Maharashtra Board Class 7 Science Chapter 14 Elements Compounds and Mixtures Solutions

Question 1. Who are my companions?

Question a.

Answer:

In simple words: This question requires matching elements, compounds, and mixtures to their correct classifications or properties. Understanding the basic definitions of each type of substance is key to correctly pairing them.

🎯 Exam Tip: Pay close attention to distinguishing between elements (pure substances), compounds (chemically combined elements), mixtures (physically combined substances), and alloys (mixtures of metals) for accurate matching in classification questions.

Question 2. Write the names of elements from the following symbols: Zn, Cd, Xe, Br, Ti, Cu, Fe, Si, Ir, Pt.
 

Question a.
Answer:

In simple words: This question asks to identify the full names of chemical elements based on their standard symbols, which is fundamental to chemistry. Each symbol uniquely represents a specific element.

🎯 Exam Tip: Memorizing common element symbols and their corresponding names is crucial for chemistry. Practice identifying them to quickly answer symbol-to-name conversion questions.

Question 3. What are the molecular formulae of the following compounds? (Hydrochloric acid, Sulphuric acid, Sodium chloride, Glucose, Methane)

Question a.
Answer:
• Hydrochloric acid - HCl
• Sulphuric acid - H2SO4
• Sodium Chloride - NaCl
• Glucose - C6H12O6
• Methane - CH4
• Water - H2O
• Carbon dioxide - CO2
• Sucrose (sugar) - C12H22O11 In simple words: This task requires recalling the chemical formulas for common compounds, demonstrating knowledge of how different elements combine to form substances. Each formula represents the precise atomic composition of a molecule.

🎯 Exam Tip: Practice writing and recognizing molecular formulae for common compounds. Understanding the valencies of elements helps in correctly deriving these formulas.

Question 4. Give scientific reasons:

Question a. Buttermilk is churned to get butter.
Answer:
1. Churning is the process of shaking up buttermilk to make butter.
2. Butter is essentially the fat of milk.
3. Churning physically agitates the cream until it ruptures the membrane surrounding milk fat
4. Fat droplets can join with each other to form clumps of fat. In simple words: Buttermilk is churned to separate butterfat from the liquid. This process agitates the fat globules, causing them to clump together and form a solid mass of butter.

🎯 Exam Tip: When explaining processes like churning, focus on the physical changes and the role of agitation in separating components based on their properties.

Question b. In Chromatography the ingredients of a mixture rise up to a limited height when water rises up to the upper end of the paper.
Answer: In Chromatography two properties of substances are used, (a) They are the stability of the substances in the solvent that moves up. The ability of the substance to stick to the stationary filter paper, (b) So all the components of the mixture do not rise all the way to the upper end of the filter paper but remain behind at limited heights. In simple words: In chromatography, different components of a mixture travel to different heights on the paper because they have varying affinities for the moving solvent and the stationary paper, allowing for their separation.

🎯 Exam Tip: For chromatography, remember the two key factors: solubility in the mobile phase and adsorption to the stationary phase. These determine the separation of mixture components.

Question c. A wet cloth is wrapped around a water storage container in summer.
Answer: A wet cloth will absorb the heat from the surroundings and it will keep the water in the container, cool for a longer time. In simple words: A wet cloth cools a water container by evaporation; as water from the cloth evaporates, it absorbs latent heat from the container and its contents, lowering the temperature.

🎯 Exam Tip: When explaining cooling by evaporation, always link it to the absorption of latent heat from the surroundings, which causes a drop in temperature.

Question 5. Explain the difference.

Question a. Metals and Non-metals
Answer:

In simple words: Metals are generally good conductors, lustrous, malleable, and ductile solids, while non-metals are typically poor conductors, dull, brittle, and can exist in all three states of matter.

🎯 Exam Tip: Focus on contrasting key physical and chemical properties like conductivity, malleability, ductility, luster, and state of matter when differentiating between metals and non-metals.

Question b. Mixture and Compound
Answer:

In simple words: Mixtures are physically combined substances where components retain their individual properties and can be separated easily, while compounds are chemically combined elements with new properties, fixed proportions, and require chemical methods for separation.

🎯 Exam Tip: Highlight the chemical vs. physical combination, fixed vs. varying proportions, retention vs. loss of individual properties, and physical vs. chemical separation methods when comparing mixtures and compounds.

Question c. Atoms and Molecules
Answer:

In simple words: Atoms are the fundamental, smallest units of an element, while molecules are formed when two or more atoms bond together, representing the smallest unit of a compound or element that can exist independently.

🎯 Exam Tip: Distinguish between atoms as individual building blocks and molecules as combinations of atoms, emphasizing that molecules can be of elements (e.g., O2) or compounds (e.g., H2O).

Question d. Separation by distillation and Separation by separating funnel
Answer:

In simple words: Distillation separates components of a miscible liquid mixture based on different boiling points, while a separating funnel is used to separate immiscible liquids that form distinct layers due to density differences.

🎯 Exam Tip: Remember that distillation is for miscible liquids with different boiling points, and separating funnel is for immiscible liquids that form layers.

Question 6. Write answers to the following questions in your own words.
 

