Problem 30 - Chemistry and Chemical Reactivity

Question

Balance the following reactions and then classify each as a precipitation, acid-base reaction, or a gas-forming reaction. (a) \(\mathrm{K}_{2} \mathrm{CO}_{3}(\mathrm{aq})+\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) \longrightarrow\) \(\mathrm{CuCO}_{3}(\mathrm{s})+\mathrm{KNO}_{3}(\mathrm{aq})\) (b) \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+\mathrm{HCl}(\mathrm{aq}) \longrightarrow \mathrm{PbCl}_{2}(\mathrm{s})+\mathrm{HNO}_{3}(\mathrm{aq})\) (c) \(\mathrm{MgCO}_{3}(\mathrm{s})+\mathrm{HCl}(\mathrm{aq}) \longrightarrow\) \(\mathrm{MgCl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{CO}_{2}(\mathrm{g})\)

Step-by-Step Solution

Answer

(a) Balance: \(2\mathrm{KNO}_{3}\), Precipitation. (b) Balance: \(2\mathrm{HCl}, 2\mathrm{HNO}_{3}\), Precipitation. (c) Balance: \(2\mathrm{HCl}\), Gas-forming.

Step 1: Balance Reaction (a)

Reaction (a) involves the reactants \( \mathrm{K}_{2}\mathrm{CO}_{3}(\mathrm{aq}) \) and \( \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) \), producing \( \mathrm{CuCO}_{3}(\mathrm{s}) \) and \( \mathrm{KNO}_{3}(\mathrm{aq}) \).1. Count the number of each type of atom on both sides: - Potassium (K): Reactants = 2, Products = 1 - Copper (Cu): Reactants = 1, Products = 1 - Carbon (C): Reactants = 1, Products = 1 - Oxygen (O): Reactants = 6, Products = 6 - Nitrogen (N): Reactants = 2, Products = 12. To balance potassium and nitrogen, adjust the coefficient of \( \mathrm{KNO}_{3} \) to 2.Revised balanced equation:\[ \mathrm{K}_{2}\mathrm{CO}_{3}(\mathrm{aq}) + \mathrm{Cu}(\mathrm{NO}_{3})_{2}(\mathrm{aq}) \rightarrow \mathrm{CuCO}_{3}(\mathrm{s}) + 2\mathrm{KNO}_{3}(\mathrm{aq}) \]

Step 2: Classify Reaction (a)

Since the product \( \mathrm{CuCO}_{3}(\mathrm{s}) \) is an insoluble solid, this reaction is a precipitation reaction.

Step 3: Balance Reaction (b)

In reaction (b), \( \mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) \) reacts with \( \mathrm{HCl}(\mathrm{aq}) \) to produce \( \mathrm{PbCl}_{2}(\mathrm{s}) \) and \( \mathrm{HNO}_{3}(\mathrm{aq}) \).1. Count the number of each type of atom: - Lead (Pb): Reactants = 1, Products = 1 - Nitrogen (N): Reactants = 2, Products = 1 - Hydrogen (H): Reactants = 1, Products = 1 - Chlorine (Cl): Reactants = 1, Products = 22. To balance nitrogen and chlorine, adjust the coefficient of \( \mathrm{HCl} \) to 2, and \( \mathrm{HNO}_{3} \) to 2.Revised balanced equation:\[ \mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) + 2\mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{PbCl}_{2}(\mathrm{s}) + 2\mathrm{HNO}_{3}(\mathrm{aq}) \]

Step 4: Classify Reaction (b)

The formation of \( \mathrm{PbCl}_{2}(\mathrm{s}) \) indicates a precipitation reaction as an insoluble solid forms.

