Frank Brothers Solutions for ICSE Class 9 Chemistry Chapter 3 Elements Compounds And Mixtures

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Question 1:
Answer:
1. Elements: An element is a pure substance which can neither be broken down into simpler substances nor formed from two or more simpler substances by any known physical or chemical process. It is made of only one kind of atoms. It can be divided into four main categories
1. Metals-Iron, magnesium
2. Non-metals-Hydrogen, oxygen
3. Metalloids-Arsenic, antimony
4. Noble gas-Helium, neon
2. Compound: A compound is a pure substance that is composed of two or more elements chemically combined in definite proportion by mass. The physical and chemical properties of a compound are different from those of its constituent elements. Hydrogen gas is combustible and oxygen is supporter of combustion, their compound water which is liquid is neither combustible nor a supporter of combustion.
3. Mixture: Mixture is a physical combination of two or more substances, whether elements or compounds, which are mixed in any proportion by mass and retain their original properties even after mixing.
Homogeneous mixture: They have same composition and the same properties throughout their entire mass. Example- Salt solution, alloys etc.
Heterogeneous mixture: They have different composition and different properties in different parts of their mass. Example-Mixture of sand and salt, mixture of iron fillings and sulphur etc.
Elements are the simplest building blocks of matter that cannot be split further. Compounds are formed when elements bond together in specific ways, while mixtures are just ingredients thrown together without a chemical bond.
Teacher's Tip: Elements are lonely (one atom type), Compounds are married (chemically bonded), and Mixtures are roommates (together but separate).
Exam Tip: Always mention that elements are made of "only one kind of atoms" to get full marks.

Question 2:
Answer:
1. Oxygen
2. Carbon, hydrogen, Oxygen
3. Mercury, Bromine
4. 1. Helium
2. Oxygen
5. Gallium, caesium
6. Two noble gases are -
7. Helium
8. Argon
This list provides specific examples of elements based on their states and classifications. For instance, mercury and bromine are unique because they are the only elements that are liquid at room temperature.
Teacher's Tip: Remember that "Noble gases" are called so because they are stable and don't like to react with other elements.
Exam Tip: Learn the liquid elements (Mercury and Bromine) as they are very common "one-word" answer questions.

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Question 3:
Answer: Air is a mixture because -
1. The composition of air is not fixed i.e. the components may be present in any proportion by mass.
2. Components of air i.e. nitrogen, oxygen etc. do not react with each other.
Air contains several gases that keep their individual properties even when they are mixed together. Because there is no chemical reaction between these gases, air is considered a physical mixture rather than a chemical compound.
Teacher's Tip: Think of air like a bowl of mixed snacks; you can have more of one kind or another, and they don't change into a new snack.
Exam Tip: Use the phrase "composition is not fixed" as a key argument for classifying any substance as a mixture.

Question 4:
Answer: Elements - Lead, Mercury, Sodium
Mixtures - Air, petrol, ink, gunpowder
Compounds - Common salt, alcohol, sand
Matter is categorized based on whether it is made of single atoms, chemical bonds, or physical blends. Understanding these classifications helps us predict how materials will react in different situations.
Teacher's Tip: If you can find it on the Periodic Table, it is an Element!
Exam Tip: "Common salt" is a compound (NaCl), but "Salt water" is a mixture; be careful with these similar terms.

Question 5:
Answer: Pure substance - A pure substance is one which is made up of only one kind of particles. These particles may be atoms or molecules. Example-Sulphur, water.
Impure substance - They are mixtures of two or more chemically different substances mixed in indefinite proportions. The constituent substances retain their properties in the mixture. Example-Mixture of salt and sand, gunpowder.
Pure substances have a uniform makeup and fixed properties throughout their structure. Impure substances, or mixtures, are simply combinations where the individual ingredients can still be identified by their properties.
Teacher's Tip: Water is pure because every part is H₂O, but tap water is a mixture because it has minerals dissolved in it.
Exam Tip: Define pure substances as having "only one kind of particles" to ensure a precise scientific definition.

