Is Matter Around Us Pure? for Class 9

Classification of Matter

Matter is incredibly diverse, existing in various forms, each with distinct properties and behaviours. Matter can be categorised into two groups: pure substances and impure substances, which are also known as mixtures.

Pure Substances

1. A "pure substance" is something that is made up of only one type of tiny building block, which can be either individual atoms or groups of atoms called molecules. An atom is the tiniest indivisible unit of a chemical element, like a single building block of matter. A molecule is a group of atoms joined together by chemical bonds, creating a more complex unit with its own unique properties.
2. Pure substances always have a consistent composition, meaning their ingredients are always in the same proportions. This makes them very predictable and uniform in nature.
3. Pure substances fall into two main categories: elements and compounds. Elements are fundamental substances that consist of just one type of atom. Examples include oxygen, hydrogen, and gold. Compounds, on the other hand, are made up of different types of atoms that are chemically bonded together. For instance, water (H ₂O) is a compound made of hydrogen and oxygen atoms.

Elements

1. Elements are the basic building blocks of matter. They are pure substances that are made up of only one type of atom. For example, elements like Silver, Potassium, Hydrogen, Helium, Oxygen, Carbon, and Nitrogen.
2. One remarkable thing about elements is that they can't be broken down into simpler substances using either physical methods (like cutting or crushing) or chemical methods (reactions). They're like the fundamental puzzle pieces of the universe.
3. Elements can be grouped into categories based on their properties. Metals are elements that generally have a shiny appearance, conduct electricity and heat well, and can be shaped easily (like gold and iron). Non-metals, on the other hand, might be dull, poor conductors of heat and electricity, and not easily shaped (like oxygen and sulphur). Metalloids are sort of in-between, having some properties of both metals and non-metals (like silicon).

Types of Elements

1. Metals

1. Metals are fundamental elements that possess unique characteristics and properties. They are typically solid at room temperature, with the exception of mercury, which remains in liquid form. One notable trait of metals is their solidity and strength, contributing to their use in construction and various applications.
2. Metals have a distinct shine, referred to as metallic lustre, and this property makes them visually appealing. Moreover, metals are often malleable, meaning they can be easily shaped without breaking. This property is important for crafting various objects and structures. Additionally, metals are ductile, which means they can be stretched into thin wires without fracturing. This property is crucial for producing wires used in electronics and other industries.
3. One of the exceptional attributes of metals is their excellent electrical and thermal conductivity. This makes metals essential for conducting heat and electricity in various devices and systems. Metals also have a high density, meaning they have considerable mass in a given volume.
4. Metals find widespread use in everyday life, industry, and technology. For instance, Aluminium is light and corrosion-resistant, making it suitable for aircraft and packaging materials. Copper's exceptional electrical conductivity makes it vital in wiring and electronics. Iron, with its strength and ability to form alloys, plays a crucial role in building structures and manufacturing machinery.
5. Metals can be classified into various categories, including base metals like iron and copper, noble metals like gold and silver, and transition metals like titanium and chromium.

2. Non-metals

1. Non-metals are a distinct group of elements with specific characteristics that set them apart from metals. Unlike metals, non-metals tend to be brittle, meaning they are prone to breaking or shattering rather than being easily moulded or shaped. They lack the malleability and ductility that metals exhibit.
2. Non-metals generally lack the shiny appearance known as metallic lustre and are not good conductors of heat and electricity. This property makes them less suitable for applications involving the efficient transfer of energy. Additionally, non-metals are relatively soft compared to metals and can be easily scratched or dented.
3. Non-metals display a wide range of physical states at room temperature. Some exist as gases, such as hydrogen, oxygen, and nitrogen. Others are liquids, like bromine. There are also non-metals that are solid at room temperature, such as sulfur, carbon (in the form of graphite), and phosphorus.
4. These elements play crucial roles in various fields. Hydrogen, for instance, is used in fuel cells and as a rocket fuel. Oxygen is essential for respiration and combustion. Nitrogen is commonly found in fertilisers and serves as an inert gas in various applications. Carbon is a key building block of life and forms the basis of organic compounds. The diversity of non-metals contributes significantly to the functioning of the natural world and human technologies.

