Question

Identify each of the following unbalanced reaction equations as belonging to one or more of the following categories: precipitation, acid-base, or oxidation-reduction. a. $\mathrm{Fe}(s)+{\mathrm{H}}_2{\mathrm{SO}}_4(aq)\to {\mathrm{Fe}}_3{\left({\mathrm{SO}}_4\right)}_2(aq)+{\mathrm{H}}_2(g)$ b. ${\mathrm{HClO}}_4(aq)+\mathrm{RbOH}(aq)\to {\mathrm{RbClO}}_4(aq)+{\mathrm{H}}_2\mathrm{O}(l)$ c. $\mathrm{Ca}(s)+{\mathrm{O}}_2(g)\to \mathrm{CaO}(s)$ d. ${\mathrm{H}}_2{\mathrm{SO}}_4(aq)+\mathrm{NaOH}(aq)\to {\mathrm{Na}}_2{\mathrm{SO}}_4(aq)+{\mathrm{H}}_2\mathrm{O}(l)$ e. $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2(aq)+{\mathrm{Na}}_2{\mathrm{CO}}_3(aq)\to {\mathrm{PbCO}}_3(s)+{\mathrm{NaNO}}_3(aq)$ f. ${\mathrm{K}}_2{\mathrm{SO}}_4(aq)+{\mathrm{CaCl}}_2(aq)\to \mathrm{KCl}(aq)+{\mathrm{CaSO}}_4(s)$ g. ${\mathrm{HNO}}_3(aq)+\mathrm{KOH}(aq)\to {\mathrm{KNO}}_3(aq)+{\mathrm{H}}_2\mathrm{O}(l)$ h. $\mathrm{Ni}{\left({\mathrm{C}}_2{\mathrm{H}}_3{\mathrm{O}}_2\right)}_2(aq)+{\mathrm{Na}}_2\mathrm{S}(aq)\to \mathrm{NiS}(s)+{\mathrm{NaC}}_2{\mathrm{H}}_3{\mathrm{O}}_2(aq)$ i. $\mathrm{Ni}(s)+{\mathrm{Cl}}_2(g)\to {\mathrm{NiCl}}_2(s)$

Short answer

a. Oxidation-reduction b. Acid-base c. Oxidation-reduction d. Acid-base e. Precipitation f. Precipitation g. Acid-base h. Precipitation i. Oxidation-reduction

Step-by-step solution

a. Identify the reaction type

In this equation $\mathrm{Fe}(s)+{\mathrm{H}}_2{\mathrm{SO}}_4(aq)\to {\mathrm{Fe}}_3{\left({\mathrm{SO}}_4\right)}_2(aq)+{\mathrm{H}}_2(g)$, we are seeing a change of oxidation states in Fe from 0 to +2 and H from +1 to 0. So, this reaction is an oxidation-reduction.

b. Identify the reaction type

In this equation ${\mathrm{HClO}}_4(aq)+\mathrm{RbOH}(aq)\to {\mathrm{RbClO}}_4(aq)+{\mathrm{H}}_2\mathrm{O}(l)$, a proton is transferred from ${\mathrm{HClO}}_4$ to $\mathrm{RbOH}$, forming water. So, this reaction is an acid-base.

c. Identify the reaction type

In this equation $\mathrm{Ca}(s)+{\mathrm{O}}_2(g)\to \mathrm{CaO}(s)$, we can observe a change in the oxidation states where Ca changes from 0 to +2 and O from 0 to -2. So, this reaction is an oxidation-reduction reaction.

d. Identify the reaction type

In this equation ${\mathrm{H}}_2{\mathrm{SO}}_4(aq)+\mathrm{NaOH}(aq)\to {\mathrm{Na}}_2{\mathrm{SO}}_4(aq)+{\mathrm{H}}_2\mathrm{O}(l)$, a proton is transferred from ${\mathrm{H}}_2{\mathrm{SO}}_4$ to $\mathrm{NaOH}$, forming water. So, this reaction is an acid-base.

