Problem 60 - Chemistry and Chemical Reactivity

Question

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

Step-by-Step Solution

Answer

(a) Precipitation, (b) Precipitation, (c) Gas-forming.

Step 1: Balance Equation (a)

The equation is \(\mathrm{K}_{2}\mathrm{CO}_{3}(\mathrm{aq})+\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) \rightarrow \mathrm{CuCO}_{3}(\mathrm{s})+\mathrm{KNO}_{3}(\mathrm{aq})\). Here is how we balance it: - Potassium (K): 2 on reactants and 1 on products. Put a coefficient 2 in front of \(\mathrm{KNO}_{3}\) to balance K.- Carbonate (CO₃) and Copper (Cu) are already balanced.- Nitrate (NO₃): 2 on both sides.Final 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 \(\mathrm{CuCO}_{3}\) (copper carbonate) forms as a solid, this is a precipitation reaction as it precipitates out of solution.

Step 3: Balance Equation (b)

The equation is \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+\mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{PbCl}_{2}(\mathrm{s}) + \mathrm{HNO}_{3}(\mathrm{aq})\). Here is how we balance it:- Lead (Pb) is balanced.- Chloride (Cl): 2 needed, so put a coefficient 2 in front of \(\mathrm{HCl}\) to balance Cl.- Nitrate (NO₃) and Hydrogen (H) are balanced.Final Balanced Equation: \[ \mathrm{Pb}(\mathrm{NO}_{3})_{2}(\mathrm{aq}) + 2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{PbCl}_{2}(\mathrm{s}) + 2 \mathrm{HNO}_{3}(\mathrm{aq}) \]

Step 4: Classify Reaction (b)

Since \(\mathrm{PbCl}_{2}\) (lead chloride) forms as a solid, this is a precipitation reaction as it precipitates out of solution.

Step 5: Balance Equation (c)

The equation is \(\mathrm{MgCO}_{3}(\mathrm{s})+\mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{MgCl}_{2}(\mathrm{aq}) + \mathrm{H}_{2}\mathrm{O}(\ell) + \mathrm{CO}_{2}(\mathrm{g})\). Here is how we balance it:- Magnesium (Mg) and Carbonate (CO₃) are balanced.- Chloride (Cl): 2 needed, so put a coefficient 2 in front of \(\mathrm{HCl}\) to balance.- Hydrogen (H) and Oxygen (O) are balanced naturally as well.Final 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 reaction forms water and carbon dioxide gas when an acid reacts with a carbonate, classifying it as a gas-forming reaction.

Key Concepts

Precipitation reaction

In chemistry, a precipitation reaction is a type of chemical reaction where two solutions containing soluble salts are mixed, resulting in the formation of an insoluble solid called a precipitate. In these reactions, the cations and anions of the reactants recombine to form the precipitate.

For example, consider the reaction between potassium carbonate \[ \mathrm{K}_{2}\mathrm{CO}_{3}(\mathrm{aq}) \]and copper(II) nitrate \( \mathrm{Cu}(\mathrm{NO}_{3})_{2}(\mathrm{aq}) \). When these solutions are mixed:

• Potassium (K) and nitrate (NO₃) ions remain dissolved.
• Copper (Cu) and carbonate (CO₃) ions combine to form copper carbonate \( \mathrm{CuCO}_{3}(\mathrm{s}) \), a solid precipitate.

This reaction specifically illustrates a typical precipitation process where solid copper carbonate separates from the aqueous medium.

To balance such equations, focus on ensuring the number of each type of atom or ion on both sides of the reaction are equal. Precipitation reactions are often visible because the formation of a solid in solution is usually noticeable as a change, such as a colorless solution turning cloudy. This is because the solid precipitate is often distinctly different from the clear surrounding liquid.

Gas-forming reaction

Gas-forming reactions are fascinating because they involve the liberation of gases from reactants, often accompanied by fizzing or bubbling. These reactions occur in situations where the reaction products include one or more gaseous substances.

A classic example is the reaction between magnesium carbonate \( \mathrm{MgCO}_{3}(\mathrm{s}) \)and hydrochloric acid \( \mathrm{HCl}(\mathrm{aq}) \). When combined:

• The carbonate ion (CO₃) reacts with the hydrogen ion (H) from the acid to form carbon dioxide gas \( \mathrm{CO}_{2}(\mathrm{g}) \).
• Water \( \mathrm{H}_{2}\mathrm{O}(\ell) \) is also produced as a byproduct.

The reaction can be observed as bubbles of carbon dioxide gas escape from the solution, clearly indicating the formation of a gas. This kind of reaction is not only important in educational demonstrations but is also applied in various industrial processes where gas production is needed.

Balancing equations here involves ensuring the number of atoms for each element, as well as charges, are the same on both sides of the equation. Gas-forming reactions are particularly insightful for understanding the principles of stoichiometry and the conservation of mass.

Acid-base reaction

Acid-base reactions, also known as neutralization reactions, occur when an acid reacts with a base, typically resulting in the formation of water and a salt. The fundamental nature of these reactions involves the donation of a proton (H⁺) from the acid to the base.

While the reactions in the original exercises are not strictly classified as acid-base reactions, it's important to understand the general mechanism.

• Acids like hydrochloric acid (HCl) donate protons.
• Bases typically accept these protons.

When an acid meets a base, they react to neutralize each other's properties, producing water \( \mathrm{H}_{2}\mathrm{O}(\ell) \) as a byproduct and forming a salt, which is usually a neutral compound.

For instance, the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) can be represented as:\[\mathrm{HCl}(\mathrm{aq}) + \mathrm{NaOH}(\mathrm{aq}) \rightarrow \mathrm{NaCl}(\mathrm{aq}) + \mathrm{H}_{2}\mathrm{O}(\ell)\]
Understanding acid-base reactions is crucial, as they are foundational to many processes in the natural world, from biochemical pathways to industrial synthesis.