Practicals - unit 3

• Determining the rate of reaction using a colorimeter

  1. Prepare a range of samples of different concentrations of the required solutions

  2. Calibrate the colorimeter using the appropriate filter and a blank solution

  3. Record the absorbance of each solution of known concentration

  4. Draw a calibration curve of absorbance against concentration

  5. Place the reaction mixture in the colorimeter and record the absorbance at different times

  6. Use the calibration curve to convert absorbance to concentration and plot a graph of concentration against time

  7. A gradient of a tangent at any concentration on the graph gives the rate at that concentration
• Determining the rate of reaction using a titration

  • The reaction is started by mixing the solutions and a sample is removed by pipette at various times
  • Quench the sample to stop the reaction by rapid cooling/adding a large volume of water/adding a chemical to remove a reactant which is not being monitored
  • Titrate the sample to find the concentration of the reactant or product
  • Plot a graph of concentration against time; the gradient of a tangent at any concentration on the graph gives the rate at that concentration.
• Determining the rate of reaction by measuring pH over time

  • Start the reaction
  • Record the pH at different times using a pH meter
  • Calculate the hydrogen ion concentration using pH = -log10[H+]
  • A graph of [H+] against time can be drawn and again gradients of tangents at various [H+] can be taken, which equal the rate at each point.
• Determining the rate of rection by measuring the volume of a gaseous product over time

  • Attach a gas syringe to a sealed reaction vessel, or collect the gas over water in an inverted measuring cylinder/burette
  • Start the reaction
  • Record the volume of gas produced at different time intervals
  • A graph of volume of gas against time can be plotted.
• Determining the rate of reaction by measuring the mass of a gaseous product

  • A flask containing one reactant is placed in a flask on a balance and the mass recorded
  • Add the second reactant and start the clock
  • Record the mass at different time intervals until the reaction is finished
  • A graph of mass against time is plotted
• Making buffer solutions from calculated quantities of salts & acids to determine their pH using a pH meter & the universal indicator

  • Use a burette to measure out calculated volumes of equimolar sol. Of a weak acid and the salt of the weak acid and add to a beaker
  • Mix w/ magnetic stirrer
  • Record the pH of the prepared buffer using universal indicator paper and a pH meter
• Determining the shape of a titration curve

  1. Place acid/base sol. of know vol. and conc. in a conical flask

  2. Record the pH of the sol. using a pH meter or narrow range pH meter

  3. Fill a burette with acid/base of known concentration

  4. Add the acid/base in 5cm3 portions from a burette, mixing w/ a magnetic stirrer

  5. Record pH after each addition

  6. Add the acid/base in in 1cm3 portions as the end point approaches

  7. Continue to add two 5cm3 portions after end point

  8. Plot a graph of pH against vol. of sol. added (titration curve)
• Determining the pH of a variety of salts using pH paper or a pH meter to illustrate the relative strengths of acids and bases

  • Prepare solutions of known conc. of a variety of salts
  • Record the pH using a pH meter or narrow range pH paper
• Preparing, recrystallising and determining the melting points of 2,4-dinitrophenylhydrazones (pt.1)

  1. Place 5cm3 of 2,4-dinitrophenylhydrazine solution in a suitable container

  2. Add some drops of the test liquid

  3. If crystals do not form, add some dilute sulfurique acid + warm the mixture

  4. Cool the mixture in iced water

  5. Filter off the crystals using suction filtration
• Suction filtration method

  • Place filter paper in a Büchner funnel
  • Place Büchner funnel in a Büchner flask
  • Attach the flask to a suction pump and suck air through the flask
• Preparing, recrystallising and determining the melting points of 2,4-dinitrophenylhydrazones (pt.2)

  • Recrystallise - dissolve the impure crystals in the minimum volume of hot solvent. Filter when hot by gravity filtration, using a hot funnel, or fluted filter paper, to remove insoluble impurities. Allow filtrate to cool and crystallise
  • Filter off the crystals using suction filtration
  • Dry by sucking air over the crystals in the Buchner and then in a dessicator
  • Determine the melting point
• Melting point method

  • Place some solid in a melting point tube, sealed at one end
  • Heat slowly
  • Record temp. at which the solid starts + finishes melting
  • Repeat and average the temps.
  • Compare the temps. with known values in a data book
• Using Fehling’s solution and Tollens’ reagent to distinguish between aldehydes and ketones

  • Add a few drops of the unknown solution to 1cm3 of Tollens’ reagent in a clean test tube
  • Warm in a hot water bath
  • Freshly prepare Fehling’s solution by mixing 1cm3 of Fehling’s solution A with 1cm3 of Fehling’s solution B
  • Add a few drops of the unknown solution to 1cm3 of freshly prepared Fehling’s solution reagent in a test tube
  • Warm in a hot water bath
• Preparing a carboxylic acid from an alcohol

