Question

On the basis of the general solubility rules given in Table \(7.1,\) predict the identity of the precipitate that forms when aqueous solutions of the following substances are mixed. If no precipitate is likely, indicate which rules apply. a. iron(III) chloride, \(\mathrm{FeCl}_{3}\), and phosphoric acid, \(\mathrm{H}_{3} \mathrm{PO}_{4}\) b. barium nitrate, \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2},\) and sodium sulfate, \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) c. potassium chloride, \(\mathrm{KCl}\), and iron(II) sulfate, \(\mathrm{FeSO}_{4}\) d. lead(II) nitrate, \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2},\) and hydrochloric acid, \(\mathrm{HCl}\) e. calcium nitrate, \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2},\) and sodium chloride, \(\mathrm{NaCl}\) f. ammonium sulfide, \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{S},\) and copper(II) chloride, \(\mathrm{CuCl}_{2}\)

Short answer

a. No precipitate forms. b. Barium sulfate (BaSO4) forms as a precipitate. c. No precipitate forms. d. Lead(II) chloride (PbCl2) forms as a precipitate. e. No precipitate forms. f. Copper(II) sulfide (CuS) forms as a precipitate.

Step-by-step solution

List the possible ions combinations for each reaction.

Write the possible ions combinations for each set of substances that would react when mixed: a. FeCl3 (iron(III) chloride) and H3PO4 (phosphoric acid) - Fe3+ and Cl- (from FeCl3) - H+ and PO4-3 (from H3PO4) b. Ba(NO3)2 (barium nitrate) and Na2SO4 (sodium sulfate) - Ba2+ and NO3- (from Ba(NO3)2) - Na+ and SO4-2 (from Na2SO4) c. KCl (potassium chloride) and FeSO4 (iron(II) sulfate) - K+ and Cl- (from KCl) - Fe2+ and SO4-2 (from FeSO4) d. Pb(NO3)2 (lead(II) nitrate) and HCl (hydrochloric acid) - Pb2+ and NO3- (from Pb(NO3)2) - H+ and Cl- (from HCl) e. Ca(NO3)2 (calcium nitrate) and NaCl (sodium chloride) - Ca2+ and NO3- (from Ca(NO3)2) - Na+ and Cl- (from NaCl) f. (NH4)2S (ammonium sulfide) and CuCl2 (copper(II) chloride) - NH4+ and S-2 (from (NH4)2S) - Cu2+ and Cl- (from CuCl2)

Identify the precipitates by applying the general solubility rules.

Using the general solubility rules from Table 7.1, identify the precipitates that would form for each combination of ions: a. Fe3+ and Cl-/ H+ and PO4-3 No precipitate is likely to form as FeCl3 and H3PO4 are both soluble. b. Ba2+ and NO3-/ Na+ and SO4-2 A precipitate is likely to form: BaSO4 (barium sulfate). Barium sulfate is insoluble, and thus will precipitate. c. K+ and Cl-/ Fe2+ and SO4-2 No precipitate is likely to form as KCl and FeSO4 are both soluble. d. Pb2+ and NO3-/ H+ and Cl- A precipitate is likely to form: PbCl2 (lead(II) chloride). Lead(II) chloride is insoluble, and thus will precipitate. e. Ca2+ and NO3-/ Na+ and Cl- No precipitate is likely to form as Ca(NO3)2 and NaCl are both soluble. f. NH4+ and S-2/ Cu2+ and Cl- A precipitate is likely to form: CuS (copper(II) sulfide). Copper(II) sulfide is insoluble, and thus will precipitate.

Final answers

a. No precipitate forms. b. Barium sulfate (BaSO4) forms as a precipitate. c. No precipitate forms. d. Lead(II) chloride (PbCl2) forms as a precipitate. e. No precipitate forms. f. Copper(II) sulfide (CuS) forms as a precipitate.

Key concepts

Understanding Ionic Compounds

Ionic compounds are chemical compounds composed of ions held together by electrostatic forces known as ionic bonds. These are usually made up of a metal and a non-metal. When dissolved in water, ionic compounds dissociate into their respective ions. For instance, when barium nitrate \( \mathrm{Ba(NO}_3)_2 \)dissolves, it separates into Ba\(^{2+} \) and NO\(_3^-\) ions. Similarly, sodium sulfate \( \mathrm{Na}_2 \mathrm{SO}_4 \)will split into Na\(^+\) and SO\(_4^{2-}\) ions. This dissociation of ions is crucial in predicting the outcome of precipitation reactions, as it determines which ions will interact to form new compounds.

• Formation of ionic compounds typically involves the transfer of electrons from the metal to the non-metal.
• The resulting ions, with their opposite charges, attract each other to form a stable ionic solid.
• Ionic compounds are usually solid at room temperature and have high melting and boiling points.

These characteristics arise because the ionic bonds are quite strong, requiring considerable energy to break.

Precipitation Reactions Explained

Precipitation reactions occur when two ionic solutions are mixed, resulting in the formation of an insoluble solid called a precipitate. This is a crucial application of solubility rules, which help predict whether a precipitate will form. For example, when barium nitrate is mixed with sodium sulfate, barium sulfate \( \mathrm{BaSO}_4 \) precipitates out of solution, because it is insoluble in water.

• The process of forming a solid precipitate involves an exchange of ions between the reacting solutions.
• Solubility rules guide us in identifying insoluble compounds, primarily focusing on common ions like sulfate, chloride, and nitrate.
• An insoluble product, or precipitate, indicates a strong ionic interaction that water cannot easily disrupt.

By understanding these rules and reactions, chemists can predict the product formation during such mixing processes.

Decoding Chemical Equations

Chemical equations represent the reactants and products involved in a chemical reaction. They are balanced to reflect the conservation of mass and charge. For example, when lead(II) nitrate \( \mathrm{Pb(NO}_3)_2 \)and hydrochloric acid \( \mathrm{HCl} \) react, the chemical equation is:\[\mathrm{Pb(NO}_3)_2 \,(aq) + \mathrm{2HCl}\,(aq) \rightarrow \mathrm{PbCl}_2\,(s) + \mathrm{2HNO}_3\,(aq) \]

• This equation shows that reactants are converted into products with no loss of matter, as each atom present is accounted for.
• The notation (s), (aq), (l), and (g) denote the physical states of the chemicals: solid, aqueous, liquid, and gas respectively.
• Coefficients in the equation provide the relative quantities of each substance involved in the reaction.

Balancing chemical equations is essential for understanding the exact stoichiometric relationships in a reaction and is a fundamental step in predicting reaction outcomes.