2024 Sec 3 Chem Notes (For circulation)

Upper Secondary Pure Chemistry

QA notes: will be given during practical 6092 CHEMISTRY GCE ORDINARY LEVEL SYLLABUS 30 NOTES FOR QUALITATIVE ANALYSIS Test for anions anion test test result carbonate (CO32–) add dilute acid effervescence, carbon dioxide produced chloride (Cl –) [in solution] acidify with dilute nitric acid, then add aqueous silver nitrate white ppt. iodide (I–) [in solution] acidify with dilute nitric acid, then add aqueous silver nitrate yellow ppt. nitrate (NO3–) [in solution] add aqueous sodium hydroxide, then aluminium foil; warm carefully ammonia produced sulfate (SO42–) [in solution] acidify with dilute nitric acid, then add aqueous barium nitrate white ppt. Test for aqueous cations cation effect of aqueous sodium hydroxide effect of aqueous ammonia aluminium (Al 3+) white ppt., soluble in excess giving a colourless solution white ppt., insoluble in excess ammonium (NH4+) ammonia produced on warming – calcium (Ca2+) white ppt., insoluble in excess no ppt. copper(II) (Cu2+) light blue ppt., insoluble in excess li ght blue ppt., soluble in excess giving a dark blue solution iron(II) (Fe2+) green ppt., insoluble in excess green ppt., insoluble in excess iron(III) (Fe3+) red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc (Zn2+) white ppt., soluble in excess giving a colourless solution white ppt., soluble in excess giving a colourless solution Test for gases gas test and test result ammonia (NH3) turns damp red litmus paper blue carbon dioxide (CO2) gives white ppt. with limewater (ppt. dissolves with excess CO2) chlorine (Cl2) bleaches damp litmus paper hydrogen (H2) ‘pops’ with a lighted splint oxygen (O2) relights a glowing splint sulfur dioxide (SO2) turns aqueous acidified potassium manganate(VII) from purple to colourless

Chapter 1: Experimental Chemistry Apparatus Pipette Measures accurate fixed volumes (e.g. 10.0cm3 or 25.0cm3) – 1 d.p. Volumetric Flask Measures accurate fixed volumes that are larger (e.g. 100 cm3 or 250 cm3) Measuring Cylinder Measures a range of volumes to the nearest 0.5 cm3 (e.g. 31.5 cm3 or 23.0 cm3) Burette Measures a range of volumes to the nearest 0.05 cm3 (e.g. 31.55 cm3 or 23.00 cm3) – most accurate (when 2 dp value, usually burette) Collection Method Water Displacement Gas must be insoluble/slightly soluble in water (e.g. Hydrogen, Oxygen, Carbon Dioxide) Downward Delivery Gas must be denser than air – Mr/Ar > 28 (e.g. chlorine, hydrogen chloride, sulfur dioxide) Upward Delivery Gas must be less dense than air – Mr/Ar < 28 (e.g. Ammonia, helium, hydrogen) Drying Agent Concentrated Sulfuric Acid Most gases except basic gas (e.g. ammonia) Quicklime (Calcium Oxide) Gases (ammonia can be dried here) except acidic gases (e.g. Sulfur Dioxide, Carbon Dioxide, Nitrogen Dioxide, Chlorine, Hydrogen Chlorine) Fused Calcium Chloride Gases except those who react with Calcium Chloride (e.g. Ammonia) à must be freshly heated before use

Separation of Mixtures Magnetic Attraction A magnet can be used to separate magnetic solids from non-magnetic solids (Solid – Solid) Sieving A sieve can be used to separate solids of different particle sizes (Solid – Solid) Suitable Solvents A suitable solvent can be used to separate solid-solid mixtures in which only one of the solids is soluble in the solvent (Solid – Solid) Sublimation Sublimation can be used to separate a substance that changes from the solid to gaseous state directly (Solid – Solid) (e.g. pure iodine, dry ice…) Filtration Filtration can be used to separate insoluble solids from liquids (Solid – Liquid) Evaporation to Dryness Evaporation to dryness is used to separate a dissolved solid from its solvent by heating the mixture until all the solvent has vapourised (Solid – Liquid) (O levels, only have NaCl) Crystallisation Crystallisation is used to obtain a pure solid from its saturated solution. A saturated solution is one in which no more solute can be dissolved (Solid – Liquid) This method is used instead of evaporation to dryness to prevent the crystals from losing its water of crystallization and becoming anhydrous Simple distillation Simple distillation is used to separate a pure solvent from a solution (Solid – Liquid) Why bulb of thermometer at entrance of condenser? à To record the boiling point of vapour collected Why water in this direction (condenser)? à To ensure condenser is fully filled with water and allows efficient cooling of vapour Separating Funnel A separating funnel is used to separate immiscible liquids (Liquid – Liquid) (immiscible = different density)

Chromatography Chromatography is used to separate a mixture of substances which have different solubilities in a given solvent Why start line in pencil? à Graphite is insoluble in all solvents and will not be separated together with the samples Why start line not in ink? à Ink is a mixture and dyes will be separated along with the sample Rf value = !"#$%&'( $*%+(,,(! -. $/( #0-#$%&'(!"#$%&'( $*%+(,,(! -. $/( #1,+(&$ ≤ 1 (no units, 2d.p) Fractional distillation Fractional distillation is used to separate miscible liquids with different boiling points Purity of a substance A pure substance has a specific melting and/or boiling point under fixed conditions (impure substances melt/boil at a range of temperatures) Chapter 2: Kinetic Particle Theory Kinetic Particle Theory The kinetic particle theory states that all matter is made up of tiny particles and these particles are in constant random motion Solid, Liquid and Gas Why temperature remains constants in change of state? à The energy provided is equal to the energy needed to overcome the forces of attraction between particles What happens when impurities are added? à The boiling point increases and melting point decreases (both occurs at a range of temperatures) (substance at liquid state at wider temp range) Diffusion Definition Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration Conditions that affect R.O.D Temperature à higher temp, higher KE, movement increase, higher ROD Mr à higher Mr = heavier, slower ROD

Chapter 3: Atomic Structure Atoms Definition An atom is the smallest particle that can still have the chemical characteristics of an element Charges Atoms are electrically neutral (charge = 0) Number of protons in an atom = number of electrons in that atom Sub-atomic particles Sub-atomic particles Proton number The Proton Number of an atom is the number of protons in its nucleus of an atom. Nucleon number The nucleon number is the total number of protons and neutrons in the nucleus of an atom Ions An ion is the particle formed when an atom or a group of atoms gains or loses electron(s), but the number of protons and neutrons remains the same Isotopes Isotopes are atoms of the same element that have the same proton number but different nucleon number. This means they have different number of neutrons. Electrons Electronic configuration 2 , 8 , 8 , 18 … outermost electron shell = valence shell electrons in outermost electron = valence electrons

Chapter 4: Chemical Bonding Ions Positive ions (cations) Positive ions (cations) have a net positive charge and usually have a noble gas electronic configuration Negative ions (anions) Negative ions (anions) have a net negative charge and have a noble gas electronic configuration Ionic bonding Ionic bond An ionic bond is the mutual electrostatic attraction between ions of opposite charges (cation and anion) Ionic structures A giant ionic crystal lattice is a three-dimensional structure of alternating positive and negative ions along the x, y and z axis Covalent bonding Valency (Covalent bond) Valency refers to the number of electron(s) that must be lost, gained or shared in order for the atom to attain a noble gas electronic configuration Metallic bonding Metallic bo