For each of the following compounds, draw the form that predominates at pH = 3, pH = 6, pH = 10, and pH = 14:
b. CH₃CH₂N⁺H₃ (pK_a= 11.0)

검증된 단계별 안내

Step 1: Understand the relationship between pH and pKa. The pKa value indicates the pH at which half of the species is protonated and half is deprotonated. When pH < pKa, the species is predominantly protonated. When pH > pKa, the species is predominantly deprotonated.

Step 2: Analyze the given compound CH3CH2N+H3. This is an ethylammonium ion, which can lose a proton to form CH3CH2NH2. The pKa of the protonated form (CH3CH2N+H3) is given as 11.0.

Step 3: Determine the predominant form at pH=3. Since pH=3 is much lower than the pKa (11.0), the compound will remain fully protonated as CH3CH2N+H3.

Step 4: Determine the predominant form at pH=6. Since pH=6 is still lower than the pKa (11.0), the compound will predominantly remain protonated as CH3CH2N+H3.

Step 5: Determine the predominant forms at pH=10 and pH=14. At pH=10, which is slightly below the pKa, the compound will still be mostly protonated as CH3CH2N+H3, but some deprotonation to CH3CH2NH2 will occur. At pH=14, which is much higher than the pKa, the compound will be fully deprotonated as CH3CH2NH2.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Acid-Base Chemistry

Acid-base chemistry involves the transfer of protons (H+) between species. The pH of a solution indicates its acidity or basicity, with lower pH values representing acidic conditions and higher values indicating basic conditions. Understanding how acids and bases behave in different pH environments is crucial for predicting the predominant form of a compound.

pKa and its Significance

The pKa value is a measure of the strength of an acid in solution, representing the pH at which half of the species are deprotonated. A lower pKa indicates a stronger acid. In this case, with a pKa of 11.0, the compound CH3CH2N+H3 will predominantly exist in its protonated form at lower pH values (like pH 3 and 6) and will start to deprotonate as the pH increases beyond its pKa.

Protonation and Deprotonation

Protonation refers to the addition of a proton (H+) to a molecule, while deprotonation is the removal of a proton. The state of a compound can change based on the pH of the solution; at low pH, compounds are more likely to be protonated, while at high pH, they tend to lose protons. For CH3CH2N+H3, this means it will remain protonated at acidic pH levels and begin to lose protons as the pH rises past its pKa.

For each of the following compounds, draw the form that predominates at pH = 3, pH = 6, pH = 10, and pH = 14:b. CH3CH2N+H3 (pKa = 11.0)