Lab Report Exercise

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LabReport Exercise


Biologicalmolecules consist of two representative groups (macromolecules andmicro molecules). The macromolecules are proteins, lipids, nucleicacids, and carbohydrates. The results can either be qualitative orquantitative. Qualitative results express the presence of themacromolecules in a solution while quantitative results express theamount of the macromolecules present in a solution.

Inthis experiment, a qualitative test uses chemical indicators to trackthe hydrolysis of starch from one step to another. Starch is apolymer (polysaccharide), made of millions of glucose units joined byglycosidic bonds. The exercise enables the students to understand theeffect of starch hydrolysis on the qualitative results. Starchhydrolysis involves the enzyme amylase that catalyzes the breakdownof starch into simpler sugars. The breakdown of starch decreases theamount of starch that can react with iodine (reagent). It means thatthe presence of starch in a solution reduces with increasedhydrolysis (breakdown).



Test tubes and racks.

10 ml, 5 ml and 2 ml pipettes.


Volumetric flasks.

Pipette pumps.

Marking pencils.

Filter paper disks.

Spot plate.

Plastic pipette.

Water baths at 95⁰ C.

Protective eyewear and gloves.

Reagents and Solutions

3% starch solution.

Benedict’s solution.

Distilled water.

Concentrated Hydrochloric acid.


Concentrated Sodium Hydroxide.


  1. Swirled the flask containing 3% starch solution and transferred 6 ml of it to the test tube using a 10 ml pipette.

  2. Used a 5 ml pipette to pipette 3 ml of distilled water into the test tube containing the starch solution.

  3. Shook the test tube thoroughly.

  4. Used a clean 2 ml pipette to transfer 1 ml of the unhydrolyzed starch solution to a clean test tube and performed Benedict`s test. Recorded the results in Table 3.4.

  5. Worn protective eyewear and gloves, went to the fume hood and carefully dispensed 3 ml of concentrated HCl from the burette into the test tube containing starch and distilled water.

  6. Mixed the acidic starch solution in the test tube gently for 15 seconds.

  7. Used a plastic pipette to place two drops of the solution from the test tube onto a spot plate and tested it with IKI for the presence of starch.

  8. Recorded the IKI results in Table 3.3 as positive (+) or negative (-) at time 0 minutes and, in Table 3.4 under the test of the unhydrolyzed starch solution.

  9. Placed the test tube into a 95⁰ C water bath.

  10. Removed two drops of the solution from the test tube after 1 minute, then placed onto the spot plate in the depression adjacent to the first sample, and tested with IKI. Recorded the results in Table 3.3.

  11. Left the test tube in the 95 C water bath and repeated the procedure in step 11, in every minute until there were negative results of the starch solution with IKI.

  12. Recorded the results in Table 3.3.

  13. The results of the last test of starch solution with IKI were recorded in Table 3.4 under the test of the completely hydrolyzed starch solution.

  14. Used a pipette to transfer 2 ml of the test solution into a test tube.

  15. Carefully dispensed 2 ml of concentrated NaOH into the test tube prepared in step 15 above.

  16. Performed the Benedict’s test on the neutralized (hydrolyzed) starch solution.

  17. Recorded the answers in Table 3.4.


Table 3.3 Starch Acid Hydrolysis as Evidenced by IKI Test.

Time (Minutes)












IKI Results ( + or -)









As Starch hydrolysis occurs the purple colour of IKI diminishes progressively until it is no longer visible.

Note that the IKI test is positive before hydrolysis while Benedict’s test is negative. After complete hydrolysis, the IKI test is negative while Benedict’s test is positive. When the final solution is tested for simple sugars by use of Benedict’s solution its positive (turns yellow).

Discussion and Conclusion

When IKI test is carried out before hydrolysis commences (at a time, 0 intervals) the purple color is observed depicting the presence of starch (complex sugars). As time progresses, and hydrolysis takes place, the purple color diminishes progressively until it is no longer visible. It is an apparent show of the breakdown of complex sugars (polysaccharides), starch, into simple sugars (monosaccharides) that are no longer reactive with IKI test. Presence of simple sugars is confirmed by Benedict’s test. This confirms that complex sugars are hydrolyzed to simple sugars.

In conclusion, HCl hydrolyzes (breaks down) the complex sugars to simple sugars. At the initial step, IKI test shows the presence of complex sugars while Benedict`s test shows the absence of simple sugars. In the final stage, Benedict`s test depicts the presence of simple sugars while the IKI test shows the absence of complex sugars. The experiment shows the gradual breakdown (hydrolysis) of complex sugars to simple sugars.


Retrieved from,

Wang, S and Copeland, L. (2015). Effect of acid hydrolysis on starch structure and functionality: a review. US National Library of Medicine. Retrieved from