NCERT Class 9 Science Solutions: Is Matter Around Us Pure
Question:
Classify the following as chemical or physical change:
Burning of paper and wood
A. Chemical change
B. Physical change
Concept in a Minute:
Physical change: A change in which the form or appearance of a substance changes, but its chemical composition remains the same. No new substances are formed. Examples include melting ice, boiling water, or breaking glass.
Chemical change: A change in which one or more new substances are formed with new properties. This involves a rearrangement of atoms and molecules, and is often accompanied by signs like heat, light, gas production, or color change. Examples include rusting of iron, cooking food, or burning fuel.
Explanation:
Burning of paper and wood is a chemical change. When paper and wood burn, they react with oxygen in the air to produce ash, smoke (which contains carbon dioxide and water vapor), and heat and light. These are all new substances with properties different from the original paper and wood. The original material is consumed and transformed into entirely new substances. Therefore, it is a chemical change.
The final answer is A
Question:
Classify the following as chemical or physical change:
Passing of electric current through water, and water breaking down into hydrogen and oxygen gases.
A. Chemical change
B. Physical change
Concept in a Minute:
A physical change alters the form or appearance of a substance but does not change its chemical composition. A chemical change results in the formation of new substances with different chemical properties.
Explanation:
The question describes two events happening simultaneously when electric current passes through water. First, passing electric current through water. In this initial stage, the water might appear to be undergoing a physical change as it’s being acted upon by electricity. However, the second part of the description clarifies the outcome: “water breaking down into hydrogen and oxygen gases.” The breakdown of water (H2O) into hydrogen (H2) and oxygen (O2) gases is a process where the chemical bonds within water molecules are broken, and new chemical bonds are formed to create entirely new substances. This is a clear indication of a chemical reaction. Therefore, the overall process described is a chemical change.
Answer: A
Question:
Classify the following as chemical or physical change:
Boiling of water to form steam.
A. Chemical change
B. Physical change
Concept in a Minute:
A physical change alters the form or appearance of a substance but does not change its chemical composition. A chemical change results in the formation of new substances with different chemical properties. Key indicators of a chemical change include the formation of gas, precipitate, color change, or release/absorption of energy.
Explanation:
Boiling of water to form steam involves a change in the state of water from liquid to gas. The chemical composition of water (H₂O) remains the same in both liquid and gaseous (steam) forms. No new substance is formed. Therefore, boiling of water is a physical change.
The final answer is $\boxed{B}$.
Question:
Classify the following as chemical or physical change:
Dissolving common salt in water.
A. Chemical change
B. Physical change
Concept in a Minute:
Physical change is a change in the form of a substance but not in its chemical composition. Chemical change involves the formation of new substances with different properties.
Explanation:
When common salt (sodium chloride, NaCl) is dissolved in water, it separates into its constituent ions, sodium ions (Na+) and chloride ions (Cl-), which are surrounded by water molecules. This process is reversible; if the water evaporates, the salt can be recovered in its original solid form. No new chemical substance is formed. Therefore, dissolving common salt in water is a physical change.
The final answer is $\boxed{B}$.
Question:
Classify the following as chemical or physical change:
Melting of butter in a pan
A. Chemical change
B. Physical change
Concept in a Minute:
A physical change alters the form or appearance of a substance but not its chemical identity. Properties like shape, size, or state of matter can change. A chemical change, on the other hand, results in the formation of new substances with different chemical properties. This typically involves breaking and forming chemical bonds.
Explanation:
When butter melts in a pan, it changes from a solid to a liquid state. The chemical composition of butter does not change. It remains butter, just in a different physical form. No new substances are created. Therefore, melting of butter is a physical change.
Answer:
B
Question:
Classify the following as chemical or physical change:
Cutting of trees
A. Chemical change
B. Physical change
Concept in a Minute:
A physical change alters the form or appearance of a substance but not its chemical composition. A chemical change results in the formation of new substances with different chemical properties.
