Question: Peter says that alcohol is a top carcinogen. Prove that he is on9.
Solution:
Using the method of contrapositive:
- Is Xylotol carcinogenic?
- Is Glycerol carcinogenic?
- Is Menthol carcinogenic?
Q.E.D.
Question: Thermal decomposition of methanol to produce town gas is a free-radical reaction on catalyst surface. Outline the complete steps.
Question: Balance the following equation on ethanol reaction:
C_2H_5OH + PBr_3 \to
Solution:
3C_2H_5OH + PBr_3 \to 3C_2H_5Br + H_3PO_3
NOT H_3PO_4
Question:
C_2H_5OH + PCl_5 \to ?
Hint: The overall reaction is non-redox.
Solution:
The products are C_2H_5Cl + POCl3 + HCl
Question:
Given 2 chemicals: C_2H_5OH and conc. H_2SO_4.
(a) What will happen if the former is in excess?
(b) What will happen if the latter is in excess?
Solution:
With heating:
(a) an ether will be formed
(b) ethene will be formed
(b) is elimination reactions,
i.e. water being the by-product,
while (a) is nucleophilic substitution reaction.
Question:
When undergoing Hofmann degradation on propan-2-ol, what products will be observed? Write the balanced chemical equation on it.
Solution:
CH_3C(OH)CH_3 + 6NaOH + 4I_2 \to CH3COONa + CHI_3 + 5NaI + H_2O
(Note: It is out of HKALE Chemistry syllabus since 2007.)
The nucleophilic substitution for ether formmation is as below:
Note: 1994-2013 HKALE Chemistry Syllabus NEVER assess ether.
Question: Write an essay on Lucas Test in determining the degree of substitution of alcohols.
Solution: Ask AI.
Sample output by Copilot:
The Lucas test uses Lucas reagent, a mixture of concentrated hydrochloric acid (HCl) and anhydrous zinc chloride (ZnCl₂), to differentiate alcohols by observing the rate at which the solution becomes turbid (cloudy) after adding the alcohol 
Vedantu+1. The test relies on the SN1 (unimolecular nucleophilic substitution) mechanism, where alcohols form carbocation intermediates that react with chloride ions to produce insoluble chloroalkanes Vedantu.
Reaction Mechanism
- The hydroxyl group of the alcohol is protonated by HCl, forming a better leaving group (water).
- A carbocation intermediate forms, the stability of which depends on the alcohol type: tertiary > secondary > primary.
- The carbocation reacts with chloride ions from ZnCl₂ to form a chloroalkane, which is insoluble and causes turbidity
Chemistry Learner+1.
Interpretation of Results
- Tertiary alcohols: React immediately, forming turbidity almost instantly.
- Secondary alcohols: React within 5–10 minutes, producing a cloudy solution.
- Primary alcohols: React very slowly or not at all at room temperature, so the solution remains clear Vedantu+1.
Preparation of Lucas Reagent
- Weigh anhydrous ZnCl₂ and dry it in an oven.
- Slowly dissolve ZnCl₂ in concentrated HCl, stirring until a clear solution forms.
- Store the reagent in a tightly sealed bottle to maintain anhydrous conditions Chemistry Learner+1.
Applications
- Alcohol classification: Distinguishes primary, secondary, and tertiary alcohols in laboratory settings.
- Educational tool: Demonstrates carbocation stability and SN1 reaction kinetics.
- Limitations: Only effective for low molecular weight alcohols (typically 3–6 carbon atoms) and less commonly used today due to modern spectroscopic and chromatographic methods
Wikipedia+1.
The Lucas test remains a classic qualitative method in organic chemistry for understanding alcohol reactivity and substitution mechanisms.
Question: How to test for haloalcohol?
