Choose and use laboratory apparatus and techniques correctly: measuring volumes and masses, heating, titration, filtration, distillation, calorimetry and electrochemical cells; state safety and environmental precautions and the reason for a given step of a method.
Tę umiejętność sprawdzają 63 zadania wzorowane na arkuszach IB z lat 2022–2026.
(b) A variety of ions are dissolved in the water of the Salton Sea. The concentrations of the major ions are shown in the table below, based on two different sources (both scientific journals). (i) Suggest two reasons for the difference in the concentration of…
(a) Outline two features of this experiment that ensure that the propanal intermediate is not a major product.
(b) Outline two safety precautions that must be taken during the preparation of propanoic acid, besides wearing a lab coat and safety goggles.
(d) The student used distillation to obtain pure propanoic acid from the reaction mixture. (i) State two impurities, apart from unreacted propan-1-ol, that were present in the propanoic acid before distillation. (ii) The approximate experimental yield of…
Before the samples were measured, an absorption spectrum was recorded to find the best wavelength to use. (i) Describe the contents of the two solutions required to record the spectrum: the reference solution and the blank. (ii) The spectrum obtained is shown.…
The ascorbic acid in the juice was determined by titration with a standard solution of iodine, I2. The method is based on the following redox reaction: C6H8O6(aq) + I2(aq) → C6H6O6(aq) + 2 I−(aq) + 2 H+(aq) (i) Deduce the oxidizing agent in this…
Outline why a standard solution of potassium manganate(VII) was needed for this analysis.
Suggest why diluting the standard solution was necessary.
State two items of glassware that the dilution required.
The titration was carried out using a burette, a volumetric pipette and a conical flask. State which of the three items should be rinsed with the solution it will hold, and which only with distilled water.
(i) The diagram shows the burette scale at the end of trial 4. The solution is deep purple, so the reading is taken at the top of the liquid. Determine the final burette reading for trial 4 and complete the table. (ii) Suggest, with a reason, whether more…
Explain how the 0.2000 mol dm−3 solution is prepared in a volumetric flask from the weighed solid.
Suggest how to prepare 100.0 cm3 of a 0.05000 mol dm−3 sodium thiosulfate solution from the 0.2000 mol dm−3 solution.
State one safety concern arising from a product of this reaction, and a precaution that should be taken because of it.
Before use, the EDTA solution was standardized against a standard solution of Cu2+ ions. An accurately weighed piece of pure copper wire was dissolved in the minimum volume of concentrated nitric acid and the mixture was warmed gently until no more…
Anhydrous copper(II) chloride, CuCl2, takes up water vapour from the air, so it cannot be weighed out accurately to make a standard solution. Suggest a laboratory procedure that would remove all of the absorbed water from a sample of solid CuCl2…
Portions of the rinse water were then titrated with the standardized EDTA solution in the presence of murexide as indicator. The burette readings are given in the table. (i) Suggest two reasons why trial 1 required a much larger volume of EDTA than the other…
(i) Suggest, giving a reason for each, two different safety precautions that should be taken when carrying out either of these preparations. (ii) Deduce the coefficients needed to balance the following equation for the reaction of silver with concentrated…
Suggest a sequence of experimental steps that would give a pure sample of each of the three components.
(i) State the independent variable and the dependent variable of the investigation. (ii) Apart from the mass of leaves and the volume of water, suggest two other conditions that should be kept constant for the comparison between boiling times to be valid.…
Describe how a standard aqueous solution of potassium manganate(VII) can be prepared from the solid.
Describe the steps by which this standard solution is turned into a calibration curve for the colorimeter.
The colorimeter can record either absorbance or percentage transmittance at a chosen wavelength. Outline why one particular wavelength has to be selected.
(i) Suggest a reason for the slight change in colour observed after the night in the oven. (ii) Suggest how the students could make sure that dehydration in the crucible was complete. (iii) Suggest one way in which the students could reduce the effect of…
Which of the following could be used to follow the progress of the reaction between calcium carbonate and dilute nitric acid? CaCO3(s) + 2 HNO3(aq) → Ca(NO3)2(aq) + H2O(l) + CO2(g) I. A balance recording the mass of the open flask and its contents II. A…
Describe how the student should prepare this standard solution from the weighed solid using a 250.0 cm3 volumetric flask.
The student pipetted 25.00 cm3 of the potassium hydroxide solution into a conical flask and titrated it with nitric acid, HNO3(aq), of concentration 0.1250 mol dm−3. The burette readings before and after the titration are…
Explain why the potassium hydroxide solution has to be standardized before it is used in the titration. Assume that there are no systematic errors in the procedure.
The student then used the potassium hydroxide solution standardized in 1c to titrate ethanoic acid, CH3COOH, whose concentration was not known. (i) Neutralizing 25.00 cm3 of the acid required 40.00 cm3 of the standardized…
State one other physical property that could be measured to identify the metal while leaving the block intact.
(i) Suggest one hazard to health or safety in Student A's procedure. (ii) Student A plotted the highest temperature of each mixture against the volume of nitric acid. With a ruler, draw two straight lines of best fit: one following the rising set of points and…
Student B pipetted 30.00 cm3 of the potassium hydroxide solution into a 150 cm3 glass beaker and added the nitric acid from a burette in portions of 4.00 cm3, recording the steady temperature after each addition. (i) From a…
Explain why the start line must be horizontal and must be above the level of the solvent when the strip is placed in the chamber.
