Everything around us from the staircase we use to the air we breathe is made up of tiny particles that form different types of matter. Understanding how these particles combine to form mixtures, elements, and compounds helps us appreciate the world around us. This chapter explores how different substances come together and their unique properties.
What Are Mixtures?
When two or more substances are mixed together where each substance retains its individual properties, it is called a mixture. The individual substances that make up a mixture are called its components. The components of a mixture do not react chemically with each other.
Types of Mixtures Based on Visibility
Non-uniform Mixtures
- Components are generally visible with the naked eye or magnifying device
- Different components can be easily identified and separated
- Examples include sprout salad with green gram, chickpeas, onion, and tomato
- Other examples are sand and water, oil and water
Uniform Mixtures
- Components are evenly distributed and cannot be distinguished
- Cannot be seen separately even with microscope
- Examples include sugar dissolved in water, air, seawater
- Components appear as single substance throughout
Alloys as Special Mixtures
Stainless steel is a uniform mixture containing iron, nickel, chromium, and small amount of carbon. These are mixed so uniformly that entire mixture appears same throughout. Such mixtures are known as alloys.
Common Alloys and Their Composition
- Brass: mixture of copper and zinc
- Bronze: mixture of copper and tin
- Stainless steel: iron, nickel, chromium, and carbon
Our Scientific Heritage
Ancient Indian texts called such mixtures Mishraloha – the name given to mixture of two or more metals that had properties distinct from constituent metals. Ancient texts like Charaka Samhita, Susruta Samhita, Rasaratna Samucchaya mention use of alloys for medicinal purposes. Bronze (Kamsya) made of copper (4 parts) and tin (1 part) was used to improve digestion and boost immunity.
Is Air a Mixture?
Air is a uniform mixture of mainly nitrogen, oxygen, argon, carbon dioxide, and water vapour. Oxygen is required by most living beings and helps in combustion. Nitrogen constitutes about 78% of air and does not take part in combustion.
Testing for Carbon Dioxide in Air
When calcium oxide (quick lime) is added to water, it forms calcium hydroxide solution called lime water. When this colorless solution is left exposed to air, it turns milky due to reaction with carbon dioxide present in air.
Chemical Equation:
Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Other Components in Air
Apart from gases, air contains suspended dust particles that are pollutants. These particles settle on surfaces and can be observed using magnifying glass. Major air pollutants include particulate matter (dust, soot) and gases like carbon monoxide, ozone, nitrogen dioxide, and sulfur dioxide.
Types of Mixtures Based on Physical States
| S.No. | Mixture Type | Examples | Nature |
|---|---|---|---|
| 1 | Gas and gas | Air | Uniform |
| 2 | Gas and liquid | Aerated water, oxygen dissolved in water | Uniform |
| 3 | Solid and gas | Carbon particles in air | Non-uniform |
| 4 | Liquid and liquid | Vinegar (acetic acid in water), oil and water | Uniform/Non-uniform |
| 5 | Solid and liquid | Seawater, sand and water | Uniform/Non-uniform |
| 6 | Solid and solid | Baking powder, alloys | Uniform/Non-uniform |
What Are Pure Substances?
In common usage, pure means unadulterated products. Adulteration is illegal process of adding cheaper or poor quality substances to increase quantity or reduce manufacturing cost, which deteriorates product quality.
In science, a pure substance is one that has no other substance present in it. Pure substance is kind of matter that cannot be separated into other kinds of matter by any physical process. When scientist says something is pure, it means substance consists of same type of particles.
Examples of Classification
- Milk: Mixture (contains water, fats, proteins, minerals)
- Packed fruit juice: Mixture (contains water, sugars, vitamins, preservatives)
- Baking soda: Pure substance (compound)
- Sugar: Pure substance (compound)
- Soil: Mixture (contains various minerals, organic matter, water)
What Are the Types of Pure Substances?
Pure substances can be classified into two main types: elements and compounds.
Elements
Elements are substances that cannot be further broken down into simpler substances. They are building blocks of all matter. Each element is made up of identical particles called atoms that are different from particles of any other element.
