Question 1. A student dissolves sugar completely in water. Which term correctly identifies the two components?
A. Sugar – solvent; water – solute
B. Sugar – solute; water – solvent
C. Sugar – solution; water – solute
D. Sugar – solvent; water – solution
Answer: B. Sugar – solute; water – solvent
Question 2. When a substance dissolves uniformly throughout a solvent, the resulting homogeneous mixture is called:
A. Suspension
B. Colloid
C. Solution
D. Compound
Answer: C. Solution
Question 3. A solution is described as saturated at a particular temperature. What does this indicate?
A. No solvent is present in the solution
B. The solution contains no dissolved solute
C. The solvent cannot dissolve any additional solute at that temperature
D. The solution must contain equal amounts of solute and solvent
Answer: C. The solvent cannot dissolve any additional solute at that temperature
Question 4. A student heats water and observes that more sugar can be dissolved in it. What does this observation indicate?
A. The solubility of sugar decreases with temperature
B. The solubility of sugar generally increases with temperature
C. Sugar changes into a solvent
D. Water loses its ability to dissolve substances
Answer: B. The solubility of sugar generally increases with temperature
Question 5. Which statement correctly describes the effect of temperature on the solubility of gases in liquids?
A. Gas solubility generally increases as temperature rises
B. Gas solubility generally decreases as temperature rises
C. Gas solubility remains completely unaffected by temperature
D. Gas solubility becomes zero at room temperature
Answer: B. Gas solubility generally decreases as temperature rises
Question 6. Fish in a pond may be affected when the water temperature becomes unusually high. What is the most appropriate explanation based on the transcript?
A. Warm water contains more dissolved oxygen
B. Oxygen becomes a liquid at higher temperature
C. The solubility of oxygen in water decreases, reducing the available dissolved oxygen
D. Fish stop requiring oxygen at higher temperatures
Answer: C. The solubility of oxygen in water decreases, reducing the available dissolved oxygen
Question 7. Ice floats on liquid water mainly because:
A. Ice has a greater density than water
B. Ice has a lower density than liquid water
C. Ice contains no water particles
D. Water becomes heavier when it freezes
Answer: B. Ice has a lower density than liquid water
Question 8. Water has its maximum density at approximately:
A. $0^\circ$C
B. $2^\circ$C
C. $4^\circ$C
D. $10^\circ$C
Answer: C. $4^\circ$C
Question 9. Density of a substance is mathematically expressed as:
A. $\rho = \frac{V}{m}$
B. $\rho = mV$
C. $\rho = \frac{m}{V}$
D. $\rho = m \times V$
Answer: C. $\rho = \frac{m}{V}$
Question 10. A stone has a mass of 10 g and displaces 4 mL of water when completely immersed. What is its density?
A. $0.4$ g/mL
B. $2.0$ g/mL
C. $2.5$ g/mL
D. $4.0$ g/mL
Answer: C. $2.5$ g/mL
Question 11. A piece of material has a density lower than that of the liquid in which it is placed. What will most likely happen?
A. It will sink
B. It will float
C. It will evaporate
D. It will dissolve immediately
Answer: B. It will float
Question 12. A liquid is heated while its mass remains unchanged. Its particles move farther apart and its volume increases. What happens to its density?
A. It increases
B. It decreases
C. It remains unchanged
D. It first becomes zero and then increases
Answer: B. It decreases
Question 13. A cube of metal has a side length of 4 cm and a mass of 128 g. What is its density?
A. $1$ g/cm³
B. $2$ g/cm³
C. $4$ g/cm³
D. $8$ g/cm³
Answer: B. $2$ g/cm³
Question 14. A substance has a mass of 80 g and occupies 40 cm³. What is its density?
A. $0.5$ g/cm³
B. $1$ g/cm³
C. $2$ g/cm³
D. $3$ g/cm³
Answer: C. $2$ g/cm³
Question 15. Why is water commonly described as a good or universal solvent?
A. It can dissolve every substance known to us
B. It can dissolve many different types of solutes
C. It has the highest density of all liquids
D. It cannot form saturated solutions
Answer: B. It can dissolve many different types of solutes
Question 1. Define the following terms
Solute
Solvent
Solution
Answer:
Solute: The substance that dissolves in a solvent.
Solvent: The substance in which the solute dissolves. It is generally present in the larger amount.
Solution: A homogeneous mixture formed when a solute dissolves uniformly in a solvent.
Question 2. Differentiate between saturated and unsaturated solutions
A student keeps adding sugar to water at a fixed temperature. After some time, additional sugar no longer dissolves and remains at the bottom. What type of solution has been formed? How is it different from an unsaturated solution?