Question 6:
Answer: Mercury is the metal which is liquid at room temperature and bromine is the non-metal which is liquid at room temperature.
While most metals are hard solids and most non-metals are gases or brittle solids, these two elements are exceptions. They exist in a flowing liquid state under normal everyday conditions.
Teacher's Tip: Think of "M" for Mercury and Metal, and "B" for Bromine and Bad-smelling non-metal.
Exam Tip: Clearly state that Mercury is a metal and Bromine is a non-metal when providing this answer.

Question 7:
Answer:
Mixture
1. Mixtures can be homogeneous or heterogeneous. They are mostly heterogeneous except in solutions which are homogeneous.
2. The constituents of a mixture may be present in varying proportions.
3. Properties are an average of those of its constituents.
4. The various constituents can be separated by simple physical means.
5. No energy change takes place in the formation of a mixture.
6. A mixture has no definite melting point or boiling point.
7. The constituents of a mixture are not chemically bound to each other.
Compound
1. A compound is always homogeneous.
2. The constituents of a compound are present in a definite proportion by mass.
3. Properties of a compound are different from those of its constituents.
4. The various constituents cannot be separated by simple physical means.
5. Generally, energy in the form of heat, light etc. is either evolved or absorbed in the formation of a compound.
6. A compound generally has a definite fixed melting point or boiling point.
7. The constituents of a compound are chemically bound to each other.
A mixture is like a crowd of people standing together, while a compound is like people holding hands very tightly. Because mixtures aren't bonded, you can pull the parts away easily using magnets or filters.
Teacher's Tip: Remember: Compounds have "Rules" (fixed ratios) but Mixtures are "Free" (any ratio).
Exam Tip: Highlight the "Energy change" point as it is a major scientific distinction between the two.

Question 8:
Answer: The schematic representation shows matter branching into Pure Substances (Elements and Compounds) and Mixtures (Homogeneous and Heterogeneous). Elements further divide into Metals, Non-metals, Metalloids, and Noble Gases.
This chart is a map of everything in the universe and how scientists group things together. It moves from general categories of matter down to specific types of elements.
Teacher's Tip: Visualizing this triangle of matter helps you organize all your chemistry notes in one place.
Exam Tip: Practice drawing the "Matter Tree" to quickly recall the relationships between elements and mixtures.

Question 9:
Answer: Two reasons for believing that copper is a metal and sulphur is a non-metal are:-
1. Copper is malleable and ductile while sulphur is neither malleable nor ductile.
2. Copper is a good conductor of heat while sulphur is not good conductor of heat.
Copper can be hammered into sheets or drawn into wires, which are physical traits typical of metals. Sulphur, being a non-metal, is brittle and will shatter if you hit it with a hammer.
Teacher's Tip: Think of "Malleable" as "Malleable Metal" - something you can mold like clay.
Exam Tip: Use the words "malleable" and "ductile" correctly to describe metallic properties.

Question 10:
Answer: Metalloids - The elements which possess properties intermediate between those of the metals and non-metals are called as metalloids. They react with both acids and alkali’s to form salts. Ex - Arsenic, antimony.
Metalloids are the "middle-ground" elements that act a bit like metals and a bit like non-metals. For example, they might look shiny like a metal but conduct electricity poorly like a non-metal.
Teacher's Tip: Think of metalloids as the "border" elements on the zigzag line of the periodic table.
Exam Tip: Always provide examples like Arsenic or Antimony to complete your definition of metalloids.

Question 11:
Answer: Graphite is a non-metal which is a good conductor of electricity.
Although graphite is made of carbon, its unique structure allows electricity to flow through it easily. This makes it an exception among non-metals, which are usually insulators.
Teacher's Tip: The lead in your pencil is actually graphite, which is why it can conduct electricity!
Exam Tip: Mention graphite specifically if asked for an exception to the rule that non-metals are insulators.

