Question

When the following solutions are mixed together, what precipitate (if any) will form? a. \(\operatorname{FeSO}_{4}(a q)+\operatorname{KCl}(a q)\) b. \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}(a q)+\mathrm{Ba}(\mathrm{OH})_{2}(a q)\) c. \(\mathrm{CaCl}_{2}(a q)+\mathrm{Na}_{2} \mathrm{SO}_{4}(a q)\) d. \(\mathrm{K}_{2} \mathrm{S}(a q)+\mathrm{Ni}\left(\mathrm{NO}_{3}\right)_{2}(a q)\)

Short answer

a. No precipitate will form. b. Al(OH)₃ will form as a precipitate. c. CaSO₄ will form a precipitate. d. NiS will form a precipitate.

Step-by-step solution

Identify the ions in each solution

In the first solution, we have Fe²⁺ and SO₄²⁻ ions present. In the second solution, we have K⁺ and Cl⁻ ions present.

Determine the possible products and their solubility

When these solutions are mixed, the possible products are FeCl₂ and K₂SO₄. According to solubility rules, all potassium (K⁺) and all chlorides (Cl⁻) salts are soluble. Therefore, no precipitate will form. #b. Mixing Al(NO3)3(aq) and Ba(OH)2(aq)#

Identify the ions in each solution

In the first solution, we have Al³⁺ and NO₃⁻ ions present. In the second solution, we have Ba²⁺ and OH⁻ ions present.

Determine the possible products and their solubility

When these solutions are mixed, the possible products are Al(OH)₃ and Ba(NO₃)₂. Al(OH)₃ is insoluble while Ba(NO₃)₂ is soluble (since all nitrates (NO₃⁻) are soluble). Therefore, Al(OH)₃ will form as a precipitate. #c. Mixing CaCl2(aq) and Na2SO4(aq)#

Identify the ions in each solution

In the first solution, we have Ca²⁺ and Cl⁻ ions present. In the second solution, we have Na⁺ and SO₄²⁻ ions present.

Determine the possible products and their solubility

When these solutions are mixed, the possible products are CaSO₄ and NaCl. According to solubility rules, CaSO₄ is slightly soluble, while all sodium (Na⁺) and all chlorides (Cl⁻) salts are soluble. Thus, CaSO₄ will form a precipitate. #d. Mixing K2S(aq) and Ni(NO3)2(aq)#

Identify the ions in each solution

In the first solution, we have K⁺ and S²⁻ ions present. In the second solution, we have Ni²⁺ and NO₃⁻ ions present.

Determine the possible products and their solubility

When these solutions are mixed, the possible products are KNO₃ and NiS. KNO₃ is soluble (since all nitrates (NO₃⁻) and all potassium (K⁺) salts are soluble), whereas NiS is insoluble. Thus, NiS will form a precipitate.

Key concepts

Solubility Rules

In chemistry, solubility rules are guidelines that help determine whether a compound will dissolve in water. These rules are particularly helpful in predicting the outcomes of reactions, such as precipitation reactions. Some general guidelines include:

• Most nitrate (NO₃⁻) salts are soluble.
• All alkali metal salts (like those of sodium (Na⁺), potassium (K⁺), etc.) are soluble.
• Most chloride (Cl⁻), bromide (Br⁻), and iodide (I⁻) salts are soluble, except for those involving silver (Ag⁺), lead (Pb²⁺), and mercury (Hg₂²⁺).
• Most sulfate (SO₄²⁻) salts are soluble, with exceptions such as barium sulfate (BaSO₄), calcium sulfate (CaSO₄), and lead sulfate (PbSO₄).
• Hydroxide (OH⁻) compounds are often insoluble, except for those of alkali metals and certain alkaline earth metals like barium (Ba²⁺).

Understanding and applying these rules allows chemists to predict whether a reaction will form a precipitate. In the given exercise, these rules determined which products are soluble and which form precipitates, such as Al(OH)₃ and NiS.

Precipitation Reactions

Precipitation reactions occur when two soluble ionic compounds are mixed, and one of the resulting products is insoluble and forms a solid, known as a precipitate. The essence of these reactions lies in the re-arrangement of ions to form new compounds, some of which may be insoluble. The general format of a precipitation reaction is:

AB(aq) + CD(aq) \( \rightarrow \) AD(s) + CB(aq) Here, "AB" and "CD" are the initial ionic compounds in solution, "AD" is the precipitate that forms, and "CB" remains in solution. To determine if a precipitate forms, chemists rely on solubility rules. In the exercise example, mixing calcium chloride and sodium sulfate potential forms the precipitate calcium sulfate (CaSO₄). By understanding the solubility of different compounds, the formation of precipitates is predictable and manageable. This process illustrates the fundamental concept of conservation of mass, where the number of atoms of each element in the reactants equals that in the products, even if they change their form.

Ionic Compounds

Ionic compounds are substances formed by the chemical bonding of positive and negative ions through electrostatic forces. These ions typically form when metals lose electrons and become positively charged cations, while non-metals gain electrons to become negatively charged anions. Ionic compounds possess distinct properties:

• High melting and boiling points due to strong ionic bonds.
• Solubility in water varies; some easily dissolve while others form precipitates.
• Conduct electricity when dissolved in water or melted, as ions are free to move.

In the exercise, compounds like FeSO₄, KCl, and others represent ionic compounds that dissociate into ions when in solution. This dissociation allows reactions to occur between the ions, potentially leading to the formation of new compounds like Al(OH)₃ and NiS. Understanding how ionic compounds behave is essential for predicting reaction outcomes, especially in aqueous solutions, where many chemical reactions take place.