School | : | St. Thomas’s Day School |
Class | : | 8 |
Exam | : | Half Yearly |
Subject | : | Chemistry |
Date | : | 19 Sept 2023 |
Time | : | 2 hours |
Marks | : | 80 |
St. Thomas’s Day School
Class 8 | Unit 2 Examination
Section A
A. Choose the correct answer from the choices given: [10]
1. The change from a gaseous state to a liquid state is called:
- condensation
- evaporation
- sublimation
- fusion
2. The substance which does not sublime on heating is:
- iodine
- sodium chloride
- camphor
- ammonium chloride
3. The gaseous state of which substance is not called a vapour;
- water
- iodine
- carbon dioxide
- bromine
4. A mixture of sawdust and iron dust can be separated by:
- winnowing
- sedimentation
- filtration
- magnetisation
5. The chemical name for lime water is:
- calcium hydroxide
- calcium oxide
- calcium chloride
- calcium carbonate
6. A gas that turns lime water milky is:
- a.oxygen
- carbon dioxide
- nitrogen dioxide
- nitrogen
7. The pie-pudding model of an atom was given by:
- J.J.Thompson
- Mendeleev
- Rutherford
- Newton
8. Which of the following is not a subatomic particle:
- electron
- proton
- neutron
- nucleus
9. K₂Cr₂O₇ is the formula of the compound;
- potassium chromate
- potassium dichromate
- potassium chromium oxide
- potassium carbonate
10. Which of the following is not a chemical change?
- growing of a tree
- melting of wax
- photosynthesis
- respiration
B. Draw the structure of the following atoms mentioning the Number of electrons, protons and neutrons. [10]
- boron
- magnesium
- potassium
- chlorine
- neon
C. Complete the following table: [10]
Elements | At No | E. Conf | Nature | Valency |
Calcium | ||||
15 | ||||
2, 8, 8 | ||||
Oxygen | ||||
2 |
D. Name the method used to separate the following mixtures: [10]
- sugar and sand
- petrol and water
- salt and water
- mud from muddy water
- dyes in ink
- sugar and salt
- husk from grains
- pebbles from cereals
- alcohol and water
- Sand and water
Section B
Answer Any 4 Questions
Question 1
- Write four postulates of Dalton’s atomic theory.
- Write the three observations and three conclusions of Rutherford’s alpha ray scattering experiment.
[4 + 6]
Question 2
- Write any three postulates of Bohr’s Atomic Theory.
- What is the significance of the 2n² formula?
- Define isotopes and isobars with one example each.
- What is radiocarbon dating?
[3+2+4+1]
Question 3
(a) Fill in the blanks:
- ____ is considered as a Universal solvent.
- The freezing point of pure water is _____.
- Water shows abnormal behaviour between _____ degrees Celsius.
- ____ water bodies cover the percent of the earth.
- On adding salt to the water, its boiling point ____.
(b) Define the atomic number and mass number of an atom.
(c) State three differences between an atom and an ion.
[5+2+3]
Question 4
(a) Three beakers contain three types of solution at 25°C. Identify them.
- Beaker A – Can dissolve more solute at that temperature.
- Beaker B – Cannot dissolve any more solute at that temperature.
- Beaker C- Holds more solute than that present in beaker B at that very temperature.
(b) How does the solubility of a gas depend on temperature and pressure?
(c) What are homogenous and Heterogenous mixtures? Give examples.
(d) Is water a mixture or a compound? Give two points in support of your answer.
[3+2+3+2]
Question 5
- Write four differences between metals and non-metals.
- What is soft water and hard water?
- What causes temporary and permanent hardness in water?
- How can you remove temporary hardness from water? Write a chemical equation.
[4+2+2+2]
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