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WJEC AS/A Level Chemistry Lab Book Summary

The Periodic Table

  • Gravimetric analysis for identifying unknown metal chlorides.
    • Use a balance (3 decimal place preferred, 2 minimum).
    • Use a drying oven.
    • Dissolve unknown chloride in deionized water with HNO3. Add AgNO3 to coagulate silver chloride.
    • Heat (but do not boil) for 10 minutes, then cool for 2 hours.
    • Decant liquid, wash precipitate, and test wash solution with HCl to check for Ag^+ ions.
    • Dry precipitate at 105 °C until constant mass.

Qualitative Analysis

  • Identifying unknown solutions by qualitative analysis.
    • Plan a table to show expected observations of interactions between solutions.
    • Test solutions (e.g., Ba(NO3)2, Pb(NO3)2, MgSO4, KI, Na2CO3, Zn(NO3)_2) with each other and record observations.

Simple Equilibria and Acid-Base Reactions

  • Preparing a soluble salt via titration.
    • Use burette, pipette, conical flasks, NaOH and HCl solutions, and phenolphthalein indicator.
    • Titrate NaOH with HCl until phenolphthalein turns colorless.
    • Repeat without indicator, heat solution to reduce volume, and allow crystals to form.
  • Standardization of an Acid Solution
    • Standardize HCl using anhydrous sodium carbonate.
    • Accurately weigh anhydrous Na2CO3, dissolve in deionized water, and make up to 250 cm³ in a volumetric flask.
    • Titrate the Na2CO3 solution with HCl using methyl orange indicator until color changes from yellow to pink/red.
  • Back Titration
    • Determine the percentage of calcium carbonate in limestone using back titration.
    • Grind limestone, react with excess HCl, then titrate excess acid with standardized NaOH using phenolphthalein indicator.
  • Double Titration
    • Determine the concentration and mass of NaOH and Na2CO3 in a mixed solution.
    • Titrate mixed solution with HCl using phenolphthalein, then add methyl orange and continue titrating to its endpoint.
    • Calculate concentrations of NaOH and Na2CO3.

Thermochemistry

  • Indirect determination of enthalpy change of reaction.
    • Use calorimeter, thermometer, HCl, MgO, and MgCO_3.
    • React MgO and MgCO_3 separately with HCl, measuring temperature changes.
    • Calculate enthalpy change for MgO(s) + CO2(g) \rightarrow MgCO3(s).
  • Determination of enthalpy change of combustion.
    • Use a spirit burner, conical flask, and thermometer to measure the heat released by combustion of methanol and ethanol.
    • Add water to a conical flask and record initial temperature then burn the alcohol to heat the water and record the final temperature.
    • Calculate the energy released and enthalpy change of combustion (\Delta_cH^\ominus).

Rates of Reaction

  • Investigating rate of reaction by gas collection.
    • React hydrochloric acid with calcium carbonate, measuring gas produced.
    • Measure volume of CO_2 produced over time using a gas syringe and record the time until the syringe reaches 100 cm3.
    • Plot rate (\frac{1}{t}) against concentration of HCl.
  • Study of an ‘iodine clock’ reaction.
    • Study kinetics of iodide ions oxidation by hydrogen peroxide in acid solution using a series of measurements of volume and concentration across multiple flasks, timing the reaction to produce the 'iodine clock'.

Halogenoalkanes

  • Nucleophilic Substitution Reaction
    • Preparing butan-1-ol from 1-bromobutane and sodium hydroxide.
    • Measure 1-bromobutane and NaOH; reflux, then distill off butan-1-ol.

Alcohols and Carboxylic Acids

  • Preparation of an ester and separation by distillation.
    • React ethanoic acid and ethanol with concentrated sulfuric acid, then distill off ethyl ethanoate.

Redox and Standard Electrode Potential

  • Construction of electrochemical cells and measurement of E_{cell}.
    • Construct a copper/zinc electrochemical cell and measure the potential difference (E_{cell}).
    • Use CuSO4 and ZnSO4 solutions, connect with a salt bridge (saturated KNO_3).

Redox Reactions

  • Simple redox titration.
    • Determine the relative molecular mass of an iron(II) salt by titration with standard potassium manganate(VII) solution.
    • Titrate prepared Fe^{2+} solution against standardized KMnO_4 solution.
  • Estimation of copper in copper(II) salts.
    • Determine percentage by mass of copper in copper(II) sulfate crystals by titrating with standard Na2S2O_3 solution.

Chemical Kinetics

  • Determination of the order of a reaction.
    • Determine the order of reaction for oxidation of iodide ions by hydrogen peroxide in acid solution, establish the rate of reaction for different concentrations, and use the data to calculate the order of the reaction.

Equilibrium Constants

  • Determination of an equilibrium constant.
    • Determine equilibrium constant for reaction of ethanol with ethanoic acid.
    • Mix reactants, allow to reach equilibrium, then titrate with NaOH to determine concentrations.

Acid-Base Equilibria

  • Titration using a pH probe.
    • Obtain titration curves for strong and weak acids and alkalis using a pH probe.
    • Calibrate pH meter, titrate acids with alkalis, and plot volume of alkali against pH.

Organic Synthesis and Analysis

  • Synthesis of a liquid organic product.
    • Synthesize 2-chloro-2-methylpropane using 2-methylpropan-2-ol and concentrated hydrochloric acid, then purify the product using separation and distillation.
  • Synthesis of a solid organic product.
    • Synthesize 2-acetoxybenzenecarboxylic acid (aspirin) from 2-hydroxybenzenecarboxylic acid and ethanoic anhydride, purify via recrystallization, and determine its melting point.
  • Two-step synthesis.
    • Synthesize 3-nitrobenzenecarboxylic acid via nitration of methyl benzenecarboxylate followed by alkaline hydrolysis.

Organic Compound Identification

  • Planning a sequence of tests to identify organic compounds.
    • Plan and carry out a sequence of tests to identify organic compounds from a given list using a flow chart with different tests such as:
      • Litmus test for acids.
      • Reaction with NaHCO_3 for carboxylic acids.
      • 2,4-DNPH for carbonyl groups.
      • Tollens' reagent for aldehydes.
      • Iodoform test for methyl ketones and secondary alcohols.
      • NaNO_2 test for primary amines.

Paper Chromatography

  • Paper chromatography including two-way separation.
    • Analyze biro inks using paper chromatography and calculate Rf values.