1. Carry out quantitative analysis on a sample of brass provided by using colorimetry and titration. You are also required to explain the function of each type of equipment and sensor used. ...
1 carry out quantitative analysis on a sample of brass provided by using colorimetry and titration you are also required to explain the function of each type of equipment and sensor used
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BTEC
PEARSON (PEARSON)
Applied Science 2010 QCF
Unit 4 - Scientific Practical Techniques
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BTEC Level 3 Extended Diploma in Applied Science
Unit 4: Scientific Practical Techniques
4.3 Instruments and Sensors
Scenario:
As a scientist working as part of a team investigating ancient artefact, you are to analyse a sample
of brass which is about 150 years old and you are asked to quantitatively analyse it. You will be
using the techniques of colorimetry and titration, to find the percentage of copper present. Your
results will be compared to each other, to decide which a more accurate technique is, as well as to
compare the composition of modern brass. You are also required to show your competency in the
use of the instruments and sensor to your project manager.
Grading Criteria to be assessed:
P4 Use the instrument/sensors to test substances or materials.
M3 Justify the choice of instruments in the practical exercises.
D3 Evaluate the accuracy of the measurements taken.
Tasks:
1. Carry out quantitative analysis on a sample of brass provided by using colorimetry and
titration. You are also required to explain the function of each type of equipment and
sensor used. (P4)
Plagiarised work will result in disciplinary procedures.
Additional guidance:
Task 1: (P4)
Practical instructions for carrying out the COLORIMETRY experiment:
, 1. Read through the instructions below and complete a risk assessment for the procedure
outlined.
2. You are provided with a sample of brass that has been filed from a piece of antique brass.
3. Using a fume cupboard, place 30cm3 of distilled water into a 250cm 3 conical flask and slowly
add 15cm3 of concentrated nitric acid to it. Stir the mixture using a glass rod.
4. Weigh out, accurately known to 2 decimal places, about 1.5g of the antique brass filings.
5. Add these slowly to the diluted nitric acid in the fume cupboard.
6. Leave the mixture for some minutes until all the brass has ‘dissolved’. During this procedure
poisonous nitrogen dioxide gas is given off and a blue solution containing copper (Cu 2+) and
zinc (Zn2+) ions is produced.
7. Remove the solution from the flask and quantitatively add it to some distilled water in a
250cm3 volumetric flask. Make the flask up to the mark using distilled water and mix well.
8. You are provided with around 100cm3 of a copper sulphate solution. This solution contains
1.60g of copper (as Cu2+ions) in 250cm3 of solution.
9. Dilute this copper sulphate solution with distilled water to make the solutions labelled a to f in
the table below. This dilution is to be done accurately using appropriate apparatus, with
mixing.
Solution Copper sulphate Water/cm3 Concentration of solution Absorption
(aq)/cm3 g Cu/250cm3
a 10 0 1.60 0.53
b 8 2 1.28 0.45
c 6 4 0.96 0.38
d 4 6 0.64 0.31
e 2 8 0.32 0.20
f 1 9 0.16 0.09
Distilled water 0.00
10. Switch on your colorimeter and allow it to warm up for five minutes.
11. Place a 700nm filter in the colorimeter and zero the instrument using a cuvette filled with
distilled water.
12. Fill six cuvettes with solutions a to f and find the absorption values for each of them in turn;
record your results in a suitable way.
13. Fill another cuvette with the ‘brass’ solution and measure the absorption of this solution too.
14. Plot a graph of absorption (y axis) against concentration of copper ions (x axis). Your graph
should be a straight line which passes through the origin (0,0).
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