Archive for the ‘class xii chemistry project’ Category

TO STUDY THE RATE OF EVAPORATION OF DIFFERENT LIQUIDS

July 29, 2008

INTRODUCTION

When a liquid is placed in an open vessel, it slowly escapes into gas phase, eventually leaving the vessel empty. This phenomenon is known as evaporation. Evaporation of liquids can be explained in terms of kinetic molecular model. Although there are strong inter-molecular attractive forces which hold molecules of a liquid together, the molecules having sufficient kinetic energy can escape into gas phase if such molecules happen to come near the surface. In a sample of liquid all the molecules do not have same kinetic energy. There is a small fraction of molecules which have enough kinetic energy to overcome the attractive forces and escape into gas phase.

Evaporation causes cooling. This is due to the reason that the molecules, which undergo evaporation, are high-energy molecules; therefore the kinetic energy of molecules which are left behind is less. Since the remaining molecules have lower average kinetic energy therefore, temperature must be lower. If the temperature is kept constant the remaining liquid will have the same distribution of molecular kinetic energies and the high-energy molecule will keep on escaping from the liquid into the gas phase. If the liquid is taken in an open vessel, evaporation will continue until whole of the liquid evaporates.

REQUIREMENTS

Apparatus:

  • Three petridishes of diameter 10 cm with covers
  • 10 ml pipette
  • Stop watch

Chemicals:

  • Acetone
  • Benzene
  • Chloroform

PROCEDURE

  • Clean and dry the petridishes and mark them as A, B, C.
  • Pipette out 10 ml of acetone to petridish A and cover it.
  • Pipette out 10 ml of benzene in petridish B and cover it.
  • Pipette out 10 ml of chloroform in petridish C and cover it.
  • Uncover all the three petridishes simultaneously and start the stop-watch.
  • Note the respective time when the liquids evaporate completely from each petridish.

OBSERVATIONS

Petridish Mark
Liquid Taken
Time taken for complete evaporation
A Acetone 53 min
B Benzene 42 min
C Chloroform 30 min

CONCLUSION

The rate of evaporation of the given three liquids is in the order:

Chloroform > Benzene > Acetone

ANALYSIS OF VEGETABLES AND FRUIT JUICES

July 29, 2008

AIM

To analyse some fruits & vegetables juice for the contents present in them.

INTRODUCTION

Fruits and vegetable are always a part of balanced diet. That means fruits vegetables provide our body the essential nutrients, i.e. Carbohydrates, proteins, vitamins and minerals. Again their presence in these is being indicated by some of our general observations, like -freshly cut apples become reddish black after some time. Explanation for it is that iron present in apple gets oxidixed to iron oxide. So, we can conclude that fruits and vegetables contain complex organic compounds, for e.g., anthocin, chlorophyll, esters(flavouring compounds), carbohydrates, vitamins and can be tested in any fruits or vegetable by extracting out its juice and then subtracting it to various tests which are for detection of different classes of organic compounds. Detection of minerals in vegetables or fruits means detection of elements other than carbon, hydrogen and oxygen.

MATERIAL REQUIRED

  • Test Tubes
  • Burner
  • Litmus paper
  • Laboratory reagents
  • Various fruits
  • Vegetables juices

CHEMICAL REQUIREMENTS

  • pH indicator
  • Iodine solution
  • Fehling solution A and Fehling solution B
  • Ammonium chloride solution
  • Ammonium hvdroxide
  • Ammonium oxalate
  • Potassium sulphocynaide solution

PROCEDURE

The juices are made dilute by adding distilled water to it, in order to remove colour and to make it colourless so that colour change can be easily watched and noted down. Now test for food components are taken down with the solution.

TEST, OBSERVATION & INFERENCE

Test
Observation
Inference
ORANGE TEST:
Test for acidity:
Take 5ml of orange juice in a test tube and dip a pH paper in it. If pH is less than 7 the juice is acidic else the juice is basic. The pH comes out to be 6. Orange juice is acidic.
Test for Startch:
Take 2 ml of juice in a test tube and add few drops of iodine solution. It turns blue black in colour than the starch is present. Absence of blue black in colour. Orange juice is acidic.
Test for Carbohydrates (FEHLING’S TEST):
Take 2 ml of juice and 1 ml of fehling solution A & B and boil it. Red precipitates indicates the presence of producing sugar like maltose, glucose , fructose & Lactose. No red coloured precipitates obtained. Carbohydrates absent.
Test for Iron:
Take 2 ml of juice add drop of conc. Nitric acid. Boil the solution cool and add 2-3 drops of potassium sulphocyanide solution .Blood red colours shows the presence of iron. Absence of blood red colour. Iron is absent.
Test for Calcium:
Take 2 ml of juice add Ammonium chloride and ammonium hydroxide solution. Filter the solution and to the filterate add 2 ml of Ammonium Oxalate solution. white ppt or milkiness indicates the presence of calcium. Yellow precipitate is obtained. Calcium is present.

CONCLUSION

From the table given behind it can be conducted that most of the fruits & vegetable contain carbohydrate & vegetable contain carbohydrate to a small extent. Proteins are present in small quantity. Therefore one must not only depend on fruits and vegetables for a balance diet.


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