Step 5: Balance Reaction (c)

In reaction (c), \( \mathrm{MgCO}_{3}(\mathrm{s}) \) reacts with \( \mathrm{HCl}(\mathrm{aq}) \) to give \( \mathrm{MgCl}_{2}(\mathrm{aq}) \), \( \mathrm{H}_{2}\mathrm{O}(\ell) \), and \( \mathrm{CO}_{2}(\mathrm{g}) \).1. Count the number of each type of atom: - Magnesium (Mg): Reactants = 1, Products = 1 - Carbon (C): Reactants = 1, Products = 1 - Oxygen (O): Reactants = 3, Products = 3 - Hydrogen (H): Reactants = 1, Products = 2 - Chlorine (Cl): Reactants = 1, Products = 22. To balance hydrogen and chlorine, adjust the coefficient of \( \mathrm{HCl} \) to 2.Revised balanced equation:\[ \mathrm{MgCO}_{3}(\mathrm{s}) + 2\mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{MgCl}_{2}(\mathrm{aq}) + \mathrm{H}_{2}\mathrm{O}(\ell) + \mathrm{CO}_{2}(\mathrm{g}) \]

Step 6: Classify Reaction (c)

This is a gas-forming reaction as \( \mathrm{CO}_{2}(\mathrm{g}) \) is released as a gaseous product.

Key Concepts

Precipitation Reactions

In precipitation reactions, two aqueous solutions combine to form an insoluble solid, known as a precipitate. This reaction occurs when the ions in the solution react to form an ionic compound that is not soluble in water. Let's explore this concept further with an example.

Consider the reaction between potassium carbonate ( K_2CO_3(aq) ) and copper(II) nitrate ( Cu(NO_3)_2(aq) ), which yields copper(II) carbonate ( CuCO_3(s) ) as a solid precipitate and potassium nitrate ( KNO_3(aq) ) as an aqueous byproduct. The balanced chemical equation is:

• 2 KNO_3 molecules, alongside one CuCO_3 solid form as products.

This reaction is classified as a precipitation reaction because CuCO_3 , the produced solid, does not dissolve in water, thus "precipitating" out of the solution.

Precipitation reactions are an important aspect in chemical processes like water treatment and salt production, where solids are separated from solutions.

Acid-Base Reactions

Acid-base reactions, also known as neutralization reactions, involve the reaction between an acid and a base to produce water and a salt. These reactions are central to understanding the behavior of acids and bases in solution.

The typical formula of an acid-base reaction can be represented as:

• Acid + Base → Salt + Water

For example, in the reaction between lead(II) nitrate ( Pb(NO_3)_2(aq) ) and hydrochloric acid ( HCl(aq) ), lead(II) chloride ( PbCl_2(s) ) is formed as a precipitate, while nitric acid ( HNO_3(aq) ) remains in solution. The balanced equation is given by:

focusing our attention on whether the products include PbCl_2 as a solid (indicating a precipitation reaction), the nature of its occurrence highlights the acid-base reaction's result of an insoluble salt alongside an acid (here HNO_3 ).

In practical terms, these reactions are vital in titrations and other analytical methods used to determine pH levels and substance concentrations in various solutions.

Gas-Forming Reactions

Gas-forming reactions are chemical reactions that result in the formation of a gas as one of the products. These reactions are noteworthy because they can be visually tracked by the effervescence or fizzing due to gas release.

Take, for example, the reaction between magnesium carbonate ( MgCO_3(s) ) and hydrochloric acid ( HCl(aq) ). In this reaction, magnesium chloride ( MgCl_2(aq) ) and water ( H_2O(l) ) are formed alongside carbon dioxide gas ( CO_2(g) ), which escapes as bubbles. The balanced chemical equation is:

• MgCO_3(s) + 2HCl(aq) → MgCl_2(aq) + H_2O(l) + CO_2(g)

Highlighting the gas formation, CO_2 being a common gas evolved in such reactions adds to the understanding of reaction types that result in visible gas output.

These reactions are critical in diverse fields, such as geology (carbonates reacting with acids) and manufacturing processes like the production of carbonated beverages.