Describe the steps the student would follow to recrystallize the crude benzoic acid.
State the most important property that water must have, with respect to benzoic acid, for it to be a suitable solvent for this recrystallization.
Outline how each of the two by-products is removed from the benzoic acid during the recrystallization. By-product that is almost insoluble in hot water: ... By-product that is much more soluble than benzoic acid: ...
The volume of hot water used to dissolve the crude solid must be chosen carefully. Deduce the effect on the yield or on the purity of the recrystallized benzoic acid of using too much water and of using too little water. Too much water: ... Too little water:…
Describe the setup that would connect the Sn4+/Sn2+ half-cell to a second half-cell for comparing the two electrode potentials.
Most pools, including this lido, are dosed with sodium hypochlorite solution, NaOCl(aq), instead of chlorine gas. Suggest why pool operators avoid dosing the water with chlorine gas itself.
The student measures the hydrogensulfite concentration by titrating samples against a standard iodine solution, with starch as the indicator. Every three days, 25.00 cm3 of cordial is withdrawn from each flask, diluted to 250.0 cm3 with…
Sketch how the combined mass of the flask, the syringe and their contents would change with time during Experiment 1, and give a reason for the shape of your sketch. Label the axes 'Total mass' and 'Time'.
State one method that could be used to follow the progress of this reaction and explain how its measurements allow the rate, in mol dm−3 s−1, to be determined.
A student determined the enthalpy change of combustion of ethanol by burning it in a spirit burner under a copper can containing 150 cm3 of water. The value obtained was less exothermic than the literature value. Which modification would improve the…
Suggest why it is important that hydrogen gas flows through the tube (i) before heating begins, (ii) from the end of heating until the product has cooled.
(i) State which two further mass measurements are needed to find the oxide composition. (ii) Outline how these measurements give the mass of oxygen removed from the sample.
Suggest why the amount of oxygen per mole of iron calculated from the results is often lower than the true value, and how this error could be reduced.
Ethyl 4-hydroxybenzoate is a preservative used in some oral medicines. It was synthesized by heating 0.745 g of 4-hydroxybenzoic acid with excess ethanol and a few drops of concentrated sulfuric acid as catalyst. C7H6O3 + C2H6O ⇌ C9H10O3 + H2O Mr…
All the species in the titration are almost colourless except MnO4−, which is intensely purple. The spinach extract, however, is coloured green by chlorophyll. (i) State the colour change at the end point. (ii) Outline how adding distilled water to the…
Suggest how the rate of this reaction could be determined experimentally.
A student separates the coloured dyes in a sample of black ink by paper chromatography, using water as the solvent. Explain how paper chromatography can separate and identify the dyes in a mixture.
A colorimeter is set to a wavelength of 550 nm. Explain why it cannot be used to follow reactions of compounds of Sc3+. Use section 5 of the data booklet.
The vitamin C content of a juice can be found by titrating a sample against a standard iodine solution. Starch is used as the indicator: it forms a dark blue-black complex with the first excess of iodine once all the vitamin C has reacted.…
The concentration of vitamin C in juice can be measured by a redox titration. A sample of acidified juice containing excess iodide ions and starch solution is titrated with potassium iodate solution. Iodate ions react with iodide ions to produce iodine…
A student electrolysed aqueous silver nitrate between two silver electrodes, as shown. Each electrode was washed, dried and weighed before and after the electrolysis. Suggest why the mass gained by the cathode is a less accurate measure of the amount of silver…
A sample of the protein is completely hydrolysed to a mixture of amino acids. Outline how paper chromatography can be used to identify the amino acids in this mixture when samples of the pure amino acids are available for comparison.
A biochemist wants to find out which of the amino acids glycine, serine and leucine are present in a short peptide. Outline how paper chromatography can be used to do this.
Benzocaine, a local anaesthetic, is the ethyl ester of 4-aminobenzoic acid. The crude product of its synthesis is purified by recrystallization. (i) Discuss two ways in which the melting point of the recrystallized benzocaine can show that it still contains…
Benzocaine is a local anaesthetic. It is made by reacting the carboxylic acid X with ethanol. (i) Discuss two ways in which the melting point of a crystallized sample of benzocaine can show that it still contains X. (ii) Deduce the range of wavenumbers in the…
A student determines the concentration of an ethanoic acid solution by titration against standard NaOH(aq) from a burette. Which action would introduce a systematic error? A. Reading the burette at slightly different eye levels in each trial B. Using a…
The concentration of ethanoic acid in a sample of vinegar is determined by titration against a solution of sodium hydroxide of known concentration. Which procedure is most likely to produce a systematic error in the calculated concentration of the acid? A.…
The graph shows the volume of hydrogen produced when a small piece of zinc reacts with a large excess of 2.0 mol dm−3 hydrochloric acid. (i) Deduce from the graph how the rate of reaction depends on the amount of zinc present. (ii) The rate is…
A student monitors the rate of a reaction using a colorimeter. In which mixture would the absorbance change as the reaction proceeds? A. NaOH(aq) + HNO3(aq) B. KCl(aq) + I2(aq) C. KI(aq) + Cl2(aq) D. CH3COOH(aq) + KOH(aq)
Which procedure is best for converting butan-1-ol into butanoic acid? A. Heat under reflux with an acidified oxidizing agent B. Heat under reflux with a reducing agent C. Heat with an acidified oxidizing agent and distil off the product as it forms D. Heat…
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