Question

Consider the following generic equation $$ \mathrm{OH}^{-}(a q)+\mathrm{HB}(a q) \longrightarrow \mathrm{B}^{-}(a q)+\mathrm{H}_{2} \mathrm{O} $$ For which of the following pairs would this be the correct prototype equation for the acid-base reaction in solution? If it is not correct, write the proper equation for the acid-base reaction between the pair. (a) hydrochloric acid and pyridine, \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{~N}\) (b) sulfuric acid and rubidium hydroxide (c) potassium hydroxide and hydrofluoric acid (d) ammonia and hydriodic acid (e) strontium hydroxide and hydrocyanic acid

Short answer

Question: Determine whether the given pairs of compounds would correctly fit into the acid-base reaction equation of OH⁻(aq) + HB(aq) → B⁻(aq) + H₂O(l). If not, write the proper equation for the acid-base reaction between the pair. a. Hydrochloric acid and pyridine Answer: No, they do not fit the given equation. The proper equation is: $$ C_5H_5N_(aq) + HCl_(aq) \longrightarrow C_5H_5NH^+_(aq) + Cl^-(aq) $$ b. Sulfuric acid and rubidium hydroxide Answer: No, they do not fit the given equation. The proper equation is: $$ H_2SO_4_(aq) + 2RbOH_(aq) \longrightarrow Rb_2SO_4_(aq) + 2H_2O(l) $$ c. Potassium hydroxide and hydrofluoric acid Answer: No, they do not fit the given equation. The proper equation is: $$ KOH_(aq) + HF_(aq) \longrightarrow KF_(aq) + H_2O(l) $$ d. Ammonia and hydriodic acid Answer: No, they do not fit the given equation. The proper equation is: $$ NH_3_(aq) + HI_(aq) \longrightarrow NH_4^+_(aq) + I^-_(aq) $$ e. Strontium hydroxide and hydrocyanic acid Answer: No, they do not fit the given equation. The proper equation is: $$ Sr(OH)_2_(aq) + 2HCN_(aq) \longrightarrow Sr(CN)_2_(aq) + 2H_2O(l) $$

Step-by-step solution

Write the reactants

First, let's write the reactants in the given equation: $$ \mathrm{OH}^{-}(a q)+\mathrm{HB}(a q) $$ In our case, the reactants are hydrochloric acid (HCl) and pyridine (C5H5N).

Identify the base and the acid

We know that hydrochloric acid is a strong acid, and pyridine is a weak base. So, the reaction will be between these two compounds: $$ \mathrm{OH}^{-}(a q)+\mathrm{HCl}(a q) $$

Write the correct generic prototype equation

Now, since pyridine is a weak base, it will accept a proton (H+) from hydrochloric acid, forming C5H5NH+. Therefore, the correct acid-base reaction equation should be: $$ \C_5H_5N_(aq) + HCl_(aq) \longrightarrow C_5H_5NH^+_(aq) + Cl^-(aq) $$ #b. Sulfuric acid and rubidium hydroxide#

Write the reactants

The reactants are sulfuric acid (H2SO4) and rubidium hydroxide (RbOH).

Identify the base and the acid

Sulfuric acid is a strong acid, and rubidium hydroxide is a strong base.

Write the correct generic prototype equation

The correct acid-base reaction equation should be: $$ H_2SO_4_(aq) + 2RbOH_(aq) \longrightarrow Rb_2SO_4_(aq) + 2H_2O(l) $$ #c. Potassium hydroxide and hydrofluoric acid#

Write the reactants

The reactants are potassium hydroxide (KOH) and hydrofluoric acid (HF).

Identify the base and the acid

Potassium hydroxide is a strong base, and hydrofluoric acid is a weak acid.

Write the correct generic prototype equation

The correct acid-base reaction equation should be: $$ KOH_(aq) + HF_(aq) \longrightarrow KF_(aq) + H_2O(l) $$ #d. Ammonia and hydriodic acid#

Write the reactants

The reactants are ammonia (NH3) and hydriodic acid (HI).