Explanation:
Cutting of trees is a physical change. The wood is still wood; its chemical composition remains the same. The change is only in its size and shape. No new substance is formed. This is in contrast to a chemical change, where a substance is transformed into a new substance (e.g., burning wood, which produces ash, smoke, and gases).
The final answer is $\boxed{B}$
Question:
Classify the following as chemical or physical change:
Rusting of almirah
A. Chemical change
B. Physical change
Concept in a Minute:
A physical change alters the form or appearance of a substance but does not change its chemical composition. A chemical change results in the formation of new substances with different chemical properties.
Explanation:
Rusting of an almirah is a chemical change because it involves a chemical reaction between iron (the material of the almirah), oxygen, and moisture. This reaction forms iron oxide (rust), which is a new substance with properties different from iron. This is an irreversible process, characteristic of chemical changes.
The final answer is A
Question:
Classify the following as chemical or physical change:
Making a fruit salad with raw fruits
A. Chemical change
B. Physical change
Concept in a Minute:
Physical changes alter the form or appearance of a substance but do not change its chemical composition. Chemical changes result in the formation of new substances with different chemical properties.
Explanation:
Making a fruit salad involves cutting fruits into smaller pieces and mixing them together. The fruits are still the same fruits; their chemical composition has not changed. No new substances are formed. This is a physical change because only the form and arrangement of the fruits are altered.
Answer: B
Question:
Which separation technique will you apply for the separation of the following?
Fine mud particles suspended in water.
Concept in a Minute:
The question requires identifying a separation technique suitable for separating a solid (fine mud particles) from a liquid (water) where the solid is suspended. This involves understanding the properties of suspensions and the methods used to separate insoluble solids from liquids. Key concepts are: suspension, insoluble solid, filtration, sedimentation, decantation.
Explanation:
For separating fine mud particles suspended in water, the most appropriate separation technique is filtration.
Here’s why:
1. Nature of the mixture: Mud particles are insoluble in water, forming a suspension. The particles are fine but still solid and dispersed within the liquid.
2. Filtration principle: Filtration uses a filter medium (like filter paper) that allows the liquid (water) to pass through but retains the solid particles (mud). The liquid that passes through is called the filtrate, and the solid retained on the filter is called the residue.
3. Other techniques:
* Sedimentation and Decantation: While sedimentation (allowing particles to settle down) and decantation (carefully pouring off the liquid) can be used for larger, heavier particles, fine mud particles may remain suspended for a long time or not settle completely, making this method less effective for complete separation.
* Evaporation: Evaporation would separate water by turning it into vapor, leaving the mud behind. However, this process destroys the water and is not typically used when both components are desired or when the solid is fine and might form a solid mass.
* Centrifugation: Centrifugation uses centrifugal force to speed up sedimentation. It can be effective for fine particles but is a more advanced technique than simple filtration.
Therefore, filtration is the most direct and effective method for separating fine mud particles suspended in water in a typical high school laboratory setting.
Question:
Classify the following into elements, compounds and mixtures:
- Sodium
- Soil
- Sugar solution
- Silver
- Calcium carbonate
- Tin
- Silicon
- Coal
- Air
- Soap
- Methane
- Carbon dioxide
- Blood
Concept in a Minute:
Elements are pure substances made up of only one type of atom. Compounds are pure substances formed when two or more different elements chemically combine in a fixed ratio. Mixtures are formed when two or more substances (elements or compounds) are physically mixed together, and their components retain their individual properties and are not chemically bonded.
Explanation:
Here’s the classification of the given substances:
Elements:
Sodium: A pure substance consisting only of sodium atoms.
Silver: A pure substance consisting only of silver atoms.
Tin: A pure substance consisting only of tin atoms.
Silicon: A pure substance consisting only of silicon atoms.
Compounds:
Calcium carbonate: Formed by the chemical combination of calcium, carbon, and oxygen atoms in a fixed ratio.
Methane: A compound formed by the chemical combination of carbon and hydrogen atoms in a fixed ratio.
Carbon dioxide: A compound formed by the chemical combination of carbon and oxygen atoms in a fixed ratio.
Mixtures:
Soil: A heterogeneous mixture of minerals, organic matter, water, and air.
