Tests Q2 From the results in Part B, which carbohydrates are ketoses? Q3 From the results in Part C, which carbohydrates give a positive fermentation test? 291abydodi) 101 2129T Q4 From the results in Part D, which carbohydrates give a blue-black color in the iodine test? peu15 1 2011 9203913 W les T Benedict’s (A) Seliwanoff’s (B) Fermentation (C) Iodine (D) Identifying an Unknown Carbohydrate Unknown No. B que gaisub1 101 125T aloibanol A What carbohydrate(s) is/are in Results with Unknown 2920 Carbohydrates Presents 15118 ciolo) anisuben your unknown? noireinsmes S (ul) #shizadosnavio4 701 tesT onibol a enoitevised01 Questions and Problems Q5 What carbohydrate(s) would give the following test results? szolymA S (okoY) a. Produces a reddish-orange solid with Benedict’s reagent and a red color with Seliwanoff’s reagent in 1 minute b. Produces a color change with Benedict’s reagent, a light orange color with Seliwanoff’s reagent after 5 min, and produces no bubbles during fermentation
The correct answer and explanation is:
To answer these questions, let’s analyze each test result and match it with the properties of carbohydrates:
Q2: From the results in Part B, which carbohydrates are ketoses?
Explanation:
The Seliwanoff’s test is designed to distinguish ketoses (e.g., fructose) from aldoses (e.g., glucose) because ketoses react more rapidly with Seliwanoff’s reagent, producing a deep red color within 1-2 minutes. Aldoses may eventually produce a color change, but it occurs much slower and is often light orange.
From the results, identify which carbohydrates gave a red color within 1 minute. Those are ketoses.
Q3: From the results in Part C, which carbohydrates give a positive fermentation test?
Explanation:
A positive fermentation test indicates that the carbohydrate can be metabolized by yeast to produce carbon dioxide (bubbles) and/or alcohol. Typical fermentable carbohydrates include glucose, fructose, and sucrose. Non-fermentable carbohydrates like lactose and starch will not show bubbles.
Refer to the results to identify which carbohydrates produced gas during fermentation.
Q4: From the results in Part D, which carbohydrates give a blue-black color in the iodine test?
Explanation:
The iodine test detects the presence of starch or polysaccharides. A positive test gives a blue-black color, indicating the presence of helical polysaccharide chains. Monosaccharides (e.g., glucose) and disaccharides (e.g., sucrose) will not give a positive result. Identify which carbohydrate(s) produced a blue-black color in the iodine test.
Q5: What carbohydrate(s) would give the following test results?
a. Produces a reddish-orange solid with Benedict’s reagent and a red color with Seliwanoff’s reagent in 1 minute.
Explanation:
- Benedict’s Test: A positive reddish-orange solid indicates the presence of a reducing sugar. Reducing sugars are carbohydrates with a free aldehyde or ketone group, like glucose, fructose, or maltose.
- Seliwanoff’s Test: A red color within 1 minute strongly indicates the carbohydrate is a ketose.
Answer: The carbohydrate is fructose because it is a reducing sugar and a ketose.
b. Produces a color change with Benedict’s reagent, a light orange color with Seliwanoff’s reagent after 5 min, and produces no bubbles during fermentation.
Explanation:
- Benedict’s Test: A positive color change indicates a reducing sugar is present.
- Seliwanoff’s Test: A light orange color after 5 minutes suggests an aldose, as aldoses react more slowly with Seliwanoff’s reagent.
- Fermentation: No bubbles indicate the carbohydrate is not fermentable, ruling out glucose, fructose, and sucrose.
Answer: The carbohydrate is lactose, a reducing sugar and non-fermentable disaccharide.
Final Summary:
- Q2: Ketoses are those that gave a rapid red color with Seliwanoff’s reagent.
- Q3: Carbohydrates that gave bubbles during fermentation are glucose, fructose, and sucrose.
- Q4: Carbohydrates that gave a blue-black color with iodine are starches.
- Q5a: Fructose.
- Q5b: Lactose.
Let me know if you need help refining or cross-checking the results!