(i) All questions are compulsory.
(ii) Questions 1 to 12 are very short answer type questions. These questions carry one mark each.
(iii) Questions 13 to 20 are short answer type questions. These questions carry two marks each.
(iv) Questions 21 to 24 are also short answer type questions. These questions carry three marks each.
(v) Questions 25 to 26 are long answer type questions and carry five marks each.
Question 1 ( 1.0 marks)
Convert 100°C into Kelvin scale.
Solution:
100°C
= 100 + 273 K
= 373 K
Question 2 ( 1.0 marks)
Define sublimation.
Solution:
Sublimation is the change of the gaseous state directly into the solid state, without going through the liquid state, and vice versa.
Question 3 ( 1.0 marks)
Name a solid solution.
Solution:
Alloy
Question 4 ( 1.0 marks)
What are colloids?
Solution:
Colloids are heterogeneous mixtures in which the particle size is too small to be visible to the naked eye, but big enough to scatter light.
Question 5 ( 1.0 marks)
What is meant by the concentration of a solution?
Solution:
The concentration of a solution is the amount of solute present in a given amount (mass or volume) of the solution.
Question 6 ( 1.0 marks)
Calculate the molecular mass of ammonia.
Solution:
Molecular Mass of NH3
= Atomic mass of nitrogen + 3 × Atomic mass of hydrogen
= 14 + 3 × 1
= 17 u
Question 7 ( 1.0 marks)
How is the chemical formula of a molecular compound determined?
Solution:
The chemical formula of a molecular compound is determined by the valency of each constituent element.
Question 8 ( 1.0 marks)
Write the formula of sodium carbonate.
Solution:
Question 9 ( 1.0 marks)
What are polyatomic ions?
Solution:
A polyatomic ion is a cluster of atoms acting as an ion.
Question 10 ( 1.0 marks)
Calculate the number of moles for 16 g of He.
Solution:
Number of moles =
= 4
Question 11 ( 1.0 marks)
Fill in the blank.
A ____________ has no charge. Its mass is nearly equal to that of a proton.
Solution:
A neutron has no charge. Its mass is nearly equal to that of a proton.
Question 12 ( 1.0 marks)
Complete the oxygen cycle.
Solution:
Question 13 ( 2.0 marks)
Is inter-conversion between the three states of matter possible? How?
Solution:
Yes, the three states of matter, i.e., solid, liquid and gas, can be inter-converted.
Temperature and pressure determine the state of a substance. On heating, the molecules of matter vibrate faster. When heated, the solid state changes into the liquid state, which on further heating, changes into the gaseous state. When cooled, the gaseous state condenses into the liquid state, which on further cooling, condenses into the solid state.
Question 14 ( 2.0 marks)
It is observed that water boils at lower temperature at higher altitudes. Why?
Solution:
Atmospheric pressure is much less at higher altitudes. So, less thermal energy is required to get the vapour pressure equal to the atmospheric pressure. Hence, water boils at lower temperature at higher altitudes.
Question 15 ( 2.0 marks)
Calculate the mass of:
(i) 5 moles of H2 gas
(ii) 5 moles of H atom
Solution:
(i) Molar mass of H2 = 2
Mass = Molar mass × Number of moles
m = M × n
= 2 + 5
= 10 g
(ii) Molar mass of H = 1
Mass = Molar mass × Number of moles
m = M × n
= 1 + 5
= 5 g
Question 16 ( 2.0 marks)
Explain the two important laws of chemical combination.
Solution:
Laws of chemical combination:
Law of conservation of mass − During a chemical reaction, the sum of the masses of the reactants is the same as the sum of the masses of the products.
Law of definite proportions − In a pure chemical compound, each element is always present in a definite proportion by mass.
Question 17 ( 2.0 marks)
Calculate the number of particles in:
(i) 69 g of Na atom
(ii) 28 g of N2 molecules
Solution:
(i) Molar mass of Na = 23 g
∴Number of atoms
 
(ii) Molar mass of N2 = 14 × 2 = 28 g
∴ Number of atoms
Question 18 ( 2.0 marks)
Answer the following questions.
