C l_{2}(a q)+N a_{2} S(a q) \rightarrow\) d. \(\operatorname{MgSO}_{4}(a q)+\mathrm{BaCl}_{2}(a q) \rightarrow\)

Step-by-Step Solution

Answer

Question: Complete and balance the chemical equation for the precipitation reaction, and write the net ionic equation for the following reactants: MgSO\(_4\) and BaCl\(_2\). Answer: The balanced chemical equation for the precipitation reaction is: MgSO\(_4\) + BaCl\(_2\) \(\rightarrow\) BaSO\(_4\) + MgCl\(_2\). The net ionic equation for this reaction is: Ba\(^{2+}\) + SO\(_4^{2-} \rightarrow\) BaSO\(_4\)(s).

Step 1: Identify the reactants and their ions

Reactants: Pb(NO\(_3\))\(_2\) and Na\(_2\)SO\(_4\) Ions present in solution: Pb\(^{2+}\), NO\(_3^-\), Na\(^+\), SO\(_4^{2-}\)

Step 2: Identify the possible products

Possible products: PbSO\(_4\) and NaNO\(_3\)

Step 3: Check if any products are insoluble and will form a precipitate

PbSO\(_4\) is insoluble, and NaNO\(_3\) is soluble. So the precipitation reaction occurs with PbSO\(_4\) formation.

Step 4: Balance the chemical equation for the overall reaction

Balanced chemical equation: Pb(NO\(_3\))\(_2\) + Na\(_2\)SO\(_4\) \(\rightarrow\) PbSO\(_4\) + 2NaNO\(_3\)

Step 5: Write the complete ionic equation

Complete ionic equation: Pb\(^{2+}\) + 2NO\(_3^-\) + 2Na\(^+\) + SO\(_4^{2-} \rightarrow\) PbSO\(_4\)(s) + 2Na\(^+\) + 2NO\(_3^-\)

Step 6: Cancel out spectator ions and write the net ionic equation

Net ionic equation: Pb\(^{2+}\) + SO\(_4^{2-} \rightarrow\) PbSO\(_4\)(s) b. \(\mathrm{NiCl}_{2}(a q)+\mathrm{NH}_{4} \mathrm{NO}_{3}(a q) \rightarrow\)

Step 1: Identify the reactants and their ions

Reactants: NiCl\(_2\) and NH\(_4\)NO\(_3\) Ions present in solution: Ni\(^{2+}\), Cl\(^-\), NH\(_4^+\), NO\(_3^-\)

Step 2: Identify the possible products

Possible products: Ni(NO\(_3\))\(_2\) and NH\(_4\)Cl

Step 3: Check if any products are insoluble and will form a precipitate

Both possible products are soluble, so there is no precipitation reaction. c. \(\operatorname{Fe} C l_{2}(a q)+N a_{2} S(a q) \rightarrow\)

Step 1: Identify the reactants and their ions

Reactants: FeCl\(_2\) and Na\(_2\)S Ions present in solution: Fe\(^{2+}\), Cl\(^-\), Na\(^+\), S\(^{2-}\)

Step 2: Identify the possible products

Possible products: FeS and NaCl

Step 3: Check if any products are insoluble and will form a precipitate

FeS is insoluble, and NaCl is soluble. So the precipitation reaction occurs with FeS formation.

Step 4: Balance the chemical equation for the overall reaction

Balanced chemical equation: FeCl\(_2\) + Na\(_2\)S \(\rightarrow\) FeS + 2NaCl

Step 5: Write the complete ionic equation

Complete ionic equation: Fe\(^{2+}\) + 2Cl\(^-\) + 2Na\(^+\) + S\(^{2-} \rightarrow\) FeS(s) + 2Na\(^+\) + 2Cl\(^-\)

Step 6: Cancel out spectator ions and write the net ionic equation

Net ionic equation: Fe\(^{2+}\) + S\(^{2-} \rightarrow\) FeS(s) d. \(\operatorname{MgSO}_{4}(a q)+\mathrm{BaCl}_{2}(a q) \rightarrow\)

Step 1: Identify the reactants and their ions

Reactants: MgSO\(_4\) and BaCl\(_2\) Ions present in solution: Mg\(^{2+}\), SO\(_4^{2-}\), Ba\(^{2+}\), Cl\(^-\)

Step 2: Identify the possible products

Possible products: MgCl\(_2\) and BaSO\(_4\)

Step 3: Check if any products are insoluble and will form a precipitate

MgCl\(_2\) is soluble, and BaSO\(_4\) is insoluble. So the precipitation reaction occurs with BaSO\(_4\) formation.

