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Group 5

Experiment No. 5
Classifications of Alcohols: Lucas Test

Q1. REACTION OF PRIMARY, SECONDARY AND TERTIARY ALCOHOLS WITH LUCAS REAGENT

ALCOHOL
IMMEDITE REACTION WITH LUCAS’ REAGENT
OBSERVATIONS AFTER 5 MINUTES AT 27 °C TO 28 °C n-butyl alcohol
No reaction occurred

Secondary butyl alcohol

cloudy
Tertiary butyl alcohol
Cloudy appears

Q2. REACTION OF SECONDARY AND TERTIARY ALCOHOLS WITH CONCENTRATED HYDROCHLORIC ACID

ALCOHOL
OBSERVATIONS
Secondary butyl alcohol

Tertiary butyl alcohol

Q3. Classify the alcohols used in this experiment as primary, secondary or tertiary.
Q4. Use your answer to question 1 and the results in Table 2 to explain how mixing an alcohol of unknown structure with Lucas. Reagent can help one to determine whether it is primary, secondary or tertiary.
Q5. Write down an equation for the reaction of tertiary butyl alcohol with concentrated hydrochloric acid.
Q6. Explain why the solution became milky white in appearance after adding 11 M HCl(aq) to the tertiary butyl alcohol.
Q7. A student is given two alcohols with which to perform Lucas Test. These are cyclohexanol and 2-methyl-2-propanol. The bottles containing each alcohol are labelled, but the propettes used are not. The student accidentally muddles the propettes. When drops of each alcohol are mixed with Lucas. Reagent and kept at 27 °C, both solutions become turbid. How can the student find out which alcohol has been placed in which propette?

Appearance of a cloudy second layer or emulsion

3o alcohols: immediate to 2-3 minutes
2o alcohols: 5 -10 minutes
1o alcohols: no reaction

A. Lucas test
Reactants Reagents Time taken Observations
2-methyl-2-propanol
Lucas reagent (concentrated hydrochloric acid, HCl and Zinc chloride, ZnCl) Immediately Solution turns cloudy with 2 obvious layers formed
2-butanol 7 minutes Solution turns cloudy with 2 layers formed n-butanol >15 minutes No reaction observed after 15 minutes
Alcohol

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