Nature of Matter: Elements, Compounds, and Mixtures

(c) mixture

(d) components

(c) retain their individual properties

(b) Sprout salad

(d) are evenly distributed and cannot be distinguished

(b) iron, nickel, chromium, and a small amount of carbon

(a) copper and zinc

(d) tin

(a) a mixture of two or more metals with properties distinct from its constituents

(c) improve digestion and boost immunity

(d) 78%

(c) Oxygen

(a) calcium hydroxide

(d) insoluble calcium carbonate

(b) heat

(c) dust particles

(b) pollutants

(a) air quality

(d) Carbon monoxide

(a) gas and liquid

(d) solid and gas

(b) uniform liquid-in-liquid mixture

(c) a non-uniform mixture

(a) baking soda and tartaric acid

(c) obtain pure substances

(a) the illegal addition of cheaper or poor-quality substances to a product

(d) cannot be separated into other kinds of matter by any physical process

(a) consists of the same type of particles

(c) hydrogen and oxygen

(d) hydrogen

(b) oxygen

(a) double

(c) cannot be further broken down into simpler substances

(a) 118

(c) Eleven

(d) non-metals

(c) mercury

(a) bromine

(b) Gallium and caesium

(c) metalloids

(b) Sulfur

(c) two atoms of oxygen

(d) Na

(b) Fe

(a) Cl

(c) fixed ratios

(b) entirely different from those of its constituent elements

(d) 2:1

(b) 1:1

(d) a soft metal and a hazardous gas

(b) charcoal (carbon)

(d) carbon, hydrogen, and oxygen

(b) iron sulfide

(a) rotten eggs

(d) native minerals

components

uniform

Brass

78

carbon dioxide

physical

atoms

molecule

2:1

charcoal (carbon)

iron sulfide

metalloids

bromine

minerals

native

False (they do not react chemically; each retains its properties)

True

True

False (nitrogen does not take part in combustion; oxygen supports it)

True

False (they are pollutants, not an integral part of air)

True

False (it means unadulterated; milk is a mixture of many substances)

False (it needs a chemical process like passing electricity; no physical method works)

True

False (most elements exist in the solid state)

True

False (the elements of a compound cannot be separated by physical methods)

False (iron sulfide is a compound with different properties and is not attracted by a magnet)

True

A–5, B–2, C–1, D–3, E–4

A–5, B–4, C–1, D–3, E–2

(c)

(b)

(a) — Nitrogen, not oxygen, makes up about 78% of air.

(d)

(b) — The pop sound confirms hydrogen, not oxygen.

(c) — Iron sulfide is a compound whose properties differ from iron; it is not attracted by a magnet.

(a) — Both statements are true, but the composition does not explain the medicinal use.

(a)

Hint: A mixture is formed when two or more substances are mixed, each retaining its properties, without a chemical reaction. Examples — poha, sprout salad, lemonade.

Hint: In a uniform mixture the components are evenly distributed and cannot be distinguished (e.g., sugar in water); in a non-uniform mixture the components are visible (e.g., sprout salad, sand in water).

Hint: Alloys are uniform mixtures of two or more metals (or metals with a small amount of non-metal) that appear the same throughout. Examples — brass (copper + zinc); bronze (copper + tin); stainless steel (iron, nickel, chromium, carbon).

Hint: Air is a uniform mixture because its gases (mainly nitrogen, oxygen, argon, carbon dioxide, water vapour) are evenly distributed and the components do not react chemically with one another.

Hint: Leave freshly prepared lime water (calcium hydroxide solution) in a petri dish, stirring at intervals. It turns milky because CO₂ in air reacts with calcium hydroxide to form insoluble calcium carbonate.

Hint: Their number and nature vary from place to place and time to time; they are suspended impurities such as soot and particulate matter, not a fixed component of air.

Hint: In common usage 'pure' means unadulterated (no cheaper substances added); in science 'pure' means the substance has no other substance present and consists of the same type of particles.