Question a. How are the components of mixture separated by simple methods?
Answer:
1. Component of mixtures are separated by straining, filtering, sifting, picking, sorting, winnowing, combing with a magnet and sublimation.
2. In a mixture, the constituent substances do not lose their identity, they can be separated easily by physical methods.
a. Sedimentation:
(i) It is a process of separating an insoluble solid from a liquid in which it is suspended, by allowing it to settle to the bottom of the container, e.g. Muddy water contains heavier particles like sand and soil,
(ii) Leave this muddy water undisturbed for some time,
(iii) The heavier soil and sand particles settle down and the clear upper water is poured out by decantation.
b. Filtration: It is used for separating insoluble solids from a liquid, e.g. mixture of chalk and water is poured through a filter paper in a funnel while the water gets
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र 'फिल्ट्रेशन विधि' को दर्शाता है, जिसमें एक कीप के माध्यम से फिल्टर पेपर का उपयोग करके ठोस कणों को तरल से अलग किया जाता है। पानी बीकर में जमा होता है, जबकि फिल्टर पेपर पर ठोस कण (जैसे चाक) रुक जाते हैं।
collected in the beaker below, chalk is retained in the filter paper.
c. Evaporation: It is used for recovering dissolved solid substances from solutions by evaporation e.g. sugar can be recovered from sugar-water.
d. Distillation: It is a process of heating a solution containing soluble solids to form vapours of the liquid and then cooling the vapours to get the liquid back. e.g. A mixture of common salt and water is taken in distillation flask and heated. Steam rises up and comes out into condenser.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र 'डिस्टिलेशन विधि' को दर्शाता है, जिसमें एक गोल-नीचे के फ्लास्क में मिश्रण को गर्म किया जाता है। थर्मामीटर तापमान को मापता है, और भाप एक कंडेनसर से गुजरती है जहाँ वह तरल में वापस ठंडी हो जाती है, जिसे एक दूसरे फ्लास्क में एकत्र किया जाता है।
e. Sublimation: It is a process in which some solids on heating are transformed directly to vapour without passing through the liquid state,
(i) It is used to separate a mixture of solids. The vapours are cooled separately,
(ii) Used to separate ammonium chloride, iodine, camphor and sulphur from any mixture.
f. Magnetic separation: A mixture with iron fillings as one of the components can be separated using magnet to attract the iron particles away from the mixture. In simple words: Components of a mixture can be separated by simple physical methods like straining, filtering, sedimentation, decantation, evaporation, distillation, sublimation, and magnetic separation, depending on the properties of the substances involved.

🎯 Exam Tip: When describing separation methods, specify the physical property (e.g., density, particle size, magnetic nature, boiling point) that each method exploits for effective separation.

Question b. Which elements (metals, non-metals) compounds and mixtures do we use in our day to day life?
Answer: Elements - non-metal
• Oxygen, nitrogen - present in air
• Hydrogen - present in water
• Silicon - in memory card
• Lithium - to make batteries
• Neon - in neon signs/lights
• Sulphur - used in water treatment, agricultural pesticides
Elements - metals
• Calcium - in milk
• Silver, gold - used in jewellery
• Aluminium, copper, iron - Kitchen vessels
• Mercury - in thermometer
• Copper - electric wires
Compounds:
• Sodium chloride - table salt
• Sodium carbonate - washing soda
• Sodium bicarbonate - baking soda
• Sodium hypochloride - bleaching powder
• Sodium hydroxide, Potassium hydroxide - in making soaps
• Calcium oxide, Calcium hydroxide - in white washing the buildings.
• Hydrochloric acid - in cleaning toilets
• Sucrose - sugar used in cooking and baking.
Mixtures:
• Bhel - mixture of puffed rice, sev, groundnuts, lemon juice
• Concrete - mixture of cement, sand and rocks
• Salad - mixture of onion, cucumber, tomato, lettuce, etc.
Sherbet and saltwater are also mixtures. In simple words: We use a wide array of elements (metals like copper, non-metals like oxygen), compounds (table salt, baking soda), and mixtures (air, bhel) daily, each serving specific purposes due to their unique properties.

🎯 Exam Tip: To score well, categorize examples clearly into elements (metals/non-metals), compounds, and mixtures, providing specific real-world applications for each item.

Question c. In everyday life, where and for what purpose do we use centrifugation?
Answer: Centrifugation: It is a process which involves application of centrifugal force.
1. It is used in industrial and laboratory settings. It is used for separation of fluids, gas or liquid based on density. In centrifugation mixture is separated through spinning and the solid settles to the bottom and the solution is clear.
2. Best example of centrifugal force is working of washing machine when it dries the clothes. The wet clothes are moving in circular path and a force acts on water particles in clothes and this force pulls water all outer side. Force involved is centrifugal force which removes the water from the clothes and clothes are dried in this way.
3. Cream separation: When the machine moves, the rod set inside milk moves and milk is pressurised and solid part from this milk goes outside due to centrifugal force and this solid part is cream. In this way the cream is separated from the milk. In simple words: Centrifugation uses centrifugal force to separate mixtures based on density, commonly seen in washing machines to dry clothes, separating cream from milk, and in labs for fluid separation.

🎯 Exam Tip: When describing centrifugation, emphasize the role of centrifugal force and density differences in separating components, and provide diverse examples from daily life and industry.

