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Investigatory Project on Analysis of Vegetable and Fruit Juices

 

Chemistry Project on Analysis of Vegetable and Fruit Juices

 

Introduction

Fruits and vegetables form an important part of our diet. They contain minerals, carbohydrates, proteins and vitamins. These materials are highly essential for normal health in human beings. Actually, fruits and vegetables furnish the basic ingredients of good nutrition, i.e., they form a part of balanced diet. Deficiency of any of these basic ingredients leads to diseases. Therefore it is important to select the food we eat. All the fruits and vegetables do not contain similar types of substances. Therefore it is highly essential to know which fruits are richer in such substances. This is possible only through knowledge about the constituents of different fruits and vegetables.

 

Aim of the investigatory project

 

The objective of this project is to analyse various fruit and vegetable juices with a view to identifying the useful ingredients in them.

 

Apparatus and chemicals

 

1. Burette, pipette

2. Conical flasks

3. Test tubes

4. pH papers, litmus papers

5. Juices of various fruits

6. Common laboratory reagents

 

Procedure

 

A. Test for acidity

 

(i) Take 5 mL each of various fruit juices in different test tubes and dip the pH paper in them. Mark the test tubes A, B, C, D etc. to identify the samples.  


(ii) Proceed to determine the acidic nature with the help of litmus paper also. Record your observations in tabular form.


(iii) Take 10 mL of well filtered juice marked A in a conical flask and dilute it to 40 mL using distilled water. Prepare a standard solution of (0.01N) sodium hydroxide and take it in the burette. Titrate the fruit juice in the conical flask against sodium hydroxide solution using phenolphthalein indicator. Calculate the strength of acids present in the juice. Repeat the experiment with other juices and tabulate your observations. (Wash the burette immediately after use.)

 

Note: Standard solution of NaOH is prepared as follows. Dissolve 0.4 g NaOH in one litre of water. Shake well. Prepare a standard solution of oxalic acid by weighing out 0.63 g oxalic acid on a chemical balance and dissolving it in a 100 mL standard flask. Make up to the mark by adding water. This is 0.1 N oxalic acid solution. Pipette out 10 ml of this into another 100 mL standard flask and make up the solution to the mark. Shake well. This is 0.01N oxalic acid solution. Pipette out 20 ml of NaOH solution into a conical flask and titrate against oxalic acid solution (0.01N) from the burette using phenolphthalein. From the volume of 0.01N oxalic acid reacting with 20 mL NaOH solution, normality of NaOH solution can be calculated.

 

B. Test for starch

 

Take 3 mL of the juice marked A, and add a few drops of iodine solution into it. Formation of a blue colouration indicates the presence of starch. Repeat the experiment with other samples.

 

C. Test for proteins

 

(i) Ninhydrin test: Take 2 mL of the juice marked A and add 2 mL of ninhydrin solution and heat. Formation of blue colour indicates the presence of proteins in the juice. Repeat the experiment with other juices also.


(ii) Biuret test: To about 3 mL of 5% NaOH solution add two drops of 1% copper sulphate solution till a permanent blue colour is obtained. Add 2 mL of the juice marked A into this and shake well. A violet colouration (or precipitate) indicates the presence of proteins in the juice. Repeat the experiment with other samples.

 

D. Test for carbohydrates

 

(i) Molisch's test: Prepare 1% solution of α - naphthol in ethyl alcohol. 2 mL of this solution is added to 2 mL of the juice taken in a test tube. Add con. H2SO4 along the sides of the test tube slowly. A violet colouration at the junction of the two layers indicates the presence of carbohydrates in the juice. Repeat the experiment with other samples.

 

E. Test for minerals

 

(i) Test for iron: Mix 2 mL of the juice with two drops of con.HNO3 and heat the mixture. Cool the mixture and add three drops of potassium thiocyanate (KCNS) solution. Formation of blood red colour indicates the presence of iron. Repeat the test with other samples.

 

(ii) Test for phosphorus: Mix 2 mL of the juice with two drops of con. HNO3 and boil the mixture. Add a few drops of ammonium molybdate reagent into this and heat again. Formation of a bright yellow precipitate or colour indicates the presence of phosphorus in the juice. Repeat the test with other samples.

 

(iii) Test for sodium and potassium


(a) Add two pellets of solid KOH into 2 mL of the juice and boil. To the hot mixture add potassium pyroantimonate solution and scratch the sides of the test tube with a glass rod. Formation of white precipitate (or milky solution) shows the presence of sodium ions. Repeat the test with other samples.


(b) Add 2 mL of picric acid solution to 2 mL of the juice. Yellow precipitate shows the presence of potassium ions. Repeat the test with other samples.

 

(iv) Test for calcium and magnesium


(a) Mix 2 mL of the juice with a little of solid NH4CI and NH4OH solution. Shake well and filter. To the filtrate add 2 mL of ammonium oxalate solution. Formation of a white precipitate (or milky solution) indicates calcium ions. Repeat the test with other samples.


(b) Add ammonium hydroxide solution to 2 mL of the juice till it is alkaline. Add excess of ammonium phosphate solution and scratch the sides of the test tube with glass rod. A white precipitate indicates the presence of magnesium ions. Repeat the test with other samples.

 

OBSERVATIONS


Table 1: Acidic and basic character

No:

Name of sample

pH

Vol of juice (mL)

Vol of 0.01N NaOH soln

Concentration of acids equt/litre

1

Orange Juice

 

 

 

 

2

Lemon Juice

 

 

 

 

3

Carrot Juice

 

 

 

 

4

Tomato Juice

 

 

 

 

5

Grape Juice

 

 

 

 

 

Table 2: Contents of juices

No

Name of sample

Starch

Proteins

Carbo Hydrates

Minerals

Fe

P

Na

K

Ca

Mg

1

Orange Juice

 

 

 

 

 

 

 

 

 

2

Lemon Juice

 

 

 

 

 

 

 

 

 

3

Carrot Juice

 

 

 

 

 

 

 

 

 

4

Tomato Juice

 

 

 

 

 

 

 

 

 

5

Grape Juice

 

 

 

 

 

 

 

 

 

 

Report

(Based on the above table, draw conclusions about the samples used and write here).

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