Question 12:
Answer: Properties - Metals - Non-metals
(a) Malleability: Metals - They are malleable i.e. they can be beaten into fine sheets. Non-metals - They are not malleable.
(b) Ductility: Metals - They are ductile i.e. they can be drawn into wires. Non-metals - They are not ductile, they are usually brittle in nature.
(c) Conductivity: Metals - Good conductor of heat and electricity. Non-metals - Bad conductor of heat and electricity.
Metals are strong and flexible materials used for building structures and wiring homes. Non-metals are often used as insulators because they block the flow of heat and electricity.
Teacher's Tip: Metals are "Tough and Tuffy" (ductile), but Non-metals are "Broke and Brittle."
Exam Tip: Use the word "brittle" to describe why non-metals cannot be drawn into wires.

Question 13:
Answer: Mixture is the general name of the materials which contain atleast two pure substances and show the properties of their constituents.
In a mixture, the ingredients are just mingling together and can be separated back into their original forms. Because there is no chemical bond, every part of the mixture keeps its original personality.
Teacher's Tip: A mixture is like a salad; the lettuce is still lettuce and the tomato is still tomato.
Exam Tip: State that mixtures "show the properties of their constituents" to score full marks.

Question 14:
Answer: 1. Sodium, 2. Bromine, 3. Arsenic, 4. Radon, 5. Mercury, 6. Oxalic acid, 7. Carbon dioxide.
This list separates simple elements from complex compounds. Elements like Sodium are made of one atom type, whereas Carbon dioxide is a molecule made of carbon and oxygen atoms.
Teacher's Tip: Remember: If the name has "Acid" or "Oxide" in it, it's usually a compound.
Exam Tip: Label each item clearly as 'Element' or 'Compound' when answering this type of question.

Question 15:
Answer:
Element
1. An element cannot be broken into simpler substances by physical or chemical process.
2. Elements have their own fixed physical and chemical properties.
3. An atom is the smallest particle of an element taking part in a chemical reaction.
Compound
1. Compound is composed of two or more elements chemically combined in definite proportion by mass.
2. Physical and chemical properties of a compound are different from those of its constituent elements.
3. A compound cannot be separated into its constituents by simple mechanical means.
An element is a pure, basic substance, whereas a compound is a new substance created through chemistry. When elements form a compound, they lose their old properties and gain completely new ones.
Teacher's Tip: Think: Elements = Ingredients, Compound = The baked cake.
Exam Tip: For compounds, always emphasize that properties are "different from those of its constituents."

Question 16:
Answer: 1. simpler substances, 2. atomic, 3. same, 4. mixture of salt and water, 5. two.
These terms are used to complete scientific sentences about matter. They define how we describe the complexity and makeup of different materials in a lab.
Teacher's Tip: "Atomic" refers to the atom, which is the tiny "lego brick" of the element world.
Exam Tip: Read the full sentence before filling the blank to make sure the scientific logic fits.

Question 17:
Answer: 1. Bronze, 2. Duralumin.
These are alloys, which are special mixtures of different metals. They are designed to be stronger or more durable than the individual metals they are made from.
Teacher's Tip: An alloy is a "Metal Smoothie" - a mix of metals to make something better!
Exam Tip: Name "Bronze" as a common mixture of elements (Copper and Tin) for a high-scoring example.

Question 18:
Answer: 1. A Molecule - The smallest particle of a substance that retains the chemical and physical properties of the substance and is composed of two or more atoms.
2. Atomicity - Atomicity of an element is defined as the number of atoms present in one molecule of that element.
Molecules are groups of atoms that act as a single unit. Atomicity tells us exactly how many of those tiny atoms are "glued" together in that single unit.
Teacher's Tip: Atomicity is like "counting heads" in a single group of atoms.
Exam Tip: Define molecule as the "smallest particle that retains properties" to get full marks.

Question 19:
Answer: Since, the constituents of a mixtures may be present in varying proportions so it cannot be expressed by a fixed chemical formula.
Because you can change the ratio of ingredients in a mixture, there is no single mathematical recipe for it. Only compounds, which have exact fixed ratios, can have specific formulas like H₂O.
Teacher's Tip: You can't write a formula for "Tea" because everyone likes a different amount of sugar!
Exam Tip: Mention "varying proportions" to explain why mixtures lack a fixed formula.

