Acid
C₂H₂NH
CH.CO,H
NH
HCN
CHOH
HCO,
CH NH
HO
CH₂OH
-pK
5
5
9
9
10
10
11
16
16
A) NH(aq) + CN-(aq) NH3(aq) +
HCN(aq)
B) CH3NH3(aq) + CH3CO₂(aq) = CH3NH2(aq) + CH3CO₂H(aq)
C) CHNH(aq) + HO-(aq) C₂H₃N(aq) + H₂O(1)
D) CH₂OH(aq) + CO3(aq) CH₂O-(aq) +
HCO3(aq)
E) HCN(aq) + CH₂O-(aq) = CN-(aq) +
CH₂OH(aq)
The Correct Answer and Explanation is :
The correct answer is E) HCN(aq) + CH₂O⁻(aq) → CN⁻(aq) + CH₂OH(aq).
Explanation:
To determine the correct answer, we need to analyze the acid-base equilibrium using pKa values. The general rule is that a stronger acid donates a proton (H⁺) to a stronger base.
Step 1: Understanding pKa values
- The pKa is the negative logarithm of the acid dissociation constant (Ka), which determines how strongly an acid donates a proton.
- A lower pKa means a stronger acid (more likely to donate H⁺).
- A higher pKa means a weaker acid (less likely to donate H⁺).
From the table:
- HCN (Hydrocyanic acid) has a pKa ≈ 9.
- CH₂OH (Methanol or related hydroxyl group) has a pKa ≈ 16.
Since HCN (pKa = 9) is a stronger acid than CH₂OH (pKa = 16), HCN will donate a proton to the CH₂O⁻ (which is the conjugate base of CH₂OH). This results in the formation of CN⁻ (cyanide ion, the conjugate base of HCN) and CH₂OH (methanol or its equivalent).
Step 2: Checking for Acid-Base Reaction Feasibility
- HCN acts as the acid, donating an H⁺.
- CH₂O⁻ acts as the base, accepting the H⁺.
- The reaction follows the expected acid-base trend, with a stronger acid (pKa 9) donating a proton to a stronger base (CH₂O⁻, which comes from CH₂OH with pKa 16).
Since this reaction obeys the acid-base principles and aligns with the pKa values, E is the correct answer.
Summary:
- The acid (HCN, pKa 9) donates a proton to the base (CH₂O⁻, pKa 16).
- The conjugate base (CN⁻) and conjugate acid (CH₂OH) are formed.
- The reaction is thermodynamically favorable due to the pKa relationship.
Now, I’ll generate an image illustrating this acid-base reaction.
Here is the chemistry diagram illustrating the acid-base reaction HCN(aq) + CH₂O⁻(aq) → CN⁻(aq) + CH₂OH(aq). It highlights the molecular structures, labels the reactants and products, and shows the proton transfer. Let me know if you need any modifications!
