Chapter 9: The Amazing World of Solutes, Solvents, and Solutions - Solutions

Question 1

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. False.
• (ii) A mixture of sand and water is a solution. False.
• (iii) The amount of space occupied by any object is called its mass. False.
• (iv) An unsaturated solution has more solute dissolved than a saturated solution. False.
• (v) The mixture of different gases in the atmosphere is also a solution. True.

Question 2

Fill in the blanks.

• (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 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.

Question 3

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

Answer: (ii) Water is denser than oil.

Question 4

A stone sculpture weighs 225 g and has a volume of 90 cm³. Calculate its density and predict whether it will float or sink in water.

Answer:

Mass of the stone sculpture = 225 g.

Volume of the stone sculpture = 90 cm³.

Density = Mass / Volume
Density = 225 g / 90 cm³ = 2.5 g/cm³

Also, the density of water is 1 g/cm³. Since 2.5 g/cm³ > 1 g/cm³, the stone sculpture will sink in water.

Question 5

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.

Answer: (iii) No more solute can be dissolved into the saturated solution at that temperature.

Reason: A saturated solution is one that contains the maximum amount of solute that can dissolve in a solvent at a given temperature. If any more solute is added, it will not dissolve and will settle at the bottom.

Question 6

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?

Answer:

Capacity of bottle = 2 L = 2000 ml
Volume of water poured = 500 ml
Remaining capacity = 2000 ml - 500 ml = 1500 ml

The bottle can hold 1500 ml more water.

Question 7

An object has a mass of 400 g and a volume of 40 cm³. What is its density?

Answer:

Density = Mass / Volume
Density = 400 g / 40 cm³ = 10 g/cm³

The density of the object is 10 g/cm³.

Question 8

Analyse Fig. 9.25a and 9.25b. Why does the unpeeled orange float, while the peeled one sinks? Explain.

[ Figure 9.25 (a) and (b): An unpeeled orange floating and a peeled orange sinking in water ]

Answer: The unpeeled orange floats because air pockets in its peel reduce overall density. The peeled one sinks as its density increases.

Question 9

Object A has a mass of 200 g and a volume of 40 cm³. Object B has a mass of 240 g and a volume of 60 cm³. Which object is denser?

Answer:

Object A:
Density = Mass / Volume = 200 g / 40 cm³ = 5 g/cm³

Object B:
Density = Mass / Volume = 240 g / 60 cm³ = 4 g/cm³

Object A is denser.

Question 10

Reema has a piece of modeling clay that weighs 120 g. She first moulds it into a compact cube that has a volume of 60 cm³. Later, she flattens it into a thin sheet. Predict what will happen to its density.

Answer:

Density = 120 g / 60 cm³ = 2 g/cm³

The density of the clay remains the same (2 g/cm³), even though its shape changes from a cube to a thin sheet.

Question 11

Observe Fig. 9.26 (a) and (b). Why does the water level in the glass tube rise when the test tube is placed in a beaker containing hot water?

[Figure 9.26 (a) and (b): Test tube with a glass tube placed in a beaker of hot water ]

Answer: When the test tube is placed in hot water, the air inside expands, its volume increases, and its density decreases. That is why the water level in the glass tube rises.