Q1. Pressure and temperature determine the state of a substance. Explain this in detail.
Ans. (1) Any matter i.e., solid, liquid or gas when experiences an increase in temperature they change their state. Example:
Take ice cubes in a beaker or heat them slowly, the temperature increases and the ice melts to form liquid. Heat this liquid further it will becomesteam.
(2) On lowering down the temperature of any matter, show change in their state.
Take the steam that is coming out of a boiling water and allow it to cool down, it condenses to form water and on further cooling of this water we get ice.
(3) On applying pressure and reducing temperature we can liquefy gases or change them into solid. Example: Take carbon-dioxide gas, reduce its temperature and apply lot of pressure on it so that it changes into solid carbon dioxide, called dry ice, which is used as refrigerant for cooling. If the pressure on it is further decreased it directly changes into gas. In LPG cylinders, the petroleum gas is first cooled and further lot of pressure change is applied to it into liquid state. While using this LPG, we release the pressure exerted on it and hence it comes out in the form of gas.
Q2. Explain giving examples the various factors on which rate of evaporation depends.
Ans. The rate of evaporation depends on the following factors:
(1) Surface area: If the surface area is increased the rate of evaporation also increases.
(a) To dry the clothes we spread them to dry faster.
(b) Tea in saucer cools faster than in a cup.
(2) Temperature: If the temperature is increased the rate of evaporation also increases. Due to increase in temperature the particles gain more kinetic energy and change their phase from liquid to gaseous. Water will evaporate faster in sun than in shade.
(3) Humidity: It is the amount of water vapour present in air. The air can hold definite amount of water vapour, at a given temperature. If the amount of water vapour is high in the air then the rate of evaporation decreases. On hot and humid day, desert coolers are not effective as the air cannot hold anymore moisture to get the cooling effect.
(4) Wind speed: With the increase in wind speed, the rate of evaporation increases. The particles of water vapour move away with the wind, decreasing the amount of water vapour in the surrounding.
Q3. Cooking gas is often stored and delivered in steel bottles. Over a period of time pressure of the gas in the steel bottles does not change.
Air and helium are gases that are often used to fill rubber balloons. Over a period of time balloons gradually shrink. Explain these observations.
Ans. The molecules of gas exert pressure on the walls of the container. The steel containers have a wall strong enough to withstand the pressure of the gas but the walls of the balloon are not that rigid and hence shrinks.
Q4. The observations given below determine whether the changes described are likely to involve the formation of new combinations of matter, or are physical changes. Analyse.
|Observation||Chemical or Physical||Scientifically Supported Judgements|
|1. Edge of towel hanging in a wet bath draws up water.|
|2. A fire cracker explodes. Producing noise, smell and smoke|
|3. Pink colored copper tap becomes green over a period of time.|
|4. . Glass of car windscreen gets all water droplets on inner surface.|
|Observation||Chemical or Physical||Scientifically Supported Judgements|
|1. Edge of towel hanging in a wet bath draws up water.||Physical||No new substance formed|
|2. A fire cracker explodes. Producing noise, smell and smoke||Chemical||Heat involved and new product formed|
|3. Pink colored copper tap becomes green over a period of time.||Chemical||New compound formed|
|4. . Glass of car windscreen gets all water droplets on inner surface.||Physical||No new substance formed|
Observation: Yes, the water is still coloured but its colour has faded in each dilution. This experiment shows that just a few crystals of potassium permanganate can colour a large volume of water. This is because potassium permanganate (matter) is made up of millions of tiny particles.
9. Collect the following:
(a) Water, cooking oil, milk, juice and cold drink.
(b) Take containers of different shapes. Put a 50 ml mark on these containers using a measuring cylinder from the laboratory.
Observation: On the stem of the funnel and near the cotton plug, solidified ammonium chloride is collected on heating the china dish. This solid ammonium chloride did not enter the phase of liquids i.e., it did not melt but fumes/vapours on heating the china dish, containing ammonium chloride, were collected on the stem of the funnel as solidified ammonium chloride again.
Inference: A solid on heating changed into a gas without changing into liquid state. This process is called sublimation.
Q1. Adil parked his bicycle on a sunny day in a parking stand of his school campus. When the school got over Adil saw his burst cycle tyre. Thereafter he kept less air in his cycle tyres and did not inflate them fully.
(a) Why did the tyre burst?
(b) Why is air compressible?
(c) What value of Adil is reflected in the above act?
Ans. (a) The tyre burst because the air inside the tyre got heated and therefore exerted greater pressure on the walls of the tyre.
(b) Air is compressible because it has large intermolecular space.
