Olympiad Science - Changes around us
Exam Duration: 45 Mins Total Questions : 30
Why is the rusting of iron termed as a chemical change?
- (a)
It is a temporary change.
- (b)
It can be cleaned and the original substance can be recovered.
- (c)
It is a slow reaction.
- (d)
A new substance is formed.
Iron reacts chemically with the oxygen and water vapour present in the air and forms a new product.
Pasteurisation of milk is a
- (a)
physical and reversible change
- (b)
chemical and reversible change
- (c)
chemical and irreversible change
- (d)
neither physical nor chemical change
Pasteurisation of milk does not involve any considerable physical or chemical change. During this process, harmful bacteria are killed and a negligible % of constituents of milk undergo change.
What is the change taking place in the following processes?
- (a)
Irreversible, physical change
- (b)
Chemical change
- (c)
Reversible, physical change
- (d)
Reversible, chemical change
The change of ice into water and then into steam is a reversible and physical change.
Sheela cooked rice in a rice cooker. What kind of change took place?
(i) irreversible change
(ii) Endothermic change
(iii) Natural change
- (a)
Only (i) and (ii)
- (b)
Only (ii) and (iii)
- (c)
Only (i) and (iii)
- (d)
(i), (ij) and (iii)
The cooking of rice requires heat. Once the rice is cooked, we cannot get back the original raw rice. So, it is irreversible, endothermic change.
If we suspend a weight using a spring, it stretches.
What type of a change is this?
- (a)
Man-made
- (b)
Reversible
- (c)
Irreversible
- (d)
Both (A) and (B)
When weight is removed, the spring comes to its original shape. It is man-made and a reversible change.
Which of the following does NOT take place during the tearing of a paper?
- (a)
Change of shape
- (b)
Change of size
- (c)
Change of substance
- (d)
All of the above
The tearing of a paper shows a change in its shape and size but there is no change in the substance. Hence, it is a physical change.
What is a chemical reaction in which heat energy is liberated called?
- (a)
An exothermic reaction
- (b)
A physical change
- (c)
An endothermic reaction
- (d)
A photochemical reaction
A chemical reaction in which heat energy changes. is liberated is called an exothermic reaction.
Which of the following is a natural, nonperiodic change?
- (a)
The heart beat of a human being
- (b)
The low and high tides
- (c)
The eruption of volcanoes
- (d)
The sunrise and sunset
The eruption of volcanoes is a natural, nonwater periodic change
What is the process of heating a liquid to a high temperature and rapidly cooling it so that the bacteria is killed called?
- (a)
Pasteurization
- (b)
Chlorination
- (c)
Bacterial disinfection
- (d)
Sublimation
The process of heating a liquid to high temperature and rapidly cooling it inorder to kill bacteria is called pasteurization.
Identify the chemical change from the following.
- (a)
The melting of ice
- (b)
The heating of sugar crystals
- (c)
The freezing of water
- (d)
The dissolution of salt in water
Sugar crystals on heating form new substance caramel and water vapour. Hence, it is a chemical change.
Which of the following is a chemical change?
- (a)
The burning of magnesium wire
- (b)
The heating of an iron rod
- (c)
The heating of water
- (d)
The dissolving of salt in water
The burning of magnesium wire is a chemical change.
What kind of change is the making of a ring from pure gold?
- (a)
An irreversible, chemical change
- (b)
An irreversible, physical change
- (c)
A reversible, chemical change
- (d)
A reversible, physical change
The making of a gold ring is only a change in the shape of gold. i.e.a physical change. The ring can once again be melted to form pure gold.
When water with sugar is stirred with a spoon, sugar is dissolved faster. Why does this happen?
- (a)
The spoon acts as a catalyst.
- (b)
On stirring, the temperature increases.
- (c)
Stirring increases the rate of interaction.
- (d)
The attraction between the molecules of sugar increases.
Stirring helps to increase the interaction between sugar molecules and water molecules which causes sugar molecule in the solid to break from each other.
Identify the periodic change from the following.
- (a)
The growth of plants
- (b)
The occurrence of storms
- (c)
The occurrence of floods
- (d)
The revolution of the earth
The revolution of the earth is a periodic change.
Which of the following is NOT a physical change?
- (a)
The tearing of paper
- (b)
A magnet losing its magnetic property
- (c)
The rusting of iron
- (d)
An inflated balloon
A new substance is formed when iron rusts. It is a chemical change.
Which of the following statements is true of the changes when a mixture of iron powder and sulphur powder are heated?
- (a)
Iron and sulphur are called the reactants.
- (b)
Iron and sulphur form a solution.
- (c)
Iron and sulphur can be easily separated after the reaction.
- (d)
A new product is formed which has all the properties of iron and sulphur.
The substances iron and sulphur which react to produce a new product are called reactants.
Karuna wrapped some green gram pulses in a wet cotton cloth. She opened it after a couple of days and found small, white thread like structures on the seeds. What change did the pulses undergo?