3. Metalloids

1. Metalloids, also known as semi-metals, are a group of elements that exhibit characteristics of both metals and non-metals. This unique combination of properties makes metalloids quite distinct from pure metals and non-metals.
2. One key feature of metalloids is their intermediate conductivity. While they are not as good conductors of electricity as metals, they are better conductors than non-metals. This property makes metalloids valuable in applications that require semiconductors, such as in electronic devices and computer chips.
3. Metalloids also tend to have varying degrees of lustre, which means they may have a somewhat metallic appearance, although not as pronounced as pure metals. They can be both brittle and somewhat malleable, displaying a mixture of characteristics from metals and non-metals.
4. Examples of metalloids include silicon, which is a fundamental component of many electronics and the basis of semiconductor materials; germanium, which has similar semiconductor applications; and arsenic, which has been used in various industrial and medical applications.

Compounds

1. Compounds are substances that are formed when two or more different elements chemically combine in specific proportions. In a compound, the elements are held together by chemical bonds, which are strong forces that keep their atoms connected in a particular arrangement.
2. Unlike mixtures, where different substances are simply mixed together without any chemical bonding, compounds have a consistent composition. This means that the ratio of the different types of atoms in a compound is always the same.
3. For example, water (H ₂O) is a compound composed of two hydrogen (H) atoms and one oxygen (O) atom. No matter where you find water, whether it's from a river, a raindrop, or a glass of water, it will always have the same proportion of hydrogen and oxygen atoms.
4. Compounds have unique properties that are different from the properties of the individual elements they are made of. When elements combine to form compounds, new chemical reactions occur, resulting in new substances with distinct characteristics. For instance, sodium (a metal) and chlorine (a non-metal) are both dangerous on their own, but when they chemically react and form a compound called sodium chloride (table salt), it become safe to consume.
5. To separate the elements from a compound and revert them back to their individual components, chemical reactions are needed. Compounds are essential in our everyday lives, as they make up many substances we encounter, such as water, salt, sugar, and even complex molecules like proteins and DNA.

Mixtures

1. A “mixture” is a substance formed by the combination of two or more distinct chemical substances that remain separate entities without forming new chemical bonds. This implies that the individual properties and identities of the components within the mixture remain unchanged, as they do not undergo chemical reactions or transformations with each other.
2. Consider the example of mixing various types of nuts – almonds, walnuts, and peanuts. Even when these nuts are mixed together, they retain their distinct characteristics, textures, and flavours, and they do not chemically alter one another.
3. Mixtures can be categorised into two main types based on the uniformity of their composition: Homogeneous Mixtures (appear as a single, uniform substance) and heterogeneous mixtures (visibly distinguishable due to their uneven distribution.)
4. An important attribute of mixtures is that they can be separated back into their original components using physical techniques, such as filtration or distillation. This distinct separability arises from the fact that the substances within a mixture do not undergo any chemical changes or reactions upon being combined.

Homogeneous Mixtures

A homogeneous mixture, also known as a solution, is a type of mixture where all the different substances or components are thoroughly mixed together on a molecular level. This results in a uniform distribution of the components throughout the mixture, creating a single and consistent phase. One remarkable characteristic of solutions is that their particles are extremely small, often less than 1 nanometer in size. In other words, you can't easily see or differentiate the individual components with the naked eye.

Key characteristics of homogeneous mixtures include:

a) Uniform Composition: In a homogeneous mixture, the composition is the same throughout the entire mixture. This means that every part of the mixture contains the same proportion of each component.

b) No Visible Boundaries: Unlike some other types of mixtures where you can see distinct boundaries between the components, homogeneous mixtures have no visible boundaries. The components are so well-mixed that they appear as a single substance.

c) Stable Structure: Homogeneous mixtures are stable and do not separate over time. The components remain evenly distributed, even when the mixture is left undisturbed.

d) Transparent Appearance: Many homogeneous mixtures are transparent or translucent because the components are evenly distributed at the molecular level, allowing light to pass through without scattering.

e) Examples: Some common examples of homogeneous mixtures include salt dissolved in water, sugar dissolved in tea or coffee, and air (which is a mixture of gases like nitrogen, oxygen, and trace amounts of other gases).

Heterogeneous Mixtures

A heterogeneous mixture is a type of mixture in which the different substances or components are not uniformly mixed and can be easily distinguished from one another. Unlike homogeneous mixtures, the components in a heterogeneous mixture are not evenly distributed at the molecular level, and you can often see distinct boundaries or separations between the different components.