Hint: Milk is made up of more than one substance (water, fats, proteins, minerals), so its particles are not all of one type; hence scientifically it is not a pure substance.

Hint: Elements are the simplest substances that cannot be further broken down into simpler substances; they are the building blocks of all matter. Examples — gold, silver, sulfur, carbon, hydrogen, oxygen, iron.

Hint: Sodium – Na; iron – Fe; chlorine – Cl; hydrogen – H; oxygen – O; carbon – C.

Hint: A molecule is a stable particle formed when two or more atoms of an element combine. Two atoms of oxygen combine to form one molecule of oxygen (O₂).

Hint: The ratio is 2:1. It was shown by the electrolysis of water, in which the volume of hydrogen collected was double the volume of oxygen.

Hint: Sodium (a soft metal) and chlorine (a hazardous gas) combine chemically in a fixed 1:1 ratio to form the harmless substance sodium chloride, whose properties differ from its elements and which cannot be separated by physical methods.

Hint: Sugar turns brown, then chars black; water droplets collect near the mouth and charcoal (carbon) is left behind. This proves sugar is a compound of carbon, hydrogen, and oxygen, not an element.

Hint: Iron sulfide + dilute hydrochloric acid → Iron chloride + Hydrogen sulfide (gas with a rotten-egg smell).

Hint: Sample A is a mixture of iron and sulfur; iron is still free and is attracted by the magnet. Sample B is iron sulfide, a compound with new properties, so the magnet has no effect.

Hint: Sample A gives colourless, odourless hydrogen that burns with a pop sound. Sample B gives colourless hydrogen sulfide with a rotten-egg-like odour.

Hint: Native minerals are minerals that are pure elements and not compounds. Examples — gold, silver, copper (metals) and sulfur, carbon (non-metals).

Hint: Quartz, calcite, mica, pyroxene, olivine, and talc are minerals. Cement is made from calcite, quartz, alumina, and iron oxide, which are minerals or obtained from minerals.

Hint: Graphene aerogel is a 'wonder' material made from carbon, said to be the lightest material on earth. It is highly porous, so it can potentially be used to clean up oil spills on seas and land.

Introduction: Elements and compounds are the two kinds of pure substances, but they differ in composition and separability.
Key Points:
1. Definition — An element cannot be broken down into simpler substances; a compound contains two or more elements combined chemically.
2. Composition — An element has only one type of atom, while a compound has elements combined in a fixed ratio.
3. Separation — Elements cannot be decomposed by physical methods; compounds also cannot be separated by physical methods into their constituent elements.
Conclusion: Oxygen is an element, while water and sodium chloride are compounds made of elements in fixed ratios.

Introduction: Mixtures and compounds both contain two or more substances, but they differ fundamentally in how components combine.
Key Points:
1. Nature of components — In mixtures, components retain their properties; in compounds, properties become entirely different from constituent elements.
2. Ratio of components — Mixture components can be in any ratio; compounds always contain elements in fixed ratios.
3. Separation — Mixture components can be separated by physical methods; compound elements cannot be separated by physical methods.
Conclusion: Air and poha are mixtures, whereas water (H:O = 2:1) and iron sulfide are compounds.

Introduction: Passing electricity through water shows that water is made of two elements, hydrogen and oxygen.
Key Points:
1. Set-up — Two water-filled test tubes are placed on the terminals of a 9 V battery inside water acidified with dilute sulfuric acid.
2. Collection — Gas bubbles form at both terminals; hydrogen collects in double the volume of oxygen.
3. Identification — Hydrogen burns with a pop sound near a candle; oxygen makes the candle flame glow brighter.
Conclusion: Water decomposes into hydrogen and oxygen in a 2:1 ratio, proving it is a compound.