Sugar solution: A homogeneous mixture of sugar (a compound) dissolved in water (a compound).
Silver: This was listed under elements above. If there is a specific alloy of silver being referred to, it would be a mixture. Assuming it refers to pure silver, it is an element.
Coal: A heterogeneous mixture primarily composed of carbon, along with varying amounts of other elements and compounds.
Air: A homogeneous mixture of gases, mainly nitrogen and oxygen, with smaller amounts of other gases.
Soap: A complex mixture of salts of fatty acids, often containing other additives.
Blood: A complex biological mixture consisting of plasma, red blood cells, white blood cells, and platelets.
Question:
Classify each of the following as a homogeneous or heterogeneous mixture.
Soda water, wood, air, soil, vinegar, filtered tea.
Concept in a Minute:
A homogeneous mixture has a uniform composition throughout, meaning its components are evenly distributed and indistinguishable. A heterogeneous mixture has a non-uniform composition, where its components are not evenly distributed and are often visible as separate phases.
Explanation:
Let’s classify each of the given substances:
Soda water: When soda water is freshly opened, the dissolved carbon dioxide gas, water, and any flavorings are evenly distributed, making it a homogeneous mixture.
Wood: Wood is composed of cellulose, lignin, and other organic compounds, along with knots, grain patterns, and potential air pockets. These components are not uniformly distributed, making wood a heterogeneous mixture.
Air: In its pure form, air is a mixture of gases like nitrogen, oxygen, argon, and trace amounts of others. These gases are uniformly mixed and indistinguishable, so air is a homogeneous mixture.
Soil: Soil contains a variety of components such as sand, silt, clay, organic matter, water, and air. These components are not evenly distributed and can often be seen as distinct particles or layers, making soil a heterogeneous mixture.
Vinegar: Vinegar is primarily a solution of acetic acid in water, often with added flavorings. The acetic acid and water are uniformly dissolved, making it a homogeneous mixture.
Filtered tea: After filtering, most of the solid tea leaves and other insoluble particles are removed. The remaining liquid, consisting of dissolved tea compounds and water, has a uniform composition, making filtered tea a homogeneous mixture.
Question:
Which separation technique will you apply for the separation of the following?
Small pieces of metal in the engine oil of a car.
Concept in a Minute:
Separation of solids from liquids based on particle size. Filtration is effective when solid particles are larger than the pores of the filter medium and the liquid can pass through.
Explanation:
The problem asks to separate small pieces of metal from engine oil. Engine oil is a liquid, and the metal pieces are solid. We need a technique that can separate a solid from a liquid.
Filtration is a technique used to separate insoluble solid particles from a liquid or gas by passing the mixture through a filter medium that allows the fluid to pass through but retains the solid particles. In this case, the engine oil is the liquid, and the small pieces of metal are the solid impurities.
If we pass the engine oil through a suitable filter (like a fine mesh sieve or a specialized oil filter), the metal pieces, being solid and likely larger than the pores of the filter, will be trapped by the filter. The engine oil, being a liquid, will pass through the filter, thus achieving the separation.
Other separation techniques are not suitable here. For example, evaporation would require heating the oil, which might damage it. Decantation is only effective if the solid settles down, and small metal pieces might remain suspended or take a very long time to settle. Magnetic separation would only work if the metal pieces are magnetic. Since the question specifies “small pieces of metal,” filtration is the most appropriate and practical method for removing such solid contaminants from engine oil.
Therefore, the separation technique to be applied is filtration.
Question:
Which of the following will show the “Tyndall effect”?
- Salt solution
- Milk
- Copper sulphate solution
- Starch solution
Concept in a Minute:
The Tyndall effect is the scattering of light by particles in a colloid or a suspension. True solutions do not exhibit the Tyndall effect because their solute particles are too small to scatter light.
Explanation:
The Tyndall effect is observed when light passes through a medium containing particles that are large enough to scatter the light.
A salt solution is a true solution, meaning the solute particles (salt ions) are dissolved at a molecular or ionic level and are too small to scatter light.