Key characteristics of heterogeneous mixtures include:

a) Non-Uniform Composition: In a heterogeneous mixture, the composition varies from one part of the mixture to another. This means that different regions of the mixture may have different proportions of the components.

b) Visible Boundaries: Unlike homogeneous mixtures where the components blend seamlessly, heterogeneous mixtures have visible boundaries or separations between the components. You can see and identify the different components with the naked eye.

c) Uneven Distribution: The components in a heterogeneous mixture do not mix thoroughly on a molecular level. Instead, they may be present in different sizes or concentrations, leading to variations in appearance and properties.

d) Potential Separation: Because the components are not uniformly mixed, heterogeneous mixtures can often be separated using physical methods such as filtration, decantation, or sedimentation.

e) Examples: Some common examples of heterogeneous mixtures include a salad with various vegetables, a mixture of sand and water, and a mixture of oil and water. Each of these mixtures contains distinct components that can be easily identified.

f) Tyndall Effect: Both suspensions and colloids show the Tyndall effect. Tyndall effect refers to the scattering of light by particles in a medium. When a beam of light is passed through a fine suspension or a colloid, the light gets scattered by the particles present in the mixture, making the path of the light visible. This effect is commonly observed when you see a beam of sunlight passing through a foggy room or when a flashlight is shone through a mist.

g) Classification: Heterogeneous mixtures can be further classified into two different types based on the size of the particles and the nature of the components: suspensions and colloids.

Types of Heterogeneous Mixtures

1. Suspensions

1. A suspension is a type of heterogeneous mixture in which solid particles are present within a liquid or gas. Unlike substances in solutions, the particles in a suspension do not dissolve but remain dispersed throughout the mixture. The particles in a suspension are relatively large, usually exceeding 100 nanometers, which makes them visible to the naked eye.
2. Because of their larger size, the particles in a suspension can settle down when the mixture is left undisturbed. This setting can lead to the separation of the solid particles from the liquid or gas medium.
3. To separate the solid particles from a suspension, a common method is filtration. Filtration involves passing the mixture through a filter that allows the liquid or gas to pass through while trapping the larger solid particles. This process effectively separates the components of the suspension.
4. An example of a suspension is a mixture of sand and water. When you mix sand in water, the sand particles do not dissolve but remain dispersed within the water. If you let the mixture sit, the sand particles will settle at the bottom. To separate the sand from the water, you can pour the mixture through a filter paper, which traps the sand particles while allowing the water to pass through.

2. Colloids

1. A colloidal solution, also known as a colloid, is another type of heterogeneous mixture. Unlike suspensions where larger solid particles are suspended in a liquid or gas, colloids consist of tiny particles that are much smaller, usually ranging from 1 to 100 nm in size. These particles are too small to be seen with the naked eye, but they are larger than the molecules present in solutions.
2. One important characteristic of colloids is that the particles remain dispersed evenly throughout the mixture and do not settle down over time. This stability is due to the fact that the particles are small enough to remain suspended by the constant collisions with the molecules of the dispersing medium.
3. Examples of colloids are quite common in everyday life. Think of milk, where tiny fat particles are suspended in the liquid, giving it its characteristic appearance. Another example is fog or mist, where tiny water droplets are suspended in the air. Even substances like gelatin desserts or whipped cream are colloidal systems.
4. Colloids come in various types based on the nature of the dispersed particles and the medium in which they're suspended. Here are a few types:

• Aerosols: In these colloids, tiny solid or liquid particles are dispersed in a gas. Examples include mist, fog, and smoke.
• Foams: Foams consist of gas particles suspended in a liquid or solid medium. For instance, whipped cream or the frothy head of a beer are examples of foams.
• Emulsions: These involve tiny droplets of one liquid suspended within another liquid. Milk and vinaigrette salad dressings are common emulsions.
• Gels: Gels are colloids where a solid medium holds a liquid. Jellies, gelatin desserts, and even some cosmetics are examples of gels.
• Sol: This type involves solid particles dispersed in a liquid medium. Milk of magnesia and certain types of paint are colloidal sols.

Solubility

Solubility refers to the maximum amount of a substance (solute) that can dissolve in a given amount of another substance (solvent) at a specific temperature to create a saturated solution. In other words, it's the highest concentration of solute that the solvent can hold at that temperature without any more solute being able to dissolve. Solubility is typically measured in terms of how much solute can dissolve in 100 grams of the solvent under the given conditions.