Question d. Where are methods of separation by distillation and by separating funnel used?
Answer:
1. Distillation: It is the process of separating the components or substances from a compound. It is a process of heating a solution containing soluble solids to form vapours of the liquid and then cooling the vapours to get the liquid back. Distillation method is used in the following:
• to separate components of air into oxygen, nitrogen, argon, etc.
• to separate salt from saltwater.
• to purify impure liquids.
• to prepare distilled water.
2. Separating funnel: When a mixture of two immiscible liquids is left undisturbed, two layers are clearly seen to have formed, (a) The heavier of the liquids remain below and the lighter liquid floats on it. (b) So two liquids in a mixture can be separated by making use of this property, e.g.
• to separate kerosene and water.
• to separate oil and water. In simple words: Distillation separates miscible liquids or soluble solids from liquids based on boiling point differences, while a separating funnel separates immiscible liquids that form distinct layers.

🎯 Exam Tip: Clearly state the type of mixture (miscible/immiscible) and the property exploited (boiling point/density) for each separation method to ensure a complete answer.

Question e. Which precaution will you take while using the methods of distillation and separation by separating funnel?
Answer: In using distillation:
1. Allow sufficient space to work in, working area should be well lit and well ventilated to prevent the accumulation of alcoholic vapours.
2. Keep a fire extinguisher handy.
3. There should be no obstruction in the piping that could cause pressure build-up in the stills and cause it to burst.
In using separating funnel:
1. Stopper should be tightly fitted so that the solution does not leak out when the separating funnel is inverted.
2. Never throw any layer away until you are absolutely sure that you isolated the final product. In simple words: For distillation, ensure proper ventilation, fire safety, and clear piping to prevent accidents. When using a separating funnel, ensure a tight stopper and confirm product isolation before discarding any layer.

🎯 Exam Tip: Emphasize safety protocols and careful observation in laboratory procedures. Specific precautions for each method demonstrate a practical understanding.

Project:
Question a. Visit a jaggery or a sugar factory. Obtain information about the methods that are used to separate the components of the mixture while making jaggery or sugar. Present it in the class.

Fill In The Blanks And Rewrite The Sentences:

Question 1. .................... and are three states of matter.
Answer: Solid, liquid, gaseous In simple words: Matter typically exists in three forms: solid, liquid, and gas, each having distinct properties.

🎯 Exam Tip: Know the three common states of matter and their basic characteristics to correctly fill in blanks related to this fundamental concept.

Question 2. Molecules in .................... phase of matter are tightly packed together.
Answer: solid In simple words: In the solid state, molecules are very closely packed and arranged in a fixed pattern, giving solids a definite shape and volume.

🎯 Exam Tip: Relate the tightness of molecular packing directly to the state of matter; tightly packed implies solid, less packed implies liquid, and widely spaced implies gas.

Question 3. A .................... has a definite volume, but not a definite shape, it takes the shape of its container.
Answer: liquid In simple words: A liquid possesses a fixed volume but conforms to the shape of its container because its molecules are close but can move past each other.

🎯 Exam Tip: Understand the properties of liquids-definite volume and indefinite shape-as distinguishing characteristics from solids and gases.

Question 4. The temperature at which a liquid becomes a solid is called .................... .
Answer: freezing point In simple words: The freezing point is the specific temperature at which a liquid transitions into its solid state.

🎯 Exam Tip: Identify the freezing point as the temperature where a phase change from liquid to solid occurs, which is a key concept in physical chemistry.

Question 5. Anything that takes up space and has mass is called .................... .
Answer: matter In simple words: Matter is defined as anything that has mass and occupies space, making up everything around us.

🎯 Exam Tip: Recall the basic definition of matter, which is fundamental to all scientific studies.

Question 6. A .................... has no definite shape and no definite volume.
Answer: Gas In simple words: A gas lacks a fixed shape and volume, expanding to fill its entire container because its molecules are widely spaced and move freely.

🎯 Exam Tip: Remember that gases have indefinite shape and volume, contrasting with solids and liquids, due to the high kinetic energy and weak intermolecular forces of their particles.

Question 7. The amount of space that matter occupies is called .................... .
Answer: volume In simple words: The volume of an object or substance refers to the quantity of three-dimensional space it occupies.

🎯 Exam Tip: Understand volume as a fundamental property of matter, representing its spatial extent.

Question 8. A .................... has a definite shape and definite volume.
Answer: solid In simple words: A solid maintains both a distinct shape and a fixed volume due to its tightly packed, ordered molecular structure.

🎯 Exam Tip: Differentiate solids by their characteristic definite shape and volume, a result of strong intermolecular forces and fixed particle positions.

Question 9. When a liquid is heated it will .................... .
Answer: expand In simple words: When heated, liquids generally expand as the increased kinetic energy of their molecules causes them to move further apart.

🎯 Exam Tip: Relate heating to expansion in liquids, as increased thermal energy causes particles to vibrate more vigorously and spread out.

Question 10. A .................... is formed by mixing different elements or compounds.
Answer: mixture In simple words: A mixture is created when two or more substances, whether elements or compounds, are combined physically without undergoing a chemical reaction.

🎯 Exam Tip: Define a mixture as a physical combination where components retain their individual properties, distinguishing it from a chemical compound.

Question 11. The substance formed by a chemical combination of two or more elements is called a .................... .
Answer: compound In simple words: A compound is a new substance formed when two or more elements chemically bond together in fixed proportions.