Answer:
A saturated solution contains the maximum amount of solute that can dissolve at a given temperature. Any additional solute remains undissolved.
An unsaturated solution can still dissolve more solute at the same temperature.
Question 3. Give an example of a gas dissolved in a liquid
Give one example in which a gas is dissolved in a liquid. Identify the solute and solvent.
Answer:
Soda water is an example.
Solute: Carbon dioxide gas ($CO_2$)
Solvent: Water
Carbon dioxide is dissolved in water under pressure.
Question 4. How does temperature affect the density of a liquid?
What happens to the density of a liquid when it is heated? Explain using the relationship between mass, volume and density.
Answer:
Density is given by:
$$\rho = \frac{m}{V}$$
When a liquid is heated, its particles move farther apart and its volume generally increases. If its mass remains constant, the density decreases.
On cooling, the particles come closer, the volume decreases and the density generally increases.
Question 5. A wooden block sinks in one liquid but floats in another
A wooden block sinks when placed in liquid A but floats when placed in liquid B. What can you conclude about the densities of liquids A and B compared with the density of the wooden block?
Answer:
When the block sinks in liquid A:
$$\rho_{\text{block}} > \rho_A$$
When it floats in liquid B:
$$\rho_{\text{block}} < \rho_B$$
Therefore,
$$\rho_B > \rho_{\text{block}} > \rho_A$$
Hence, liquid B is denser than liquid A.
Question 6. Why does a carbonated drink lose its fizz?
A carbonated drink is left open and gradually becomes warm. Explain why its fizz decreases.
Answer:
Carbonated drinks contain dissolved carbon dioxide. As temperature increases, the solubility of a gas in a liquid decreases. Therefore, dissolved $CO_2$ escapes from the liquid, causing the drink to lose its fizz.
Question 7. Numerical: Will the metal piece float or sink?
A metal piece has a mass of $200$ g and a volume of $40$ cm³. The density of water is $1$ g/cm³. Determine whether the metal piece will float or sink.
Answer:
Density of the metal:
$$\rho = \frac{m}{V}$$
$$\rho = \frac{200}{40}=5\text{ g/cm}^3$$
Since
$$5 > 1$$
the density of the metal is greater than that of water.
Therefore, the metal piece will sink.
Question 8. Why is water called a universal solvent?
Water is often referred to as a universal solvent. Why is this description used, and what limitation does water have?
Answer:
Water is called a universal solvent because it can dissolve a large variety of substances.
However, it cannot dissolve every substance. For example, substances such as oil do not dissolve in water. Also, even for soluble substances, water can dissolve only a limited amount at a particular temperature.
Question 9. Design an experiment to study the effect of temperature on solubility
Design a simple experiment to investigate how temperature affects the solubility of a solid in a liquid. Include:
Materials required
Procedure
Observation
Conclusion
Answer:
Materials: Water, baking soda, beaker, measuring cylinder, thermometer, stirring rod and heater.
Procedure:
1. Measure a fixed volume of water and place it in a beaker.
2. Add baking soda gradually while stirring.
3. Continue adding it until some solid remains undissolved, indicating saturation.
4. Record the temperature and amount of dissolved solute.
5. Heat the solution gradually.
6. Add more baking soda and record the amount that dissolves at the higher temperature.
Observation: More baking soda dissolves when the temperature is increased.
Conclusion: The solubility of the solid in the liquid increases with temperature.
Question 10. How does adding solute affect the density of a solution?
A large quantity of solute is dissolved in a fixed volume of solvent. Assume that the volume does not change significantly during mixing. What happens to the density of the resulting solution?
Answer:
Density is:
$$\rho = \frac{m}{V}$$
Since the volume remains constant while the addition of solute increases the mass:
$$m \uparrow \quad \Rightarrow \quad \rho \uparrow$$
Therefore, the density of the solution increases.
Question 11. Why does more salt dissolve at a higher temperature?
At $20^\circ$C, a certain amount of water can dissolve $12$ g of salt. When the water is heated to $60^\circ$C, up to $20$ g of salt can dissolve. Explain this observation.
Answer:
The observation shows that the solubility of the solid salt in water increases with temperature.
At $20^\circ$C, the solution becomes saturated after dissolving $12$ g. On increasing the temperature, its capacity to dissolve salt increases, allowing additional salt to dissolve.
Question 12. Why does hot air rise above cold air?
Explain why heated air tends to rise above colder surrounding air using the concept of density.
