Pontypridd High School
BTEC 2012-2013
Assignment brief
Qualification
Unit number and title
BTEC Level 3 Certificate in Applied Science
Unit 4: Scientific Practical Techniques
Start date
4th December 2012
Deadline
29th January
Assessor name
Rebecca Cassells
Assignment title
Assignment 4.2: Separating substances and estimating purity
The purpose of this assignment is to develop methods for analysing and purifying products
Scenario
You are moved to the research lab of Superchem, a laboratory which develops methods for analysing and
purifying substances.
You have been given several tasks to support the manufacturing side of the company. You will need to keep
detailed records of your work.
Separate a range of substances in mixtures following given methods.
You will have to calculate the percentage of different substances present in some cases.
Carry out measurements of some of the properties of the substances separated.
Record your results.
As a guide for people repeating your work, you need to describe the factors that will alter the purity of the
substances.
Task 1
The first part of this assignment you will demonstrate separation techniques.
You will be assessed on;
(1) Your practical technique for the methods listed below
The practical’s you will be conducting are;
1. Separation of ink solutions (distillation)
2. Distillation of ethyl ethanoate (distillation/solvent extraction)
3. Extracting plant pigments from grass (chromatography/centrifugation)
4. Synthesis of Asprin (precipitation/crystallisation/filtration/drying)
5. Separation of DNA (gel electrophoresis)
The evidence you will submit will be;

Witness statements for each practical assessment
For each practical you must include a risk assessment
This provides evidence for P2
Task 2
You will estimate the purity of three of your extracted products
The techniques you will be using are; (only three of these are required for the pass criteria)
1. Estimating purity by melting point (aspirin)
2. Estimating purity by titration (aspirin)
3. Estimating purity by boiling point (ethyl ethanoate)
4. Estimating purity by Rf values (plant pigments)
The evidence you will submit will be;

Written reports on techniques used

Witness statements for each practical assessment

Results and calculations
For each practical you must include a risk assessment
This provides evidence for P3
Task 3
This part of the assignment allows you to discuss the factors that influence purity.
1.
2.
3.
4.
5.
Carry out a recrystallization of the aspirin produced in Task 2.
Calculate the purity of your recrystallized product (melting point)
Compare purity of recrystallized aspirin to original product
Compare melting point of aspirin to reference data and discuss the difference
Discuss the factors that affect purity and identify aspects of your method that may have affected the
purity of your product
The evidence you will submit will be;

Results and Calculations

Witness statements for each practical assessment

Written report discussing the factors that influence purity
For each practical you must include a risk assessment
This provides evidence for M2
Task 4
Evaluate the accuracy of the methods chosen to estimate purity.
For each of the practical activities in Task 2;
1.
Compare results to those supplied by the lab technician.
2. Evaluate the accuracy of your results
3. Identify any errors that can be accounted for through techniques you used
4. Identify any other sources of errors
The evidence you will submit will be;

Written report on the accuracy of the methods chosen
This provides evidence for D2
Sources of information
Annets F, Foale S, Hartley J, Hocking S, Hudson L, Kelly T, Llewellyn R, Musa I and Sorensen J – BTEC Level 3
National Applied Science Student Book (Pearson, 2010) ISBN 9781846906800
Coyne G S – The Laboratory Companion: A Practical Guide to Materials, Equipment and Technique
(John Wiley & Sons, 2005) ISBN 9780471780861
Dean J R et al – Practical Skills in Chemistry (Prentice Hall, 2001) ISBN 9780130280022
Lawn R and Prichard E – Practical Laboratory Skills Training Guide: Measurement of Mass (The Royal Society of
Chemistry, 2003) ISBN 9780854044634
Prichard E and Lawn R – Practical Laboratory Skills Training Guide: Measurement of Volume (The Royal Society of
Chemistry, 2003) ISBN 9780854044689
This brief has been verified as being fit for purpose
Assessor
Signature
Date
Internal verifier
Signature
Date