Milk is a colloid. It contains fat globules and protein particles dispersed in water, which are large enough to scatter light, thus showing the Tyndall effect.
A copper sulphate solution is a true solution, similar to a salt solution, where the copper sulphate dissolves into ions and does not scatter light.
A starch solution, if prepared correctly (e.g., boiled starch in water), can form a colloidal dispersion where starch molecules are dispersed in water. These particles are large enough to scatter light, hence showing the Tyndall effect.
However, when considering common examples taught at the high school level, milk is the most prominent and consistent example of a substance that readily exhibits the Tyndall effect due to its colloidal nature. While a starch solution can also show the effect, the question asks “Which of the following *will show*”, implying a definite and readily observable phenomenon. Milk is universally recognized for this.
Therefore, milk will show the Tyndall effect.
Question:
Explain the following giving an example.
Saturated solution
Concept in a Minute:
Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature. A solution is formed when a solute dissolves in a solvent.
Explanation:
A saturated solution is a solution that contains the maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature. At this point, the dissolved solute is in dynamic equilibrium with any undissolved solute. This means that the rate at which solute particles dissolve is equal to the rate at which dissolved solute particles crystallize out of the solution. Adding more solute to a saturated solution will not result in more solute dissolving; instead, it will remain undissolved at the bottom of the container.
Example:
Imagine you have a glass of water at room temperature and you start adding sugar to it, stirring after each addition. Initially, the sugar dissolves readily. As you continue to add sugar, you’ll notice that it takes longer and longer for the sugar to dissolve. Eventually, you’ll reach a point where no matter how much more sugar you add and stir, it will simply settle at the bottom of the glass without dissolving. At this point, the sugar solution is saturated. If you were to heat this saturated solution, you would be able to dissolve more sugar because the solubility of sugar in water increases with temperature.
Question:
Explain the following giving an example.
Suspension
Concept in a Minute:
A suspension is a heterogeneous mixture where solid particles are dispersed in a liquid or gas but do not dissolve. These particles are large enough to be visible and will eventually settle out if left undisturbed.
Explanation:
A suspension is a type of mixture where solid particles are spread throughout a fluid (liquid or gas) but do not dissolve. Unlike a solution, where the solute particles are uniformly distributed and invisible, in a suspension, the dispersed particles are relatively large. These larger particles are visible to the naked eye or under a microscope and can scatter light. Because of their size, these solid particles are not held in a stable state and will gradually settle down to the bottom of the container due to gravity if the mixture is left undisturbed for a period of time. The components of a suspension can be separated by simple filtration.
Example:
Muddy water. When soil or mud is mixed with water, it forms a suspension. The soil particles are dispersed throughout the water, making the water appear cloudy or opaque. If you let this muddy water stand for a while, you will observe that the mud particles gradually settle to the bottom of the container, leaving the water clearer at the top. You can also separate the mud from the water by filtering the mixture through a filter paper.
Question:
List the points of differences between homogeneous and heterogeneous mixtures with examples.
Concept in a Minute:
Mixtures are combinations of two or more substances that are not chemically bonded. They can be classified into homogeneous and heterogeneous mixtures based on the uniformity of their composition and properties.
Explanation:
Points of Differences between Homogeneous and Heterogeneous Mixtures:
| Feature | Homogeneous Mixture | Heterogeneous Mixture |
|——————-|—————————————————-|—————————————————-|
| Composition | Uniform throughout | Non-uniform throughout |
| Appearance | Single phase, looks the same everywhere | Two or more distinct phases, visible boundaries |
| Particle Size | Particles are not visible even under a microscope | Particles are often visible to the naked eye or under a microscope |
| Separation | Components cannot be easily separated by simple physical methods like filtration | Components can often be separated by simple physical methods like filtration, decantation, or handpicking |
| Examples | Saltwater, air, sugar dissolved in water, alloys (like brass) | Sand and water, oil and water, salad, granite, soil |
Question:
To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.
