Problem 56 - Chemistry and Chemical Reactivity

Question

Complete and balance the equations below, and classify them as precipitation, acid-base, gas-forming, or oxidation-reduction reactions. Show states for the products \((\mathrm{s}, \ell, \mathrm{g}, \mathrm{aq}),\) and then balance the completed equation. (a) \(\mathrm{NiCO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow\) (b) \(\mathrm{Co}(\mathrm{OH})_{2}+\mathrm{HBr} \rightarrow\) (c) \(\mathrm{AgCH}_{3} \mathrm{CO}_{2}+\mathrm{NaCl} \rightarrow\) (d) \(\mathrm{NiO}+\mathrm{CO} \rightarrow\)

Step-by-Step Solution

Answer

(a) Gas-forming: \(\mathrm{NiSO}_{4}(\mathrm{aq})+\mathrm{H}_{2}O(\ell)+\mathrm{CO}_2(\mathrm{g})\) (b) Acid-base: \(\mathrm{CoBr}_2(\mathrm{aq})+2\mathrm{H}_2\mathrm{O}(\ell)\) (c) Precipitation: \(\mathrm{AgCl}(\mathrm{s})+\mathrm{NaCH}_3\mathrm{CO}_2(\mathrm{aq})\) (d) Oxidation-reduction: \(\mathrm{Ni}(\mathrm{s})+\mathrm{CO}_2(\mathrm{g})\)

Step 1: Balance Equation (a)

**Equation (a):** \( \mathrm{NiCO}_{3} + \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \)First, identify the products:\[ \mathrm{NiCO}_{3}(\mathrm{s}) + \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \rightarrow \mathrm{NiSO}_{4}(\mathrm{aq}) + \mathrm{H}_{2}O(\ell) + \mathrm{CO}_2(\mathrm{g}). \]This is a gas-forming reaction (release of \(\mathrm{CO}_2\)).Balancing the equation:The equation is already balanced as-is.Each element is balanced, with the same number of atoms on each side.

Step 2: Balance Equation (b)

**Equation (b):** \( \mathrm{Co(OH)}_2 + \mathrm{HBr} \rightarrow \)Identify the products:\[ \mathrm{Co(OH)}_2(\mathrm{s}) + 2\mathrm{HBr}(\mathrm{aq}) \rightarrow \mathrm{CoBr}_2(\mathrm{aq}) + 2\mathrm{H}_2\mathrm{O}(\ell). \]This is an acid-base reaction (formation of water).Balancing the equation:1. Balance the \(\mathrm{Br}\) by making sure there are 2 bromine atoms on the right, 2 \(\mathrm{Br}\) from \(\mathrm{HBr}\).2. Balance \(\mathrm{O}\) atoms by forming 2 \(\mathrm{H}_2\mathrm{O}\).The equation is now balanced.

Step 3: Balance Equation (c)

**Equation (c):** \( \mathrm{AgCH}_3\mathrm{CO}_2 + \mathrm{NaCl} \rightarrow \)Identify the products:\[ \mathrm{AgCH}_3\mathrm{CO}_2(\mathrm{aq}) + \mathrm{NaCl}(\mathrm{aq}) \rightarrow \mathrm{AgCl}(\mathrm{s}) + \mathrm{NaCH}_3\mathrm{CO}_2(\mathrm{aq}). \]This is a precipitation reaction (formation of \(\mathrm{AgCl}\)).Balancing the equation:The equation is already balanced, with all atoms accounted for on each side.

Step 4: Balance Equation (d)

**Equation (d):** \( \mathrm{NiO} + \mathrm{CO} \rightarrow \)Identify the products:\[ \mathrm{NiO}(\mathrm{s}) + \mathrm{CO}(\mathrm{g}) \rightarrow \mathrm{Ni}(\mathrm{s}) + \mathrm{CO}_2(\mathrm{g}). \]This is an oxidation-reduction reaction (transfer of electrons between nickel and carbon).Balancing the equation:1. Balance nickel and carbon atoms; both are already balanced.2. Check oxygen atoms on both sides; already balanced.The equation is already balanced.

Key Concepts

Balancing Chemical Equations

Balancing chemical equations is an essential skill in chemistry because it ensures the law of conservation of mass is upheld. This principle states that matter cannot be created or destroyed, and thus, the number of atoms for each element must be the same on both sides of a chemical equation. To successfully balance a chemical equation, follow these steps:

• Identify the reactants and products: Determine the chemical formulas for each substance involved in the reaction.
• Count the number of each type of atom: For each side of the equation, tally up the atoms for each element to determine what is unbalanced.
• Balance one element at a time: Use coefficients to equalize the number of atoms for that element on both sides. Start with the most complex molecules.
• Check your work: Verify that all elements are balanced and that you have used the simplest set of coefficients possible.

For example, in equation (a) of the problem, \[\text{NiCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{NiSO}_4 + \text{H}_2\text{O} + \text{CO}_2\]each type of atom was already balanced initially. Thus, no coefficients were needed besides those implied by the chemical formulas themselves. Balancing chemical equations is like solving a puzzle; practice helps improve speed and accuracy.

Reaction Types

Chemical reactions can be categorized into different types based on the changes that occur during the reaction. Understanding these types helps in predicting the products of unfamiliar reactions. Here are some common reaction types:

• Precipitation Reactions: These reactions occur when two aqueous solutions combine, forming an insoluble solid called a precipitate. For example, equation (c) results in the formation of silver chloride (\(\mathrm{AgCl}\)) as a precipitate from a solution.
• Acid-Base Reactions: In these reactions, an acid and a base react to form water and a salt. Equation (b) showcases this reaction type, with cobalt(II) hydroxide reacting with hydrobromic acid to produce water and cobalt(II) bromide.
• Gas-Forming Reactions: These produce a gas as one of the products. In equation (a), carbon dioxide gas is released during the reaction.
• Oxidation-Reduction (Redox) Reactions: These involve electron transfer between substances. In equation (d), nickel is reduced, and carbon is oxidized.

Knowing the type of reaction provides insight into the reaction mechanism and potential products. Each type has distinguishing features that make them predictable once understood.

States of Matter in Reactions

The states of matter in a chemical reaction describe the physical forms of the reactants and products. Recognizing these states is crucial for understanding how substances interact. In chemical equations, these states are often indicated by the following symbols:

• (s): Solid - Indicates a substance is in the solid form. For instance, \(\mathrm{NiCO}_3\) is a solid reactant in equation (a).
• (l): Liquid - Represents a liquid state, such as water in equation (a) and (b).
• (g): Gas - Used for gaseous products like \(\mathrm{CO}_2\) which is formed in equations (a) and (d).
• (aq): Aqueous - Refers to a substance dissolved in water. In equation (c), both \(\mathrm{AgCH}_3\mathrm{CO}_2\) and \(\mathrm{NaCl}\) are aqueous before reacting.

Knowing the states can help predict phase changes and the direction of reaction. Understanding these notations also aids in balancing equations, especially for checking the conservation of mass in terms of moles and molecules accordingly. Identifying the states effectively structured the solutions to the given equations by linking the reactants to their probable outcomes.