Chem 100, Spring 2025 Pre-lab 15

Experiment 15: Carbohydrates and Proteins

Purpose

• Understand properties and chemical tests for carbohydrates and proteins.

Materials

• Reagents & Equipment: Parchment paper, spray oil, cookie sheet, saucepan, sugar, corn syrup/honey, baking soda, stove/microwave, pot, scissors, mixer, bowls, utensils, alcohol, vinegar, gelatin, containers, plastic wrap, indicator strips, salt, ammonia, vinegar, fruits.

Quiz Preparation

• Vocabulary: Monosaccharide, disaccharide, polysaccharide, carbohydrates, reducing sugar, glycosidic linkage, etc.

Background

Carbohydrates

• Primary energy source, classified into mono-, di-, poly-saccharides.
  • Monosaccharides: Simple sugars (e.g., glucose, galactose, fructose).
  • Disaccharides: Two monosaccharides linked (e.g., maltose, lactose, sucrose).
  • Polysaccharides: Long chains (e.g., starch, glycogen, cellulose).
  • Reducing Sugars: Can be oxidized (e.g., glucose, fructose).

Chemical Tests

• Benedict's Test: Identifies reducing sugars (color change indicates positive).
• Iodine Test: Identifies starch (color change to blue-black indicates positive).

Proteins

• Made of polypeptide chains of amino acids.
  • Biuret Test: Detects peptide bonds (violet color indicates positive).
  • Xanthoproteic Test: Detects benzene rings in amino acids (yellow color indicates positive).

Experiment Stations

Station A: Benedict's Test for Sugars

• Objective: Test sugars for reducing properties.
• Procedure:
  • Dissolve sugars, add Benedict’s reagent, heat, observe color change.
  • Record results for glucose, fructose, sucrose, lactose, starch, hydrolyzed sucrose, and starch.

Station B: Iodine Test for Starch

• Objective: Test for presence of starch.
• Procedure:
  • Add iodine to sugar solutions, observe color change.
  • Record results for glucose, fructose, sucrose, lactose, starch, hydrolyzed sucrose, and starch.

Station C: Color Tests for Proteins

• Objective: Apply Biuret and Xanthoproteic tests.
• Procedure:
  • Biuret: Add copper sulfate and sodium hydroxide to protein solutions.
  • Xanthoproteic: Add nitric acid and ammonium hydroxide.

Station D: Denaturing Egg Albumin

• Objective: Observe denaturing of proteins under different conditions.
• Procedure:
  • Use water, alcohol, vinegar, and heat to treat egg whites.
  • Observe immediate and long-term changes in consistency and color.

Station E: Denaturing and Enzyme Activity

• Objective: Impact of denaturing on enzyme bromelain.
• Procedure:
  • Treat gelatin with various pineapple juices and observe effects.
  • Determine if proteases are active or denatured.

Key Concepts

• Denaturation: Unfolding of protein chains affecting functionality.
• Enzyme Activity: Affected by temperature and pH changes.

Questions & Observations

• Complete questions related to each station to reinforce learning and document observations.

Conclusion

• Successfully understand and document the properties and reactions of carbohydrates and proteins through practical experiments and tests.

This document provides a comprehensive guide and summary for conducting the experiments and pre-lab preparation for Chem 100, Spring 2025.