INTEC Chemistry Blog

CHM456 labs. Questions for Expt 1 and 2

Posted on: April 15, 2013

CHM456 labs. Questions. – UPDATED.
Answer the questions briefly, yet informatively.

Week 1. Experiment: Acid-Base Extraction
See lab manual for first set of Q’s… then,
6) What was the purpose of adding NaOH?
7) What was the purpose of adding HCl?
8) Why was ether used in the extraction and not methanol?
9) Would the procedure work for methanoic acid? Give reasons.

Week 2. Experiment: Preparation of 4-methylcyclohexene from dehydration of 4-methylcyclohexanol
See lab manual (which refers to Q’s in Pavia)
Additional Q’s

a) What is the function of H2SO4?

b) Suggest two reasons why conc acid is used and not dilute H2SO4

c) Why is the c.H2SO4 added slowly and under cooling?

d) Sometimes the bromo alkane layer is at the top and sometimes it is on the bottom. Why?

e) Why should the trying agent (anhydrous CaCl2 or anhydrous Na2SO4 or anhydrous NaHSO4) removed before distillation

f) We do NOT distil to dryness. Why?


2 Responses to "CHM456 labs. Questions for Expt 1 and 2"

salam sir.
for experiment 2, we need to calculate the theoretical yield. we should know the mol of the alcohol first, right? the question here is, when calculating the mol, should I consider the volume of the alcohol or the mass of the alcohol we weighed?

Yes. Convert reactant mass to moles and do the same for the product, i.e. convert its mass to moles. Then use the stoichiometry of the equation to figure out how many moles of product you should get in theory [if the reaction went to completion]. They divide actual moles obtained by the theoretical number of moles then multiple by 100.

Some people like to work out the theoretical mass. They then divide the actual mass by the theoretical mass, but I much prefer students to do moles.

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