Understanding Pure Substances and Mixtures

• 'Pure' means no adulteration to a common person.
• To a scientist, 'pure' means all constituent particles of a substance are the same in chemical nature.
• A pure substance contains only one type of particle.
• Most matter exists as mixtures of two or more pure components.
• Seawater, minerals, and soil are examples of mixtures.

What is a Mixture?

• Mixtures consist of more than one kind of pure matter.
• Dissolved sodium chloride can be separated from water by evaporation.
• Sodium chloride and sugar are pure substances that cannot be separated into chemical constituents by physical processes.
• Soft drinks and soil are not single pure substances.
• A pure substance has the same characteristic properties regardless of the source.
• Mixtures contain more than one pure substance.

Types of Mixtures

• Types of mixtures depend on the nature of the components.
• Groups A and B obtained a mixture with a uniform composition throughout, called homogeneous mixtures or solutions.
• Salt and sugar dissolved in water are examples of homogeneous mixtures.
• Homogeneous mixtures can have variable compositions.
• Groups C and D obtained mixtures with physically distinct parts and non-uniform compositions, called heterogeneous mixtures.
• Mixtures of sodium chloride and iron filings, salt and sulphur, and oil and water are examples of heterogeneous mixtures.
• Suspension formed in group C.
• Colloidal solution formed in group D.

Activity 2.2

• Four groups are given different samples to mix with water: copper sulphate crystals, copper sulphate powder, chalk powder/wheat flour, and milk/ink.
• Observations include particle visibility, light beam visibility, mixture stability, and residue after filtration.
• Groups A and B have a solution, Group C has a suspension, and Group D has a colloidal solution.

What is a Solution?

• A solution is a homogeneous mixture of two or more substances.
• Lemonade and soda water are examples of solutions.
• Solutions can be liquid, solid (alloys), or gaseous (air).
• Solutions have homogeneity at the particle level.
• Lemonade tastes the same throughout, indicating even distribution of sugar or salt.

Alloys

• Alloys are mixtures of two or more metals or a metal and a non-metal.
• Alloys cannot be separated into components by physical methods.
• Alloys are considered mixtures because they show the properties of their constituents and have variable composition.
• Brass is a mixture of approximately 30% zinc and 70% copper.

Solution Components

• A solution has a solvent and a solute.
• The solvent dissolves the other component and is usually present in a larger amount.
• The solute is dissolved in the solvent and is usually present in a smaller quantity.

Examples of Solutions

• Sugar in water (solid in liquid): sugar is the solute, water is the solvent.
• Tincture of iodine (iodine in alcohol): iodine is the solute, alcohol is the solvent.
• Aerated drinks (gas in liquid): carbon dioxide is the solute, water is the solvent.
• Air (gas in gas): oxygen (21%) and nitrogen (78%) are the main constituents.

Properties of a Solution

• Solutions are homogeneous mixtures.
• Solution particles are smaller than 1 nm and cannot be seen with the naked eye.
• Solutions do not scatter a beam of light passing through, so the path is not visible.
• Solute particles cannot be separated by filtration.
• Solute particles do not settle, making the solution stable.

Concentration of a Solution

• The proportion of solute and solvent can be varied.
• Solutions can be dilute, concentrated, or saturated, depending on the amount of solute.
• Dilute and concentrated are comparative terms (e.g., Group A's solution is dilute compared to Group B's).
• At a particular temperature, a saturated solution has dissolved as much solute as it is capable of.
• When no more solute can be dissolved at a given temperature, the solution is saturated.
• Solubility is the amount of solute present in a saturated solution at a specific temperature.
• An unsaturated solution contains less solute than the saturation level.
• Different substances have different solubilities in a given solvent at the same temperature.
• Concentration of a solution is the amount of solute present in a given amount of solution.

Ways to Express Concentration

• Mass by mass percentage: (Mass of solute / Mass of solution) x 100
• Mass by volume percentage: (Mass of solute / Volume of solution) x 100
• Volume by volume percentage: (Volume of solute / Volume of solution) x 100

Suspensions

• Suspensions are non-homogeneous systems where solids are dispersed in liquids.
• Suspension is a heterogeneous mixture in which solute particles do not dissolve but remain suspended.
• Particles in a suspension are visible to the naked eye.
• Suspension is a heterogeneous mixture.
• The particles of a suspension can be seen by the naked eye.
• Suspension particles scatter a light beam, making its path visible.
• The solute particles settle, making the suspension unstable.
• Suspensions can be separated by filtration
• The suspension breaks when particles settle and it does not scatter light any more.

