Problem 102 - General Chemistry

Question

Complete and balance each of the following molecular equations, including phase labels, if a reaction occurs. Then write the net ionic equation. If no reaction occurs, write \(N R\) after the arrow. a. \(\mathrm{HClO}_{4}+\mathrm{BaCO}_{3} \longrightarrow\) b. \(\mathrm{H}_{2} \mathrm{CO}_{3}+\mathrm{Sr}(\mathrm{OH})_{2} \longrightarrow\) c. \(\mathrm{K}_{3} \mathrm{PO}_{4}+\mathrm{MgCl}_{2} \longrightarrow\) d. \(\mathrm{FeSO}_{4}+\mathrm{MgCl}_{2} \longrightarrow\)

Step-by-Step Solution

Answer

(a) BaCO3(s) + 2H+(aq) → Ba2+(aq) + CO2(g) + H2O(l); (b) Sr2+(aq) + CO3^2-(aq) → SrCO3(s); (c) 3Mg^2+(aq) + 2PO4^3-(aq) → Mg3(PO4)2(s); (d) NR.

Step 1: Analyze Reaction a

Begin by predicting the products of the reaction between perchoric acid \((\mathrm{HClO}_4)\) and barium carbonate \((\mathrm{BaCO}_{3})\). The products will be barium perchlorate \((\mathrm{Ba(ClO}_{4})_{2})\), carbon dioxide \((\mathrm{CO}_{2})\), and water \((\mathrm{H}_2\mathrm{O})\). The reaction can be written as: \[\mathrm{2HClO}_{4}(aq) + \mathrm{BaCO}_{3}(s) \rightarrow \mathrm{Ba(ClO}_{4})_{2}(aq) + \mathrm{CO}_{2}(g) + \mathrm{H}_2\mathrm{O}(l)\] This is a double displacement reaction followed by a decomposition of \(\mathrm{H}_2\mathrm{CO}_3\) formed as an intermediate.

Step 2: Write Net Ionic Equation for Reaction a

In the net ionic equation, highlight the ions that change during the reaction. The barium carbonate is insoluble, so it does not dissociate, while perchloric acid dissociates into ions. The net ionic equation is: \[\mathrm{BaCO}_{3}(s) + 2\mathrm{H}^+(aq) \rightarrow \mathrm{Ba}^{2+}(aq) + \mathrm{CO}_{2}(g) + \mathrm{H}_2\mathrm{O}(l)\] This equation shows that the solid \(\mathrm{BaCO}_{3}\) reacts with hydrogen ions to form carbon dioxide, water, and aqueous barium ions.

Step 3: Analyze Reaction b

Predict the products when carbonic acid \((\mathrm{H}_2\mathrm{CO}_3)\) reacts with strontium hydroxide \((\mathrm{Sr(OH)}_2)\). The acid and the base react to form strontium carbonate \((\mathrm{SrCO}_3)\) and water. The equation is: \[\mathrm{H}_2\mathrm{CO}_3(aq) + \mathrm{Sr(OH})_{2}(aq) \rightarrow \mathrm{SrCO}_{3}(s) + 2\mathrm{H}_2\mathrm{O}(l)\] This is an acid-base neutralization reaction that results in the formation of a precipitate.

Step 4: Write Net Ionic Equation for Reaction b

Identify the ions participating in the reaction. Since SrCO3 precipitates, the hydrogen ions and carbonate ions react with strontium ions. The net ionic equation is: \[\mathrm{Sr}^{2+}(aq) + \mathrm{CO}_3^{2-}(aq) \rightarrow \mathrm{SrCO}_3(s)\] This equation shows the formation of solid strontium carbonate from aqueous ions.

Step 5: Analyze Reaction c

Predict the products of the reaction between potassium phosphate \((\mathrm{K}_3\mathrm{PO}_4)\) and magnesium chloride \((\mathrm{MgCl}_2)\). These will form magnesium phosphate \((\mathrm{Mg_3(PO_4)_2})\) and potassium chloride \((\mathrm{KCl})\). The equation is: \[2\mathrm{K}_3\mathrm{PO}_4(aq) + 3\mathrm{MgCl}_2(aq) \rightarrow \mathrm{Mg_3(PO_4)_2}(s) + 6\mathrm{KCl}(aq)\] This is a double displacement reaction resulting in the formation of a precipitate.

Step 6: Write Net Ionic Equation for Reaction c

Write the net ionic equation that indicates only the participation of ions forming the precipitate. The net ionic equation is:\[3\mathrm{Mg}^{2+}(aq) + 2\mathrm{PO}_4^{3-}(aq) \rightarrow \mathrm{Mg_3(PO_4)_2}(s)\] This shows the precipitation of magnesium phosphate from aqueous ions.

Step 7: Analyze Reaction d

Consider the possible reaction between iron(II) sulfate \((\mathrm{FeSO}_4)\) and magnesium chloride \((\mathrm{MgCl}_2)\). Both salts are soluble and no driving force like the formation of a precipitate, gas, or water in a notable way occurs. Hence, there is no reaction: \[\mathrm{FeSO}_{4}(aq) + \mathrm{MgCl}_{2}(aq) \rightarrow NR\] This indicates the absence of any visible reaction outcome.

Key Concepts

Chemical Reactions

Chemical reactions involve the transformation of reactants into products. In a chemical equation, the substances on the left are transformed through chemical processes to form new substances on the right. Each chemical reaction can be classified by the changes occurring in the reaction. Chemical reactions can typically be categorized by the following:

• Synthesis: Where two or more simple substances combine to form a more complex product.
• Decomposition: A complex molecule breaks down into simpler ones.
• Single replacement: An element reacts with a compound and takes the place of another element in that compound.
• Double replacement: The ions of two compounds exchange to form two new compounds.

In reaction (a), the perchloric acid reacts with barium carbonate in a double displacement reaction, eventually leading to the decomposition of carbonic acid into carbon dioxide and water. These types of reactions frequently occur in chemistry and are important for understanding how various substances interact.

Acid-Base Reactions

Acid-base reactions are a fundamental type of chemical reaction where an acid and a base interact to form water and a salt. In its simplest form, an acid is a substance that donates protons ( H^+ ), while a base accepts protons. The sharing of protons between acids and bases leads to neutralization, a common result of acid-base reactions. This neutralization is characterized as:

• Acid: Proton donor, contains H^+ ions.
• Base: Proton acceptor, contains OH^- ions.

In reaction (b), carbonic acid reacts with strontium hydroxide, resulting in the formation of strontium carbonate and water. The hydroxide ions from the base accept protons from the acid, resulting in neutralization, and the formation of a precipitate in the solution.

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions combine, and an insoluble solid known as a precipitate forms. This solid precipitate results when the product of the ionic exchange is not soluble in water, thus separating from the solution. Key aspects of precipitation reactions include:

• Formation of solid: A solid product called a precipitate forms from the reaction.
• Double displacement: Most precipitation reactions involve the exchange of ions between two reactants.

For instance, in reaction (c), when potassium phosphate reacts with magnesium chloride, magnesium phosphate precipitates as an insoluble solid, confirming it as a precipitation reaction. This type of reaction is significant in fields like analytical chemistry, where separation and purification processes are essential.