Introduction: Sample A is a mixture of iron filings and sulfur; Sample B is the compound formed by heating it.
Key Points:
1. Appearance — Sample A shows separate black and yellow particles, while Sample B is a uniform black mass throughout.
2. Magnet test — In Sample A the magnet attracts iron filings; in Sample B the magnet has no effect.
3. Gas test — With dilute hydrochloric acid, Sample A gives odourless hydrogen, while Sample B gives hydrogen sulfide smelling of rotten eggs.
Conclusion: Sample A is a mixture whose components retain properties, whereas Sample B is iron sulfide, a new compound.

Introduction: Mixtures are classified by the physical states of their components — gas, liquid, or solid.
Key Points:
1. Gas mixtures — Gas in gas gives air; gas in liquid gives aerated water and oxygen dissolved in water.
2. Solid-containing mixtures — Solid in gas gives carbon particles in air; solid in liquid gives sand and water.
3. Liquid and solid mixtures — Liquid in liquid gives vinegar and oil-water; solid in solid gives baking powder and alloys.
Conclusion: The type of mixture depends on the physical states of the components mixed together.

Introduction: Air surrounds us everywhere and is a mixture of several gases plus suspended particles.
Key Points:
1. Main components — Air is mainly nitrogen (about 78%), oxygen, argon, carbon dioxide, and water vapour.
2. No chemical reaction — The gases do not react chemically and each retains its own properties, like nitrogen not supporting combustion.
3. Even distribution — The gases are evenly distributed, so air is a uniform mixture, not a compound.
Conclusion: Air is a uniform mixture whose components keep their individual properties.

Introduction: Alloys are uniform mixtures of two or more metals mixed so thoroughly that individual substances cannot be seen.
Key Points:
1. Definition — An alloy appears the same throughout because its components are mixed uniformly, like a mixture, not a compound.
2. Examples — Stainless steel contains iron, nickel, chromium, and a little carbon; brass contains copper and zinc; bronze contains copper and tin.
3. Usefulness — Stainless steel is stronger and more durable than pure iron, so engineers prefer alloys for utensils and structures.
Conclusion: Alloys give materials better properties than their pure constituent metals.

Introduction: The word 'pure' is used differently in daily life and in science.
Key Points:
1. Scientific meaning — A pure substance contains no other substance and has only one type of particle.
2. Physical separation — A pure substance cannot be separated into other kinds of matter by any physical process.
3. Types — Pure substances are of two kinds: elements, like oxygen, and compounds, like water and sugar.
Conclusion: Only elements and compounds qualify as pure substances; everything else is a mixture.

Introduction: Elements are classified according to their properties into metals, non-metals, and metalloids.
Key Points:
1. Metals — Gold, silver, magnesium, iron, and aluminium are metals used in construction and utensils.
2. Non-metals — Carbon, sulfur, hydrogen, and oxygen are non-metals; all gaseous elements are non-metals.
3. Metalloids — Silicon and boron have intermediate properties between metals and non-metals.
Conclusion: The 118 known elements are broadly grouped into these three classes.

Introduction: Of the 118 elements known at present, elements exist in solid, liquid, and gaseous states at room temperature.
Key Points:
1. Solids and gases — Most elements are solids; eleven gaseous elements exist, all of them non-metals.
2. Liquids — Only two elements are liquid: mercury, a metal, and bromine, a non-metal.
3. Low-melting solids — Gallium and caesium are solids but turn liquid at around 30 °C.
Conclusion: The physical state of an element at room temperature varies across the periodic table.

Introduction: Minerals are natural, solid substances found on the Earth with a fixed chemical composition.
Key Points:
1. Native minerals — A few minerals are pure elements, not compounds, such as gold, silver, copper, sulfur, and carbon.
2. Compound minerals — Most minerals are compounds of more than one element, like quartz, calcite, mica, pyroxene, and olivine.
3. Everyday use — Cement is made from calcite, quartz, alumina, and iron oxide; talcum powder is made from talc.
Conclusion: Most rocks are mixtures of these minerals, which supply many daily-use materials.

