Chemistry

Chemistry

Problem

When hydrogen sulfide gas dissolves in water, it can undergo two successive deprotonation steps in the presence of hydroxide ions. The overall process can be represented by the sequence below. Step 1: H2S(aq)+OH−(aq)→HS−(aq)+H2O(l)H_2S(aq)+OH^-(aq)\rightarrow HS^-(aq)+H_2O(l) Step 2: HS−(aq)+OH−(aq)→S2−(aq)+H2O(l)HS^-(aq)+OH^-(aq)\rightarrow S^{2-}(aq)+H_2O(l) Answer the following questions about this two-step process. (a) For Step 1, identify the conjugate acid–base pair created by the proton transfer. (b) For Step 2, identify the conjugate acid–base pair created by the proton transfer. (c) Write the net ionic equation obtained by adding Step 1 and Step 2, and list every distinct conjugate acid–base pair that appears in the overall reaction sequence. (d) Explain how the presence of two acidic protons in H2SH_2S is reflected in the sequence of conjugate pairs you identified.
Intuitive explanation

This problem explores successive deprotonation — how a polyprotic acid loses protons one at a time in basic conditions. The key insight is that each step removes one acidic hydrogen, converting H2SH_2S first to HS−HS^- (still weakly acidic) and then to S2−S^{2-} (fully deprotonated). Understanding which species is the acid and which is the base in each step, and recognizing that the second deprotonation is typically harder than the first, will help you predict equilibrium positions and compare the relative strengths of the two acids involved.

Intuitive explanation

This problem explores successive deprotonation — how a polyprotic acid loses protons one at a time in basic conditions. The key insight is that each step removes one acidic hydrogen, converting H2SH_2S first to HS−HS^- (still weakly acidic) and then to S2−S^{2-} (fully deprotonated). Understanding which species is the acid and which is the base in each step, and recognizing that the second deprotonation is typically harder than the first, will help you predict equilibrium positions and compare the relative strengths of the two acids involved.

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