Question 20:
Answer: 1. Air, 2. Cement, 3. Milk, Sugar solution.
These are common examples of mixtures found in nature and construction. Each one contains different substances that are physically combined but not chemically bonded.
Teacher's Tip: Even "Milk" is a mixture of water, fats, and proteins!
Exam Tip: Use "Air" and "Sugar solution" as classic examples of homogeneous mixtures.

Question 21:
Answer: If a mixture of powdered iron and sulphur is heated in a test tube, a black shiny compound iron(II) sulphide (FeS) is formed.
The heat provides the energy needed for the iron and sulphur atoms to bond together chemically. This transformation turns two separate elements into a single, new compound with its own unique look.
Teacher's Tip: Before heating, you can use a magnet to pull the iron out. After heating, the magnet won't work!
Exam Tip: Write the chemical formula FeS to show you know the product formed.

Question 22:
Answer: 1. Tungsten, Mercury, 2. Graphite, Iodine.
These examples highlight elements with interesting physical states or properties. Tungsten is known for its high melting point, while iodine is a non-metal that can turn into a purple gas.
Teacher's Tip: Tungsten is what makes old-fashioned light bulbs glow bright without melting.
Exam Tip: Remember "Mercury" is the metal that breaks the solid-state rule.

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Question 23:
Answer:
1. Solid-solid mixture: Homogeneous - Alloys, e.g., brass (zinc + copper), bronze (zinc + tin + copper). Heterogeneous - Sand + common salt; iron + sulphur.
2. Solid-liquid mixture: Homogeneous - Salt + water; sugar + water; sulphur + carbon disulphide. Heterogeneous - Mud + water, sand + water.
3. Liquid-liquid mixture: Homogeneous - Amalgamated zinc which is a mixture of mercury in zinc. Heterogeneous - Water + oil, petrol + water.
4. Liquid-solid mixture: Homogeneous - Alcohol + water, diesel + petrol.
5. Gas-liquid mixture: Homogeneous - Carbon dioxide + water. Heterogeneous - Water + oil, petrol + water.
6. Gas in gas: Homogeneous - Ammonia + water. Heterogeneous - Air (mixture of oxygen, nitrogen and carbon dioxide).
This table categorizes mixtures by the states of matter involved and how well they mix. It shows that almost any combination of solid, liquid, or gas can form a mixture.
Teacher's Tip: "Homogeneous" means it looks the same throughout, like clear salt water.
Exam Tip: Be ready to categorize "Air" as a homogeneous mixture of gases for your test.

Question 24:
Answer: 1. Chromatography - The chromatography is a technique of separating pure substances from the mixture. Advantages of chromatography -
1. It requires a very small amount of the substance or sample.
2. The components retain their individuality during the process.
3. Chromatography finds application in easy separation of substances with similar physical and chemical properties.
Chromatography is a sensitive laboratory tool often used to separate the different dyes in ink or chemicals in blood. It is powerful because it can tell the difference between substances that look exactly the same to the human eye.
Teacher's Tip: Think of it as a race; different chemicals run through the paper at different speeds.
Exam Tip: List "requires a very small amount" as a primary advantage of this technique.

Question 24 (Continued):
Answer: 2. Filtration - It is a separation technique for separating a mixture in which one component should be solid and insoluble in the other liquid component. Example- Barium sulphate in water.
3. Fractional distillation - It is a technique used to separate two liquids which dissolve in one another. The separation relies on the differences in boiling points of the two liquids. No, mixture of chloroform and water cannot be separated by this method.
4. Centrifugation - It is a method for separating the suspended particles of a substance from a liquid in which the mixture is rotated at a high speed in centrifuge machine. Application - The clay particles in water (which are very fine) can be separated by centrifugation.
These methods use physical properties like size, boiling point, and weight to pull mixtures apart. For instance, centrifugation uses spinning force to push heavy particles to the bottom of a container.
Teacher's Tip: Filtration is like using a sieve, while distillation is like using steam to separate things.
Exam Tip: For fractional distillation, always mention that it depends on the "difference in boiling points."

