The most remarkable feature of Dalton's atomic theory was that of atomic mass.Since determining atomic mass of an individual atom was a difficult task, the relative atomic, masses were determined using the laws of chemical combinations and the compounds formed.In 1961, carbon-12 isotope was chosen as the standard reference for measuring atomic masses.It says that one atomic mass unit is a mass unit equal to exactly 1/12th the mass of one atom of carbon-12 Since experimentally t was observed that 3g cabon-12 combines with 4g of oxygen to form CO, further 4g sulphur combines with 4g oxygen to form SO₂
(a) Calculate the atomic mass of sulphur.
(b) How was the concept of relative masses utilized in olden times?Was it successful?

Lavosier along with other scientists observed that many compounds were formed from two or more elements.All these compounds had the same elements in the same proportions, irrespective of the source of compound.For example, in a compound such as water, the ratio of mass of hydrogen to the mass of oxygen is 1:8 whether water is taken from sea, well or rain.Similarly in ammonia, nitrogen and hydrogen are always present in the ratio 14:3 by mass whatever the method or source from which it is obtained.
(a) What name was given to this behaviour of chemical compounds?How is it formulated?
(b) Does such properties of a compound relate to human behaviour?

(i) Convert into mole 20 g of water (Atomic mass of hydrogen and oxygen are 1 and 16 respectively).
(ii) Convert into mole 22 g of carbon dioxide.

In what ways air can be considered as matter?

Sodium salt and sugar have similar appearance.Why are these classified as different substances?

What is matter?

(a) Convert 359 K to Celsius scale
(b) What is the value of boiling point of water on Kelvin scale of temperature?

5 mL of water was taken in a test tube and china dish separately.These samples then kept under different conditions as below:
(a) Both the samples are kept under a fan
(b) Both the samples are kept inside a cupboard.
state in which case evaporation will be faster?Give reason to support your answer.
How will the rate of evaporation change if above activity is carried out on a rainy date.Justify your answer.

Ghee freezes at room temperature but mustard oil does not(in winter).Which of these has a higher point and lower intermolecular forces?

Give reasons:
(a) Naphthalene balls disappear with time without leaving any solid.
(b) A gas exerts pressure on the walls of the container.

Isotopes differ from each other in ............

Molar mass of 2 moles of NH₃ is ..............

A group of ....... atoms, molecules or ions is called one mole.

___________ is the change of liquid state to solid state.

A material in liquid state can have any ___________

Why is ice at 273 K more effective in cooling than water at the same temperature?

(a) What temperature in Kelvin scale is equal to \(50°C\)?
(b) Describe an activity to show that rate of evaporation increases with surface area.
(c) State two differences between evaporation and boiling.

Since early times human beings have been trying to understand their surroundings. As we look our surroundings we have a larger variety of things with different shapes, sizes and textures. Everything in this universe includes the air we breathe, the food we eat or store, clouds, stars, plants, elements, even a drop of water or a particle of water or a particle of sand. We can also see as we look around us that all the things mentioned are either visible or invisible.
(a) What do you call all these materials in one word?
(b) Write at least two characteristics that you can draw from above observation.
(c) In how many forms these materials are available to us?
(d) Can you consider smell or love as materials?
(e) What social consideration can draw from above findings?