Who said this -"a stage would come beyond
which further division will not be possible'.
Answers
Answer:
Atoms and Molecules
Ancient Indian and Greek philosophers have always wondered about the unknown and unseen form of matter. The idea of divisibility of matter was considered long back in India, around 500 BC. An Indian philosopher Maharishi Kanad, postulated that if we go on dividing matter (padarth), we shall get smaller and smaller particles. Ultimately, a time will come when we shall come across the smallest particles beyond which further division will not be possible. He named these particles Parmanu. Another Indian philosopher, Pakudha Katyayama, elaborated this doctrine and said that these particles normally exist in a combined form which gives us various forms of matter.
Around the same era, ancient Greek philosophers – Democritus and Leucippus suggested that if we go on dividing matter, a stage will come when particles obtained cannot be divided further. Democritus called these indivisible particles atoms (meaning indivisible). All this was based on philosophical considerations and not much experimental work to validate these ideas could be done till the eighteenth century.
By the end of the eighteenth century, scientists recognised the difference between elements and compounds and naturally became interested in finding out how and why elements combine and what happens when they combine.
Antoine L. Lavoisier laid the foundation of chemical sciences by establishing two important laws of chemical combination.
Laws of Chemical Combination
The following two laws of chemical combination were established after much experimentations by Lavoisier and Joseph L.Proust.
Law of Conservation of Mass
Is there a change in mass when a chemical change (chemical reaction) takes place?
Activity 1
• Take one of the following sets, X and Y of chemicals– X Y
copper sulphate sodium carbonate
barium chloride sodium sulphate
lead nitrate sodium chloride
• Prepare separately a 5% solution of any one pair of substances listed under X and Y in water.
• Take a little amount of solution of Y in a conical flask and some solution of X in an ignition tube.
• Hang the ignition tube in the flask carefully; see that the solutions do not get mixed. Put a cork on the flask (Fig. 1).
• Weigh the flask with its contents carefully.
• Now tilt and swirl the flask, so that the solutions X and Y get mixed.
• Weigh again.
What happens in the reaction flask? Do you think that a chemical reactionhas taken place? Why should we put a cork on the mouth of the flask? Does the mass of the flask and its contents change?
Law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction.