Biology 11–12 · Year 12

Vitamin C in fruit juices by DCPIP titration: a nutritional disease investigation

Module 8: Non-infectious Disease and Disorders (Causes and Effects: nutritional diseases)

Practical, model not builtLow risk

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

Vitamin C decolourises the blue dye DCPIP in a fixed ratio, so the volume of dye a juice can decolourise measures its vitamin C, the nutrient whose lack causes scurvy.

What you need

Vitamin C (ascorbic acid) standard 0.1 percent (1 mg/mL), freshly made; DCPIP solution 0.1 percent (the CLEAPSS recipe concentration the source cites; the source protocol uses 1 percent)
Burette or 5 mL graduated pipette; 2 mL pipette and filler; test tubes
Fruit juices: freshly squeezed orange juice, long-life orange juice, a juice boiled for 5 minutes and cooled, a fruit drink; distilled water for dilutions

How to do it

Pipette 2 mL of the vitamin C standard into a test tube and add DCPIP from the burette drop by drop, shaking after each drop, until the colour of the last drop no longer disappears: in the acidic vitamin C solution the excess DCPIP shows as a persistent pale pink rather than blue, because DCPIP stays pink in acid, as the source notes; record the volume and repeat to agreement.
Repeat with 2 mL of each juice; if more than 5 mL of DCPIP is decolourised, dilute the juice and repeat, and if the juice's colour hides the end point, dilute it.
Calculate each juice's vitamin C concentration: concentration = 1 mg/mL x (DCPIP volume for the juice / DCPIP volume for the standard) x any dilution factor.
Compare fresh, long-life and boiled juice and test the hypothesis that heating destroys vitamin C.
Calculate the volume of each juice that supplies the Recommended Dietary Intake of 40 mg per day for 14 to 18-year-olds (NHMRC Nutrient Reference Values).
Relate the result to scurvy as a nutritional disease and to how diet prevents it.

What you should see

Vitamin C reduces DCPIP one molecule to one, so 2 mL of the 1 mg/mL standard (2 mg, 0.0114 mmol) decolourises 3.29 mL of 0.1 percent DCPIP (computed with molar masses 176.12 g/mol for ascorbic acid and 290.08 g/mol for the sodium salt of DCPIP); the measured standard titre sets the working ratio for the juices, and a titre far from 3.29 mL shows that a solution has degraded or that the DCPIP salt is hydrated. Freshly squeezed juice decolourises more DCPIP than the same juice after boiling, as the source's heat hypothesis predicts. A juice measured at 0.40 mg/mL would need 100 mL to supply 40 mg (computed). The learner knows it worked when replicate titres agree within 0.1 mL and the boiled juice gives a smaller titre than the fresh juice.

What changes

What you change: juice type or treatment (fresh, long-life, boiled)
What you measure: volume of DCPIP decolourised and calculated vitamin C concentration
What you keep the same: sample volume
DCPIP batch and concentration
end-point rule
temperature

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Juice labelled orange always holds plenty of vitamin C; processing and heating lower it.
Scurvy is a disease of the past only; it occurs wherever intake of vitamin C stays very low.
More DCPIP decolourised means less vitamin C; the more dye a sample decolourises, the more vitamin C it holds.

Safety card

Low riskLearners carry it out

Hazards

Burette glass
DCPIP stains
Juices in a laboratory

Controls

Clamp the burette and fill it below eye level
Wipe spills; wear eye protection
No tasting; juices used in the laboratory are laboratory reagents

Note

DCPIP and ascorbic acid are low hazard at these concentrations per the source; see RiskAssess (https://www.riskassess.com.au/) and the NSW Department of Education Chemical Safety in Schools package (https://education.nsw.gov.au/content/dam/main-education/asset-management/chemical-safety/1._Section_1_-_General_information_for_all_staff.pdf).

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Biology Stage 6 Syllabus (2017), current: Year 11 taught to the end of 2026 and Year 12 to Term 3 2027BIO12-15 BIO11/12-5 BIO11/12-6
Biology 11–12 Syllabus (2025), Year 12 focus area Diseases; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-12-02
Biology 11–12 Syllabus (2025), Year 12 Working scientifically; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-12WS-02 BI-12WS-03 BI-12WS-04
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

All Concept Studio activities