Question

When each of the following pairs of aqueous solutions is mixed, does a precipitation reaction occur? If so, write balanced molecular, total ionic, and net ionic equations: (a) Potassium carbonate + barium hydroxide (b) Aluminum nitrate \(+\) sodium phosphate

Short answer

Precipitation occurs. Net ionic equations: CO3²⁻ (aq) + Ba²⁺ (aq) → BaCO3 (s), Al³⁺ (aq) + PO4³⁻ (aq) → AlPO4 (s).

Step-by-step solution

- Determine the Products

To determine if a precipitation reaction occurs when the solutions are mixed, begin by identifying the potential products using the double displacement reaction format. This format involves swapping the cations and anions of the reactants.

- Write the Possible Reactions

(a) Potassium carbonate (K2CO3) + barium hydroxide (Ba(OH)2): The possible products are potassium hydroxide (KOH) and barium carbonate (BaCO3). (b) Aluminum nitrate (Al(NO3)3) + sodium phosphate (Na3PO4): The possible products are aluminum phosphate (AlPO4) and sodium nitrate (NaNO3).

- Check Solubility Rules

Use solubility rules to determine if any of the products are insoluble in water, indicating a precipitate will form. (a) Barium carbonate (BaCO3) is insoluble, so a precipitate will form. (b) Aluminum phosphate (AlPO4) is insoluble, so a precipitate will form.

- Write the Balanced Molecular Equations

(a) K2CO3 (aq) + Ba(OH)2 (aq) → 2 KOH (aq) + BaCO3 (s) (b) Al(NO3)3 (aq) + Na3PO4 (aq) → AlPO4 (s) + 3 NaNO3 (aq)

- Write the Total Ionic Equations

(a) 2 K⁺ (aq) + CO3²⁻ (aq) + Ba²⁺ (aq) + 2 OH⁻ (aq) → 2 K⁺ (aq) + 2 OH⁻ (aq) + BaCO3 (s) (b) Al³⁺ (aq) + 3 NO3⁻ (aq) + 3 Na⁺ (aq) + PO4³⁻ (aq) → AlPO4 (s) + 3 Na⁺ (aq) + 3 NO3⁻ (aq)

- Write the Net Ionic Equations

(a) CO3²⁻ (aq) + Ba²⁺ (aq) → BaCO3 (s) (b) Al³⁺ (aq) + PO4³⁻ (aq) → AlPO4 (s)

Key concepts

double displacement reactions

A double displacement reaction is a type of chemical reaction where two compounds exchange their positive and negative ions to form two new compounds. These reactions often take place in aqueous solutions and can result in the formation of a precipitate, gas, or water. For instance, when potassium carbonate (K2CO3) and barium hydroxide (Ba(OH)2) are mixed, their ions swap places creating potassium hydroxide (KOH) and barium carbonate (BaCO3), where the barium carbonate is a solid precipitate.

• Molecular: K2CO3 (aq) + Ba(OH)2 (aq) → 2 KOH (aq) + BaCO3 (s)
• Total Ionic: 2 K⁺ (aq) + CO3²⁻ (aq) + Ba²⁺ (aq) + 2 OH⁻ (aq) → 2 K⁺ (aq) + 2 OH⁻ (aq) + BaCO3 (s)
• Net Ionic: CO3²⁻ (aq) + Ba²⁺ (aq) → BaCO3 (s)

Notice how reactants' ions recombine to create new products, evidencing the double displacement nature.

solubility rules

Solubility rules help predict whether a precipitate will form when two aqueous solutions are mixed. These rules state which ionic compounds dissolve in water and which do not. For instance, Barium carbonate (BaCO3) and aluminum phosphate (AlPO4) are both insoluble in water, leading to precipitation when their respective solutions are mixed.

• BaCO3 (insoluble) forms from potassium carbonate (K2CO3) and barium hydroxide (Ba(OH)2).
• AlPO4 (insoluble) forms from aluminum nitrate (Al(NO3)3) and sodium phosphate (Na3PO4).

Knowing these rules allows us to write the correct molecular, total ionic, and net ionic equations for these reactions.

ionic equations

Ionic equations represent chemical reactions in their ionic form. They show the ions present in the reaction mixtures and differentiate between species that remain in solution and those that form precipitates. There are three types of ionic equations:

• Molecular Equation: Shows the complete formulas without indicating the ionic nature. For example, Al(NO3)3 (aq) + Na3PO4 (aq) → AlPO4 (s) + 3 NaNO3 (aq).
• Total Ionic Equation: Displays all strong electrolytes as ions. For example, Al³⁺ (aq) + 3 NO3⁻ (aq) + 3 Na⁺ (aq) + PO4³⁻ (aq) → AlPO4 (s) + 3 Na⁺ (aq) + 3 NO3⁻ (aq).
• Net Ionic Equation: Shows only the species undergoing change, omitting spectator ions. For example, Al³⁺ (aq) + PO4³⁻ (aq) → AlPO4 (s).

These equations help clarify the actual chemical changes occurring during the reaction.