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The experiment titled “Detection of Carbohydrates (Glucose)” aims to investigate two distinct methods: Benedict’s test and Fehling’s test employed for testing the presence of glucose, one of the prevalent carbohydrates found in various food samples.
Benedict’s test uses its solution with copper ions. If reducing sugars like glucose are present in the sample, they react with copper ions, causing a colour change from blue to green, yellow, orange, or brick-red. The colour intensity correlates with glucose concentration.
In contrast, Fehling’s test employs a reagent, Fehling’s A and B, containing copper sulphate, potassium tartrate, and sodium hydroxide. Upon heating, reducing sugars produce a brick-red copper(I) oxide precipitate, confirming glucose presence.
The experiment involves a series of steps to be followed:
- Firstly, we will cut small pieces of banana, apple, and grapes and crush them separately to strain the juices in the different test tubes.
- Then we will extract the juice of onion bulb leaves by boiling it for 2-3 minutes and filtering it.
- We will take the milk sample in a separate test tube.
1. Benedict’s Test
- We will add 2 mL of juice/milk/onion leaf juice in separate test tubes.
- Next, we need to add 2 mL of Benedict’s reagent to each sample and boil it using a water bath.
- Now observe each test tube and note down the colour change.
2. Fehling’s Test
- Mix equal volumes of Fehling’s solution A and B in a beaker.
- Now add 2 mL of juice/milk/onion leaf juice in separate test tubes.
- Next, add an equal volume of Fehling’s solution to each sample and boil it using a water bath.
- Now observe each test tube and note down the colour change.
Overall, the experiment aims to provide students with hands-on experience in utilising these two common methods to detect the presence of glucose, an essential carbohydrate, within various food samples. By observing the characteristic colour changes and precipitate formation, participants gain insights into the carbohydrate composition of different foods, helping them to understand better the nutritional content and potential applications of these techniques in food analysis.
FAQs on Detection of Carbohydrates (Glucose)
Q.1 What is Fehling’s reagent composed of?
Ans. Fehling’s reagent is made up of two separate solutions, Fehling’s A and Fehling’s B. Fehling’s A contains copper sulphate (CuSO4), while Fehling’s B contains potassium tartrate and sodium hydroxide. When these solutions are mixed in equal proportions, they form the reactive Fehling’s reagent.
Q.2 How does Benedict’s test work for glucose detection in food samples?
Ans. Benedict’s solution contains copper ions that react with reducing sugars. In the presence of glucose, the blue copper(II) ions are reduced to form a reddish-brown copper(I) oxide precipitate. The intensity of the colour change can be used to estimate the amount of glucose present.
Q.3 Are there any safety precautions for performing these tests?
Ans. Both tests involve the use of potentially hazardous chemicals, such as copper salts and strong alkalis. Safety precautions, such as wearing appropriate protective gear (gloves, goggles), working in a well-ventilated area, and using proper lab techniques, should be followed to minimise the risk of accidents or exposure.
Q.4 What colour change indicates a positive result for glucose in Benedict’s test?
Ans. A positive result for glucose in Benedict’s test is indicated by a colour change from blue to green, yellow, orange, or brick-red, with the intensity of the colour corresponding to the concentration of reducing sugars in the sample.
Q.5 Which types of food samples can be tested using Fehling’s test?
Ans. Fehling’s test can be applied to a variety of food samples containing reducing sugars, such as fruits, fruit juices, honey, syrups, and certain carbohydrate-rich foods.
JEE Main