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A comprehensive and visually detailed revision guide covering key chemistry topics for practical and theoretical understanding. Includes laboratory equipment, safety, experimental design, separation techniques, electrolysis, rates of reaction, thermal chemistry, salt preparation, and both qualitative and quantitative analysis. Perfect for students preparing for high school or early undergraduate level chemistry exams
Typology: Lecture notes
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COMMON LABORATORY EQUIPMENT
o This is also known as the Erlenmeyer flask. o A conical flask is usually used for mixing reagents together and conducting reactants. o The graduations (markings) on a conical flask are not very accurate. o The tapered edges towards the top prevent spillage and make these flasks ideal for clamping.
o Used for gravity filtration, where cotton wool or filter paper is placed on top.
o Used to pick up small amounts of solids.
o Used to stir a solution manually.
o Used to transfer small, fixed amounts of liquid accurately.
o Used for titration experiments. o Have an upside-down graduation, to easily tell the volume used.
o Used to crush up a solid into powder. o The mortar is the bowl, and the pestle is the blunt thing we use to crush the solid.
o Used to boil the liquid when we do not want to lose any volume. o Has a water jacket that condenses the vapor, making it drip down back into the solution. o Never block the top of the condenser, as pressure will be built up, causing an explosion
o Used to hold up glassware, keeping them locked in place. o Be careful of weight distribution, making sure the stand does not topple over.
o Used for filtration experiments, a finer grading filters a solution on slowly. o Also used to passively dry solids, as they tend to absorb liquids.
o Used when you need to leave a wet solid to dry off.
o Used to hold hot things like a crucible or a strip of burning metal (like magnesium).
MEASURING VARIOUS QUANTITIES
o Time can be measured using a stopwatch. o Digital stopwatches can be used to measure time accurately up to two decimal places.
o Mass can be measured approximately in spatula amounts, like “add 1 spatula of X.” o Mass can be measured more accurately using a top pan balance, where a simple top pan balance can measure up to two decimal places, a balance with a higher resolution can measure to three or more decimal places.
o Temperature is measured in degrees Celsius using a thermometer. o A simple mercury or spirit-based thermometer can measure temperature up to the nearest degree, digital temperature probes can measure to greater resolutions such as one or more decimal places.
o Gas syringe or inverted (upside-down) measuring cylinder is used to measure gaseous volume; use gas syringe when gas is soluble in water (like co 2 ). Gas syringes are also more accurate, hence avoid using inverted measuring cylinders. o Put a bung with a hole on the apparatus in which the reaction takes place and fix a delivery tube into the gas syringe or measuring cylinder. o Attach a Bunsen valve at the end on the delivery tube in an inverted measuring cylinder setup if the reaction is exothermic, to avoid water being sucked back into the tube, making the glass cool instantly and crack. o Use graduated beaker when measuring large volumes where accuracy is not needed (like a 100cm^3 water bath).
SAFETY HAZARDS
o All concentrated mineral acids are corrosive, hence should be handled using thick leather gloves or long tongs, whilst wearing safety googles for eye protection.
HOW TO PLAN AN EXPERIMENT
o Pick a hypothesis and state what all is going to be tested. o Plan how are you going to test these ideas, which variable is being tested and what is constant, what chemicals and apparatus are needed, etc. o Carry out the experiment, mentioning what values will be recorded and how often. o Enter the values in a suitable table and plot a suitable graph. o For the graph, plot the independent variable on the x axis and the dependent variable on the y axis. o The scales do not need to start from the origin unless mentioned. o Make the scales as large as possible. o Label each axis with the name of the variable followed by suitable units. o Plot a best-fit line, which can either be straight or a curve, where it is not necessary all points are on the line. o Examine the results and arrive to a conclusion; mention any formulas/ criteria used to say if the result proves the hypothesis true or not.
o Measure the volume of a liquid in a measuring cylinder from the bottom of the meniscus. o Random errors are unpredictable variations in the results, due to human errors. Whilst Systematic errors are consistently caused by an error with the experimental design or apparatus used. It is ok to omit anomalous results for the line of best fit. o Look perpendicular to avoid parallax error. o Repeat the experiment at least thrice and take an average. o Make sure all electronic equipment is the well calibrated using samples of known values to avoid zero error. o Make sure the experiment is repeatable, allowing reproducible results. o Make sure the readings taken are both accurate and precise.
SEPERATION TECHNIQUES
o Used when separating a mixture of two solids, using a solvent which only dissolves one of them. o Filter the mixture, the residue is the insoluble solid and the filtrate contains the soluble solid, which could be extracted by evaporating the filtrate, leaving the solids pure dry crystals. o Organic compounds do not usually dissolve in water; hence hexane is to be sued as a solvent instead. o Toluene can be used to dissolve sulphur.
o It is the separation of an insoluble solid from a liquid using a fine filter paper which does not allow the solid to pass through. o The liquid which passed through the filter paper is called the filtrate, whilst the solid left behind is called the residue. o A Buchner funnel can be used in combination with a vacuum flask to filter out very fine solids.
o The Buchner funnel has a perforated plate which is covered by a circle of a filter paper. o A vacuum pump is connected to the side arm of a flask; it speeds up the flow of the liquid through the funnel.
o The process of forming crystals from a saturated solution. o Heat the solution by placing an evaporating basin over a beaker of boiling water, which prevents the material being lost from the rapid boiling of the liquid itself. o Remember to heat the beaker with a gauze underneath to make sure heat is transferred evenly and reduces the chance of the beaker being damaged due to the direct heat. o To obtain larger crystals, evaporate only a little bit of water and then leave the solution to cool at room temperature, then dry the crystals between two filter papers.
o Used to separate a liquid solvent from a solution containing dissolved solids.
condenses and drips down back into the mixture. o The thermometer reading stays 78 degrees until all the ethanol has distilled over. o There is a range of temperatures in the fractionating column. The higher temperature is at the bottom of the fractionating column, and the lower temperature is at the top. o Fractional distillation is used in industrial processes such as the separation of petroleum and liquid air.
Solid Solid Solvent Sand & sodium chloride (salt) Insoluble solid Liquid Filtration Sand & water Soluble solid Liquid Crystallisation Copper sulphate & water Liquid(miscible) Liquid(miscible) Distillation Crude oil
o All pure substances melt/boil at a fixed temperature, which is used to determine its purity.
o A small sample of the solid is placed in a capillary tube, attached to a thermometer, and melted using an oil or water bath. o This can also be done using an electrically heated melting point apparatus, where the capillary tube is placed in the heating block and the melting is viewed through a magnifying lens. o An impurity often reduces the melting point and increases the boiling point.
o A technique employed for the separation of mixtures of dissolved substances, which was originally used to separate coloured dyes. o Paper chromatography is used to separate soluble pigments using a filter paper (we will however refer to the paper as chromatography paper instead). o The solvent is called the mobile phase, and the chromatography paper is called the stationary phase. o These coloured substances separate if: o The pigments have different solubilities in the solvent. o The pigments have different degrees of attraction for the filter paper.
