Qualification

Pearson BTEC Level 3 National Extended Diploma in Applied Science

Unit number and title

Unit 19: Practical Chemical Analysis

Learning aim

A: Investigate quantitative analysis on the components of matrices to determine their composition

Name

Assignment title

Analyte determination

Assessor

Issue date

01/03/2021

Hand in deadline

26/03/2021

Vocational Scenario or Context

Your school is supporting a charity called ‘Educate Africa’ and you have been asked to make an educational video and accompanying tutorial notes. The target audience are sixth form students attending a school in remote town in Africa that have no laboratory equipment in school to carry out practicals themselves.

You will make an individual video and supporting tutorial booklet that demonstrates how to accurately determine the composition and concentration of an analyte in a matrices, comparing ‘primary and secondary’ titrimetric standards and analysing sources of error.

Task

Using your lesson notes and research into primary and secondary titrimetric standards you will make an individual video that demonstrates accurately how to determine the amount of analyte in the following matrices:

1) the percentage of copper in brass (by reacting with acid and using colorimetry)

2) the concentration of bicarbonate in bottled water (by pH titration with standardised 0.01mol dm^-3 hydrochloric acid)

3) the concentration of iron(II) ions in a commercial iron tablet (by titration with standardised potassium manganate(VII) )

Your tutor will provide you with standard methods to determine the content of each of the three analytes. In the case of the titrations, your method will include the standardisation of your titrant, as you will be using secondary standard solutions (i.e. for 2) you will need to standardise the hydrochloric acid and quantitatively dilute it from Investigate quantitative analysis on the components of matrices to determine their composition

0.1 mol dm^-3 to 0.01 mol dm^-3; for 3) you will need to standardise the potassium manganate(VII) with sodium ethanedioate (oxalate) solution)

Each method must be carried out independently and you must demonstrate competence by showing good skills in weighing and making volumetric measurements.

You will then prepare a tutorial booklet that outlines your work and that explains how to use your results to carry out calculations to determine the amount of each of the three analytes.

You will need to describe the complete composition of each of the three matrices. To do this you will need to carry out research into the typical compositions of brass, bottled water and iron tablets. For each of the three matrices, you will need to describe each component and provide an approximate percentage or concentration. You will then need to compare your results with other learners and with your research of what the typical concentration or percentage should be.

Discuss the measures taken to ensure accuracy in determining the amount of analyte present. You will need to consider aspects of good colorimetric and volumetric practice, to include the justification of the following:

• Use of a burette and other volumetric equipment
• Choice of a specific indicator
• Colorimeter calibration
• Repeat readings

The percentage error in your calculations could be used to support your arguments.

Compare the use of secondary and primary standard solutions. You will need to define primary and secondary standards, and explain why a secondary standard must be standardised with a primary standard solution. You will then justify for your specific practical titrimetric work why the use of secondary standards was chosen in preference to primary standards.

Analysis of specific errors in each method. You will need to consider how the presence of other analytes / components in the matrices may affect the accuracy of the results. This should include a comparison of how the results from these experiments may be different from those where a technician may have made solutions of pure compounds for analysis.

You will then prepare a tutorial booklet as a reference document for the students in Africa that details all the work you have done and compares ‘primary and secondary’ titrimetric standards. Investigate quantitative analysis on the components of matrices to determine their composition

Checklist of evidence required

• A video that demonstrates accurately how to determine the amount of analyte in the following matrices:
  • Determination of the copper percentage content in brass
  • Determination of the bicarbonate concentration in bottled water
  • Determination of the iron(II) percentage content in a commercial iron tablet
• A tutorial booklet that contains:
  • An outline of the practical work carried out, including a description of the matrices analysed
  • Calculations of concentrations or percentages of the components in each matrices
  • A discussion of the accuracy of the methods, including a comparison of primary and secondary titrimetric techniques
  • An analysis of errors Unit 19: Practical Chemical Analysis