Introduction: Common salt is a compound formed from two dangerous-looking elements that combine into a harmless substance.
Key Points:
1. Constituents — Sodium is a soft metal and chlorine is a hazardous gas.
2. Formation — They combine chemically in a fixed 1:1 ratio to form sodium chloride.
3. Different properties — The compound is harmless and taste-enhancing, unlike its constituent elements.
Conclusion: Sodium chloride shows that a compound's properties differ completely from its elements.

Introduction: Heating sugar in a boiling tube reveals that sugar is a compound of three elements.
Key Points:
1. Observation — Sugar first turns brown, then chars to a blackish mass on gentle heating.
2. Products — Small droplets of water collect near the open end and charcoal (carbon) remains behind.
3. Conclusion — Since water itself contains hydrogen and oxygen, sugar must consist of carbon, hydrogen, and oxygen.
Conclusion: Sugar is a chemical compound, not an element, because it decomposes into simpler substances.

Introduction: Elements, compounds, and mixtures are all around us and support everyday life and innovation.
Key Points:
1. Everyday examples — Air is a mixture of gases, water is a compound, and iron and aluminium build bridges and vehicles.
2. Innovation — Chemists create life-saving medicines, vaccines, and fertilisers by studying how elements combine into compounds.
3. Materials — Engineers design alloys like stainless steel; wood, steel, and concrete used in buildings are all mixtures.
Conclusion: Understanding elements, compounds, and mixtures is the key to innovation and progress.

Introduction: Matter is anything that has mass and occupies space; most things around us are matter.
Key Points:
1. Definition — Matter is made of tiny particles and includes everything with mass and volume.
2. Non-matter examples — Light, heat, and electricity are important parts of our world but are not matter.
3. Thoughts too — Even thoughts and emotions, though real, are not made of matter.
Conclusion: Knowing what is matter — and what is not — helps us better understand the world around us.

Hint: (a) Non-uniform mixture — the components are visible separately and unevenly distributed. (b) Uniform mixture (solution) — sugar and water cannot be seen separately. (c) Green gram, chickpeas, onion, and tomato.

Hint: (a) Carbon dioxide in air reacts with calcium hydroxide to form insoluble calcium carbonate. (b) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water. (c) It demonstrates the presence of carbon dioxide in air.

Hint: (a) Dust particles; they are not an integral part of air. (b) They are pollutants. (c) AQI (Air Quality Index); major pollutants include particulate matter, carbon monoxide, ozone, nitrogen dioxide, and sulfur dioxide.

Hint: (a) Pop sound → hydrogen; brighter flame → oxygen. (b) Hydrogen : oxygen = 2 : 1. (c) Water is a compound made of hydrogen and oxygen combined in a fixed ratio.

Hint: (a) Charcoal (carbon). (b) The water came from the dry sugar itself, not from the air, since the tube is being heated. (c) Sugar is a compound because it decomposes on heating into carbon and water, and water itself contains hydrogen and oxygen.

Hint: (a) Sample B is iron sulfide; being a compound with new properties, it is not attracted by a magnet. (b) Iron sulfide + dilute hydrochloric acid → Iron chloride + Hydrogen sulfide. (c) Sample A gives colourless, odourless hydrogen that burns with a pop; Sample B gives hydrogen sulfide with a rotten-egg smell.

Hint: (a) They are alloys — uniform mixtures in which the metals are mixed so thoroughly that individual substances cannot be seen. (b) Stainless steel = iron, nickel, chromium, and a small amount of carbon; brass = copper and zinc. (c) Stainless steel is stronger and more durable than pure iron.

Hint: (a) Cement is made from calcite, quartz, alumina, and iron oxide — minerals or substances obtained from minerals. (b) Talc. (c) Most minerals are compounds (e.g., quartz, calcite); a few are pure elements called native minerals (e.g., gold, copper, sulfur, carbon).

