Unit 4: Laboratory Techniques and their Application Assignment Answer

This Unit 4: Laboratory Techniques and their Application assignment answer guide covers the whole unit from the Pearson BTEC Level 3 National in Applied Science (2016 specification), across all four learning aims. It explains every Pass, Merit and Distinction criterion, shows how to structure each report, and gives short model-answer extracts plus a fully worked yield calculation you can check your own results against.

What the Unit 4 assignments ask you to do

Unit 4 is usually assessed through four separate assignments, one per learning aim. Each one puts you in a workplace role so that your writing is about a real scientific organisation rather than a textbook summary.

• Learning aim A: you act as a health and safety inspector visiting a science-based company (for example a pharmaceutical, plastics or cosmetics manufacturer). You report on how two different working environments, such as a production plant and a research and development laboratory, meet UK health and safety law.
• Learning aim B: you work as a laboratory technician who must make and purify an organic liquid (most centres use ethyl ethanoate), test its purity and compare your bench method with industrial manufacture.
• Learning aim C: the same approach for an organic solid, usually aspirin (2-ethanoyloxybenzoic acid), with recrystallisation and melting point or thin-layer chromatography as purity tests.
• Learning aim D: you explain how a workplace laboratory records, stores and communicates scientific information, including traceability and the use of large data sets.

If you only need the health and safety report, our separate Applied Science Unit 4 Learning aim A answer guide goes into that inspection report in much more depth.

Learning aims for Unit 4

Pass, Merit and Distinction criteria explained

How to answer Learning aim A: health and safety in scientific organisations

Choose one organisation and two clearly different environments. Your marks depend on linking each measure to the right law, not on listing laws.

1. Introduce the organisation and what each environment does.
2. Hazard table for each environment (chemical, biological, physical, fire, ergonomic).
3. Explain the measures and the legislation they satisfy: Health and Safety at Work etc. Act 1974, Management of Health and Safety at Work Regulations 1999, Control of Substances Hazardous to Health Regulations 2002 (COSHH), Personal Protective Equipment at Work Regulations 1992, RIDDOR 2013 and the Regulatory Reform (Fire Safety) Order 2005.
4. Compare the two environments (A.M1), then evaluate (A.D1).

How to answer Learning aim B: making and testing an organic liquid

For ethyl ethanoate, ethanol and ethanoic acid are heated under reflux with a concentrated sulfuric acid catalyst, then distilled. The crude ester is washed with sodium carbonate solution to remove acid, separated in a separating funnel, dried with anhydrous calcium chloride and redistilled, collecting the fraction near 77 °C.

• Write a method in the past tense with quantities, apparatus and safety controls.
• Record mass of product, boiling point range and an IR spectrum (look for C=O near 1735–1750 cm^-1 and no broad O–H band).
• Describe industrial esterification: continuous reactors, reactive distillation, recycling of unreacted ethanol, in-line quality control by gas chromatography.
• Compare lab and industry (B.M3) and analyse yield and purity factors (B.D2).

How to answer Learning aim C: making and testing an organic solid

Aspirin is made by reacting 2-hydroxybenzoic acid (salicylic acid) with ethanoic anhydride, using a few drops of acid catalyst. The crude solid is collected by vacuum filtration, recrystallised from a hot ethanol and water mixture, dried and weighed.

• Melting point: pure aspirin melts at about 135–136 °C; a lower, wider range indicates impurities.
• TLC: run crude product, recrystallised product and salicylic acid side by side; calculate Rf values.
• Iron(III) chloride test: a purple colour shows remaining phenol groups from unreacted salicylic acid.
• Industrial manufacture: large batch reactors, controlled temperature, centrifuging and drying, then tablet formulation under Good Manufacturing Practice.

How to answer Learning aim D: storing and communicating scientific information

Follow one sample from receipt to report. Explain unique sample identifiers, chain of custody, laboratory notebooks, LIMS records, calibration logs, review and sign-off, and certificates of analysis. Show how each step allows the result to be traced back. Link this to Good Laboratory Practice, ISO/IEC 17025 accreditation and the UK GDPR and Data Protection Act 2018 where personal data is involved.

Worked example: percentage yield of aspirin

A student reacts 2.00 g of salicylic acid with excess ethanoic anhydride and obtains 1.85 g of dry, recrystallised aspirin.

1. Equation: C₇H₆O₃ + (CH₃CO)₂O → C₉H₈O₄ + CH₃COOH. The mole ratio of salicylic acid to aspirin is 1 : 1.
2. Molar masses: salicylic acid = 138.12 g mol^-1; aspirin = 180.16 g mol^-1.
3. Moles of salicylic acid = 2.00 g ÷ 138.12 g mol^-1 = 0.01448 mol.
4. Theoretical mass of aspirin = 0.01448 mol × 180.16 g mol^-1 = 2.61 g.
5. Percentage yield = (1.85 g ÷ 2.61 g) × 100 = 70.9%.

For B.D2 or C.D3, do not stop at the number. Explain where the missing 29% went: product left dissolved in the recrystallisation solvent, crystals lost on filter paper, incomplete reaction and transfer losses. Then explain how industry limits each loss, for example by recycling mother liquor and using closed transfer systems.

Common mistakes that cost marks

• Listing legislation without linking each law to a real measure in your chosen organisation.
• Choosing two environments that are too similar, which leaves nothing to compare for A.M1.
• Copying the method from the worksheet instead of recording what you actually did and observed.
• Quoting a percentage yield with no calculation shown or with the wrong molar masses.
• Calling a product “pure” without boiling point, melting point, TLC or IR evidence.
• Describing industrial manufacture in general terms rather than for your specific compound.
• Explaining LIMS in theory only, with no example of a real type of laboratory.

How to move from Merit to Distinction

All four Distinction criteria ask for judgement. For A.D1, weigh how well each measure works, its cost and its limits, and make recommendations. For B.D2 and C.D3, analyse why your yield and purity turned out as they did, using your own data, and connect each factor to how industry controls it (catalysts, conditions, continuous removal of product, recycling). For D.D4, consider security, storage costs, regulation and the benefits of sharing, then reach a clear conclusion. A Distinction answer always ends with a supported judgement, not a summary.

FAQs

How many assignments are there in BTEC Applied Science Unit 4?

Most centres set four assignments, one for each learning aim, although some combine B and C into one practical assignment. Check the briefs your centre has issued.

Which organic liquid and solid are usually made in Unit 4?

Ethyl ethanoate is the most common liquid and aspirin the most common solid, but your centre may choose other esters or solids. The same structure of method, purity test and industrial comparison applies.

What if my percentage yield is very low?

A low yield does not stop you passing. What matters is that you report it honestly and, for Distinction, analyse the reasons in detail.

Is Unit 4 internally or externally assessed?

It is internally assessed. Your teacher marks the assignments against the criteria and the work is then internally verified and sampled by Pearson.

Which laws should I mention for Learning aim A?

The Health and Safety at Work etc. Act 1974, the Management of Health and Safety at Work Regulations 1999, COSHH 2002, the PPE at Work Regulations 1992 and RIDDOR 2013 are the core set. Add others only if they fit your organisation.

Need one-to-one support from a subject specialist? Our BTEC Level 3 assignment help service covers planning, feedback on drafts and referencing.

If you are stuck on a practical write-up or need feedback before submission, you can get expert help with your BTEC assignment. For the practical skills unit that leads into this one, see our Unit 2 Practical Scientific Procedures and Techniques answer guide.