The Amazing World of Solutes, Solvents, and SolutionsClass 8 Science NCERT Solutions
12 Solutions
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Solution 1 of 12
Q1Keep the curiosity alive
State whether the statements given below are True [T] or False [F]. Correct the false statement(s).
(i)
Oxygen gas is more soluble in hot water rather than in cold water.
(ii)
A mixture of sand and water is a solution.
(iii)
The amount of space occupied by any object is called its mass.
(iv)
An unsaturated solution has more solute dissolved than a saturated solution.
(v)
The mixture of different gases in the atmosphere is also a solution.
Solution
(i) False
Reason: The solubility of gases in liquids, such as oxygen in water, generally decreases as the temperature increases. Therefore, oxygen gas is more soluble in cold water than in hot water.
(ii) False
Reason: A mixture of sand and water is a non-uniform mixture (a suspension), not a solution. In a solution, the components are evenly distributed, but sand settles at the bottom of the water.
(iii) False
Reason: The amount of space occupied by any object is called its volume. Mass is the quantity of matter present in the object.
(iv) False
Reason: A saturated solution contains the maximum amount of solute that can be dissolved at a given temperature. An unsaturated solution contains less solute than a saturated solution and can dissolve more solute.
(v) True
Reason: Air is a uniform mixture of gases. Such a mixture is considered a gaseous solution, where nitrogen is the solvent and other gases like oxygen, argon, and carbon dioxide are solutes.
Q2Keep the curiosity alive
Fill in the blanks.
(i)
The volume of a solid can be measured by the method of displacement, where the solid is ______ in water and the ______ in water level is measured.
(ii)
The maximum amount of ______ dissolved in ______ at a particular temperature is called solubility at that temperature.
(iii)
Generally, the density ______ with increase in temperature.
(iv)
The solution in which glucose has completely dissolved in water, and no more glucose can dissolve at a given temperature, is called a ______ solution of glucose.
Solution
(i) The volume of a solid can be measured by the method of displacement, where the solid is immersed in water and the rise in water level is measured.
(ii) The maximum amount of solute dissolved in a fixed quantity of a solvent at a particular temperature is called solubility at that temperature.
(iii) Generally, the density decreases with increase in temperature.
(iv) The solution in which glucose has completely dissolved in water, and no more glucose can dissolve at a given temperature, is called a saturated solution of glucose.
Q3Keep the curiosity alive
You pour oil into a glass containing some water. The oil floats on top. What does this tell you?
(i)
Oil is denser than water
(ii)
Water is denser than oil
(iii)
Oil and water have the same density
(iv)
Oil dissolves in water
Solution
Answer: (ii) Water is denser than oil
Explanation:
When two immiscible liquids are mixed, the liquid with the lower density floats on top of the liquid with the higher density. Since oil floats on water, it means that oil is less dense than water, or conversely, water is denser than oil.
Q4Keep the curiosity alive
A stone sculpture weighs 225 g and has a volume of . Calculate its density and predict whether it will float or sink in water.
Solution
Given:
Mass of the stone sculpture,
Volume of the stone sculpture,
To Find:
- The density of the stone sculpture.
- Whether the sculpture will float or sink in water.
Formula:
Solution:
-
Calculating the density:
-
Predicting float or sink: The density of water is approximately . An object with a density greater than water will sink, while an object with a density less than water will float. The density of the sculpture () is greater than the density of water (). Therefore, the stone sculpture will sink in water.
Final Answer:
The density of the stone sculpture is . It will sink in water.
Q5Keep the curiosity alive
Which one of the following is the most appropriate statement, and why are the other statements not appropriate?
(i)
A saturated solution can still dissolve more solute at a given temperature.
(ii)
An unsaturated solution has dissolved the maximum amount of solute possible at a given temperature.
(iii)
No more solute can be dissolved into the saturated solution at that temperature.
(iv)
A saturated solution forms only at high temperatures.
Solution
Answer: (iii) No more solute can be dissolved into the saturated solution at that temperature.
Explanation:
-
Statement (iii) is correct because it accurately defines a saturated solution: a solution in which the maximum possible amount of solute has been dissolved in the solvent at a specific temperature. Any additional solute will not dissolve.
-
Statement (i) is not appropriate because it contradicts the definition of a saturated solution. If a solution can dissolve more solute, it is unsaturated.
-
Statement (ii) is not appropriate because it describes a saturated solution, not an unsaturated one. An unsaturated solution can still dissolve more solute.
-
Statement (iv) is not appropriate because a saturated solution can be formed at any temperature. The amount of solute required to achieve saturation depends on the temperature, but saturation itself is not limited to high temperatures.