Hint: (a) Graphene aerogel, made from carbon. (b) It is highly porous with a high absorbing capacity, so it can absorb oil. (c) Brass or bronze (used in Dhokra art).

Hint: (a) The wax is melted out, leaving a hollow clay mould that the molten metal fills and hardens in. (b) Molten brass or bronze gives strength and a shiny golden colour. (c) Copper — element; bronze — alloy (mixture); beeswax — mixture.

Introduction: Most things around us are not made of one substance but are mixtures of two or more substances.
Key Points:
1. Definition — A mixture is formed when two or more substances are mixed, each retaining its properties without a chemical reaction.
2. Components — The individual substances in a mixture are called components; they do not react chemically with each other.
3. Uniform mixtures — In a uniform mixture the components are evenly distributed and cannot be seen separately, like sugar dissolved in water and air.
4. Non-uniform mixtures — In a non-uniform mixture the components are visible, like sprout salad, sand and water, and muddy water.
5. By physical state — Mixtures may be gas-in-gas (air), liquid-in-liquid (vinegar), or solid-in-solid (baking powder, alloys).
Conclusion: Mixtures are everywhere and are classified by how evenly the components are distributed.

Introduction: Elements are the simplest substances and the building blocks of all matter.
Key Points:
1. Definition — An element cannot be further broken down into simpler substances and is made up of identical atoms.
2. Metals — Gold, silver, magnesium, iron, and aluminium are metals used in construction and utensils.
3. Non-metals — Carbon, sulfur, hydrogen, and oxygen are non-metals; all gaseous elements are non-metals.
4. Metalloids — Silicon and boron have intermediate properties between metals and non-metals.
5. States at room temperature — Of 118 elements, most are solid, eleven are gases (all non-metals), and only mercury and bromine are liquid.
Conclusion: Elements are classified as metals, non-metals, and metalloids and exist in all three states at room temperature.

Introduction: When different elements combine chemically in fixed ratios, they form entirely new substances called compounds.
Key Points:
1. Definition — A compound is formed when two or more elements combine chemically in a fixed ratio to form something entirely new.
2. Fixed ratio — The constituent elements are combined in a fixed ratio, as in water where hydrogen to oxygen is 2:1.
3. Different properties — A compound's properties differ from those of its constituent elements, like water extinguishing fire though hydrogen is a fuel and oxygen supports combustion.
4. Non-separable physically — The constituents of a compound cannot be separated by any physical method.
5. Examples — Sodium chloride is formed from sodium and chlorine in 1:1 ratio; sugar is made of carbon, hydrogen, and oxygen.
Conclusion: Compounds are pure substances whose properties and fixed composition distinguish them from mixtures.

Introduction: The iron-and-sulfur activity clearly shows how a mixture differs from the compound formed by heating it.
Key Points:
1. Mixture (Sample A) — Sample A is a mixture of iron and sulfur; black and yellow particles can be seen separately.
2. Retained properties — In Sample A, iron is still attracted by a magnet, showing that components retain their properties.
3. Compound (Sample B) — Heating forms iron sulfide, a uniform black mass whose properties differ entirely.
4. Lost separability — The magnet has no effect on Sample B, and iron and sulfur can no longer be separated physically.
5. Gas test difference — Sample A gives odourless hydrogen with HCl; Sample B gives rotten-egg-smelling hydrogen sulfide.
Conclusion: Sample A is a mixture, while Sample B (iron sulfide) is a compound with completely new properties.

Introduction: Simple activities show that air contains carbon dioxide gas as well as suspended dust particles.
Key Points:
1. Lime water preparation — Calcium oxide is added to water to form calcium hydroxide (lime water), releasing heat.
2. CO₂ test — Lime water left in a petri dish turns milky as CO₂ forms insoluble calcium carbonate.
3. Word equation — Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water.
4. Dust activity — A clean black sheet of paper left near an open window collects tiny particles.
5. Pollutants and AQI — These particles are pollutants, and the AQI is a tool used to describe air quality.
Conclusion: Air is a mixture containing gases like CO₂ and suspended dust particles that are pollutants.

