The Carbohydrates Reducing and Non-Reducing Sugars, And Starch

[cs_content][cs_section parallax=”false” separator_top_type=”none” separator_top_height=”50px” separator_top_angle_point=”50″ separator_bottom_type=”none” separator_bottom_height=”50px” separator_bottom_angle_point=”50″ style=”margin: 0px;padding: 45px 0px;”][cs_row inner_container=”true” marginless_columns=”false” style=”margin: 0px auto;padding: 0px;”][cs_column fade=”false” fade_animation=”in” fade_animation_offset=”45px” fade_duration=”750″ type=”1/1″ style=”padding: 0px;”][cs_text]Forensic Chemistry > 2. Analysis of organic material can distinguish plant and animal material > The Carbohydrates Reducing and Non-Reducing Sugars, And Starch >[/cs_text][cs_text style=”color: #800000;font-family: “Oxygen”,sans-serif;”]Choose equipment, plan and perform a first-hand investigation to carry out a series of distinguishing tests for the carbohydrates reducing and non-reducing sugars, and starch[/cs_text][cs_text]Benedict’s Test

  • Test for qualitative determination of reducing sugars

Iodine Test

  • Test for qualitative determination of starch

Experiment

Reagents: Iodine and Benedict’s reagent (mixture of sodium carbonate, sodium citrate and copper(II) sulfate pentahydrate)

Methodology:

  1. Prepare two controlled test tubes of distilled water. Add Iodine solution to the 1st tube and Benedict’s solution to the 2nd Record for any observations.
  2. In another 3 test tubes (Set 1), transfer 10 mL cold water to each, and add half a teaspoon of powdered glucose to tube A, sucrose to B and starch to C.
  3. Shake the mixture and record the solubility of each in water.
  4. Transfer half of the each test tube solution (5 mL) in Set 1 into separate test tubes (Set 2). To the 1st set of tubes, add iodine solution. Shake and record the colour changes in A, B and C.
  5. For Set 2, add Benedict’s solution to each tube. Shake and warm gently in a water bath and record for any colour changes.

Results:[/cs_text][cs_text][/cs_text][cs_text]Analysis of Solubility Test

  • Glucose and sucrose have many polar sites capable of having hydrogen bonding with water molecules, thereby allowing them to be soluble with each other.
  • Although starch has many polar sites capable of exhibiting hydrogen bonding towards water molecules, it is relatively long in which the effect of the non-polar part becomes significant. Thus, becomes insoluble with water however can absorb water molecules due to its structure and large polar parts.

Analysis of Iodine Test

  • The change in colour of starch in the presence of iodine solution is due to the formation of starch-iodide complex, specifically between the several branches in the structure of starch and iodine

[/cs_text][cs_text][/cs_text][cs_text]Analysis of Benedict’s Test

  • The glucose reduced the Benedict’s solution from Cu2+ to Cu+ and then to Cu2 Benedict’s Redox Equation:

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  • In the structure of glucose, the aldehyde group (CHO) was oxidized by Benedict’s solution to form a carboxylic acid group (COOH), indicating that glucose is a reducing sugar

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  • The sucrose and starch showed no changes in color in the presence of Benedict’s reagent, indicating that these were non-reducing sugars.

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