Formation of Molecules
Atoms of most elements cannot exist independently. Two or more atoms combine to form stable particle called molecule. For example:
- Two hydrogen atoms combine to form one hydrogen molecule
- Two oxygen atoms combine to form one oxygen molecule
Classification of Elements
- Metals: Gold, silver, magnesium, iron, aluminum
- Non-metals: Carbon, sulfur, hydrogen, oxygen
- Metalloids: Silicon, boron (have intermediate properties)
States of Elements
- 118 elements are known at present
- Most exist in solid state
- 11 elements exist in gaseous state at room temperature (all non-metals)
- Only 2 elements are liquid at room temperature: mercury (metal) and bromine (non-metal)
- Gallium and caesium become liquid around 30°C
Elements in Technology
More than 45 different elements like aluminum, copper, silicon, cobalt, lithium, gold, silver are used in manufacturing mobile phones including screen, battery, and other components.
Compounds
Compounds are formed when different elements combine in fixed ratios to form something entirely new. Properties of compounds are different from those of elements forming that compound. Constituent elements of compound cannot be separated by any physical method.
Example: Water as Compound
When electricity is passed through water, it breaks down into hydrogen and oxygen gases. This shows water is composed of two different elements – hydrogen and oxygen combined in 2:1 ratio.
Testing the Gases:
- Hydrogen gas burns with pop sound when tested with burning candle
- Oxygen gas makes candle flame glow brighter
Other Examples of Compounds
- Common salt (Sodium chloride): Sodium (soft metal) + Chlorine (hazardous gas) = harmless taste-enhancing substance
- Sugar: Contains carbon, hydrogen, and oxygen. When heated, sugar decomposes to form carbon (charcoal) and water
Formation of Iron Sulfide Compound
When mixture of iron filings and sulfur powder is heated, it forms iron sulfide compound:
| Property | Iron + Sulfur Mixture | Iron Sulfide Compound |
|---|---|---|
| Appearance | Black and yellow particles visible | Uniform black mass |
| Magnetic property | Iron attracted to magnet | Not attracted to magnet |
| Separation | Components can be separated | Cannot be separated |
| Reaction with acid | Iron reacts, sulfur doesn’t | Iron sulfide reacts differently |
| Gas produced | Hydrogen (no smell, pop sound) | Hydrogen sulfide (rotten egg smell) |
How Do We Use Elements, Compounds, and Mixtures?
Understanding elements, compounds, and mixtures is key to innovation in various fields:
In Medicine and Agriculture
- Chemists study how elements combine to create life-saving medicines and vaccines
- Knowledge helps create fertilizers enhancing crop production for growing population
In Engineering and Materials Science
- Engineers design materials with unique properties using compounds and mixtures
- Alloys like stainless steel are stronger and more durable than pure iron
- Wood, steel, concrete used as building materials are all mixtures
Wonder Materials
Graphene aerogel made from carbon is lightest material on earth. It’s so light that grass can hold it. Being highly porous with high absorbing capacity, it can be used as environmental cleaner for oil spills and in energy-saving devices.
What Are Minerals?
Most rocks are mixture of minerals that can be viewed with eyes, magnifying glass, or microscope. Minerals are natural, solid substances found on Earth with fixed chemical composition.
Types of Minerals
- Native minerals: Pure elements like gold, silver, copper, sulfur, carbon
- Compound minerals: Made of more than one element like quartz, calcite, mica, pyroxene, olivine
Everyday Uses of Minerals
- Cement: Made from calcite, quartz, alumina, iron oxide
- Talcum powder: Made from mineral talc
- Many everyday items contain minerals or elements extracted from minerals
Our Scientific Heritage in Indian Art
Dhokra art from Bihar and Odisha uses different metals to create beautiful nature-inspired figures. Process involves:
- Shaping design in beeswax
- Covering wax model with clay to make mould
- Melting out wax leaving hollow space
- Filling space with molten brass or bronze
- Creates strong art with shiny golden color reflecting tribal creativity
Classification Summary
Matter Classification:
| Category | Definition | Examples |
|---|---|---|
| Mixtures | Two or more substances mixed retaining individual properties | Air, seawater, alloys, sprout salad |
| Pure Substances | Single type of particles throughout | Elements and compounds |
| Elements | Cannot be broken down further by chemical means | Gold, oxygen, hydrogen, iron |
| Compounds | Elements combined in fixed ratios with new properties | Water, salt, sugar, carbon dioxide |
Pure Substances Include:
- All elements (hydrogen, oxygen, gold, iron, etc.)
- All compounds (water, carbon dioxide, sodium chloride, etc.)
Not Matter:
Light, heat, electricity, thoughts, and emotions are important but not made of matter as they don’t have mass or take up space.
This understanding of matter’s nature helps us appreciate how tiny particles combine in different ways to create the diverse world around us.
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