🎯 Exam Tip: Understand that a compound involves a chemical reaction and a fixed ratio of elements, resulting in properties distinct from its constituent elements.

Question 12. The elements that show some properties of metals and non-metals are called .................... .
Answer: metalloids In simple words: Metalloids are elements that exhibit properties intermediate between those of metals and non-metals.

🎯 Exam Tip: Identify metalloids by their dual nature, possessing characteristics of both metals and non-metals, such as electrical conductivity that can be altered.

Question 13. Elements are generally classified into .................... and .................... .
Answer: metal, non-metals In simple words: Elements are broadly categorized into metals, which are typically lustrous and conductive, and non-metals, which lack these properties.

🎯 Exam Tip: The primary classification of elements is into metals, non-metals, and metalloids, based on their distinct physical and chemical characteristics.

Question 14. The smallest particles of substances are called .................... .
Answer: molecules In simple words: Molecules are the smallest units of a substance that can exist independently and retain the chemical properties of that substance.

🎯 Exam Tip: Note that while atoms are the fundamental building blocks, for many substances, the smallest independent unit is a molecule (e.g., O2, H2O).

Question 15. To date, scientists have discovered .................... elements and of these .................... elements occur in nature.
Answer: 118, 92 In simple words: Currently, 118 elements are known, with 92 of them naturally occurring on Earth.

🎯 Exam Tip: Remember the approximate total number of known elements and the number of those that are naturally occurring, as these figures are commonly tested. (Note: These numbers can vary slightly in different contexts, but 118 and 92 are standard for foundational science.)

Question 16. .................... was the first scientist to use symbols for elements.
Answer: Berzelius In simple words: Jöns Jacob Berzelius introduced the system of using one or two letters as symbols for elements, simplifying chemical notation.

🎯 Exam Tip: Recall Berzelius as the scientist credited with developing the modern system of chemical symbols, which revolutionized how elements are represented.

Question 17. Symbol for Tungsten is .................... and it is derived from its German name .................... .
Answer: W, Wolfram In simple words: The symbol for Tungsten is 'W', which comes from its German name 'Wolfram'.

🎯 Exam Tip: Be aware that some element symbols are derived from their Latin or German names, rather than their English names, such as 'W' for Tungsten from Wolfram.

Question 18. 22-carat gold is an .................... of gold.
Answer: alloy In simple words: 22-carat gold is an alloy, meaning it's a mixture of gold with other metals to increase its hardness and durability.

🎯 Exam Tip: Understand that pure gold is too soft for most jewelry, so it is often made into an alloy (a mixture of metals) to enhance its strength and wear resistance.

Question 19. .................... of a compound is a short form of its name written using symbols of its constituent elements.
Answer: Molecular formula In simple words: A molecular formula is a concise representation of a compound's name, showing the symbols of its constituent elements and the number of atoms of each.

🎯 Exam Tip: Recognize that molecular formulas provide essential information about the types and quantities of atoms present in a compound, serving as a chemical shorthand.

Question 20. For separating insoluble particles of blood (blood cells) from its liquid part (plasma), .................... method is used.
Answer: centrifugation In simple words: Centrifugation is the method employed to separate blood cells, which are insoluble particles, from the liquid plasma component of blood due to differences in density.

🎯 Exam Tip: Connect the specific example of blood separation to centrifugation, highlighting how density differences are exploited to isolate components in a biological context.

Give Scientific Reason.

Question 1. Saltwater is a mixture.
Answer: 1. The salt and water are mixed to give saltwater and can both be separated. 2. It can be separated by boiling saltwater. 3. Water can be obtained by condensation whereas the salt will be leftover. 4. As the salt and water do not react chemically and they are separated by simple processes therefore saltwater is called a mixture.
In simple words: Saltwater is a mixture because salt and water are physically combined, not chemically, allowing them to be separated by simple physical methods like boiling and condensation.

🎯 Exam Tip: Understanding the difference between physical mixing and chemical reaction is key to identifying mixtures versus compounds.

Question 2. Classify the following substances according to their properties (water, thermocol, soil, iron, coal, paper, rubber, copper, coir, plastic)
Answer:

In simple words: Substances are classified based on whether they are metals, mixtures (physically combined), or compounds (chemically combined) according to their unique properties.

🎯 Exam Tip: Be able to identify common substances and categorize them correctly into elements (metals/non-metals), compounds, or mixtures based on their defining characteristics.

Can You Tell?

Question 1. What are objects made of?
Answer: An object is made of a certain substance,
(i) The term matter is also used as a synonym of substance,
(ii) Object is made of matter.
In simple words: All objects are made of matter, which is essentially any substance that has mass and occupies space.

🎯 Exam Tip: Remember that "matter" and "substance" are often used interchangeably to describe what objects are composed of.

Question 2. What are these articles of everyday use made of?
Answer: - Electric wire - copper-metal - Kitchen utensils - stainless steel, Brass-alloy (aluminium-metal). - Nails - iron-metal - Tables, chairs - wood, plastic - Sugar - sucrose - Window panes - glass - Salt - NaCl (Sodium chloride) it is a compound.
In simple words: Everyday items are made from a variety of materials, including metals, alloys, organic compounds like sugar, and inorganic compounds like salt, chosen for their specific properties.

