Question

Write the conjugate base for each of the following acids. a. \(\mathrm{HBrO}\) b. \(\mathrm{HNO}_{2}\) c. \(\mathrm{HSO}_{3}^{-}\) d. \(\mathrm{CH}_{3} \mathrm{NH}_{3}{ }^{+}\)

Short answer

The conjugate bases for each of the given acids are: a. \(BrO^{-}\) b. \(NO_{2}^{-}\) c. \(SO_{3}^{2-}\) d. \(CH_{3}NH_{2}\)

Step-by-step solution

Identify the acidic proton

For each acid, identify the acidic proton that will be removed to form the conjugate base. This proton is usually attached to an electronegative atom such as oxygen or nitrogen or present in an ionic form, which makes it more readily ionizable.

Remove the acidic proton

For each acid, remove the acidic proton, and rewrite the molecule or ion without that proton.

Adjust the charge

Since the removal of a proton results in the loss of a positive charge, adjust the charge of the molecule or ion accordingly to account for the removed proton. #Step 1, 2 & 3 applied to each acid:# a. HBrO

Identify the acidic proton

The acidic proton in HBrO is the hydrogen (H) attached to the oxygen.

Remove the acidic proton

Removing the acidic proton gives: BrO

Adjust the charge

After removing the acidic proton, we have lost a positive charge. Therefore, the charge on the conjugate base BrO will be negative. Thus, the conjugate base is: BrO⁻ b. HNO₂

Identify the acidic proton

The acidic proton in HNO₂ is the hydrogen (H) attached to the oxygen.

Remove the acidic proton

Removing the acidic proton gives: NO₂

Adjust the charge

After removing the acidic proton, we have lost a positive charge. Therefore, the charge on the conjugate base NO₂ will be negative. Thus, the conjugate base is: NO₂⁻ c. HSO₃⁻

Identify the acidic proton

The acidic proton in HSO₃⁻ is the hydrogen (H) attached to the oxygen.

Remove the acidic proton

Removing the acidic proton gives: SO₃

Adjust the charge

After removing the acidic proton from the negatively charged ion, the charge will decrease by one unit. Thus, the conjugate base is: SO₃²⁻ d. CH₃NH₃⁺

Identify the acidic proton

The acidic proton in CH₃NH₃⁺ is one of the hydrogens (H) attached to the nitrogen.

Remove the acidic proton

Removing the acidic proton gives: CH₃NH₂

Adjust the charge

After removing the acidic proton from the positively charged ion, the charge will decrease by one unit. Thus, the conjugate base is: CH₃NH₂ (neutral molecule) The conjugate bases of the given acids are: a. BrO⁻ b. NO₂⁻ c. SO₃²⁻ d. CH₃NH₂

Key concepts

Acid-Base Reactions

Understanding acid-base reactions is crucial in chemistry, as these reactions are pervasive in both lab work and biological processes. The reaction involves the transfer of a proton (H⁺) from what we call an 'acid' to an 'acceptor' termed the 'base'. The strength of an acid or base determines the direction and completeness of this proton transfer. Typically, a strong acid will easily donate a proton, whereas a strong base will readily accept it.

In the context of the exercise, identifying the proton that is likely to be transferred is key. This process forms the basis of the reaction and leads to the production of a 'conjugate base', which is essentially the acid after it has lost the proton. Similarly, once the base accepts a proton, it becomes a 'conjugate acid'. The pair of an acid and its conjugate base, or a base and its conjugate acid, together are commonly referred to as a 'conjugate pair'.

Removing Acidic Proton

The concept of removing an acidic proton revolves around identifying and then disconnecting the hydrogen cation (H⁺) from the parent acid molecule. This process is typically governed by the acid's tendency to either hold on to or release its proton, which is influenced by the surrounding chemical environment and the stability of the formed conjugate base.

The stability can be attributed to various factors including electronegativity of elements, resonance structures, and inductive effects. In the provided exercise, the acidic protons are attached to electronegative atoms, such as oxygen or nitrogen, which facilitate their removal due to the atoms' affinity for electrons. Once the acidic proton is removed, the remaining structurally modified species is the conjugate base which is now more negatively charged, reflecting the loss of the positively charged proton.

Charge Adjustment Chemistry

Charge adjustment chemistry is an integral part of understanding chemical reactions, especially those involving ions. When an acidic proton is removed from an acid, the loss of the positive hydrogen ion results in a negative shift in the overall charge of the species. It's important to meticulously tally charges before and after the reaction to ensure the conservation of charge – a fundamental principle in chemistry.

In the conjugate base formation, the loss of a proton from a neutral acid results in the emergence of a negatively charged conjugate base. If the initial acid was an anion (negatively charged), the removal of an H⁺ would lead to a decrease in its overall negative charge. This concept is excellently illustrated in the provided exercise, particularly with the sulfite ion, where the removal of the proton results in a negatively charged species becoming even more negative, hence transforming from HSO₃⁻ to SO₃²⁻.

Chemical Ionization

Chemical ionization is a process that converts a neutral molecule into an ion, typically through the addition or removal of charged particles such as electrons, protons, or other ions. In the formation of conjugate bases, we witness ionization as a result of removing a proton.

This is different from other types of ionization where electrons might be added or removed, as seen in processes like electron capture or ionization in mass spectrometry. The key outcome of chemical ionization in the context of acid-base reactions is the production of an ion with a charge that reflects the new balance of protons and electrons. The exercise provided is a classic example where acids transform to their respective conjugate bases through this process—demonstrating how chemical ionization is fundamental to acid-base chemistry.