(c) Adil showed the value of intelligence, awareness and self responsibility.
Q2. Akshay’s friend visited his house in Mumbai and he was surprised to see air conditioners installed in all of his rooms. His friend advised Akshay to use watercoolers and save electricity. On this Akshay told him that the water-cooler is not at all effective in coastal areas.
(a) Why are water-cooler not effective in coastal areas?
(b) What are the other two factors on which evaporation of water depends?
(c) What value of Akshay’s friend is seen in this act?
Ans. (a) Water coolers are not effective in coastal areas due to high humidity.
(b) The other two factors on which evaporation of water depends are temperature and surface area.
(c) Akshay’s friend showed the value of concerned citizen, morally responsible and friendly in nature.
Q3. Sita lived in a village and could not afford refrigerator in her house. She knew how to keep water cold and preserve all perishable items in her house. She kept wet cloth surrounding the earthen pot to keep water cool, she also kept vegetables fresh by keeping them in wet gunny bag and timely sprinkled water over it.
(a) Why did Sita keep wet cloth surrounding the earthen pot?
(b) Suggest one more method of keeping the house cool in summer.
(c) What value of Sita is reflected in the above case?
Ans. (a) The wet cloth gave the cooling effect to the pot, as the water in the cloth evaporated and evaporation causes cooling effect. (b) By sprinkling some water on the lawn/veranda of the house can keep the house cool. (c) Sita showed the value of responsible behaviour.
Q4. Shreya commutes in a CNG fitted van to school every day along with many other students. She told the van driver to get the CNG connection certified and timely checked it for any leakage or loose connection of pipes. She told the driver to be more careful during summers.
(a) What is CNG?
(b) Why should one be more careful with CNG cylinders during summer?
(c) What value of Shreya is seen in the above act?
Ans. (a) CNG is Compressed Natural Gas used as fuel.
(b) During summers, the CNG connections and cylinder need to be checked because the gas expands due to heat and if there would be any leakage then it would cause fire in the vehicle.
(c) Shreya showed the value of concerned citizen and morally responsible behaviour
Practical Based Questions (Solved)
Q1. How many grams of magnesium bromide are needed to make 1.0 L of a 4.0 M magnesium bromide solution?
Q2. What are the three different types of mixtures? Define each one.
Ans. Suspensions, Colloids, and Solutions. Suspensions: A suspension is a heterogeneous mixture containing particles that are distinct from the surrounding medium. Colloids: A colloid is a suspension in which a solute-like phase is dispersed throughout a solvent-like phase. Solutions: A solution is a liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent).
Q3. How is a solution different from the other two types of mixtures?
Ans. A solution is different from the other types of mixtures as it is homogeneous. While a suspension is made up of different phases and a colloid is made up of two distinct, different phases. A solution is made up of a solute and a solvent and solution cannot be separated easily into its components.
Q4. Describe (in detail) the three steps involved in solution formation.
Ans. Step 1: Take a required amount of solvent in a beaker
Step 2: Add the required amount of solute into it.
Step 3: Stir the solute into the solvent till it gets completely dissolved in it, if needed you may heat it for fast dissolution.
Q5. Use the solubility graph below to answer the following questions
(a) Which salt is least soluble at 20°C?
(b) How many grams of KBr can be dissolved in 100g of water at 60°C?
(c) How many grams of NaCl can be dissolved in 100 g of water at 100°C?
(d) Classify the type of solution: At 40°C, 180g of NaClO3 is dissolved in 100g of water.
(e) Classify the type of solution: At 70°C, 70g of KBr is dissolved in 100g of water.
Ans. (a) KNO3
(d) It is supersaturated
Q6. Not all solutions of solids are dissolved in liquids. Provide two examples of other types of solutions other than this.
Ans. (a) Gas dissolved in liquid: CO2 in H2O (carbonated beverage). (b) Solid dissolved in solid: Alloys like steel solution of carbon atoms in iron atoms
Q7. How could you tell by looking at a solution that it was saturated?
Ans. If the additional solute is added and it remains undissolved the solution can be considered as saturated.
Q8. What is the Tyndall Effect? Cite a common example of this effect.
Ans. The Tyndall Effect occurs when light is scattered by particles in a colloid or particles in a fine suspension. For example—The sky appears blue due to the scattering of light by dust particles suspended in it.
Q9. Given an unknown mixture consisting of two substances, explain how a scientist could use lab techniques to determine whether the mixture is a true solution, a colloid, or a suspension.
Ans. If the unknown mixture can be separated by filtration then it is a suspension. If the scattering of light by the particles is observed then it is a colloid. Otherwise all others are true solutions.