🎯 Exam Tip: When listing materials, specify if they are elements, compounds, or mixtures where appropriate, as seen with copper-metal or NaCl (Sodium chloride) compound.

Question 3. What do the short-forms Dr, H.M., AC, Adv., C.M., DC stand for?
Answer: Short forms of Dr. - Doctor, H.M. - Headmaster, AC - Air conditioner, Adv - Advance, C.M. - Chief Minister, DC - Direct current
In simple words: Short forms are abbreviations used for common titles, designations, or terms to represent them concisely.

🎯 Exam Tip: This question tests general knowledge and the ability to recognize common abbreviations.

Question 4. Which metals do we use in day-to-day life?
Answer: - Gold and silver - used in jewellery, computer and solar cells - Iron, copper, aluminium - used to make utensils - Copper - used in electrical gadgets - Tungsten - used in electric bulbs. - Zinc - for coating on iron to prevent rusting - Tin - for coating on copper and brass vessels - Iron - nails, agricultural equipments, in construction of buildings, to make steel
In simple words: Many metals like gold, silver, iron, copper, aluminum, tungsten, zinc, and tin are essential in our daily lives, serving various purposes from jewelry to construction and electronics due to their unique properties.

🎯 Exam Tip: Focus on linking each metal with its primary applications, demonstrating an understanding of their practical uses.

Question 5. Are metals elements?
Answer: Yes, metals are elements.
In simple words: Metals are pure substances that cannot be broken down further by chemical means, classifying them as elements.

🎯 Exam Tip: Remember the definition of an element: a pure substance consisting only of atoms that all have the same numbers of protons in their nuclei.

Question 6. Which element helps combustion?
Answer: Oxygen helps combustion.
In simple words: Oxygen is the element necessary for the process of combustion, or burning, to occur.

🎯 Exam Tip: Clearly state the element's name; avoid providing additional, unrequested information.

Question 7. Does water help combustion?
Answer: 1. Water is formed by a combination of hydrogen and oxygen but does not help combustion. 2. It is used to extinguish a fire.
In simple words: No, water does not help combustion; instead, it is commonly used to put out fires because it cools and smothers the flame.

🎯 Exam Tip: Distinguish between the constituent elements of water (hydrogen and oxygen) and water itself as a compound with different properties.

Question 8. What are the mixtures used in everyday life?
Answer: Oil and water, lemon juice and sherbet, bhel, honey and tea, milk and chocolate, coffee and cream, salt and water, smog (smoke + fog) air (oxygen + nitrogen), salad, milk.
In simple words: Everyday life involves many mixtures, such as oil and water, various food items like bhel and salad, beverages like tea and coffee, and even the air we breathe.

🎯 Exam Tip: Provide a diverse list of common examples to show a broad understanding of mixtures in daily contexts.

Question 9. Are all mixtures useful to us?
Answer: No, adulterated foodstuff is also a kind of mixture and it is not useful. It is harmful, because when an unwanted and harmful substance is mixed with another substance the resulting mixture no longer remains useful.
In simple words: Not all mixtures are useful; some, like adulterated food, can be harmful because they contain unwanted substances that compromise their quality or safety.

🎯 Exam Tip: Provide a clear example of a harmful mixture (e.g., adulterated food) to support your answer effectively.

Question 10. How will you separate each component from a mixture of semolina, salt and iron filings?
Answer: 1. If a magnet is moved through this mixture all iron filings will stick to the magnet, remove them. 2. Add water to the remaining mixture, all salt will dissolve and then filter through filter paper. 3. Samolina will settle in filter paper. 4. The filtrate will be saltwater and salt can be separated by evaporation or distillation.
In simple words: To separate semolina, salt, and iron filings, first use a magnet to remove the iron, then dissolve the salt in water and filter out the semolina, and finally evaporate the water to recover the salt.

🎯 Exam Tip: Break down the separation process into distinct, sequential steps, explaining the physical principle used for each component.

Use Your Brainpower!

Question 1. In day to day life we come across many things in our surroundings. We touch them, we study their properties. Are all these things made from only one kind of matter or from more than one kind of matters?
Answer: 1. Things are made from only one kind of matter or may be made from more than one kind of matter. 2. When a matter is made up of only one type of atoms it is called an element. 3. We find many elements in our surroundings. 4. But we also see many substances which are made up of two or more elements they are called compounds. 5. Also we see many substances which are formed by physically mixing two or more elements, they are called mixtures.
In simple words: Objects in our surroundings can be made from a single type of matter (elements) or multiple types, which are either chemically combined (compounds) or physically mixed (mixtures).

🎯 Exam Tip: Clearly define and differentiate between elements, compounds, and mixtures to demonstrate a fundamental understanding of matter composition.

Question 2. Classify the following according to the nature of matter in them - whether it is made from one kind of matter or from more than one kind of matter, and whether it is in solid, liquid or gaseous state: an engraved idol, gold, milk, water, a plank, concrete, salt, soil, coal, smoke, sherbet, cooked khichadi, steam.
Answer:

In simple words: This table categorizes various common substances by their physical state (solid, liquid, gaseous) and whether they are composed of one type of particle (elements/compounds) or multiple types (mixtures).

🎯 Exam Tip: Practice classifying different everyday materials based on their state and composition to reinforce understanding of basic chemistry principles.