(i) Write the electronic configuration of neon.
(ii) If Z = 14, find the number of valence electrons.
Solution:
(i) Electronic configuration of Ne = 2, 8
(ii) Z = 14
Electronic configuration = 2, 8, 4
∴Valency = 4
Question 19 ( 2.0 marks)
What are isotopes? Name the three isotopes of hydrogen.
Solution:
Isotopes are defined as the atoms of the same element, having the same atomic number, but different mass numbers.
The three isotopes of hydrogen are −
(i) Protium
(ii) Deuterium
(iii) Tritium
Question 20 ( 2.0 marks)
What are the main factors on which the life on earth depends?
Solution:
The life on earth depends on resources such as soil, water, air and solar energy.
Question 21 ( 3.0 marks)
Answer the following questions.
(i) What is cohesive force?
(ii) What are the various factors affecting evaporation?
(iii) Write two characteristics of matter.
Solution:
(i) The force present between the particles of matter is called cohesive force.
(ii) The various factors affecting evaporation are surface area, temperature, wind speed and humidity.
(iii) Matter has a definite mass and it occupies space.
Question 22 ( 3.0 marks)
Define mixture. Name the different types of mixture. How will you separate a mixture of sodium chloride and water?
Solution:
Mixtures are composed of more than one kind of pure form of matter.
Mixture can be of two types.
(i) Homogeneous mixture
(ii) Heterogeneous mixture
A mixture of sodium chloride and water can be separated by the physical process of evaporation.
Question 23 ( 3.0 marks)
Write the important features of Rutherford’s experiment.
Solution:
Features of Rutherford’s experiment:
(i) A positively charged centre exists in an atom. This centre is called the nucleus. Nearly all the mass of the atom resides in the nucleus.
(ii) The electrons revolve in well-defined orbits around the nucleus.
(iii) The size of the nucleus is very small as compared to the size of the atom.
Question 24 ( 3.0 marks)
Answer the following questions.
(i) What role does the atmosphere play in climate control?
(ii) Explain the factors affecting the movement of air.
Solution:
(i) Air is a bad conductor of heat. The atmosphere keeps the average temperature of the earth fairly steady during a day, and even during the course of an entire year. The atmosphere prevents the sudden increase in temperature during daytime, and during night time, it slows down the escape of heat into outer space.
(ii) The movement of air results in diverse atmospheric phenomena. It is affected by the uneven heating of the atmosphere in different regions of the earth, which in turn is due to the heating of air and the formation of water vapour. The rotation of the earth and the presence of mountains in the paths of wind also affect the movement of air.
Question 25 ( 5.0 marks)
Answer the following questions.
(a) How can you separate:
(i) Different colours in a dye
(ii) A mixture of salt and ammonium chloride
(iii) Cream from milk
(b) What kind of a mixture is air, and how can it be separated?
Solution:
(a)
(i) The different colours in a dye can be separated by chromatography.
(ii) A mixture of salt and ammonium chloride can be separated by sublimation.
(iii) Cream can be separated from milk by centrifugation.
(b) Air is a homogeneous mixture. It can be separated into its components by fractional distillation. In this process, air is first compressed by increasing its pressure. It is then cooled by decreasing its temperature so as to get liquid air. This liquid air is allowed to warm slowly in a fractional distillation column. The gases then get separated at different heights, depending upon their boiling points.
Question 26 ( 5.0 marks)
Answer the following questions.
(i) Mention the importance of the sun in the formation of soil.
(ii) What is humus?
(iii) Write two methods by which carbon dioxide is added to the atmosphere.
Solution:
(i) During the day, the sun heats up rocks, thereby making them expand. At night, these rocks cool down and contract. However, all parts of a rock do not expand and contract at the same rate. This leads to the formation of cracks, which finally leads to the breaking up of big rocks into smaller pieces.
(ii) Soil is a mixture. It contains organic matter such as bits of decayed living organisms. This organic matter is called humus.
(iii) Carbon dioxide is released into the atmosphere by animals during the process of respiration. It is also released during volcanic eruptions.
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