Atoms and Molecules — Science STD 9 — Question

A student placed a gas jar containing air in the upside down position over a gas jar full of red-brown bromine vapours. He observed that the red brown colour spread upwards into the jar containing air. Based on this observation, the student concluded that it is only the bromine vapour which moves up and diffuses into air in the upper jar, the air from the upper jar does not move down by diffusion into the lower jar containing bromine vapours. Do you agree with this conclusion of the student? Give reason for your answer.

The solubility of ammonium chloride in water at various temperatures is given below:

Temperature:	10°C	20°C	40°C	60°C	80°C
Solubility:	24g	37g	41g	55g	66g

What mass of ammonium chloride whould be needed to make a saturated solution of ammonium chloride in fifty grams of water at 40°C?

What is the fraction of the mass of water due to neutrons?

What are the three groups into which all the elements can be divided? Name two elements belonging to each group.

A 0.24g sample of compound of oxygen and boron was found by analysis to contain 0.096g of boron and 0.144g of oxygen. Calculate the percentage composition of the compound by weight.

What do you understand by the tern "electronic configuration" of an element? Write down the electronic configuration of oxygen (At. No. = 8).

The composition of two atomic particles is given below:

	X	Y
Protons	8	8
Neutrons	8	9
Electrons	8	8

1. What is the mass number of X?
2. What is the mass number of Y?
3. What is the relation between X and Y?
4. Which element/ elements do they represent?

Define a compound. Give two points of evidence to show that sodium chloride is a compound.

Why direct heating of ink is avoided, during separation of ink?

Define gram molecular mass of a substance. How much is the gram molecular mass of oxygen?