Chemistry syllabus notes

1 1. Experimental Chemistry 1.1 Experimental Design (a) name appropriate apparatus for the measurement of time, temperature, mass and volume; including burettes, pipettes, measuring cylinders and gas syringes Time: stopwatch (s), Mass: Electronic balance (kg, g), Temperature: Alcohol thermometer (k), Volume: Pipette (accurate volume 10.0cm3), Volumetric flask (large accurate volume 100cm3), Measuring cylinder (nearest 0.5cm3), Burette (nearest 0.05cm3) (b) suggest suitable apparatus, given relevant information, for a variety of simple experiments, including drying and collection of gases and measurement of rates of reaction Water displacement: Insoluble/slightly soluble (h2, o2, co2), Downward delivery: Denser than air (cl2, hcl, so2). Upward delivery: Less dense than air (nh3) Concentrated sulfuric acid: Remove water from acidic gas, Quicklime [freshly heated before use]: Remove water from alkaline gas, Calcium chloride [freshly heated before use]: Neutral gas (neither acidic nor alkaline) 1.2 Methods of Purification and Analysis (a) describe methods of separation and purification for the components of mixtures, to include: (i) use of a suitable solvent, filtration and crystallization or evaporation Use of suitable solvent: Separate solids of different solubility (s-s mixture, only one solid is soluble in solvent used) Filtration: Separate insoluble solids from liquids (Passes through filter paper is filtrate, remains on filter paper is residue) Crystallization: If solute is easily decomposed, this method is used. Obtaining pure solid from saturated solution. (saturated is when no more solute can be dissolved.) Cool saturated solution until crystals appear. Pour mixture to funnel to collect crystals. Crystals are washed with cold water to remove impurities and dried between 2 sheets of filter paper. Evaporation: Heat cause water to be evaporated, leaving salt behind. Substance with lower bp will turn into gas first, leaving another behind. Heat the solute till a solid is left behind. (ii) Sublimation Sublimation: Separate a substance that changes from solid to gaseous state directly. (iii) distillation and fractional distillation (see also 11.1(b)) Distillation: Separate pure solvent from a solution. Relies on the diff in bp (l-g) Salt water heated and vapor rises through the condenser and exit to the conical flask. Water vapor cools in the condenser and condenses back to the liquid. Pure water is collected as distillate. As more water vaporizes, the salt concentration gets more concentrated and a solid residue remains in the distillation flask . Boiling chips: Smooth boiling Fractional distillation: Separate miscible liquids with diff bp. When solution is heated, both ethanol and water vapor rises and the water with a higher bp will condense on the cool surface of the fractionating column and returns back to the liquid. Hot ethanol will cool and condense into liquid in the condenser and flow into conical flask. Glass bead: Provide large surface for vapor to condense. Thermometer: Measure temperature (temp stays constant during boiling) Condenser: Condense vapor, water enters from the bottom (goes against gravity to make it more efficient) (iv) use of a separating funnel Separating funnel: separate immiscible liquids, each component can be removed by opening the tap at the bottom and collect in diff beakers. (v) paper chromatography Chromatography: Used to separate a mixture of substances which have different solubilities in given solvent. As solvent is absorbed by paper, it travels towards opp edge. More soluble travel more rapidly towards solvent front and the less soluble will more at a slower rate. (when they travel at diff speed, they get separated.) Rf is the distance travelled by substance/distance travelled by solvent (ratio of distance)

2 Diff solvent have diff Rf Starting line drawn with pencil: Pencil is graphite and will not be separated. Small sample: Prevent spots from overlapping Solvent front as high as possible: components separated fully Solvent front do not reach the edge of paper: Allow actual distance to be measured (b) suggest suitable separation and purification methods, given information about the substances involved in the following types of mixtures: (i) solid-solid (diff in solubility, size, magnetism, state) (ii) solid-liquid (diff in solubility, bp) (iii) liquid-liquid (miscible and immiscible) (diff in bp. Immiscible, rf) (c) interpret paper chromatograms including comparison with ‘known’ samples and the use of Rf values Rf can compare chromatograms with known substance under the same temperature and solvents. If solvent is diff. the rf of the same substance will change. (d) explain the need to use locating agents in the chromatography of colorless compounds (knowledge of specific locating agents is not required) They are chemicals which reacts with colorless substance to from colored spot. Examine under UV light will also work. (e) deduce from given melting point and boiling point data the identities of substances and their purity Pure substances has a specific mp or bp under fixed boiling point. Mixtures melt/boil over a range of temperature. The greater the impurities, the larger the change in mp/bp. Identify purity with chromatography, melting, boiling point. (f) explain the importance of measuring the purity in substances used in everyday life, e.g. foodstuffs and drugs. Impurities in medicines may cause harmful side effects. Silicon in computer chips need to have a certain purity in order to function effectively. 2. The Particulate Nature of Matter 2.1 Kinetic Particle Theory (a) describe the solid, liquid and gaseous states of matter and explain their interconversion in terms of the kinetic particle theory and of the energy changes involved Solid state: Closely packed in an orderly arrangement. Vibrate or rotate about their fixed position and have a low KE. The particles experience strong attractive forces, so a lot of energy is needed to break the regular arrangement. Have a definite volume and shape. Liquid state: Their arrangement is closely packed in an disorderly arrangement. The particles slide past one another freely. The particles spacing in liquids is larger than solid that the attractive forces are less strong. Liquid has no definite volume but no definite shape. Gaseous state: The particles are found far apart in an disorderly manner. The particles can move quickly and randomly in any direction. The particles spacing are large that the attractive force between them is weak. (b) describe and explain evidence for the movement of particles in liquids and gases (the treatment of Brownian motion is not required) Diffusion: It is the net movement of particles from a region of higher concentration to a lower concentration.

3 6 Movement of particles in gases: As the particles of air move about, they collide with the solid particles of dust and make the dust appear to move randomly under light (c) explain everyday effects of diffusion in terms of particles, e.g. the spread of perfumes and cooking aromas; tea and coffee grains in water Tea: The particles of tea diffuses out of the bag into the water. The particles move from higher concentrations to lower concentrations. Perfume: When the liquid is sprayed, the violatile substance vaporize immediately and the other substance falls as liquids onto the surface of skin. Perfume diffuse away from bottle. (d) state qualitatively the effect of molecular mass on the rate of diffusion and explain the dependence of rate of diffusion on temperature. The smaller the mr, the faster it moves as it require lesser KE to move at a given speed, therefore it diffuses faster The higher the Mr, there is more thermal energy converted to KE, increasing diffusion 2.2 Atomic Structure (a) state the