  • Add conc. sulphuric acid to water in a round bottomed flask
  • Swirl the solution and cool the flask to dissipate the heat and to prevent spitting
  • Add potassium dichromate (VI) solution and swirl the mixture
  • Add anti-bump granules
  • Attach vertical condenser
  • Add the alcohol slowly, down the condenser, to the acidified potassium dichromate (VI) solution, cooling the reaction flask in a water bath
  • Heat the mixture under reflux
  • Distil off the acid
• Test tube reactions of a carboxylic acid with sodium carbonate, sodium hydroxide and aqueous ammonia and measure the pH changes 

  • Place 1cm3 of the carboxylic acid in a boiling tube
  • Record the pH using a pH meter
  • Add a spatula measure of sodium carbonate + record observations
  • Record the pH using pH paper
  • Repeat the experiment using 1cm3 of sodium hydroxide solution instead of sodium carbonate
  • Repeat the experiment using 1cm3 of aqueous ammonia instead of sodium carbonate
• Preparing a liquid ester from a carboxylic acid and an alcohol (pt.1)

  • Place a mixture of the alcohol and conc. sulfuric acid in a round bottomed flask
  • Add a mixture of the alcohol and carboxylic acid slowly from a dropping funnel
  • Swirl the mixture
  • Add some anti-bump granules and heat under reflux
  • Arange the apparatus for distillation, heat the mixture gently and collect the distillate around 2°C either side of the boiling point of the ester
  • Place the crude ester in a separating funnel and shake with sodium carbonate solution. Invert the funnel and open the tap occasionally to release pressure
• Preparing a liquid ester from a carboxylic acid and an alcohol (pt.2)

  • Remove stopper allow the layers to separate and discard the aqueous layer (to determine which layer is the aqueous one, add 5cm3 to the separating funnel, and the aqueous layer gets bigger)
  • Add spatula measure of anhydrous calcium chloride (drying agent) to the organic layer in a flask, stopper and shake. Repeat until the ester changes from cloudy to clear
  • Filter or decant to remove calcium chloride
  • Redistill to remove any remaining organic impurities, collecting the fraction at the boiling point.
• Preparation of methyl-3-nitrobenzoate

  1. Dissolve solid methyl benzoate in conc. sulfuric acid

  2. Cool the mixture in ice

  3. Prepare a nitrating mixture containing equal amounts of conc. nitric acid + conc. sulfuric acid

  4. Cool the nitrating mixture in ice

  5. Add the nitrating mixture drop-wise to the solution of methyl benzoate, using an ice bath to keep the temp. Of the mixture below 10°C

  6. Allow the mixture to stand at room temp. For 15 minutes

  7. Pour the reaction mixture onto crushed ice and stir until all the ice has melted and crystalline methyl 3-nitrobenzoate is formed

  8. Filter the crystals using Büchner filtration

  9. Wash with cold water

  10. Recrystallise from ethanol

  11. Filter off and dry
• Titrating iodine with sodium thiosulfate solution using starch and hence estimate oxidising agents by their reaction with excess acidified potassium iodide

  1. Rinse pipette with potassium iodate (V) solution

  2. Pipette 25.0cm3 of standard potassium iodate (V) solution into a conical flask

  3. If hydrogen peroxide is used: pipette 25.0cm3 of hydrogen peroxide into a conical flask, add a few drops of ammonium molybdate catalyst and proceed

  4. Add approx. 1.5g of potassium iodide (excess) and excess of sulfuric acid (via measuring cylinder)

  5. Rinse burette with the standard sodium thiosulfate, and then fill the burette with sodium thiosulfate, making sure the tap is filled

  6. Add standard sodium thiosulfate solution from the burette until the solution is straw/yellow in colour and add 3 drops of starch indicator solution

  7. Titrate until the indicator changes colour

  8. Repeat until results are concordant
• Titrating acidified potassium manganate (VII) solution with reducing agents

  • Rinse the pipette with a solution of a reducing agent and use the pipette and safety filler to pipette 25.0cm3 into a conical flask
  • Rinse the burette with a standard solution of potassium manganate (VII) and then fill the burette ensuring the tap is filled
  • Add excess sulfuric acid using a measuring cylinder, to the conical flask
  • Add potassium manganate (VII) solution from the burette into the conical flask and swirl until the solution turns from colourless to pink
  • Repeat until results are concordant
• Determining the purity of a Group II metal oxide or carbonate by back titration


  1. Weigh out a mass of the solid (Group II metal, oxide or carbonate)

  2. Add an excess of hydrochloric acid

  3. Add the solution to a 250cm3 volumetric flask & make up with deionised water until the bottom of the meniscus is on the mark

