Question

Classify each of the following statements as true or false. (a) Barium chloride, ${\mathrm{BaCl}}_{2^{\prime }}$ is a weak electrolyte in aqueous solution. (b) In the reaction ${\mathrm{H}}^{-}(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(1)\to {\mathrm{H}}_2(\mathrm{g})+$ ${\mathrm{OH}}^{-}(\mathrm{aq}),$ water acts as both an acid and an oxidizing agent. (c) A precipitate forms when aqueous sodium carbonate, ${\mathrm{Na}}_2{\mathrm{CO}}_3(\mathrm{aq}),$ is treated with excess aqueous hydrochloric acid, HCl(aq). (d) Hydrofluoric acid, $\overline{\mathrm{HF}}$, is a strong acid in water. (e) Compared with a 0.010 M solution of ${\mathrm{NaNO}}_3$, a $0.010\mathrm{M}$ solution of $\mathrm{Mg}{\left({\mathrm{NO}}_3\right)}_2$ is a better conductor of electricity.

Short answer

Statement (a) is false, Statement (b) is false, Statement (c) is false, Statement (d) is false, Statement (e) is true.

Step-by-step solution

Statement (a) evaluation

BaCl2 is a salt of a strong acid (HCl) and a strong base (Ba(OH)2), so it completely ionises in aqueous solution. Therefore, it's a strong electrolyte, not a weak one. So, the statement is false.

Statement (b) evaluation

In this reaction, water is behaving as a base (accepting a proton from the hydride ion) and it's not involved in an electron transfer process to qualify as an oxidizing agent. Therefore, it's false to say that water is acting as both an acid and an oxidizing agent. So, the statement is false.

Statement (c) evaluation

When Na2CO3 reacts with HCl, it undergoes a double displacement reaction to produce NaCl and H2CO3. The H2CO3 then further decomposes into H2O and CO2 gas. So, there is no precipitate formed in this reaction. Therefore, the statement is false.

Statement (d) evaluation

HF, or hydrofluoric acid, is generally classified as a weak acid in water due to its relatively low level of ionization compared to the strong acids. So, the statement is false.

Statement (e) evaluation

A 0.010 M solution of Mg(NO3)2 will produce three times as many ions per liter as a 0.010 M solution of NaNO3. Because the conductivity of a solution is proportional to its ion concentration, the Mg(NO3)2 solution would be a better conductor of electricity. Thus, the statement is true.

Key concepts

Strong vs Weak Electrolytes

Electrolytes are substances that dissolve in water to form solutions that conduct electricity. They can be categorized into strong and weak electrolytes. Strong Electrolytes:

• Completely ionize in water.
• Produce a large number of ions, enhancing electrical conductivity.
• Examples include salts like sodium chloride (NaCl), strong acids like hydrochloric acid (HCl), and strong bases like sodium hydroxide (NaOH).

Weak Electrolytes:

• Partially ionize in water.
• Produce fewer ions, resulting in lower electrical conductivity.
• Common examples are acetic acid (CH₃COOH) and ammonia (NH₃).

Understanding whether a substance is a strong or weak electrolyte is crucial for predicting the behavior of solutions in chemical reactions. In the original exercise, barium chloride (${\mathrm{BaCl}}_2$) is classified as a strong electrolyte because it completely dissociates in water, producing a high concentration of ions.

Acid-Base Reactions

Acid-base reactions involve the exchange of protons (${\mathrm{H}}^{+}$) between substances. These reactions are central to various chemical processes and can be understood through different theories, such as the Brønsted-Lowry theory.Brønsted-Lowry Theory:

• Acids are proton donors; they release ${\mathrm{H}}^{+}$ ions in solution.
• Bases are proton acceptors; they accept ${\mathrm{H}}^{+}$ ions from acids.

For example, when hydrofluoric acid (HF) dissolves in water, it donates a proton to water, acting as an acid. However, HF is a weak acid because it doesn't fully ionize, leading to a limited degree of proton donation. In acid-base reactions, the concept of conjugate acid-base pairs is also important. For instance, in the reaction of water with an acid, water acts as a base by accepting protons, forming hydronium ions (${\mathrm{H}}_3{\mathrm{O}}^{+}$). This dual nature can sometimes lead to misconceptions, like assuming water is an oxidizing agent, which is not the case.

Ionization in Solutions

Ionization refers to the process where molecules dissociate into ions when dissolved in a solvent, typically water. This process is crucial for the electrical conductivity of solutions and influences many chemical properties and reactions.Total Ionization:

• Occurs in strong electrolytes leading to the production of numerous ions. This is expressed as complete dissociation in equations, for instance, $\mathrm{NaCl}$ dissolves as: $\mathrm{NaCl}(aq)\to {\mathrm{Na}}^{+}(aq)+{\mathrm{Cl}}^{-}(aq)$.

Partial Ionization:

• Observed in weak electrolytes, which dissociate to a lesser extent. For weak acids like acetic acid, ionization equilibrium is established: ${\mathrm{CH}}_3\mathrm{COOH}\rightleftharpoons {\mathrm{CH}}_3{\mathrm{COO}}^{-}+{\mathrm{H}}^{+}$.

The degree of ionization directly affects a solution's pH and electrical conductivity. For example, magnesium nitrate (${\mathrm{Mg}(\mathrm{NO}}_3{)}_2$) in water produces more ions than sodium nitrate (${\mathrm{NaNO}}_3$), making it a better conductor, as seen in the textbook solution.