Factors Affecting Solubility

Solubility is influenced by several factors. These factors determine how much of a solute can dissolve in a given solvent under specific conditions. Some key factors affecting solubility are:

a) Temperature: In general, as temperature increases, the solubility of solid solutes in liquids also increases. This is because higher temperatures provide more energy to the particles, allowing them to break apart and mix more readily. However, for some substances, like gases in liquids, higher temperatures can actually decrease solubility. This is because gases tend to escape from liquids as the temperature rises.

b) Pressure: Pressure has a significant impact on the solubility of gases in liquids. When pressure increases, the solubility of gases in liquids generally increases as well. This is why, for example, carbon dioxide gas dissolves in soda under pressure, but bubbles out when the pressure is released after opening the bottle.
For solids and liquids, changes in pressure have minimal impact on solubility.

c) Nature of Solute and Solvent: The chemical nature of the solute and solvent greatly influences solubility. Similar substances often dissolve well in each other (like dissolving salt in water), while dissimilar substances may have lower solubility (like oil in water).

d) Particle Size: Smaller particles of a solute have a larger surface area in contact with the solvent, which can lead to faster dissolution. Finely powdered substances tend to dissolve more quickly than larger chunks.

e) Stirring: Agitating or stirring the mixture increases the contact between the solute and solvent, facilitating faster dissolution. This is especially important for solid solutes.

f) Type of Solvent: Different solvents have varying abilities to dissolve different solutes. A solvent with similar properties to the solute is more likely to dissolve it effectively.

g) Presence of Other Solutes: The presence of other solutes in the solution can impact the solubility of a particular solute. Common ions from other solutes can reduce the solubility of a compound that shares those ions.

Classification of Solutions Based on Concentration

Depending on the amount of solute present in a solvent, solutions can be categorised into three types:

Dilute Solution

1. A dilute solution contains a relatively small amount of solute dissolved in a larger amount of solvent.
2. The concentration of the solute is low compared to the solvent.
3. For example, a few drops of ink in a glass of water would create a dilute solution.

Concentrated Solution

1. A concentrated solution contains a substantial amount of solute dissolved in a smaller amount of solvent.
2. The concentration of the solute is relatively high compared to the solvent.
3. Adding a large quantity of sugar to a cup of water and stirring until no more sugar can dissolve would result in a concentrated sugar solution.

Saturated Solution

1. A saturated solution is one in which the maximum amount of solute has been dissolved in the solvent at a particular temperature and pressure.
2. If more solute is added to a saturated solution, it will not dissolve and will remain as undissolved particles at the bottom.
3. An example is preparing a cup of tea: if you continue adding sugar to the tea and it stops dissolving, you have reached a saturated sugar solution.

Concentration of Solution

The concentration of a solution can be expressed in different ways, each providing insight into the relative amounts of solute and solvent.
These concentration percentages help describe how much solute is present in relation to the solution as a whole, whether by mass or by volume. They are commonly used in various fields, such as chemistry, pharmacy, and medicine, to accurately communicate the strength or composition of solutions.

The formulas for different concentration measurements are:

a) Mass by Mass Percentage (w/w%): This measures the mass of the solute in grams per 100 grams of the entire solution.

Formula:

b) Mass by Volume Percentage (w/v%): This measures the mass of the solute in grams per 100 millilitres of the solution.

Formula:

c) Volume by Volume Percentage (v/v%): This measures the volume of the solute in millilitres per 100 millilitres of the solution.

Formula:

Separation of Mixtures

The separation of mixtures is the process of isolating different substances or components from a mixture by using various methods based on their physical properties. Mixtures are combinations of two or more substances that are not chemically bonded together, and they can be composed of solids, liquids, or gases.

Different substances in a mixture can have distinct properties such as solubility, volatility, density, and boiling points. To extract specific components or substances from a mixture, various techniques are employed. Here are some common methods of separation:

1. Filtration

1. This method is used to separate solid particles from a liquid or gas using a filter. The mixture is poured through a porous material that allows the liquid or gas to pass through while trapping the solid particles.
2. Example: Removing sand from water: Pouring a mixture of sand and water through a filter paper, the sand gets trapped on the filter while the water passes through.

2. Evaporation

1. When a solution contains a soluble solid dissolved in a liquid, heating the solution causes the liquid to evaporate, leaving the solid behind.
2. Example: Separating salt from saltwater: Heating a solution of saltwater causes the water to evaporate, leaving behind salt crystals.

3. Distillation

1. This process is used to separate liquids from a solution based on differences in their boiling points. The mixture is heated, and the vapour with the lower boiling point is collected and condensed back into liquid form.
2. Example: Separating alcohol from a water-alcohol mixture: Heating the mixture causes the alcohol to vaporise first due to its lower boiling point. The alcohol vapour is then condensed back into liquid form.