Question 3. Which of the following are mixtures? (water, sharbet, iron, steel, coal, air, salt, copper, brass, soil)
Answer: Mixtures: sherbet, steel, air, brass and soil
In simple words: Among the given substances, sherbet, steel, air, brass, and soil are mixtures because they consist of multiple components physically combined.

🎯 Exam Tip: Identify mixtures by looking for substances where multiple components are present but not chemically bonded, maintaining their individual properties.

Question 4. Which elements are present in air?
Answer: Nearly all of the earth's atmosphere is made up of gases - Nitrogen, Oxygen, Carbon dioxide, Argon and Neon, Helium and Krypton.
In simple words: Air is a mixture of gases primarily composed of Nitrogen and Oxygen, with smaller amounts of Carbon dioxide, Argon, Neon, Helium, and Krypton.

🎯 Exam Tip: Recall the major components of air, noting that Nitrogen and Oxygen are the most abundant elements.

Question 5. Is carbon dioxide an element?
Answer: No, carbon dioxide is a compound. A molecule of the compound CO2 contains one atom of the element carbon and two atoms of the element oxygen.
In simple words: Carbon dioxide is a compound, not an element, because it is formed from the chemical combination of carbon and oxygen atoms.

🎯 Exam Tip: Understand that elements are single types of atoms, while compounds are formed by two or more different elements chemically bonded together.

Question 6. What are the properties of elements due to?
Answer: Properties of elements are due to molecules present in it. The molecules are made of one or more atoms which are exactly alike. The mass and volume of atoms of different elements are different.
In simple words: The unique properties of an element arise from the characteristics of its constituent atoms and how these atoms are arranged within its molecules.

🎯 Exam Tip: Focus on the atomic structure as the basis for an element's properties, noting that atoms of different elements vary in mass and volume.

Question 7. Are the atoms of different elements similar or dissimilar?
Answer: The atoms of different elements are dissimilar.
In simple words: Atoms of different elements are dissimilar because they have distinct numbers of protons, neutrons, and electrons, leading to different chemical and physical properties.

🎯 Exam Tip: Remember that each element is defined by its unique atomic number (number of protons), making its atoms distinct from those of other elements.

Question 8. Is the water that falls from clouds naturally pure?
Answer: 1. Any form of water that falls from the clouds is known as precipitation. Several forms - rain, snow, hail stones. 2. Yes, it is pure as water vapours condense to form rain. 3. The same process is used in distillation to obtain the purest water.
In simple words: Water from clouds is generally considered pure because it forms from condensed water vapor, similar to distillation, but it can pick up atmospheric pollutants on its way down.

🎯 Exam Tip: Recognize that while condensed water vapor is pure, precipitation can become slightly impure by dissolving gases and particles from the atmosphere.

Question 9. Which properties of a liquid are seen in the distillation method?
Answer: Liquid when boiled turns into gaseous state (e.g. water vapours) and on cooling it condenses to liquid.
In simple words: Distillation utilizes the properties of a liquid to vaporize when heated and then condense back into liquid form upon cooling, separating it from impurities or other liquids with different boiling points.

🎯 Exam Tip: Understand that distillation relies on the differences in boiling points and the ability of liquids to undergo phase changes (vaporization and condensation).

Question 10. For what purposes is distilled water used?
Answer: Distilled water is used in pharmacy as a solvent, in photography to wash the negatives, in laboratory experiments and in cleaning medical tools.
In simple words: Distilled water is used where high purity is required, such as in pharmaceutical preparations, photographic development, laboratory work, and medical equipment cleaning.

🎯 Exam Tip: List a variety of applications to show the importance of pure water in different fields.

Answer the following questions:

Question 1.a. Take a piece of chalk and keep on dividing it in to smaller pieces, what will happen?
Answer: We will get very tiny particles of chalk.
In simple words: Dividing a piece of chalk repeatedly will result in smaller and smaller particles of chalk, but it will still be chalk.

🎯 Exam Tip: This illustrates that physical changes (like breaking) do not change the fundamental composition of a substance, only its size.

Question b. Wipe a drop of ink with a handkerchief what effect does it have on the cloth of the handkerchief?
Answer: The cloth will absorb the ink drop and cloth will have a stain mark on it.
In simple words: The handkerchief will absorb the ink, leaving a permanent stain because ink particles get trapped within the fabric fibers.

🎯 Exam Tip: Consider the principles of absorption and capillary action when explaining how liquids interact with porous materials.

Question c. What happens when the lid of a bottle of perfume is opened?
Answer: The molecules of perfume move out of the bottle and collide with other molecules in the air and eventually perfume spreads throughout the room.
In simple words: When a perfume bottle is opened, its molecules diffuse into the air, spreading throughout the room due to their kinetic energy and collisions with air particles.

🎯 Exam Tip: This demonstrates the concept of diffusion, where particles move from an area of higher concentration to lower concentration.

Question 2. Fill water in a spray pump, spray the water and observe the spray.
Answer: When we spray the water, spray is composed of small particles of water. They are very tiny that we can not see them.
In simple words: A water spray consists of many tiny, unseeable water droplets, formed when the pump breaks the liquid into fine particles.

🎯 Exam Tip: Observe that spraying changes the physical form of the water into fine particles, demonstrating the particulate nature of matter.

