How to Answer Resonance, Acidity and NaH Questions in KOT122

To score well on resonance, NaH and acidity questions in an organic chemistry tutorial such as KOT122, follow one chain of logic: find the most acidic proton, compare the stability of the conjugate bases using pKa and four factors, and show every electron move with curved arrows. Always state the final answer, the reason and the units or labels the marker expects.

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What this kind of tutorial asks

The KOT122 Assignment 1 brief is a 20-mark tutorial with four questions. Students must draw resonance structures and a hybrid for a cation (6 marks), predict products when three compounds react with sodium hydride (6 marks), rank compounds by acidity and name the strongest conjugate base (5 marks), and compare two sunscreen molecules, avobenzone and dioxybenzone, for water solubility (3 marks). The tutorial also lists exercises from Smith’s Organic Chemistry, Chapters 1 to 3.

Each question rewards reasoning, not just a drawing. You can browse related worked solutions in our answers library, and a worked example of all four parts is in our KOT122 Assignment 1 sample, which is for reference only and must not be submitted as your own work.

Step-by-step approach

1. Redraw the structure with all lone pairs and charges. Many resonance mistakes start from a missing lone pair.
2. Locate the charge or the acidic site. For a cation, find the empty orbital. For acid questions, list every X–H bond.
3. Move electrons with curved arrows. Arrows start at a pi bond or lone pair and end where the electrons arrive. Atoms stay put.
4. Check octets and total charge in every form. A second-row atom must not exceed eight electrons.
5. Pick the major contributor (full octets, fewer charges, negative charge on the more electronegative atom).
6. Draw the hybrid with dashed bonds and δ+ or δ– labels.
7. For NaH questions, find the lowest pKa among the acidic protons, remove it, and add H₂ to the equation.
8. For ranking, draw each conjugate base and compare stability using the factor table below.
9. Write one sentence of justification per answer, using the marker’s vocabulary.

Resonance: what markers look for

Markers check three things: every valid contributor is present, curved arrows are correct, and the hybrid is drawn as one structure rather than a list. A cation next to a double bond (allyl type) or next to an oxygen lone pair will usually have more than one form. In an oxygen-stabilised cation such as CH₃–O–CH₂⁺, the form CH₃–O⁺=CH₂ is the major contributor because all atoms have full octets.

Do not draw forms that move atoms, break a sigma bond without reason, or leave carbon with five bonds. Those are the fastest ways to lose marks.

NaH: the base that makes hydrogen gas

Sodium hydride delivers H^–, whose conjugate acid H₂ has a pKa of about 35 (UCLA Department of Chemistry and Biochemistry, n.d.). In these tutorial questions, hydride acts as a base, not a nucleophile. It takes the most acidic proton and leaves the sodium salt of the conjugate base, with hydrogen gas as the by-product.

Want a second pair of eyes on your reaction predictions before you submit? Our assignment review service checks working against the marking logic.

Acidity ranking: factors compared

The step students most often reverse is the last one. The strongest acid has the weakest conjugate base, so the strongest conjugate base comes from the weakest acid in the list. Compare pKa values to confirm: ethanol (about 16) is a weaker acid than acetic acid (about 4.8), so ethoxide is a stronger base than acetate (UMass Amherst, n.d.).

The sunscreen question: reasoning, not recall

The avobenzone and dioxybenzone part is only 3 marks, but it rewards a clear structure-to-property argument. Dioxybenzone has two OH groups that can hydrogen bond to water, while avobenzone carries a bulky nonpolar tert-butylphenyl group. Dioxybenzone is therefore the more water-washable of the two. Mention that both molecules also form intramolecular hydrogen bonds, which keeps the conclusion relative rather than absolute.

Prefer guided support on your own diagrams? Our assignment help request page explains how a subject specialist can walk you through the method.

