Methods of Separation

Boiling:

• Process of converting a liquid into gas by heating it to its boiling point.

• Used to separate a dissolved solid from a liquid.

• The liquid boils away, leaving behind the solid residue.

• Examples include separating salt from water in saltwater.

Simple Distillation:

• Used to separate a mixture of two or more liquids with different boiling points.

• The mixture is heated, and the liquid with the lower boiling point evaporates first.

• The vapour is then condensed back into liquid form.

• Examples include separating water from ethanol in alcoholic beverages.

Centrifugation:

• Involves spinning a mixture at high speeds in a centrifuge.

• Separates components based on their density.

• Heavier components move towards the bottom while lighter components remain at the top.

• Used in laboratories to separate solid particles from liquid solutions, such as blood cells from plasma.

Sedimentation:

• Process of allowing solid particles to settle at the bottom of a liquid.

• Takes advantage of the differences in density between the solid and liquid phases.

• Used in wastewater treatment plants to separate suspended solids from water.

Filtration:

• Separates solid particles from a liquid or gas by passing it through a porous barrier.

• The solid particles are retained by the filter, while the liquid or gas passes through.

• Examples include using filter paper to separate coffee grounds from brewed coffee.

Fractional Distillation:

• Similar to simple distillation but used for separating a mixture of liquids with closer boiling points.

• Involves multiple distillation steps to separate different fractions of the mixture.

• Widely used in the petroleum industry to separate crude oil into various components like gasoline, diesel, and kerosene.

Chromatography:

• Separation technique based on the differential movement of components through a medium.

• Components with different affinities to the medium move at different rates.

• Used extensively in chemistry labs to separate and analyse mixtures of chemicals, such as separating pigments in ink.

Separator Funnel:

• Used to separate immiscible liquids (liquids that don't mix) based on their density.

• The less dense liquid forms a layer on top and can be drained from the bottom of the funnel.

• Often used in organic chemistry labs to separate organic solvents from aqueous solutions.

Periodic Properties

Structure of an Atom:

• Electrons orbit the nucleus in energy levels or shells.

• The nucleus contains protons (positive charge) and neutrons (no charge).

Trends in the Periodic Table:

• Atomic Size: Decreases across periods (left to right), increases down groups.

• Ionisation Energy: Increases across periods (left to right), decreases down groups.

• Electronegativity: Increases across periods (left to right), decreases down groups.

• Reactivity: Metals lose electrons, non-metals gain electrons.

Reactivity Series of Metals:

• A list of metals in order of reactivity.

• Highly reactive metals react vigorously, while less reactive metals react less vigorously.

• Helps predict the behaviour of metals in chemical reactions.

Bonds

Types of Bonds:

• Ionic Bonds: Formed by the transfer of electrons, resulting in oppositely charged ions.

• Covalent Bonds: Atoms share electrons to achieve stability.

• Metallic Bonds: Formed by the sharing of outer electrons in metals, creating a "sea" of delocalised electrons.

  • Can give rise to cold-welding—a phenomenon where two clean metallic surfaces bond together in a vacuum or a space environment due to the sharing of free electrons, forming a metallic bond.

Acids

• Acids are substances that release H⁺ ions (protons) when dissolved in water.

  • Hydrogen ions have a single positive charge.

  • The term "acid" comes from the Latin word "acidus," meaning sour.

• Acid solutions contain negative ions (anions), which give the acid its name and determine the salt produced after neutralisation.

• Examples of acids: HCl(Hydrochloric Acid), CH₃COOH(Acetic Acid), H₂SO₄(Sulphuric Acid), HNO₃(Nitric Acid).

• Strong vs. Weak Acids:

  • Strong acids completely ionise in aqueous solutions.

    • E.g., HCl ionises into H⁺ and Cl⁻ ions, fully dissociating its components.

    • Examples of strong acids: hydrochloric acid, sulphuric acid, nitric acid etc.

  • Weak acids do not fully ionise in aqueous solutions.

    • E.g., Acetic Acid ionises partially as follows: CH₃COOH(aq) ⇌ H⁺(aq) + CH₃COO⁻ (aq).

    • Examples of weak acids: acetic acid, citric acid, carbonic acid.

• Classification of Acids:

  • Based on the number of H⁺ ions they release when dissolved in water:

    • Monoprotic acids release 1 proton.

    • Diprotic acids release 2 protons.

    • Polyprotic acids release 3+ protons.

  • Concentration of Acids:

    • Concentrated vs. Dilute:

      • Concentrated solutions have more of the substance per unit volume.

      • Dilute solutions have less of the substance per unit volume.

      • The substance is always added to water, not the other way around.

• Indicators:

  • Blue Litmus paper:

    • Turns red in the presence of an acid.

    • Remains blue for neutral and basic solutions.

  • Universal indicator paper:

    • Acids turn red.

    • Neutrals turn green.

    • Bases turn violet.

    • The strip can be placed directly onto a wet substance or a few drops of the solution can be dropped onto the universal indicator using dropping equipment.

Bases

• Bases are substances that release OH⁻ ions.

  • Bases are also known as alkalis when soluble in water.

  • Examples include NaOH(Sodium Hydroxide), KOH(Potassium Hydroxide), Ca(OH)₂(Calcium Hydroxide).

• All alkali solutions have pH values greater than 7.

• Bases react with acids to produce salts and water only in a neutralisation reaction.

• Most metal oxides and ALL hydroxides are considered bases.

  • Metal oxides (e.g., magnesium oxide) are basic in nature.

  • Non-metal oxides (e.g., carbon dioxide) are acidic in nature.

• Properties of Bases:

  • React with acids to produce salts and other products.

  • Turn red litmus paper blue, phenolphthalein pink, and keep bromothymol blue blue.

  • Have a pH greater than seven at standard conditions.

Salts

• Salts are ionic compounds formed by the reaction of an acid with a base.

  • They contain positively charged metal ions and negatively charged non-metal ions.

• Common salts include nitrates, sulphates, and chlorides.

• Salts are categorised based on the negative ion they contain.

• All salts can conduct electricity and have various uses.

  • Examples include ammonium chloride in flashlight batteries, ammonium sulphate in fertilisers, calcium carbonate in the extraction of iron, and potassium nitrate in gunpowder.

Acid Rain

• Acid rain is any form of precipitation with acidic components.

• It results from emissions of sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) into the atmosphere, which react with water, oxygen, and other chemicals to form sulphuric and nitric acids.

• Sources of SO₂ and NOₓ include burning fossil fuels, vehicle emissions, manufacturing, and industrial processes.

• Effects of acid rain include:

  • Harm to acid-sensitive wildlife.

  • Restriction of tree growth.

  • Episodic acidification.

  • Corrosion of buildings and infrastructure.

  • Health issues from inhaling sulphate and nitrate particles.