Q6Keep the curiosity alive
You have a bottle with a volume of 2 litres. You pour 500 mL of water into it. How much more water can the bottle hold?
Solution
Given:
Total volume of the bottle =
Volume of water poured into the bottle =
To Find:
How much more water the bottle can hold.
Conversion:
First, convert the total volume of the bottle to millilitres (mL) for consistency.
We know that .
So, .
Solution:
To find the remaining capacity, subtract the volume of water already in the bottle from the total volume.
This can also be expressed in litres: .
Final Answer: The bottle can hold (or ) more water.
Q7Keep the curiosity alive
An object has a mass of 400 g and a volume of . What is its density?
Solution
Given:
Mass of the object,
Volume of the object,
To Find:
The density of the object.
Formula:
Solution:
Final Answer: The density of the object is .
Q8Keep the curiosity alive
An unpeeled orange floats in water, while the same orange with its peel removed sinks. Explain this observation.
Solution
Observation: An unpeeled orange floats, but a peeled orange sinks.
Explanation:
This phenomenon is explained by the concept of average density.
-
Unpeeled Orange (Floats): The peel of an orange is porous and contains many tiny pockets of air. These air pockets significantly increase the total volume of the orange without adding much mass. The average density of an object is its total mass divided by its total volume. Because of the large volume contributed by the air-filled peel, the average density of the unpeeled orange becomes less than the density of water (approximately ). Objects with a density less than water will float.
-
Peeled Orange (Sinks): When the peel is removed, the orange loses the extra volume provided by the air pockets. The remaining part of the orange (the pulp and juice) is denser than water. Without the buoyant effect of the peel, the average density of the peeled orange is now greater than the density of water, causing it to sink.
In summary, the peel acts like a life jacket for the orange, making its overall density low enough to float.
Q9Keep the curiosity alive
Object A has a mass of 200 g and a volume of . Object B has a mass of 240 g and a volume of . Which object is denser?
Solution
Given:
For Object A:
Mass,
Volume,
For Object B:
Mass,
Volume,
To Find:
Which object is denser.
Formula:
Solution:
First, calculate the density of each object.
Density of Object A:
Density of Object B:
Now, compare the densities:
Density of Object A () > Density of Object B ().
Final Answer: Object A is denser than Object B.
Q10Keep the curiosity alive
Reema has a piece of modeling clay that weighs 120 g. She first moulds it into a compact cube that has a volume of . Later, she flattens it into a thin sheet. Predict what will happen to its density.
Solution
Given:
Mass of the modeling clay,
Volume of the modeling clay,
To Predict:
What will happen to the density of the clay when its shape is changed from a cube to a thin sheet.
Reasoning:
Density is an intrinsic property of a substance, defined as mass per unit volume ().
- Mass: When Reema changes the shape of the clay, she is not adding or removing any material. Therefore, the mass of the clay remains constant at .
- Volume: Modeling clay is largely incompressible. Changing its shape from a cube to a sheet rearranges the material but does not change the total space it occupies. Therefore, its volume also remains constant at .
Since both the mass and the volume of the clay do not change, its density will also remain unchanged.
Calculation (for confirmation):
Initial density (cube) =
Final density (sheet) =
Final Answer: The density of the modeling clay will remain the same. Changing the shape of an object does not change its density, as long as its mass and volume are constant.
Q11Keep the curiosity alive
A block of iron has a mass of 600 g and a density of . What is its volume?
Solution
Given:
Mass of the iron block,
Density of iron,
To Find:
The volume of the iron block.
Formula:
Density is defined as Mass / Volume. We can rearrange this formula to solve for Volume:
Solution:
Rounding to one decimal place, the volume is .
Final Answer: The volume of the iron block is approximately .
Q12Keep the curiosity alive
A test tube is filled with a liquid and sealed with a stopper that has a narrow glass tube inserted through it. The liquid rises to a certain level in the narrow tube. When this apparatus is placed in hot water (), the liquid level in the narrow tube rises further. How does this heating affect the density of the liquid?
Solution
Observation:
When the liquid in the test tube is heated, its level rises in the narrow glass tube.
Explanation:
- Effect on Volume: The rise in the liquid level indicates that the liquid has expanded upon heating. This means its volume has increased.
- Effect on Mass: Heating the liquid does not add or remove any matter from it. Therefore, the mass of the liquid remains constant.
- Effect on Density: Density is calculated as the ratio of mass to volume ().
- The mass () is constant.
- The volume () has increased.
When the denominator (volume) of a fraction increases while the numerator (mass) stays the same, the value of the fraction decreases. Therefore, the density of the liquid decreases when it is heated.
Final Answer: Heating the liquid causes it to expand, which increases its volume while its mass remains unchanged. This results in a decrease in the density of the liquid.