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. \(\mathrm{K}_{2} \mathrm{SO}_{4}(a q)+\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(a q) \rightarrow \mathrm{BaSO}_{4}(s)+\mathrm{KNO}_{3}(a q)\) b. \(\mathrm{HCl}(a q)+\mathrm{Zn}(s) \rightarrow \mathrm{H}_{2}(g)+\mathrm{ZnCl}_{2}(a q)\) c. \(\mathrm{HCl}(a q)+\mathrm{AgNO}_{3}(a q) \rightarrow \mathrm{HNO}_{3}(a q)+\mathrm{AgCl}(s)\) d. \(\mathrm{HCl}(a q)+\mathrm{KOH}(a q) \rightarrow \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{KCl}(a q)\) e. \(\operatorname{Zn}(s)+\mathrm{CuSO}_{4}(a q) \rightarrow \mathrm{ZnSO}_{4}(a q)+\mathrm{Cu}(s)\) f. \(\mathrm{NaH}_{2} \mathrm{PO}_{4}(a q)+\mathrm{NaOH}(a q) \rightarrow \mathrm{Na}_{3} \mathrm{PO}_{4}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\) g. \(\mathrm{Ca}(\mathrm{OH})_{2}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{CaSO}_{4}(s)+\mathrm{H}_{2} \mathrm{O}(l)\) h. \(\mathrm{ZnCl}_{2}(a q)+\mathrm{Mg}(s) \rightarrow \mathrm{Zn}(s)+\mathrm{MgCl}_{2}(a q)\) i. \(\mathrm{BaCl}_{2}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{BaSO}_{4}(s)+\mathrm{HCl}(a q)\)

Short answer

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

Step-by-step solution

a. K2SO4(aq)+Ba(NO3)2(aq)→BaSO4(s)+KNO3(aq)#

An insoluble solid (BaSO4) forms as a result of this reaction, indicating that this is a precipitation reaction. There is no electron or proton transfer, so it isn't an acid-base or oxidation-reduction reaction.

b. HCl(aq)+Zn(s)→H2(g)+ZnCl2(aq)#

This reaction doesn't form an insoluble product, but electrons are transferred from Zn to H+ ions, making this an oxidation-reduction reaction. It also involves an acidic substance reacting with a metal, but it doesn't form water, so it's not an acid-base reaction.

c. HCl(aq)+AgNO3(aq)→HNO3(aq)+AgCl(s)#

This reaction forms an insoluble solid (AgCl), indicating that it's a precipitation reaction. The transfer of a proton from HCl to NO3- forms HNO3, showing that it's also an acid-base reaction. There is no electron transfer, so it isn't an oxidation-reduction reaction.

d. HCl(aq)+KOH(aq)→H2O(l)+KCl(aq)#

This is a classic acid-base reaction, as it involves the transfer of a proton (H+) from the acidic HCl to the basic OH- to form water (H2O). There is no insoluble product or electron transfer, so it is not a precipitation or oxidation-reduction reaction.

e. Zn(s)+CuSO4(aq)→ZnSO4(aq)+Cu(s)#

In this reaction, the electrons are transferred from Zn to Cu2+, making this an oxidation-reduction reaction. There is no insoluble product or proton transfer, so it isn't a precipitation or acid-base reaction.

f. NaH2PO4(aq)+NaOH(aq)→Na3PO4(aq)+H2O(l)#

This reaction involves the transfer of a proton from the acidic NaH2PO4 to the basic OH- ion, forming water, which makes it an acid-base reaction. There is no insoluble product or electron transfer, so it isn't a precipitation or oxidation-reduction reaction.

g. Ca(OH)2(aq)+H2SO4(aq)→CaSO4(s)+H2O(l)#

This reaction forms an insoluble solid (CaSO4), indicating that it's a precipitation reaction. The transfer of a proton from H2SO4 to OH- ions forms water, making it an acid-base reaction too. There is no electron transfer, so it isn't an oxidation-reduction reaction.

h. ZnCl2(aq)+Mg(s)→Zn(s)+MgCl2(aq)#

This reaction involves the transfer of electrons from Mg to Zn2+, making it an oxidation-reduction reaction. There is no insoluble product or proton transfer, so it isn't a precipitation or acid-base reaction.

i. BaCl2(aq)+H2SO4(aq)→BaSO4(s)+HCl(aq)#

This reaction forms an insoluble solid (BaSO4), indicating that it's a precipitation reaction. The transfer of a proton from H2SO4 to Cl- ions forms HCl, making it an acid-base reaction too. There is no electron transfer, so it isn't an oxidation-reduction reaction.