Answer:
When air is heated, its particles move farther apart. As a result, its volume increases while its mass remains essentially unchanged.
Since
$$\rho = \frac{m}{V}$$
an increase in volume causes the density of the hot air to decrease. Thus, hot air becomes less dense than the surrounding cold air and rises.
Question 13. Two liquids contain a floating and sinking wooden block
A wooden block floats in liquid A but sinks in liquid B. Without directly measuring the densities, determine which liquid is denser.
Answer:
The block floats in liquid A, so:
$$\rho_A > \rho_{\text{block}}$$
The block sinks in liquid B, so:
$$\rho_B < \rho_{\text{block}}$$
Therefore:
$$\boxed{\rho_A > \rho_B}$$
Hence, liquid A is denser than liquid B.
Question 14.
A student takes two identical glasses containing equal volumes of water. He adds the same amount of salt to both glasses. One glass contains water at $20^\circ$C, while the other contains water at $60^\circ$C. He observes that more salt dissolves in the hot water.
Questions:
1. Which property of the salt-water system is being demonstrated?
2. Why can more salt dissolve in the hot water?
3. If the solution at $20^\circ$C is already saturated, what is likely to happen to its ability to dissolve more salt when it is heated?
Answer:
1. The experiment demonstrates the effect of temperature on the solubility of a solid in a liquid.
2. The solubility of many solids in liquids increases with increase in temperature. Hence, more salt can dissolve at the higher temperature.
3. Its solubility increases on heating, so the previously saturated solution can dissolve additional salt and becomes unsaturated with respect to the new temperature.
Question 15. The disappearing fizz
Riya opens a bottle of a carbonated drink and leaves it on a table for several hours. The drink becomes warm and gradually loses its fizz.
Questions:
1. Which gas is mainly responsible for the fizz?
2. What happens to the solubility of this gas when the temperature of the drink increases?
3. Explain why keeping the bottle open makes the loss of fizz faster.
Answer:
1. The gas is carbon dioxide ($CO_2$).
2. The solubility of a gas in a liquid decreases when temperature increases.
3. As the drink becomes warm, dissolved $CO_2$ becomes less soluble and escapes from the liquid. Keeping the bottle open allows the gas to leave the drink continuously, so the fizz is lost.
Question 16. The mysterious liquids
A wooden block is placed separately in two liquids, A and B. It floats in A but sinks in B. The student does not measure the densities of the liquids.
Questions:
1. Which liquid has greater density?
2. Compare the density of the wooden block with the densities of A and B.
3. Arrange the densities in increasing order.
Answer:
1. Liquid A is denser than liquid B.
2. Since the block floats in A:
$$\rho_A > \rho_{\text{block}}$$
Since it sinks in B:
$$\rho_B < \rho_{\text{block}}$$
3. Therefore, the order is:
$$\boxed{\rho_B < \rho_{\text{block}} < \rho_A}$$
The question tests whether students can use the condition for floating and sinking to compare densities rather than merely calculate density.
Question 17. A solution becomes denser
A student has $100$ mL of water in a container. He gradually dissolves a large quantity of salt in it. For this question, assume that the volume remains unchanged.
Questions:
1. What happens to the mass of the solution?
2. What happens to its density?
3. Explain your Answer using the equation for density.
4. Would the solution be denser or less dense than the original water?
Answer:
1. The mass increases because salt is being added.
2. The density increases.
3. Density is given by:
$$\rho = \frac{m}{V}$$
Since the volume is constant and mass increases:
$$m\uparrow,\quad V=\text{constant}$$
Therefore:
$$\rho\uparrow$$
4. The resulting salt solution is denser than the original water.
---
Question 18. A metal piece in water
A metal piece has a mass of $200$ g and occupies a volume of $40$ cm³. It is placed in water whose density is $1$ g/cm³.
A student says, "The object is made of metal, so it must sink."
Questions:
1. Is the student's reasoning scientifically correct?
2. Calculate the density of the metal piece.
3. Predict whether it will float or sink.
4. What property should actually be compared to determine whether an object floats or sinks?
Answer:
1. No. The fact that an object is made of metal alone is not sufficient to determine whether it will float or sink. Its density must be compared with that of the liquid.
2.
$$\rho = \frac{m}{V}$$
$$\rho = \frac{200}{40}=5\text{ g/cm}^3$$
3. Since:
$$5\text{ g/cm}^3 > 1\text{ g/cm}^3$$
the metal piece is denser than water and will sink.
4. We compare the density of the object with the density of the liquid. An object sinks when its density is greater than that of the liquid and floats when its density is lower.