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Quizzes > Science > Chemistry

Is H2SO3 Weak or Strong? Take the Quiz

Dive into H2SO3 acidity and properties of sulfurous acid - can you ace it?

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration for a quiz on sulfurous acid H2SO3 strength and properties on a sky blue background

This quiz helps you figure out if H2SO3 (sulfurous acid) is weak or strong and what that means in water. Work through short questions on acidity, dissociation, and conjugate pairs to practice and spot gaps before a test, then review basics with the acid-base practice quiz .

Is sulfurous acid (H2SO3) classified as a strong acid or a weak acid?
Weak acid
Neither, it's neutral
Strong acid
It is a base
Sulfurous acid is a diprotic weak acid, meaning it does not completely dissociate in water and has relatively small acid dissociation constants. Strong acids fully dissociate in aqueous solution, while weak acids only partially dissociate. H2SO3's first dissociation constant (Ka1) is around 1.5×10?2, indicating partial dissociation. For more information, see .
Which term best describes the acid-base behavior of H2SO3 in aqueous solution?
Weak monobasic acid
Strong monobasic acid
Strong diprotic acid
Weak diprotic acid
Sulfurous acid is diprotic because it can donate two protons, and it is classified as weak because neither proton donation goes to completion. Its first dissociation (Ka1) is about 1.5×10?2 and its second dissociation (Ka2) is much smaller, around 6.9×10?8. Strong acids fully dissociate and monobasic acids donate only one proton. See .
What is the approximate value of the first acid dissociation constant (Ka1) for H2SO3?
1.0×10?7
1.5×10?2
1.0
1.0×10?5
The first acid dissociation constant Ka1 for sulfurous acid is approximately 1.5×10?2, indicating it is a weak acid that partially dissociates. This value is much smaller than Ka of strong acids (Ka?1) and larger than typical very weak acids (Ka?10?5). The second dissociation constant is much lower (around 6.9×10?8). More details at .
What is the conjugate base formed after the first deprotonation of H2SO3?
SO42?
HSO3?
SO3?
S2O52?
When H2SO3 loses its first proton, it forms the bisulfite ion (HSO3?). The second deprotonation leads to the sulfite ion (SO3^2?). The sulfate ion (SO4^2?) is formed by oxidation, not simple deprotonation. For more, see .
Given pKa1 ? 1.9 and pKa2 ? 7.0 for H2SO3, which dissociation step is stronger?
The first dissociation (pKa1)
They are equally strong
Neither is dissociation-controlled
The second dissociation (pKa2)
A lower pKa value indicates a stronger acid. Since pKa1 (~1.9) is much lower than pKa2 (~7.0), the first proton is released more readily than the second. Therefore, the first dissociation is stronger. For pKa definitions, see .
In a buffer solution of H2SO3 and HSO3?, what is the ratio [H2SO3]/[HSO3?] when the pH equals the first pKa?
1:1
Cannot be determined
2:1
1:2
According to the Henderson - Hasselbalch equation, pH = pKa + log([base]/[acid]). When pH = pKa, log([base]/[acid]) = 0, so [base] = [acid], giving a 1:1 ratio of H2SO3 to HSO3?. See .
What is the approximate pH of a 0.10 M H2SO3 solution (Ka1 = 1.5×10?2)?
2.5
3.7
1.4
0.7
For a weak acid HA, [H+] ? sqrt(Ka·C). Here C = 0.10 M and Ka = 0.015, so [H+] ? sqrt(0.015×0.10) ? 0.0387 M. Taking - log[H+] gives pH ? 1.41. This approximation neglects the second dissociation, which contributes negligibly. Further reading at .
What are the products when H2SO3 reacts completely with 2 equivalents of NaOH?
Na2SO4 + H2
NaHSO3 + H2O
Na2SO3 + 2 H2O
NaSO3 + H2O
Sulfurous acid neutralized by two equivalents of NaOH forms sodium sulfite (Na2SO3) and water. The balanced reaction is H2SO3 + 2 NaOH ? Na2SO3 + 2 H2O. Sodium hydrogen sulfite (NaHSO3) would form with only one equivalent of base. See .
Which spectroscopic technique is most useful for confirming the S=O bond vibrations in sulfurous acid?
Mass spectrometry
Infrared (IR) spectroscopy
1H NMR spectroscopy
UV-Visible spectroscopy
Infrared spectroscopy is ideal for detecting vibrational modes of functional groups like S=O bonds. Sulfurous acid displays characteristic S=O stretching bands around 1100 - 1350 cm?1. NMR measures nuclear environments, UV-Vis electronic transitions, and MS gives molecular masses, so IR is best for vibrational analysis. See .
What is the isoelectric point (pI) pH of the bisulfite ion (HSO3?), where it acts as both acid and base?
~4.45
~3.30
~5.70
~2.45
For an amphiprotic species like HSO3?, pI ? (pKa1 + pKa2)/2. With pKa1 ? 1.9 and pKa2 ? 7.0 for sulfurous acid, the pI is about (1.9 + 7.0)/2 ? 4.45. At this pH, HSO3? is in equal protonated and deprotonated forms. See .
During the titration of 0.10 M H2SO3 with 0.10 M NaOH, how many equivalence points are observed, and what is the approximate pH at the first equivalence?
Three equivalence points; first at pH ~10
Two equivalence points; first at pH ~4
Two equivalence points; first at pH ~8
One equivalence point at pH ~7
Sulfurous acid is diprotic, so its titration shows two equivalence points. After the first proton is neutralized, the solution is a conjugate base (sulfite), giving a basic pH around 8. The second equivalence occurs at higher pH when sulfite is neutralized to sulfate. More details at .
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Study Outcomes