Key concepts

Precipitation Reaction

Precipitation reactions are a fundamental aspect of chemistry where certain dissolved substances react to form an insoluble solid, known as a precipitate. In a typical scenario, two aqueous solutions mix and an insoluble salt is formed that falls out of solution. A classic example of this can be seen in the combination of aqueous potassium sulfate \( \mathrm{K}_{2} \mathrm{SO}_{4}(aq) \) and barium nitrate \( \mathrm{Ba(NO}_{3})_{2}(aq) \) which react to form solid barium sulfate \( \mathrm{BaSO}_{4}(s) \) and aqueous potassium nitrate \( \mathrm{KNO}_{3}(aq) \). \
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\To recognize a precipitation reaction, look for the formation of a solid in the product side of the chemical equation. These reactions are important in various fields such as qualitative analysis, where they are used for chemical tests, and in water treatment processes to remove unwanted ions from solutions.

Acid-Base Reaction

Acid-base reactions, also known as neutralization reactions, involve the transfer of hydrogen cations, or protons, from an acid to a base. This transfer typically results in the formation of a salt and water, demonstrating the neutralization of the acid and base properties. \
\
\For example, hydrochloric acid \( \mathrm{HCl}(aq) \) reacts with silver nitrate \( \mathrm{AgNO}_{3}(aq) \) to produce nitric acid \( \mathrm{HNO}_{3}(aq) \) and silver chloride \( \mathrm{AgCl}(s) \), the latter being a precipitate. Here, the hydrogen ion from \( \mathrm{HCl} \) combines with the nitrate ion from \( \mathrm{AgNO}_{3} \) to form \( \mathrm{HNO}_{3} \) in a classic display of acid to base proton transfer. \
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\Acid-base reactions are very common in both laboratory chemistry and everyday life, including the simple act of neutralizing stomach acid with an antacid.

Oxidation-Reduction Reaction

Oxidation-reduction reactions, or redox reactions, involve the movement of electrons from one substance to another. During these reactions, oxidation—loss of electrons—and reduction—gain of electrons—occur simultaneously. A clear example of a redox reaction is the interaction between solid zinc \( \mathrm{Zn}(s) \) and aqueous copper(II) sulfate \( \mathrm{CuSO}_{4}(aq) \), which leads to zinc sulfate \( \mathrm{ZnSO}_{4}(aq) \) and solid copper \( \mathrm{Cu}(s) \). \
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\Electron transfer can be tracked by assigning oxidation numbers to the elements involved in the reaction. In the given example, zinc is oxidized (increased oxidation state) as it loses electrons, while copper is reduced (decreased oxidation state) as it gains electrons. Redox reactions are fundamental to numerous biological processes, industrial applications, and even the generation of energy as seen in batteries.

Chemical Equations

Chemical equations are a concise way of representing chemical reactions using symbols and formulas. A balanced chemical equation ensures that the same amount of atoms is present on both the reactant and product sides, adhering to the Law of Conservation of Mass. \
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\For instance, the reaction \( \mathrm{Ca(OH)}_{2}(aq) + \mathrm{H}_{2} \mathrm{SO}_{4}(aq) \rightarrow \mathrm{CaSO}_{4}(s) + \mathrm{H}_{2} \mathrm{O}(l) \) is understood to describe the reaction of calcium hydroxide with sulfuric acid to produce calcium sulfate, a solid, and liquid water. \
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\The act of balancing equations involves adjusting coefficients in front of compounds to ensure that the number of atoms for each element is equal on both sides. Mastering the art of writing and balancing chemical equations is essential for understanding and predicting the outcomes of chemical reactions.

Electron Transfer

Electron transfer is a key concept in chemistry that is especially pertinent in the context of oxidation-reduction (redox) reactions. It refers to the movement of electrons from one atom or molecule to another, which results in the change of oxidation states of the involved substances. \
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\For example, when magnesium \( \mathrm{Mg}(s) \) reacts with aqueous zinc chloride \( \mathrm{ZnCl}_{2}(aq) \) to form solid zinc \( \mathrm{Zn}(s) \) and magnesium chloride \( \mathrm{MgCl}_{2}(aq) \), magnesium atoms transfer their electrons to zinc ions, illustrating an oxidation process for magnesium and reduction for zinc. \
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\This transfer is crucial for many chemical processes including photosynthesis, cellular respiration, and electrochemistry. Understanding how electrons move allows students to predict the direction and feasibility of chemical reactions, and it is also the basis for the entire field of electrochemistry.