4. Sublimation

1. Sublimation involves heating a solid substance to convert it directly into vapour without passing through the liquid phase. This method is useful when one component can sublimate while the other remains unchanged.
2. Example: Separating iodine from a mixture with sand: Heating the mixture gently causes iodine crystals to sublimate, leaving sand behind.

5. Centrifugation

1. In this technique, a mixture is rotated at high speeds in a centrifuge. The denser components settle at the bottom due to centrifugal force, allowing separation from the less dense components.
2. Example: Separating cream from milk: Centrifuging milk causes the denser cream to move towards the outer edge, allowing it to be separated from the less dense milk.

6. Chromatography

1. This method separates components of a mixture based on their differential migration through a medium. Different substances travel at varying rates, allowing their separation.
2. Example: Separating different colours in ink: Applying a drop of ink on a strip of paper and dipping it in water allows the different ink components to travel at different rates, resulting in distinct colour separation.

7. Decantation

1. It involves carefully pouring off the upper layer of liquid from a solid that has settled at the bottom. This is often used for separating immiscible liquids.
2. Example: Separating oil from water: Allowing oil and water to stand still, oil floats on top of the water, and the oil can be carefully poured off.

8. Separating Funnel

1. It is used for separating immiscible liquids with different densities. The liquids form distinct layers in the funnel and can be drained out separately.
2. Example: Separating oil and water: When oil and water are mixed in a separating funnel, they form separate layers due to their differing densities. The lower layer (water) can be drained out, leaving the upper layer (oil) behind.

Physical and Chemical Changes

Physical Changes

1. Physical changes are alterations that affect the physical properties of a substance, such as its shape, size, colour, or state, without leading to the formation of new substances. In other words, the fundamental composition of the material remains unchanged. During a physical change, no new chemical bonds are formed, broken, or rearranged. Instead, the particles within the substance experience a rearrangement or change in their arrangement.
2. These changes are often reversible, meaning that the substance can be brought back to its original state. For instance, melting an ice cube to obtain liquid water is a physical change, and the process can be reversed by freezing the water again. Similarly, boiling a liquid to form vapour is a physical change that can be reversed by condensing the vapour back into a liquid.
3. It's important to note that physical changes do not involve the conversion of one substance into another; they only involve modifications in the way the substance looks or behaves. Physical changes also do not involve a change in energy at the molecular level, so no heat is released or absorbed during these processes.

Chemical Changes

1. Chemical changes, also known as chemical reactions, occur when a substance transforms into an entirely new substance with distinct physical and chemical properties. These changes involve the breaking and forming of chemical bonds between atoms and molecules. Unlike physical changes, chemical changes result in the creation of new substances that have different compositions from the original ones.
2. Chemical changes are often irreversible, meaning that once the reaction occurs, it's not possible to revert the substances back to their original state. The properties of the elements or compounds involved in the reaction are altered as they combine or rearrange to form new compounds.
3. Energy changes are commonly associated with chemical reactions. The process may release or absorb energy, often in the form of heat or light. For example, when wood or paper burns, it undergoes a chemical change that releases heat and light as new compounds are formed. Similarly, souring of milk involves a chemical change due to the growth of bacteria that convert lactose into lactic acid, changing the taste and properties of the milk.

Frequently Asked Questions

1. Can an element exist in different forms but still be considered pure?

Yes, an element can exist in different forms known as allotropes but is still considered a pure substance. For example, carbon exists as graphite and diamond, which are different structural forms (allotropes) but are still made of pure carbon atoms.

2. Can a pure substance be separated by physical methods?

No, a pure substance cannot be separated into its components by physical methods (such as filtration or distillation) because its components are chemically bonded. It can only be separated by chemical reactions.

3. Is there a limit to how concentrated a solution can be?

Yes, the concentration of a solution has a limit, known as the saturation point. Once this point is reached, no more solute can dissolve in the solvent at a given temperature, and any additional solute will remain undissolved.

4. Does the type of solvent affect solubility?

Yes, the type of solvent significantly affects solubility. Polar solvents like water dissolve polar substances (like salt) well, while non-polar solvents like oil dissolve non-polar substances (like fat). "Like dissolves like" is a common rule of thumb in solubility.

5. Why is rusting considered a chemical change?

Rusting is considered a chemical change because iron reacts with oxygen in the presence of water to form iron oxide (rust), a new substance with different properties from iron.