Mark-maximising checklist

• Every curved arrow starts at electrons and ends at an atom or bond.
• Lone pairs and formal charges are shown on every structure.
• The major resonance contributor is identified with a reason.
• The hybrid has dashed bonds and partial charges.
• NaH equations are balanced and include H₂.
• pKa values are quoted with their source or marked “approximate”.
• The acidity ranking states direction (increasing or decreasing) in words.
• The conjugate base question is answered from the weakest acid.
• Explanations use one named factor each (element, resonance, inductive, hybridisation).
• Textbook exercises are attempted before the tutorial deadline so you can compare methods.

Common mistakes

• Moving an atom instead of electrons when drawing resonance forms.
• Treating resonance forms as separate molecules in equilibrium rather than contributors to one hybrid.
• Choosing the wrong acidic proton, for example the C–H instead of the O–H in an alcohol.
• Forgetting hydrogen gas in the NaH equation.
• Confusing a stronger acid with a stronger conjugate base.
• Writing “it is more soluble” with no mention of hydrogen bonding or polarity.

Student pain points

Forums and study groups keep returning to the same worries. How do I know when I have found every resonance structure? When should I use pKa rather than the four factors? Why does NaH not attack the carbonyl? Why does the pKa table show ranges rather than one number? The short answers are: stop when no further legal arrow exists, use pKa for numerical comparison and the factors for explanation, hydride is too small and too basic to behave as a nucleophile here, and values vary slightly with solvent and source.

Many students also say they can follow a worked solution but freeze when the structure is new. Practise with unseen compounds from the Chapter 1 to 3 exercises, and write your reasoning aloud. You can read feedback from other students on our reviews page.

Frequently asked questions

How many resonance structures should I draw?

Draw every valid contributor, which means every form reachable by legal curved arrows with correct octets. The number depends on the structure, so check by asking whether another electron shift is possible.

Is the resonance hybrid the same as the major contributor?

No. The hybrid is a weighted blend of all contributors. The major contributor resembles it most closely, but the hybrid shows delocalised charge and partial bonds.

Why is H₂ produced when NaH reacts with an alcohol?

Hydride takes the acidic proton, forming H–H. Because H₂ is a very weak acid (pKa about 35), the reaction is effectively irreversible.

Does a lower pKa always mean a better leaving group or stabler anion?

A lower pKa means a stronger acid and a more stable conjugate base. Leaving-group ability follows a similar trend, but it also depends on the reaction conditions.

Do I need to memorise pKa values?

Memorise approximate anchors: carboxylic acid about 5, phenol about 10, alcohol about 16, terminal alkyne about 25, H₂ about 35. Then use the four factors to place unfamiliar compounds around them.

Can I copy a sample answer into my tutorial?

No. Samples are for learning the method only. Submitting someone else’s work as your own can breach your university’s academic integrity rules, so adapt the reasoning to your own structures.

About the expert

For science questions, the closest specialist on our expert panel is Harith R., who holds an MSc in Medical-Surgical and Adult Health from Monash University Malaysia and lists pharmacology and APA 7 referencing among his specialisms. For details about how we work, see our about us page.

References

Clayden, J., Greeves, N., & Warren, S. (2012). Organic chemistry (2nd ed.). Oxford University Press.

Department of Chemistry, Indiana University. (n.d.). Approximate pKa chart of the functional groups: Values to know. https://www.chem.indiana.edu/wp-content/uploads/2018/03/pka-chart.pdf

Smith, J. G. (2023). Organic chemistry (7th ed.). McGraw Hill.

University of California, Los Angeles, Department of Chemistry and Biochemistry. (n.d.). Sodium hydride. In Illustrated glossary of organic chemistry. https://www.chem.ucla.edu/~harding/IGOC/S/sodium_hydride.html

University of Massachusetts Amherst. (n.d.). pKa table for organic and inorganic Brønsted acids. https://owl.umass.edu/departments/OrganicChemistry/appendix/pKaTable.html