Raffles Chem FE Notes

1. General Experimental Design: Gas volumes measured using a graduated syringe Liquid volumes measured using a (i) burette - 2d.p. (ii) pipette - 1d.p. (iii) measuring cylinder - various precisions Use an digital mass balance to measure mass Name of gas Solubility in water Density relative to air Collection method Hydrogen Not soluble Less dense Displacement of water Carbon dioxide Slightly soluble Denser Displacement of water Oxygen Slightly soluble Slightly denser Displacement of water Chlorine Soluble Denser Downward delivery Ammonia Very soluble Less dense Upward delivery Sulfur dioxide Very soluble Denser Downward delivery Drying agents - Concentrated sulfuric acid (not for alkaline gases - will react) - Calcium oxide (not suitable for acidic gases - will react) - Anhydrous calcium chloride Anhydrous copper (II) sulfate is used as an indicator for water vapour It turns from white to blue when hydrated - CuSO4 → CuSO4 · 5H2O Universal Indicator

Gas Tests Gas Test Result if present Hydrogen Insert lighted splint into test tube Lighted splint extinguishes Oxygen Insert glowing splint into test tube Splint relights Carbon dioxide Bubble gas through limewater (aq calcium hydroxide) White ppt (calcium carbonate) forms Ammonia (NH3) Insert moist red litmus paper Moist red litmus paper turns blue, pungent smell Chlorine Insert moist blue litmus paper Most blue litmus paper turns red then bleaches Sulfur dioxide Bubble through aq acidified potassium manganate (VII) Aq acidified potassium manganate (VII) turns from purple to colourless Purification Techniques: If it’s solid + solid dissolved in water (solution), 1. Filter mixture and collect residue/filtrate 2. A. Wash residue with deionised water and pat dry B. Heat filtrate in an evaporating dish until all the water evaporates, collect remaining solid If solid dissolved in water is thermally unstable, do crystallisation instead: 1. Heat solution in evaporating dish, stop heating when there is about ⅓ of solution left 2. Let solution cool to allow crystals to form 3. Filter the mixture to obtain crystals, then pat dry To collect the solvent from a solution (where solute and solvent have different boiling points) - use simple distillation To separate a mixture of two miscible liquids, which have different boiling points - use fractional distillation As vapours go up the fractionating column, they condense when they reach a part of the column that is below their boiling point Liquid with the lower boiling point is collected as distillate Fractionating beads increase the surface area for the condensation of vapour, making separation of vapours more efficient To separate two immiscible liquids - separating funnel To separate a solid from a solid that sublimes easily under heat - sublimation

2. Bonding and Structure 𝑍 𝐴 𝑋A is the nucleon number, Z is the atomic number Isotopes are atoms with the same number of protons but different number of neutrons Relative molecular mass represents the average mass of one atom of an element taking into account the different isotopes and their relative abundances (Ar) Ar = (Mr of isotope) x (abundance in %) + (Mr of other isotope) x (abundance in %)... Chemical Bonding All chemical bonds are electrostatic forces of attraction Simple molecular structure Giant covalent structure Giant ionic structure Giant metallic structure Particles in solid Molecules Molecules Cations and Anions Positive metal ions and sea of delocalised electrons Bonds between particles Weak intermolecular forces of attraction Strong covalent bonds Strong ionic bonds Strong metallic bonds Physical state in room conditions Aqueous Solid Solid Solid except mercury Bpt/Mpt Low High High High Example Water, Oxygen, Carbon Dioxide Diamond Sodium Chloride Iron Physical Properties: mpt, bpt, conductivity and solubility Ionic Bonds - Usually formed when a metal reacts with a non-metal - Soluble in water - the charge of water molecules are attracted to the charges of ions in giant ionic structure and pulls the ions away from their regular arrangement - Can conduct electricity in solid/aq state due to presence of free-moving ions Covalent Bonds - Forces pulling together molecules of non-metals

- Giant Covalent: Insoluble in almost all solvents, poor conductors of electricity except graphite (ONLY MENTION GIANT COVALENT FOR GRAPHITE OR DIAMOND) - Simple Molecular: Insoluble unless polar, do not conduct electricity (e.g ammonia, CO2, water) - The greater the difference in electronegativities between the 2 bonded atoms in a covalent bond, the greater the polarity of the bond - The more polar the molecules in a substance, the more soluble it is in water (e.g NH3) Metallic Bonds - 1, 2 or 3 valence electrons - Insoluble in water, metal bonds do not dissolve in water - Metallic bonds are between positive metal ions and sea of delocalised electrons - Malleable and ductile: layers of atoms can easily slide against each other - Good conductors of electricity due to movement of delocalised electrons Graphite vs Diamond Diamond: Strong covalent bonds holding carbon atoms together in a giant covalent structure Graphite: Strong covalent bonds holding carbon atoms together in layers, WEAK Van der Waals forces (intermolecular forces of attraction) in between layers. Graphite has a giant covalent structure where each carbon atom is covalently bonded to 3 other carbons in a hexagonal ring and has a 4th electron that is delocalised within each layer - conduct electricity.

3. Formulae and Mole Concept Amount = Mole Conc. x Vol Mass (g) = Mass Conc. x Vol Mass (g) = Amount x Molar Mass (Mr) Number of Particles = Amount x (6 x ) 10 23 Gas @ rtp: Vol = N x 24 𝑑𝑚 3 For gases - Mole ratio = Vol ratio Percentage Composition by Mass = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 × 100% Percentage yield = 𝑎𝑐𝑡𝑢𝑎𝑙 𝑦𝑖𝑒𝑙𝑑 ( 𝑢𝑠𝑢𝑎𝑙𝑙𝑦 𝑔𝑖𝑣𝑒𝑛 𝑖𝑛 𝑞𝑢𝑒𝑠𝑡𝑖𝑜𝑛 ) 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑 ( 𝑢𝑠𝑢𝑎𝑙𝑙𝑦 𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 ) × 100% Percentage purity = 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑝𝑢𝑟𝑒 𝑠𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 × 100% Empirical Formula - Simplest ratio of atoms Molecular formula - Actual number of atoms Molecular formula = Empirical formula x N H O … Assume 100g of _______, mass of element present/g Amount/mol (divide by Mr) Divide by smallest no. of moles Simplest ratio The reactant completely used up is the limiting reactant - it determines the amount of products formed The reactant with more than the required quantity is the excess reactant

4. Acids, Bases and Salts Reactions Acid dissociates in water to form H+ ions Base dissociates in water to form OH- ions Acid + Base → Salt + Water Acid + Carbonate → Salt + Water + Carbon Dioxide Acid + Metal → Salt + Hydrogen Base + Ammonium Salt