Identify the base and the acid

Ammonia is a weak base, and hydriodic acid is a strong acid.

Write the correct generic prototype equation

The correct acid-base reaction equation should be: $$ NH_3_(aq) + HI_(aq) \longrightarrow NH_4^+_(aq) + I^-_(aq) $$ #e. Strontium hydroxide and hydrocyanic acid#

Write the reactants

The reactants are strontium hydroxide (Sr(OH)2) and hydrocyanic acid (HCN).

Identify the base and the acid

Strontium hydroxide is a strong base, and hydrocyanic acid is a weak acid.

Write the correct generic prototype equation

The correct acid-base reaction equation should be: $$ Sr(OH)_2_(aq) + 2HCN_(aq) \longrightarrow Sr(CN)_2_(aq) + 2H_2O(l) $$

Key concepts

Strong and Weak Acids and Bases

Understanding the nature of acids and bases is crucial in chemistry, particularly when dealing with acid-base reactions. An acid is a substance that usually donates protons (H+ ions) in a reaction, whereas a base is one that accepts protons.

Acids and bases can be classified as either strong or weak, depending on their ability to dissociate in water. Strong acids and bases dissociate completely, meaning they break apart into their constituent ions when dissolved in water. Examples include hydrochloric acid (HCl) and sodium hydroxide (NaOH). On the other hand, weak acids, like hydrofluoric acid (HF), and weak bases, such as ammonia (NH3), do not fully dissociate and exist in equilibrium with their undissociated form in solution.

What determines the strength of an acid or base? It is the extent to which they dissociate in water. This quality is important because it affects the pH level of the solution and the outcome of acid-base reactions. A strong acid or base will shift the pH more than a weak one.

Acid-Base Reaction Equations

Acid-base reaction equations represent the chemical processes where acids donate protons to bases. Writing these reactions involves identifying the reactants and predicting the products formed.

For instance, in the reaction between hydrochloric acid (HCl) and the weak base pyridine (\( C_5H_5N \)), the proton is transferred to pyridine, forming the conjugate acid \( C_5H_5NH^+ \) and chloride ion (\( Cl^- \)). In these types of reactions, the resultant products are typically a salt and water, which is evident in reactions involving strong acids and bases.

Identifying the Reactants and Predicting Products

In creating balanced reaction equations, it is necessary first to identify all reactants, categorize each one as an acid or a base, and then to use this information to predict the products. As showcased in the original exercise, if you mix sulfuric acid (\( H_2SO_4 \)) with rubidium hydroxide (\( RbOH \)), since both are strong, the acid will donate two protons to the base, resulting in the products rubidium sulfate (\( Rb_2SO_4 \)) and water (\( H_2O \)).

Remember that the key to mastering acid-base reaction equations is to practice identifying the reactants and predicting the products according to their acidic or basic nature.

Chemical Equilibrium

In an acid-base reaction, not all reactants turn into products, especially when dealing with weak acids or bases; this is where the concept of chemical equilibrium comes in. Equilibrium defines the state in a reaction where the rate of the forward reaction equals the rate of the reverse reaction. As a result, the concentrations of reactants and products remain constant over time.

The idea of equilibrium is vital in understanding reactions involving weak acids or bases. The reactions do not go to completion, meaning not all of the reactants are converted into products. Instead, they establish a balance between the reactants and the products. For example, the reaction between potassium hydroxide (\( KOH \)), a strong base, and hydrofluoric acid (\( HF \)), a weak acid, does not drive to full completion as HF does not fully dissociate.

Relevance of Equilibrium Constants

The equilibrium state can be quantified by the equilibrium constant (\( K_{eq} \)), which is a measure of the propensity of the reaction mixture to form products from reactants at a particular temperature. By using the equilibrium constant, chemists can predict the extent of a reaction and make informed decisions in synthesizing chemicals, buffering solutions, and more.

Understanding chemical equilibrium helps grasp why substances react in the manner they do and is fundamental in fields like pharmacology, environmental science, and industrial chemistry.