Question 25:
Answer: 1. The vapour state which is obtained by heating solid without passing through liquid state is called sublimate.
2. A liquid condensed from vapour in distillation is called distillate.
3. The liquid produced after filtering a suspension of a solid in a liquid is called filtrate.
4. Supernatant liquid is the upper layer of fluid found after a mixture has been centrifuged.
5. If there is a heterogeneous mixture containing an insoluble solid in a liquid, then the solid substance that settle down is called sediment.
These terms describe the specific parts of a mixture after they have been separated by scientific methods. Knowing the difference between a "filtrate" and a "distillate" helps you describe exactly what you collected in an experiment.
Teacher's Tip: Filtrate = Fluid that passed the filter; Distillate = Drilled down/dripped down from steam.
Exam Tip: Distinguish between "sediment" (bottom) and "supernatant" (top) for questions about settling or centrifugation.

Question 26:
Answer: We use fractional distillation to separate alcohol from a mixture of alcohol and water since the difference in boiling point between alcohol and mixture is very less.
When two liquids are mixed together, standard boiling might evaporate both at once. Fractional distillation uses a special column to carefully catch the alcohol as it boils off first, before the water gets hot enough.
Teacher's Tip: Think of the fractionating column as a "filter for steam."
Exam Tip: Use the term "difference in boiling point" to explain why this method is chosen over regular distillation.

Question 27:
Answer: 1. We obtain pure water from sea water by distillation.
2. A sample of pure iodine and sodium chloride is obtained by sublimation.
Distillation leaves the salt behind and collects the water as steam, which then turns back into pure liquid. Sublimation works because iodine turns straight into gas when heated, leaving the solid salt in the dish.
Teacher's Tip: Distillation is like making "artificial rain" in a lab to get pure water.
Exam Tip: Identify "sublimation" as the correct method whenever Iodine or Camphor is involved in a mixture.

Question 28:
Answer: The separation of the mixture depends upon 1. Size of the constituents, 2. Magnetic properties of constituents, 3. Mass of the constituents, 4. Solubility of the constituents, 5. Miscibilities of the constituents, 6. Boiling point of the constituents, 7. Diffusion rate of the constituents.
Every separation method is a "test" of a specific physical property of the ingredients. By finding one property that is different between two substances, scientists can pull them apart efficiently.
Teacher's Tip: Separation is just "finding the difference" and using it to your advantage.
Exam Tip: List at least four factors to give a comprehensive answer on how separation methods are chosen.

Question 29:
Answer: This is a separation technique of solid-solid mixture. This method involves the use of a solvent in which only one of the solid present in the mixture dissolves. Undissolved solid is removed by filtration. Mixture of ammonium chloride and silver chloride is separated by this method.
By picking a liquid that only likes one of the solids, you can "wash" that solid away into a solution. The solid that doesn't like the liquid stays as a powder that can be caught in a filter.
Teacher's Tip: It's like using water to separate sugar from sand; only the sugar disappears into the water.
Exam Tip: Mention "filtration" as the second step in this process to collect the insoluble solid.

Question 30:
Answer: 1. By distillation and fractional distillation we separate the mixture of two liquids.
2. Yes, mixture of chloroform (B.P. = 61° C) and carbon tetrachloride (B.P. = 77°C) be satisfactorily separated by the process of fractional distillation which is used for separating the various fractions of petroleum. For this purpose we will make two fractionating columns in the apparatus.
Distillation works best when there is a significant difference in how hot the liquids need to be to turn into gas. Because these two chemicals have boiling points 16°C apart, they can be separated by carefully controlling the heat.
Teacher's Tip: B.P. stands for Boiling Point, the specific temperature where a liquid becomes a gas.
Exam Tip: Mention the specific boiling points provided in the question to show your calculation of the difference.

Question 31:
Answer:
1. Solid-solid mixtures
1. Magnetic separation method-Separation of iron ore from impurities
2. Gravity separation-Mixture of saw dust and sand
3. Solvent extraction-Mixture of sulphur and sand
2. Solid- liquid mixtures
1. Evaporation-Water and sodium chloride
2. Distillation-Iodine in chloroform
3. Filtration-Barium sulphate in water
3. Liquid-liquid mixtures
1. By separating funnel-Oil and water mixture
2. Distillation-Acetone and water
3. Fractional distillation-Ethyl alcohol and water
This summary shows the wide variety of tools chemists use to break down everyday mixtures. Each choice depends on whether the ingredients are solids, liquids, or gases and how they interact with each other.
Teacher's Tip: Use a "Separating Funnel" for things that "hate" each other, like Oil and Water.
Exam Tip: Be ready to name the specific equipment, like a "separating funnel," for liquid-liquid mixtures that don't mix.