  1. Understand Acid Strength Concepts -

    Readers will grasp the fundamental difference between strong and weak acids, including how dissociation impacts acidity.

  2. Analyze H2SO3 Dissociation -

    Readers will analyze the stepwise dissociation constants of sulfurous acid to determine its relative strength.

  3. Explain Molecular Structure -

    Readers will explain how the molecular structure of H2SO3 influences its acid properties and dissociation behavior.

  4. Evaluate Sulfurous Acid Properties -

    Readers will evaluate key properties of sulfurous acid, such as pKa values and ionization levels, to assess its acidity.

  5. Compare with Strong Acids -

    Readers will compare H2SO3 to well-known strong acids, identifying why it classifies as a weak acid.

  6. Apply Knowledge in Quiz Scenarios -

    Readers will apply their understanding of H2SO3 acidity to interactive quiz questions, reinforcing their learning.

Cheat Sheet

  1. Diprotic Dissociation Behavior -

    Sulfurous acid (H2SO3) is diprotic, with first dissociation constant Ka1≈1.3×10−2 and second Ka2≈6.9×10−8, both far below 1, confirming its weak acidity. A simple mnemonic "Ka tells the tale" helps recall that smaller Ka values mean weaker acids, so h2so3 weak or strong is decisively weak.

  2. Resonance Stabilization of Sulfite Ion -

    After losing a proton, HSO3− exhibits three equivalent resonance structures that distribute negative charge over oxygen atoms. This resonance stabilization is significant but not enough to make sulfurous acid strong, distinguishing the properties of sulfurous acid from stronger analogs.

  3. Comparison with Sulfuric Acid -

    In contrast to strong, fully dissociated H2SO4, H2SO3 only partially ionizes in water, making it a weak acid. Recognizing is sulfurous acid weak or strong by comparing their Ka values (H2SO4's Ka≫1 vs H2SO3's Ka≪1) cements the concept.

  4. Environmental and Practical Roles -

    Sulfurous acid appears in aqueous SO2 solutions, contributing to acid rain and acting as a reducing agent in bleaching and food preservation. Understanding these properties of sulfurous acid links molecular acidity to real-world chemistry applications.

  5. Equilibrium Formation in Aqueous Solution -

    H2SO3 forms via the reversible reaction SO2(g) + H2O(l) ⇌ H2SO3(aq), with equilibrium lying to the left due to poor stabilization of the acid. This equilibrium context is key to why H2SO3 remains weak and why concentrations in solution are relatively low.

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