e. Identify the reaction type

In this equation $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2(aq)+{\mathrm{Na}}_2{\mathrm{CO}}_3(aq)\to {\mathrm{PbCO}}_3(s)+{\mathrm{NaNO}}_3(aq)$, we can see the formation of a solid ${\mathrm{PbCO}}_3$. So, this reaction is a precipitation reaction.

f. Identify the reaction type

In this equation ${\mathrm{K}}_2{\mathrm{SO}}_4(aq)+{\mathrm{CaCl}}_2(aq)\to \mathrm{KCl}(aq)+{\mathrm{CaSO}}_4(s)$, a solid ${\mathrm{CaSO}}_4$ is formed. So, this reaction is a precipitation reaction.

g. Identify the reaction type

In this equation ${\mathrm{HNO}}_3(aq)+\mathrm{KOH}(aq)\to {\mathrm{KNO}}_3(aq)+{\mathrm{H}}_2\mathrm{O}(l)$, a proton is transferred from ${\mathrm{HNO}}_3$ to $\mathrm{KOH}$, forming water. So, this reaction is an acid-base reaction.

h. Identify the reaction type

In this equation $\mathrm{Ni}{\left({\mathrm{C}}_2{\mathrm{H}}_3{\mathrm{O}}_2\right)}_2(aq)+{\mathrm{Na}}_2\mathrm{S}(aq)\to \mathrm{NiS}(s)+{\mathrm{NaC}}_2{\mathrm{H}}_3{\mathrm{O}}_2(aq)$, we can see the formation of a solid $\mathrm{NiS}$. So, this reaction is a precipitation reaction.

i. Identify the reaction type

In this equation $\mathrm{Ni}(s)+{\mathrm{Cl}}_2(g)\to {\mathrm{NiCl}}_2(s)$, the oxidation states change for both Ni (from 0 to +2) and Cl (from 0 to -1). So, this reaction is an oxidation-reduction reaction.

Key concepts

Precipitation Reactions

A precipitation reaction occurs when two solutions are mixed and an insoluble solid, called a precipitate, forms out of the solution. This is due to a double displacement reaction where the ions exchange partners, resulting in a compound that is not soluble in the solvent, often water.

For instance, in the reaction involving lead nitrate and sodium carbonate:

• $${\text{Pb(NO}}_3{\text{)}}_2(aq)+{\text{Na}}_2{\text{CO}}_3(aq)\to {\text{PbCO}}_3(s)+{\text{NaNO}}_3(aq)$$
• A white solid, PbCO₃, forms, which is evidence of a precipitation reaction.

Precipitation reactions are important for their applications in removing unwanted ions from solutions or in qualitative analysis for identifying ions present in a mixture.

Acid-Base Reactions

Acid-base reactions, also known as neutralization reactions, occur when an acid and a base react to form water and a salt.

Here, the acid donates a proton (H⁺) to the base. An example is the reaction between hydrochloric acid and potassium hydroxide:

• $${\text{HClO}}_4(aq)+\text{RbOH}(aq)\to {\text{RbClO}}_4(aq)+{\text{H}}_2\text{O}(l)$$
• In this equation, the ${\text{H}}^{+}$ from HClO₄ combines with the ${\text{OH}}^{-}$ from KOH to form water.

These reactions are crucial for many processes, including digestion in biology and chemical manufacture in industry, as well as lab titrations to determine concentrations.

Oxidation-Reduction Reactions

Oxidation-reduction reactions, commonly referred to as redox reactions, are characterized by the transfer of electrons between substances, leading to a change in oxidation numbers.

In a redox reaction, one element is oxidized (loses electrons) while another is reduced (gains electrons). Consider the example of calcium reacting with oxygen:

• $$\text{Ca}(s)+{\text{O}}_2(g)\to \text{CaO}(s)$$
• Here, calcium (Ca) is oxidized as it loses electrons to become ${\text{Ca}}^{2+}$ , and oxygen is reduced by gaining these electrons to form O²⁻.

Redox reactions are vital for energy production, such as in cellular respiration and battery operation, as well as in synthesis processes in industry.