Unit 19: Practical Chemical Analysis
A: Investigate quantitative analysis on the components of matrices to determine their composition
BTEC/CTEC Level 3 Extended Diploma in Applied Science
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a investigate quantitative analysis on the components of matrices to determine their composition
btec level 3 extended diploma in applied science
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BTEC
PEARSON (PEARSON)
Applied Science 2016 NQF
Unit 19 - Practical Chemical Analysis
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UNIT 19
Unit 19: Calculating the composition of matrices through quantitative analysis
Primary and secondary titrimetric standards:
Primary-
These are very unreactive in their pure forms which is useful compared to an unreliable reagent that
will easily react and change with its surroundings such as oxygen or H2O. Extremely reactive
chemicals cannot be properly used because of their instability as a standard. A standard should be
anhydrous meaning it doesn’t have any H2O bonded within its molecular formula. In addition, it
shouldn’t be too hygroscopic as it shouldn’t absorb water and it’s molecular weight should be high.
Secondary-
These are implicated within laboratories that produce materials for other labs for example, a
secondary standards and reagents. They use primary standards for primary calibrators or primary
reference materials. In a smaller lab however the secondary standard is used to calibrate control
material for analysing unknown concentrations of a drug. In summary, Secondary standard is
unusually used for external quality control in smaller labs and leads to standardisation of secondary
standards against primary standards first.
Percentage of copper in brass using Colorimetry
Equipment
1. Clamp
2. Stand
3. Pipette and filler
4. Wash bottles with distilled/de-ionised
water
5. Glass beakers
6. Burette
7. Balance
8. 250cm conical flask
9. 250cm Volumetric flask
10. Starch solution
11. Potassium iodide standard solution- Kl
(aq), 0.5 mol dm
12. Sodium thiosulfate- Na 20g, 0.1mol dm
Method
1. Dissolve 2.5g of brass in 10cm of strong
nitric acid.
2. Carefully transfer the obtained solution
to a 250cm graduated flask and add
0.5mol dm-3 sodium carbonate until the copper carbonate precipitate appears to signal
neutralisation
3. Add a few drops of 1 mol dm-3 ethanoic acid until the precipitate is entirely dissolved.
4. Titrate at least three times and increase the volume of the solution to 250cm3.
This is already given to us prepared by the lab, using the prepared solution we used the
method below to complete the experiment.
Second part- titration of thiosulfate:
1. Pipette 10ml of the Brass solution into a 100ml conical flask using a 10ml glass pipette.
2. Using a measuring cylinder, add 10ml of potassium iodide to the liquid, which will turn
brown.
3. Titrate with Sodium thiosulfate solution (in burette)
, UNIT 19
4. When the mixture has turned pale yellow, add 3-4 drops of 1% starch.
5. The mixture will take on a blue/black hue.
6. Continue titrating until the colour becomes nearly white.
7. Continue until you get two consistent results.
Precautions
1. When handling NO2, we should use a fume cupboard to prevent inhalation of nitrogen
dioxide fumes.
2. Gloves and goggles were used for extra safety measures
Results
Final 7.30 20.00 29.50 45.20 13.00
volume/cm3
Titre/cm3 7.30 12.70 9.50 15.7 13.00
Average titre: 13.58
Calculations
Comparison
After comparing my results with a few of my classmates, I could see that our results are similar
meaning I had done the experiment correctly. Most of my classmates received received results that
had more than 50% of copper in the brass solution which shows that not many errors were made
that would create a vast change in results.
Evaluation
Brass is a copper and zinc alloy, with copper serving as the primary component.
Brass screws are composed primarily from 60-65 percent copper by mass. This process will have two
major stages: first, the reaction of brass with acid, followed by the reaction with KI and thiosulfate
titration.
By mixing copper iodine with the brass solution, iodine solution created will slowly turn brown and
as it is titrated, it turns pale yellow. A few drops of 1% of starch is added to change the solution from
pale yellow to dark blue/black. At the beginning, I had some trouble adding starch solution because I
added too much however I restarted and learnt from my mistake. This colour change demonstrates
the iodine bonding to the starch. After titration the residual iodine completely, the blue colour fades
away completely into a creamy white colour. Near the end of the experiment we transferred the
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