Question 3. Take water in a tea pot and cover it, heat the water to a boil. What do you see on the inside of the lid?
Answer: 1. When we boil the water in a tea pot it boils and changes into gaseous state. 2. We find vapours (steam) but when we cover it with a lid, the water vapour cools down, condenses into liquid. So we find water droplets on the inside of the lid. Liquid
\( \implies \) gaseous
\( \implies \) liquid (Heat) (Cools)
In simple words: Boiling water turns it into steam, which then cools and condenses into visible water droplets on the cooler surface of the lid.

🎯 Exam Tip: This experiment illustrates the phase changes of water: liquid to gas (evaporation/boiling) and gas to liquid (condensation).

Question 4.a. Take sugar in a test tube and heat the test tube. Observe what happens. What remains behind?
Answer: When a test tube containing sugar is heated, the sugar melts and then it loses water leaving behind a black substance. This black substance is carbon. Sugar is sucrose, a molecule of sugar is composed of 12 atoms of carbon, 22 atoms of hydrogen and 11 atoms of oxygen. (C12H22O11). 1. Sugar is a compound made from these three elements carbon, hydrogen, oxygen. 2. It is a Carbohydrate.
In simple words: Heating sugar causes it to melt, decompose, and lose water, leaving behind black carbon, demonstrating that sugar is a compound made of carbon, hydrogen, and oxygen.

🎯 Exam Tip: This experiment shows the decomposition of a compound (sugar) into its constituent elements (carbon) and other products (water), indicating a chemical change.

Question b. Using tongs hold a magnesium ribbon in a flame and observe what changes took place?
Answer: When a magnesium ribbon is ignited, light and heat are produced. Magnesium reacts chemically with oxygen in the air \[2Mg(s) + O_2(g) \rightarrow 2MgO(s)\] Magnesium oxide is produced.
In simple words: Burning a magnesium ribbon in a flame produces intense light and heat as magnesium chemically reacts with oxygen to form magnesium oxide.

🎯 Exam Tip: This is a classic example of a chemical reaction where a new substance (magnesium oxide) with different properties is formed, accompanied by energy release.

Question c. What does the name carbon dioxide imply - how many and which elements is this substance made of?
Answer: 1. Carbon dioxide is a compound. It is a tasteless, odourless gas. It is a natural product of respiration. 2. Plants use this to produce food. 3. Humans breath out the CO2. [A molecule of the compound carbon dioxide contains one atom of the element carbon and two atoms of the element oxygen.]
In simple words: Carbon dioxide, a compound, implies it's made of one carbon atom and two oxygen atoms, crucial for plant photosynthesis and a byproduct of human respiration.

🎯 Exam Tip: The prefix "di-" in dioxide directly indicates the presence of two oxygen atoms, aiding in understanding its chemical composition.

Question d. Which of these are compound, which are elements?
Answer: - Water - compound H2O (hydrogen + oxygen), Oxygen - Element - Carbon dioxide - compound CO2 (Carbon + Oxygen)
In simple words: Oxygen is an element, while water and carbon dioxide are compounds because they are formed by the chemical combination of two or more different elements.

🎯 Exam Tip: Differentiate elements from compounds based on whether they consist of a single type of atom or multiple types chemically bonded.

Question e. What is the smallest particle of a compound called?
Answer: The smallest particle of a compound is called molecule.
In simple words: The smallest unit of a compound that still retains its chemical properties is a molecule.

🎯 Exam Tip: Remember that for elements, the smallest particle is an atom, but for compounds, it is a molecule.

Question 5. From the internet or reference books obtain information about elements and prepare a table according to the format given below:
Answer:

In simple words: This table provides key information about various elements, including their names, symbols, discoverers, physical states, and common applications in different fields.

🎯 Exam Tip: Focus on memorizing the symbols and primary uses of common elements, as well as recognizing their state at room temperature.

Question 6. Some methods of separating the components of a mixture.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र विभिन्न मिश्रणों को अलग करने के साधारण तरीकों को दर्शाता है। इसमें (1) ओसाना (विनोइंग), (2) छानना (फिल्ट्रेशन), (3) हाथ से चुनना (हैंड पिकिंग), (4) मथना (चर्निंग), और (5) छलनी से छानना (सीविंग) शामिल हैं।
Answer: 1. Winnowing 2. Filteration 3. Hand picking 4. Churning 5. Sieving
In simple words: The diagram illustrates common physical methods for separating mixture components, such as winnowing for lighter particles, filtration for insoluble solids, hand picking for larger impurities, churning for separating liquids of different densities, and sieving for different-sized solids.

🎯 Exam Tip: Be prepared to identify and describe various simple separation techniques based on visual representations or practical scenarios.

Question 7. What is a molecular formula?
Answer: Like an element, a compound is also written in an abridged form. A molecule of a compound is formed by a chemical combination of atoms of two or more elements. Therefore a molecular formula is used to represent a compound. Molecular formula of a compound is a short form of its name written with the help of the symbols of constituent elements and the number of their respective atoms, e.g.: Nael - Sodium chloride.
In simple words: A molecular formula is a concise representation of a compound, showing the symbols of its constituent elements and the exact number of atoms of each element present in one molecule.

🎯 Exam Tip: Understand that a molecular formula provides both qualitative (which elements) and quantitative (how many atoms of each) information about a compound.