Question 32:
Answer:
The chromatography is the technique of separating pure substances from the mixtures. The chromatographic techniques was first employed by a Russian scientist Michael Tswett in 1903 for the separation of coloured substance from the mixture.
Principle of chromatography: The principle of chromatography is based on the difference in the extent of interaction (absorption) of various substances with a stationary phase and a mobile phase. A substance which interacts strongly with the mobile phase goes ahead of the other substance which interacts strongly with the stationary phase.
In chromatography, substances are essentially "dragged" along a surface by a moving liquid. Those that stick less to the surface and more to the liquid travel much further and faster than the others.
Teacher's Tip: Remember: Mobile Phase = Moving Liquid; Stationary Phase = Still Paper.
Exam Tip: Use the words "stationary phase" and "mobile phase" when explaining the principle for full marks.

Question 33:
Answer: Ink generally contain more than one dye. This mixture of ink is used as moving phase. Different constituents of ink move at different speed. The solvent rises up the filter paper over the spot and carries the different coloured components of ink to different heights on the filter paper. Each spot thus obtained at a particular height on the filter paper contains a particular constituent of the ink. Thus, the components of the ink are separated.
This experiment allows us to see the "hidden" colors that make up black or blue ink. As the water moves up the paper, it pulls the light dyes higher than the heavy dyes, creating a colorful strip.
Teacher's Tip: You can try this at home with a coffee filter, a black marker, and a drop of water!
Exam Tip: Explain that dyes move at "different speeds" to clarify how they get separated on the paper.

Question 34:
Answer: By the help of fractional distillation we separate the components of liquid air.
Air is cooled until it turns into a liquid, and then it is slowly warmed up. Because nitrogen, oxygen, and argon all turn back into gas at different temperatures, we can catch them one by one.
Teacher's Tip: This is how hospitals get pure oxygen tanks for patients!
Exam Tip: Identify air as a mixture of gases that can be separated after being liquefied.

Question 35:
Answer: 1. Increase in weight - Sulphuric acid and iron, 2. Decrease in weight - Sodium carbonate crystals, 3. No change in weight - Sodium chloride.
Weight changes occur when substances absorb moisture from the air or lose water to the environment. Sodium chloride (table salt) is stable and usually stays the same weight unless the room is very humid.
Teacher's Tip: Sulphuric acid is "thirsty" and sucks water out of the air, which makes it heavier.
Exam Tip: Link "Increase in weight" to the absorption of atmospheric moisture.

Question 36:
Answer: By filtration, we will separate a mixture of chalk powder and water.
Chalk does not dissolve in water, so its large particles will get stuck in the tiny holes of the filter paper. The clear water will pass through easily, leaving the white chalk behind.
Teacher's Tip: Filtration only works if the solid is "Insoluble" (doesn't disappear) in the liquid.
Exam Tip: Specify "filtration" as the best method for chalk because it is an insoluble solid.

Question 37:
Answer: Pure water is obtained by distillation from a salt water mixture. The apparatus used is a distillation flask connected to a Liebig condenser.
The salt water is boiled to create steam, which is pure water vapor. This steam then travels through a cold tube (Liebig condenser) where it cools down and turns back into liquid drops of pure water.
Teacher's Tip: The "Liebig Condenser" is named after the scientist who invented this clever cooling tube.
Exam Tip: Be able to label the "Distillation flask" and "Condenser" in a diagram of this setup.

Question 38:
Answer: Fractionating column avoid the collection of distillate and re-distillation of distillate several times during fractional distillation.
The column acts like an obstacle course for the vapors, ensuring only the purest gas reaches the top. This saves time and energy by doing several "mini-distillations" all at once inside the column.
Teacher's Tip: Think of the column as a "quality control" checkpoint for steam.
Exam Tip: State that the column provides "efficient separation" of liquids with close boiling points.

