, CHEMISTRY ATOMS AND MOLECULES
Atoms and Molecules
Laws of Chemical Combination
Law of Conservation of Mass
PRINCIPLE: The Law of Conservation of Mass states that mass can neither be created nor destroyed in a
chemical reaction.
Total Mass of the Reactant = Total Mass of the Product
DIAGRAM:
TECHNIQUE:
Take a solution of calcium chloride in a flask labelled A and a solution of sodium sulphate in a test
tube labelled B.
Tie a thread to the test tube and carefully lower it into the flask. Seal the flask with a cork to make it
airtight.
Weigh the flask on a balance. It weighs around 300.23 grams.
Tilt and swirl the flask and allow the contents of the test tube to come in contact with the contents of
the flask.
OBSERVATION:
Calcium chloride reacts with sodium sulphate to form a white precipitate of calcium sulphate and a
solution of sodium chloride.
Weigh the flask again. There will be no change in the weight of the flask. It is found to weigh 300.23
grams.
CONCLUSION:
Scientists noticed that if chemical reactions were carried out in a closed container, there was no
change in the mass.
The total mass of the reactants was equal to the total mass of the products.
Law of Constant Proportion
According to the Law of Constant Proportion, in a chemical substance, elements are always present in
a definite proportion by mass.
For example, water obtained from any source will have the same two elements, namely hydrogen and
oxygen present in it.
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Atoms and Molecules
Laws of Chemical Combination
Law of Conservation of Mass
PRINCIPLE: The Law of Conservation of Mass states that mass can neither be created nor destroyed in a
chemical reaction.
Total Mass of the Reactant = Total Mass of the Product
DIAGRAM:
TECHNIQUE:
Take a solution of calcium chloride in a flask labelled A and a solution of sodium sulphate in a test
tube labelled B.
Tie a thread to the test tube and carefully lower it into the flask. Seal the flask with a cork to make it
airtight.
Weigh the flask on a balance. It weighs around 300.23 grams.
Tilt and swirl the flask and allow the contents of the test tube to come in contact with the contents of
the flask.
OBSERVATION:
Calcium chloride reacts with sodium sulphate to form a white precipitate of calcium sulphate and a
solution of sodium chloride.
Weigh the flask again. There will be no change in the weight of the flask. It is found to weigh 300.23
grams.
CONCLUSION:
Scientists noticed that if chemical reactions were carried out in a closed container, there was no
change in the mass.
The total mass of the reactants was equal to the total mass of the products.
Law of Constant Proportion
According to the Law of Constant Proportion, in a chemical substance, elements are always present in
a definite proportion by mass.
For example, water obtained from any source will have the same two elements, namely hydrogen and
oxygen present in it.
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