Question 8. Collect information and prepare table:
Answer:

In simple words: This table compiles detailed information on several common compounds, outlining their constituent elements, atomic composition, molecular formulas, and key characteristics or uses.

🎯 Exam Tip: Pay close attention to the number of atoms for each element within a compound to correctly write its molecular formula and understand its properties.

Write Short Notes On:

Question a. Atoms
Answer: Atoms are basic building blocks of matter. Desk, chair, air are made up of atoms.
In simple words: Atoms are the fundamental, indivisible particles that make up all matter, forming the basis of everything around us.

🎯 Exam Tip: Define atoms as the smallest units of an element that retain its chemical identity.

Question b. Compounds
Answer: 1. A compound is a pure substance that contains two or more elements. Compounds are chemical combination of elements with properties that are different from the elements that formed them. 2. Substance is a compound only if its molecules are made up of atoms of different types e.g. Water, one molecule of water is made of two atoms of hydrogen and one atom of oxygen.
In simple words: Compounds are pure substances formed when two or more different elements chemically combine in a fixed ratio, resulting in a new substance with properties distinct from its constituent elements.

🎯 Exam Tip: Emphasize that compounds involve chemical bonding and result in new properties, unlike mixtures.

Question c. Mixtures
Answer: 1. A mixture is two or more elements or compounds which are combined physically but no chemical reaction occurs. 2. This means you can separate them again, e.g. air, brass.
In simple words: Mixtures are formed by the physical combination of two or more substances (elements or compounds) without any chemical reaction, allowing their components to be separated by physical means.

🎯 Exam Tip: The key characteristic of mixtures is that components retain their individual properties and can be separated physically.

Question 9. Write short notes on: (1) Distillation (2) Sublimation (3) Magnetic separation (4) Sedimentation (5) Filtration (6) Evaporation
Answer: 1. Distillation: It is a process of heating a solution containing soluble solids to form vapours of the liquid and then cooling the vapours to get the liquid back. e.g. A mixture of common salt and water is taken in distillation flask and heated. Steam rises up and comes out into condenser. 2. Sublimation: It is a process in which some solids on heating are transformed directly to vapour without passing through the liquid state,
(i) It is used to separate a mixture of solids. The vapours are cooled separately,
(ii) Used to separate ammonium chloride, iodine, camphor and sulphur from any mixture. 3. Magnetic separation: A mixture with iron fillings as one of the components can be separated using magnet to attract the iron particles away from the mixture. 4. Sedimentation:
(i) It is a process of separating an insoluble solid from a liquid in which it is suspended, by allowing it to settle to the bottom of the container, e.g. Muddy water contains heavier particles like sand and soil,
(ii) Leave this muddy water undisturbed for some time,
(iii) The heavier soil and sand particles settle down and the clear upper water is poured out by decantation. 5. Filtration: It is used for separating insoluble solids from a liquid, e.g. mixture of chalk and water is poured through a filter paper in a funnel while the water gets collected in the beaker below, chalk is retained in the filter paper. 6. Evaporation: It is used for recovering dissolved solid substances from solutions by evaporation e.g. sugar can be recovered from sugar-water.
In simple words: These are physical separation techniques: Distillation separates liquids based on boiling points; Sublimation converts solids directly to gas; Magnetic separation uses magnets for magnetic components; Sedimentation settles heavy insoluble solids; Filtration uses a filter to trap insoluble solids; and Evaporation recovers dissolved solids from a liquid.

🎯 Exam Tip: For each method, know its principle of separation, what type of mixture it's suitable for, and a common example.

Question 10. Name the method you will use to separate the following mixtures:
1. Cream from buttermilk. 2. Mud from muddy water. 3. Stones from grains. 4. Tea leaves from boiled tea. 5. Salt from water. 6. Kerosene and water. 7. Blood cells and plasma. 8. Ink from water
Answer: 1. Churning 2. Sedimentation and decantation 3. hand picking 4. filtration 5. distillation 6. separating funnel 7. Centrifugation 8. Chromatography
In simple words: Different mixtures require specific separation methods: churning for cream, sedimentation for mud, hand picking for stones, filtration for tea leaves, distillation for salt from water, a separating funnel for immiscible liquids, centrifugation for blood components, and chromatography for ink components.

🎯 Exam Tip: Match the appropriate separation technique to each mixture, considering the physical properties (e.g., density, particle size, miscibility) of its components.

Question 11. Draw the experimental setup of weperation using separating funnel:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक पृथक्करण कीप (separating funnel) का उपयोग करके दो अमिश्रणीय तरल पदार्थों, जैसे कि केरोसिन और पानी, को अलग करने की प्रक्रिया को दर्शाता है। इसमें भारी तरल नीचे बैठ जाता है और हल्का तरल ऊपर रहता है, जिसे स्टॉपकॉक खोलकर अलग किया जा सकता है।

Answer: The experimental setup for separation using a separating funnel visually depicts a funnel with two immiscible liquids, like kerosene (lighter) floating above water (heavier), with a stopcock at the bottom to control the drainage of the heavier liquid.
In simple words: A separating funnel is used to separate two immiscible liquids by allowing the denser liquid to settle at the bottom and then draining it out through a stopcock.

🎯 Exam Tip: When describing the setup, highlight the key components like the separating funnel, the layers of immiscible liquids, and the stopcock for controlled separation.