Question 39:
Answer: Two pair of liquids which can be separated by using a separating funnel 1. Oil and water, 2. Chloroform and water.
A separating funnel works because these liquids are "immiscible," meaning they refuse to mix and form separate layers. By opening a tap at the bottom, we can let the bottom layer out and stop exactly when the top layer reaches the hole.
Teacher's Tip: It's like pouring the juice out of a bottle but stopping before the pulp comes out.
Exam Tip: Use the term "immiscible" to describe liquids that form layers and can be separated this way.

Question 40:
Answer: At first, with the help of magnet, iron nails will separate. Then, by sublimation camphor will separate from common salt.
This three-step process uses different physical rules to pull a complex mixture apart. Magnets take the metal, heat takes the camphor, and only the salt is left in the dish at the end.
Teacher's Tip: Always use the magnet first so the iron doesn't get in the way of the heating step!
Exam Tip: When asked to separate three things, describe the process in the correct chronological order.

Question 41:
Answer:
(a) 1. Decantation: This method is used to separate a heterogeneous mixture containing an insoluble solid in a liquid.
2. Filtration: This method is used when a light, suspended insoluble solid has to be recovered from the solid in a liquid.
(b) 1. Filtrate: The liquid collected after filtration is called as filtrate.
2. Distillate: The liquid that has been condensed from vapour during distillation is called as distillate. It is a purified form or a fraction of an original liquid.
Decantation is a quick but "messy" way to pour off liquid, while filtration is much more precise and clean. The terms filtrate and distillate identify exactly how a liquid was purified during your experiment.
(c) 1. Fractional distillation: This method is based upon the difference in boiling points of the components of the liquid-liquid mixture.
2. Fractional crystallization: This method is based upon the difference in the solubilities of the two components of a solid-solid in a particular solvent.
(d) 1. Metal: Metal are monoatomic and generally hard solids.
2. Metalloid: These are the elements which possess properties intermediate between those of the metals and non-metals.
Crystallization uses the fact that some solids like sugar dissolve better in hot water than cold water. Metalloids are unique because they don't have the "shiny" look (luster) that metals always have.
Teacher's Tip: Crystallization is like making "rock candy" from a sugar solution.
Exam Tip: Mention "intermediate properties" to define metalloids effectively.

Question 42:
Answer: 1. When a magnet is moved over ‘X’, iron fillings are pulled away and stick to the magnet. When a magnet is moved over ‘Y’, it remained unaffected.
2. When ’X’ is treated with carbon disulphide, sulphur dissolves but not iron. While, when ’Y’ is treated with carbon disulphide, iron sulphide does not dissolve but sinks to the bottom of the test tube.
3. When ‘X’ is treated with dilute HCl, a colourless, odourless gas hydrogen is evolved which burns with a blue flame and is extinguished with a pop sound. While, when ‘Y’ is treated with dilute HCl, a colourless gas with the smell of rotten eggs is evolved which is H₂S.
There is difference in the behavior of ‘X’ and ‘Y’ because ‘X’ is a mixture while ‘Y’ is a compound. The component of a mixture do not react chemically, so retain their identity in the mixture while the components of compound react chemically, so do not retain their identity in the compound.
This experiment proves that a chemical reaction creates something entirely new. In the mixture (X), iron is still iron, but in the compound (Y), the iron has bonded with sulphur to become something that doesn't care about magnets.
Teacher's Tip: If it still acts like iron, it's a mixture. If it acts totally different, it's a compound!
Exam Tip: Mention the "rotten eggs smell" for H₂S and the "pop sound" for Hydrogen to identify the gases correctly.

Question 43:
Answer: Centrifugation is used in milk dairies to separate cream from milk dairies.
By spinning the milk very fast, the lighter cream is forced to separate from the heavier milk. This is the industrial version of the same spinning force you feel when you go around a sharp corner in a car.
Teacher's Tip: Think of centrifugation as a "Super-Fast Spin Cycle" like in a washing machine.
Exam Tip: Use "Centrifugation" as the standard answer for any question about separating cream from milk.