- (a)
They have undergone a physical change.
- (b)
They became fresh as usual by washing and drying.
- (c)
They have undergone a chemical change.
- (d)
They have undergone a reversible, physical change.
In the presence of moisture and air, pulses germinate. Germination is a chemical change.
Identify a change that is NOT man-made and is irreversible.
- (a)
The burning of paper
- (b)
The stretching of a spring by a suspended weight
- (c)
Soil erosion due to floods
- (d)
The boiling of an egg
Soil erosion due to floods is not man-made. It is a natural and an irreversible change.
Which of these is NOT a physical change
- (a)
Sulphur dissolved in carbon disulphide
- (b)
Resin dissolved in alcohol
- (c)
The fermentation of cane juice
- (d)
The glowing of an electric bulb
Fermentation of cane juice is a chemical change.
Given below is a change that occurs in butter.
Identify X and Y that cause change in the state of butter.
- (a)
X - Heat lost, Y - Heat gained
- (b)
X - Heat gained, Y - Heat lost
- (c)
X - Release of energy, Y - Absorption of energy
- (d)
X - Decrease in temperature, Y - Increase in temperature
Butter changes its state when it gains or loses heat.
Which of the following changes is slow and periodic?
- (a)
The rotation of the earth
- (b)
The rusting of iron
- (c)
The curdling of milk
- (d)
The evaporation of petrol
The rotation of the earth takes 24 hrs.lt is a slow and periodic change.
If two substances interact to produce a change, they will do so
- (a)
under any condition.
- (b)
only if they are not in close contact with each other.
- (c)
under any temperature.
- (d)
under the right conditions.
Changes generally occur when two or more things interact with each other under the right conditions.
If we are able to reverse a change easily and get the substances back in their original form, then such a change is a
- (a)
reversible change.
- (b)
irreversible change.
- (c)
chemical change.
- (d)
no change
In reversible changes we get back the original things
A tray of water was kept in the freezer. The water changed into ice. What kind of change it is?
- (a)
irreversible.
- (b)
chemical change.
- (c)
reversible.
- (d)
no change.
Ice can be melted back into water.
If 'X' number of grams of sugar can get dissolved in 100 g of water, then 'X' is the
- (a)
solubility.
- (b)
solubility of sugar in water.
- (c)
solubility of a solute in water
- (d)
solubility of sugar in any solvent
Solubility is the number of grams of solute that can dissolve in 100 g of the solvent. In this case, solute is sugar and the solvent is water. They together form a sugar solution. The solubility measures the concentration of a saturated solution. A saturated solution is the one in which no more solute can be dissolved in the solution at the given temperature. Below this level the solution is unsaturated. Solubility of different solutes in different solvents or the same solvent will be different.
The solute can be______________.
- (a)
solid
- (b)
liquid
- (c)
gas
- (d)
Solid, liquid or gas
Most often we think of solute as solid but it can be solid (table salt), liquid (copper sulphate solution in water; fruit juice in water; milk in water) or gas (oxygen).
Which one of these is an irreversible change?
- (a)
growth and reproduction
- (b)
curdling of milk
- (c)
formation of cheese from milk
- (d)
all of these
We cannot obtain the original thing if we try to reverse the process.
Select the right match
Column A | Column B |
i) Heating of mixture of iron and sulphur | A) reversible |
ii) Melting of ice-cream | B) irreversible and chemical change |
iii) Cracking of hot glass in cold water | C) irreversible and physical change |
- (a)
i-C; ii-B; iii-A
- (b)
i-B; ii-A; iii-C
- (c)
i-A; ii-C; iii-B
- (d)
i-B; ii-C; iii-A
Heating of mixture of iron and sulphur leads to formation of black iron sulphide (new substance with different properties). Melted ice-cream can be frozen again by lowering the temperature. Hot glass cracks under cold water because the outer surface of the glass which is in direct contact with cold water contracts more than its inner surface (which is not in direct contact with cold water). But no new substance is formed here so the change is physical but irreversible.
Mixing of iron and sulphur is a
- (a)
physical and irreversible change
- (b)
chemical and reversible change
- (c)
chemical and irreversible change
- (d)
reversible change.
Mixing of iron and sulphur is a physical and reversible change because we can easily remove iron using a magnet. But when this mixture is heated a new substance iron sulphide is formed indicating a chemical change. The formation of iron sulphide is also an irreversible change.
Addition of more sugar will not lead to any dissolution of sugar in an already saturated solution. More water or heat will lead to dissolution of more sugar to the saturated solution as the concentration of the solution becomes lower.
- (a)
Baking of clay pot is an irreversible change.
- (b)
Making of clay pot is a reversible change.
- (c)
Both the changes require energy.
- (d)
All of these.
Energy is used in various forms. It can be a change in temperature or change in electric energy to mechanical energy.