Colloidal Solutions

• Colloids are mixtures where particles are uniformly spread throughout the solution.
• Colloids appear homogeneous but are heterogeneous.
• Colloid particles are small and cannot be seen with the naked eye.
• Colloids scatter a beam of visible light, known as the Tyndall effect.
• The Tyndall effect is the scattering of light by colloid particles.
• The Tyndall effect can be observed when a fine light enters a room through a hole, due to dust and smoke.
• Colloids are big enough to scatter a beam of light through it.
• Colloids do not settle, so they are quite stable.
• Colloids cannot be separated by filtration.

Components of Colloidal Solutions

• A special separation technique like centrifugation can be used separate colloids.
• The components of a colloidal solution are the dispersed phase and the dispersion medium.
• The dispersed phase is the solute-like component.
• The dispersion medium is the component in which the dispersed phase is suspended.
• Colloids are classified by the state of the dispersing medium and dispersed phase.

Physical Properties

• Properties like color, hardness, rigidity, fluidity, density, melting point, and boiling point are physical properties.
• The interconversion of states is a physical change and does not affect the chemical composition.
• Ice, water, and water vapor are chemically the same despite different physical properties.

Chemical Properties

• Chemical properties include odor and inflammability.
• Oil burns, while water extinguishes the fire, illustrating a chemical property.
• Burning is identified as a chemical change.
• During chemical change, one substance reacts with another, leading to a change in chemical composition.
• When the substance goes through a chemical change, it leads to a new substance being created.
• During candle burning, both physical and chemical changes occur.

Elements

• Elements can't be broken down into simpler substances by chemical reactions.
• Elements are normally classified into metals, non-metals, and metalloids.

Metals

• Metals have lustre, are silvery-grey or golden-yellow, conduct heat and electricity.
• Metals are ductile (can be drawn into wires), malleable (can be hammered into sheets), and sonorous (make a ringing sound when hit).
• Examples of metals are gold, silver, copper, iron, sodium, and potassium.
• Mercury is the only metal that is liquid at room temperature.

Non-Metals

• Non-metals display a variety of colors.
• Non-metals are poor conductors of heat and electricity.
• Non-metals are not lustrous, sonorous, or malleable.
• Examples of non-metals hydrogen, oxygen, iodine, carbon (coal, coke), and bromine.

Elements Facts

• The number of elements present is > 100.
• The majority of elements are solids.
• There are 11 elements in a gaseous state at room temperature.
• Mercury and bromine are the only 2 liquid elements at room temperature.
• Gallium and cesium become liquid at slightly above room temperature (303 K).

Compounds

• A compound is a substance composed of two or more elements chemically combined in a fixed proportion.
• Elements or compounds mix without forming new compounds when a form a mixture.
• Elements react to form new compounds.
• The material obtained by group II (heating iron and sulphur) is a compound.
• Heating two elements strongly results in a compound with different properties compared to the combining elements.

Mixtures vs Compounds

• Mixtures combine elements or compounds without forming new compounds; compounds form when elements react.
• Mixtures have variable compositions; compounds have fixed compositions.
• Mixtures show properties of constituent substances; compounds have totally different properties.
• Mixtures can be separated by physical methods; compounds require chemical or electrochemical reactions to separate.
• The texture and color are the same throughout.
• A mixture contains more than one substance (element and/or compound) mixed in any proportion.
• A solution is a homogeneous mixture of two or more substances.
• Mixtures can be separated into pure substances using appropriate separation techniques.

Final Notes

• Colloids are heterogeneous mixtures with particles too small to see but large enough to scatter light.
• The concentration of a solution is the amount of solute present per unit volume or mass of solution.
• Materials insoluble in a solvent form a suspension and are visible to the naked eyes.
• Pure substances are elements or compounds that cannot be broken down by chemical reactions.