Step 4: Balance the chemical equation for the overall reaction

Balanced chemical equation: MgSO\(_4\) + BaCl\(_2\) \(\rightarrow\) BaSO\(_4\) + MgCl\(_2\)

Step 5: Write the complete ionic equation

Complete ionic equation: Mg\(^{2+}\) + SO\(_4^{2-}\) + Ba\(^{2+}\) + 2Cl\(^-\) \(\rightarrow\) BaSO\(_4\)(s) + Mg\(^{2+}\) + 2Cl\(^-\)

Step 6: Cancel out spectator ions and write the net ionic equation

Net ionic equation: Ba\(^{2+}\) + SO\(_4^{2-} \rightarrow\) BaSO\(_4\)(s)

Key Concepts

Net Ionic Equation

In chemistry, a net ionic equation is used to show only those elements, ions, or compounds that are directly involved in the chemical reaction, specifically the formation of a precipitate. This kind of equation excludes spectator ions, which do not participate in the formation of the solid product.
The process of writing a net ionic equation begins with writing the balanced molecular equation, then the complete ionic equation, and finally removing the spectator ions to focus on the net ionic reaction.
For instance, in the reaction between lead(II) nitrate and sodium sulfate, the net ionic equation is derived by focusing on the ions that form the insoluble precipitate lead(II) sulfate. Here's how it looks:

• Balanced molecular equation: Pb(NO extsubscript{3}) extsubscript{2} + Na extsubscript{2}SO extsubscript{4} → PbSO extsubscript{4}(s) + 2NaNO extsubscript{3}
• Complete ionic equation: Pb extsuperscript{2+} + 2NO extsubscript{3} extsuperscript{-} + 2Na extsuperscript{+} + SO extsubscript{4} extsuperscript{2-} → PbSO extsubscript{4}(s) + 2Na extsuperscript{+} + 2NO extsubscript{3} extsuperscript{-}
• Net ionic equation: Pb extsuperscript{2+} + SO extsubscript{4} extsuperscript{2-} → PbSO extsubscript{4}(s)

By focusing on the substances that change state or participate directly, the net ionic equation provides a clear view of the essence of the chemical reaction.

Solubility Rules

Solubility rules are essential guidelines that help determine whether a compound will dissolve in water to form ions. They are particularly helpful in predicting whether a precipitation reaction will occur when two aqueous solutions are mixed. Understanding these rules allows you to anticipate which products will remain dissolved and which will form a solid.
Some of the key solubility rules include:

• Most nitrate (NO extsubscript{3} extsuperscript{-}), acetate (CH extsubscript{3}COO extsuperscript{-}), and alkali metal compounds are soluble.
• Most chloride (Cl extsuperscript{-}), bromide (Br extsuperscript{-}), and iodide (I extsuperscript{-}) salts are soluble, except for those of lead (Pb extsuperscript{2+}), silver (Ag extsuperscript{+}), and mercury (Hg extsubscript{2} extsuperscript{2+}).
• Sulfate ( ext{SO}_4^{2-}) salts are generally soluble, with notable exceptions for barium (Ba extsuperscript{2+}), lead (Pb extsuperscript{2+}), and calcium (Ca extsuperscript{2+}).
• Most hydroxide (OH extsuperscript{-}) and sulfide (S extsuperscript{2-}) salts are minimally soluble, except for those of alkali metals and some alkaline earth metals like Ba extsuperscript{2+}.

By applying these rules to potential products in a reaction, you can predict which will precipitate. For example, in the reaction of magnesium sulfate with barium chloride, barium sulfate precipitates due to its limited solubility, whereas magnesium chloride remains in solution.

Balancing Chemical Equations

Balancing chemical equations is a crucial skill that ensures the conservation of mass, where the number of atoms of each element is the same on both sides of the equation. This process involves adjusting stoichiometric coefficients to achieve balance.
Here are steps to balance chemical equations effectively:

• Write the unbalanced equation with reactants and products.
• Identify the different elements involved in the reaction.
• Adjust the coefficients to ensure the same number of atoms for each element on both sides of the equation. Start by balancing elements that appear in only one compound on each side.
• Repeat and verify each step, ensuring that polyatomic ions, if unchanged, remain balanced as units.

Let's take the precipitation reaction between iron(II) chloride and sodium sulfide as an example:
Unbalanced equation: FeCl extsubscript{2} + Na extsubscript{2}S → FeS + NaCl
Balanced equation: FeCl extsubscript{2} + Na extsubscript{2}S → FeS + 2NaCl
By balancing equations, you ensure the reaction aligns with the law of conservation of mass, enabling accurate predictions of quantities and processes in chemical reactions.