  4. Rinse a pipette with the solution from the volumetric flask, and use the pipette and pipette filler to pipette 25.0cm3 into a conical flask

  5. Add 3 drops of phenolphthalein indicator

  6. Rinse a burette with standard alkali solution, and fill the burette

  7. Add alkali from the burette, to the conical flask until the indicator changes colour

  8. Repeat until results are concordant
• Paper and thin-layer chromatography and measure the Rf values of the components and interpret the chromatograms


  1. Draw a base line using a pencil close to the bottom of the paper/thin-layer plate

  2. Spot the samples onto the paper/thin-layer plate using a capillary tube. Allow the spots to dry. Repeat to make to spots concentrated

  3. Place the paper in the tank containing a shallow amount of solvent, cover with a lid, and allow the solvent, cover the lid, and allow the solvent to run up over the spots until the solvent almost reaches the top of the paper/thin-layer plate. Mark solvent front. Allow to dry.

  4. If the substances to be separated are colourless, the spots are made visible by spraying with a locating agent e.g. ninhydrin

  5. Measure the distance travelled by the solvent front and the distance moved by each spot (to centre of spot) and calculate the Rf values
• Using ethylene diamine, phenylamine and aqueous ammonia to demonstrate ligand replacement based on lone pair availability

  • Place 2 cm3 of a metal ion solution in a boiling tube
  • Add 1 cm3 of phenylamine, shake and record observations
  • Add 1 cm3 of aqueous ammonia solution, shake and record observations
  • Add 1 cm3 of ethylene diamine, shake and record observations
• Demonstrating the relative strengths of ligands using hexaaquacopper(II) ions in solution and hydrochloric acid

  • Add 2 cm3 of a hexaaquacopper(II) ion solution to a test tube
  • Add 2 cm3 of concentrated hydrochloric acid and record observations.
• Carrying out qualitative detection tests for the formation of transition metal hydroxides with sodium hydroxide solution and aqueous ammonia

  • Add 2 cm3 of a solution of the transition metal ion to a test tube
  • Add a few drops of aqueous ammonia and record observations
  • Add excess (5 cm3) of aqueous ammonia and record observations
  • Repeat using sodium hydroxide solution instead of aqueous ammonia.
• Carrying out the reduction of acidified ammonium vanadate (V) [ammonium metavanadate] with zinc and observing the sequence of colours

  • Dissolve some ammonium vanadate(V) (ammonium metavanadate) in hydrochloric acid in a conical flask
  • Add two spatulas of zinc as a reducing agent
  • Stopper the flask with cotton wool, to allow the hydrogen to escape, and slow down the entry of air.
  • Observe the sequence of colours
• Determining the electrode potentials of a series of cells and predicting their values using standard electrode potentials

  • Set up a half-cell - a metal dipping into a 1 M solution of its ions in a beaker
  • Attach via wires, and a voltmeter to a second half-cell using a different metal and a 1 M solution of its ions
  • Use a salt bridge to connect the two beakers
  • Record the voltage.
• Determining the amount of a carbonate in an indigestion tablet 

  As magnesium hydroxide and calcium carbonate are insoluble in water, their percentage in an indigestion remedy can be determined by back titration
• Preparing aspirin using salicylic acid and ethanoic anhydride

  • place 1.0 g of 2-hydroxybenzoic acid in a dry pear shaped flask and add 2 cm3 of ethanoic anhydride.
  • safely add 8 drops of concentrated phosphoric(V) acid
  • heat under reflux for 30 minutes.
  • add water to hydrolyse any unreacted ethanoic anhydride to ethanoic acid
  • pour the mixture onto 400 g of crushed ice in a beaker.
  • remove the product by suction filtration,
  • recrystallise from water
  • dry in a desiccator/low temperature oven
  • determine the melting point
• Using chromatography to compare the purity of lab-made aspirin with commercial tablets

  1. Draw a baseline using a pencil close to the bottom of the paper/thin-layer plate

  2. Draw two pencil crosses on the baseline

  3. Place some of the laboratory-made aspirin solid on a watch glass and dissolve in a few drops of solvent such as ethanol

  4. Use a capillary tube to place a spot of the solvent on a pencil cross

  5. Allow the spot to dry and repeat, ensuring the diameter of the spot is no more than 0.5 cm

  6. Repeat this for the commercial solid

  7. Place the paper/thin-layer plate in the tank containing a shallow amount of solvent, cover with a lid and allow the solvent to run up over the spots until the solvent reaches the top of the paper

  8. Mark the solvent front

  9. Allow to dry

  10. The spots are made visible by placing the paper/thin-layer plate in a beaker containing iodine crystals

  11. Measure the distance travelled by the solvent front, and the distance moved by the centre of each spot and calculate the Rf value of each spot