Introduction: The word 'pure' is used differently in common usage and in science.
Key Points:
1. Everyday meaning — In common usage, 'pure' means unadulterated, with no cheaper or poor-quality substances added.
2. Adulteration — Adulteration is the illegal addition of cheaper substances to a product to increase quantity or reduce cost.
3. Scientific meaning — In science, a pure substance has no other substance present and consists of the same type of particles.
4. No physical separation — A pure substance cannot be separated into other kinds of matter by any physical process.
5. Types — Pure substances are of two kinds: elements (oxygen) and compounds (water, sugar).
Conclusion: A label saying 'pure' may not make a substance scientifically pure if it contains more than one type of particle.

Introduction: Passing electricity through water proves that water is a compound of hydrogen and oxygen.
Key Points:
1. Set-up — A 9 V battery is placed in water acidified with a few drops of dilute sulfuric acid, with two water-filled test tubes on its terminals.
2. Observation — Gas bubbles form at both terminals and collect in the test tubes over 10–15 minutes.
3. Volume ratio — The volume of hydrogen collected is double the volume of oxygen, giving a 2:1 ratio.
4. Hydrogen test — Bringing a burning candle near one test tube produces a pop sound, confirming hydrogen.
5. Oxygen test — The candle flame glows brighter near the other test tube, confirming oxygen.
Conclusion: Water is a compound of hydrogen and oxygen combined chemically in a 2:1 ratio.

Introduction: Elements, compounds, and mixtures are all around us and drive both everyday life and scientific innovation.
Key Points:
1. Everyday examples — Air we breathe is a mixture of gases; water is a compound; iron and aluminium build bridges and vehicles.
2. Medicines and vaccines — Chemists study how elements combine into compounds to invent life-saving medicines and vaccines.
3. Fertilisers — Knowledge of compounds helps create fertilisers that enhance crop production to feed the growing population.
4. Alloys — Engineers develop alloys like stainless steel that are stronger and more durable than pure iron.
5. Wonder materials — Material scientists have developed graphene aerogel, the lightest material on earth, useful for oil-spill clean-up.
Conclusion: Understanding elements, compounds, and mixtures is the foundation of materials, medicines, and innovation.

Introduction: Minerals are natural, solid substances found on the Earth with a fixed chemical composition.
Key Points:
1. In rocks — Most rocks are mixtures of minerals that can be viewed with the eyes, a magnifying glass, or a microscope.
2. Native minerals — A few minerals are pure elements, not compounds, such as gold, silver, copper, sulfur, and carbon.
3. Compound minerals — Most minerals are compounds of more than one element, like quartz, calcite, mica, pyroxene, and olivine.
4. Cement — Cement is made from calcite, quartz, alumina, and iron oxide, which are minerals or obtained from minerals.
5. Talcum powder — Talcum powder is made from the mineral talc.
Conclusion: Minerals supply many materials of daily life and may be pure elements or compounds.

Introduction: Substances can be classified as elements, compounds, or mixtures based on their composition.
Key Points:
1. Elements — Aluminium, gold, oxygen, nitrogen, sulfur, and hydrogen are elements made of one type of atom.
2. Compounds — Carbon dioxide, magnesium oxide, rust, iron sulfide, glucose, water, sodium chloride, and baking soda are compounds.
3. Mixtures — Sand, seawater, muddy water, air, and fruit juice are mixtures of two or more substances.
4. Pure substances — The elements and compounds listed above are all pure substances.
5. Reason — Pure substances have the same type of particles and cannot be separated by physical methods, unlike mixtures.
Conclusion: Correct classification requires checking whether a substance has one type of particle (pure) or many (mixture).