Concept in a Minute:
The concept needed to solve this question is the definition of concentration of a solution, specifically in terms of mass percentage. Concentration represents the amount of solute present in a given amount of solvent or solution. Mass percentage is a common way to express concentration, calculated as (mass of solute / mass of solution) * 100.
Explanation:
To find the concentration of the saturated solution, we need to determine the mass percentage of sodium chloride (the solute) in the solution.
First, identify the mass of the solute and the mass of the solvent.
Mass of solute (sodium chloride) = 36 g
Mass of solvent (water) = 100 g
Next, calculate the mass of the solution. The mass of the solution is the sum of the mass of the solute and the mass of the solvent.
Mass of solution = Mass of solute + Mass of solvent
Mass of solution = 36 g + 100 g = 136 g
Now, we can calculate the concentration of the solution in terms of mass percentage.
Concentration (mass percentage) = (Mass of solute / Mass of solution) * 100
Concentration = (36 g / 136 g) * 100
Perform the calculation:
Concentration = (36 / 136) * 100
Concentration ≈ 0.2647 * 100
Concentration ≈ 26.47%
Therefore, the concentration of the saturated solution of sodium chloride at 293 K is approximately 26.47%.
Question:
Which separation technique will you apply for the separation of the following?
Iron pins from sand.
Concept in a Minute:
Separation techniques are used to separate mixtures based on the different physical properties of the components. Magnetic separation is a technique used to separate magnetic materials from non-magnetic materials.
Explanation:
The question asks for a separation technique to separate iron pins from sand. Iron is a magnetic material, while sand is not. Therefore, we can use a magnet to separate the iron pins from the sand. When a magnet is brought near the mixture, the iron pins will be attracted to the magnet and will be separated from the sand. This technique is called magnetic separation.
Steps:
1. Identify the components of the mixture and their properties. In this case, the components are iron pins and sand. Iron is magnetic, and sand is non-magnetic.
2. Choose a separation technique that exploits the difference in properties. Magnetic separation is suitable because iron is magnetic.
3. Apply the chosen technique. Bring a magnet close to the mixture of iron pins and sand.
4. Observe the separation. The iron pins will stick to the magnet, leaving the sand behind.
5. Collect the separated components. Remove the iron pins from the magnet.
Question:
Explain the following giving an example.
Colloid
Concept in a Minute:
A colloid is a type of mixture where one substance is dispersed evenly throughout another substance. The particles of the dispersed substance are larger than those in a true solution but smaller than those in a suspension, making them invisible to the naked eye.
Explanation:
A colloid is a heterogeneous mixture in which tiny particles of one substance are dispersed evenly throughout another substance. These dispersed particles are larger than the molecules in a true solution but too small to be seen with the naked eye. They remain suspended and do not settle out over time. Colloids exhibit the Tyndall effect, which is the scattering of light as a light beam passes through the colloid.
Example:
Milk is a common example of a colloid. In milk, fat globules are dispersed in water. These fat globules are larger than the molecules in a true solution but do not settle out. When a beam of light is passed through milk, it is scattered, making the beam visible. Other examples include fog (water droplets dispersed in air), smoke (solid particles dispersed in air), and gelatine (protein molecules dispersed in water).
Question:
Which separation technique will you apply for the separation of the following?
Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
Concept in a Minute:
Sublimation is a process where a solid changes directly into a gas without passing through the liquid state. This property can be used to separate a sublimate substance from non-sublimate substances.
Explanation:
The mixture contains ammonium chloride and sodium chloride. Ammonium chloride is a sublimate substance, meaning it can be converted directly from solid to gas upon heating. Sodium chloride, on the other hand, does not sublime. Therefore, the separation technique to be applied is sublimation.
To perform the separation:
1. Take the mixture in an evaporating dish.
2. Place a wire gauze over the evaporating dish and put a funnel, mouth downwards, over the wire gauze.
3. Heat the evaporating dish gently.
4. Ammonium chloride will sublime, turn into vapor, rise up, and then condense on the cooler inner walls of the funnel, forming solid ammonium chloride crystals.
5. Sodium chloride will remain at the bottom of the evaporating dish as it does not sublime.
6. After cooling, the solid ammonium chloride can be scraped off from the inner walls of the funnel.
Question:
Which separation technique will you apply for the separation of the following?
Different pigments from an extract of flower petals.
Concept in a Minute:
Chromatography is a technique used to separate mixtures of soluble substances. Different components of a mixture travel at different rates through a stationary phase depending on their solubility and affinity to the stationary phase.
Explanation:
To separate different pigments from an extract of flower petals, the technique of chromatography will be applied. Specifically, paper chromatography is a suitable method for this purpose. In paper chromatography, the extract of flower petals is placed as a spot on a piece of filter paper (the stationary phase). The edge of the paper is then dipped into a suitable solvent (the mobile phase), such as water or a mixture of solvents. As the solvent moves up the paper by capillary action, it carries the pigments with it. Different pigments will dissolve to different extents in the solvent and will be adsorbed to different degrees onto the paper. This differential movement causes the pigments to separate into distinct spots at different heights on the paper, allowing for their individual identification and separation.
Question:
Which separation technique will you apply for the separation of the following?
Wheat grains from husk.
Concept in a Minute:
Separation techniques are used to separate different components of a mixture based on their physical properties like size, density, magnetic properties, or boiling points. Understanding these properties is key to choosing the correct technique.
Explanation:
The separation of wheat grains from husk is a common example of separating solid components based on their difference in size and weight. Husk particles are generally lighter and smaller than wheat grains.
The technique best suited for this separation is winnowing.
Winnowing involves:
1. Taking the mixture of wheat grains and husk to a height. This can be done by holding the mixture in a wide, shallow container or on a plate.
2. Allowing the mixture to fall gently. As the mixture falls, the wind or a gentle breeze carries away the lighter husk particles.
3. The heavier wheat grains fall down closer to the person. This is because they are not carried away by the wind as easily.
Therefore, winnowing effectively separates the wheat grains from the lighter husk.
Question:
Which separation technique will you apply for the separation of the following?
Oil from water.
Concept in a Minute:
Immiscible liquids have different densities and do not mix. Separation techniques exploit differences in physical properties.
Explanation:
The separation of oil from water can be done using a separating funnel. This technique is used to separate two immiscible liquids that have different densities. When the mixture is allowed to stand undisturbed, the two liquids will form distinct layers, with the less dense liquid (oil in this case) floating on top of the denser liquid (water). The separating funnel has a stopper at the top and a tap at the bottom. By opening the tap, the lower layer (water) can be drained out first. Once all the water has been removed, the tap can be closed, leaving the oil behind in the funnel.
Question:
Which separation technique will you apply for the separation of the following?
Tea leaves from tea.
Concept in a Minute:
The separation of insoluble solids from a liquid is achieved by a technique that allows the solid particles to be retained while the liquid passes through.
Explanation:
To separate tea leaves from tea, the most suitable separation technique is filtration. Tea leaves are insoluble in the brewed tea (which is a liquid). Filtration involves passing the mixture through a filter medium (like a sieve or a filter paper) that has pores small enough to allow the liquid (tea) to pass through but large enough to trap the solid particles (tea leaves). Thus, the tea leaves are separated from the liquid tea.
Question:
Which separation technique will you apply for the separation of the following?
Butter from curd.
Concept in a Minute:
Separation of mixtures based on physical properties like density and state of matter.
Explanation:
The question asks for a separation technique to separate butter from curd. Curd is a semi-solid mixture where butter is dispersed. Butter is less dense than the other components of curd (water, proteins, lactose). When curd is churned vigorously, the fat globules (butter) coalesce and separate from the watery portion. This physical process of agitating the mixture to separate components based on density is called churning. Therefore, churning is the appropriate separation technique.
Next Chapter: Matter in Our Surroundings
Refer Is Matter Around Us Pure Notes
Practice Is Matter Around Us Pure Extra Questions
Conquer Maths & Science – with LearnTheta’s AI-Practice!
✅ All Topics at One Place
🤖 Adaptive Question Practice
📊 Progress and Insights