Draw a conclusion justified by the data, compare it with the accepted value or theory, identify limitations and sources of error in the method, and suggest realistic improvements.
Tę umiejętność sprawdza 51 zadań wzorowanych na arkuszach IB z lat 2022–2026.
(a) The graph shows how the water level of the Salton Sea has changed since 1950. The reference point for the water level is sea level. (i) Suggest a reason why the values plotted on the vertical axis are negative. (ii) The surface area of the Salton Sea was…
(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…
(c) A simple set-up was used to compare the conductivity of water samples obtained from the Salton Sea at different depths. The following data were obtained: (i) State the independent and the dependent variable in this experiment. (ii) Suggest two variables,…
Discuss the range of the independent variable and the quantity of data in this investigation.
Suggest why the light intensity rose during the first minutes of each run.
The graph shows the maximum rate of decrease in light intensity for each run, plotted against temperature. (i) Draw the best-fit curve on the graph. (ii) Suggest two possible conclusions that can be drawn from the investigation.
Suggest two modifications to the procedure that would make the data more reliable.
The student repeated the experiment using Method 2, with the same quantities of acid and solid. (i) Calculate the volume of gas that will have collected in the measuring cylinder once the reaction has finished, measured at T = 22 °C and…
(c) After 30 minutes, the student stopped heating the mixture and titrated a sample of the solution remaining in the flask with NaOH to determine the experimental yield of propanoic acid. Explain why the titrated sample will give an incorrect value for the…
The student decided to ignore the uncertainty in the mass of ethanol burnt when calculating the specific energy. Discuss whether this decision is valid, using the percentage uncertainties for trial 5.
Calculate the percentage error in the mean specific energy of ethanol. Literature value of the specific energy of ethanol = 29.7 kJ g−1
Suggest two ways in which the error in this experiment could be reduced.
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…
The students wished to compare their result for ascorbic acid with the value given for pink grapefruit juice in a food-composition database. Suggest two aspects of the data or of the samples that the students must check before judging whether their value…
The enthalpy change for the combustion of propane is calculated from bond enthalpy data and compared with the literature value. C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(l) Which statement best explains why the calculated value is less negative than the…
The three percentages in 2b add up to more than 100 %. Suggest an error that would explain this result and how it could be reduced or eliminated.
The results did not support the student's hypothesis. Suggest what the student overlooked when forming the hypothesis.
(i) State what the graph shows about the relationship between the boiling time and the amount of oxalate ions extracted. (ii) Comment on the range of boiling times and on the number of measurements made in the investigation.
The hypothesis being tested was that a longer boiling time would extract more oxalate ions from the leaves. (i) Evaluate the hypothesis in the light of the results, giving a reason. (ii) Suggest one way in which the investigation could be changed so that it…
The data show that the first ionization energy and the atomic radius are related. (i) State what kind of relationship links the two variables. (ii) Compare and contrast the trends observed for the three groups.
Using the table below, state the name of the metal from which the block is made.
Deduce, from the results obtained, two sources of systematic error in this procedure.
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…
The iron(II) concentration is found by titrating against a standard solution of potassium manganate(VII), KMnO4. At intervals of a few days, a 20.00 cm3 sample is withdrawn from each flask and made up to 250.0 cm3 with water;…
The student's results are shown in the graph. (i) Calculate the average rate at which the iron(II) concentration fell in the 24 h flask during the 21 days. Include units. (ii) Before starting, the student proposed the hypothesis: "The longer a solution is left…
Suggest one way of extending the investigation so that further recommendations about storing the iron(II) solution could be made.
The enthalpy of combustion of C19H40 is −12 660 kJ mol−1. (i) Calculate the maximum energy released when 1.50 g of C19H40 is burned completely. (ii) Determine the maximum temperature increase when 400.0 cm3 of water…
The data for 0.6 g of catalyst seem anomalous. Suggest a possible cause.
(i) Determine the molar enthalpy of combustion of butan-1-ol, in kJ mol−1, and state one assumption you made. If you did not obtain an answer to 2a(i), use 20 000 J, but this is not the correct value. (ii) Calculate the percentage error of your…
Deduce what the graph shows about the water in hydrated magnesium sulfate.
Atmospheric carbon dioxide and the pH of surface seawater were measured at a monitoring station over nineteen years. The graph shows the annual mean values. (i) Outline the relationship between the carbon dioxide mixing ratio and the pH of the seawater. (ii)…
(i) The ideal PMI, which corresponds to the greenest possible process, is 1. Estimate the ideal value of each of the other three metrics. (ii) Identify the metric in the table that cannot be affected by the choice of solvent. (iii) Suggest one reason why the…
Two methods of making ethyl ethanoate are compared using the Eco-Scale. The penalty points are given in the table. Method 1: ethanoic acid reacts with ethanol, with concentrated sulfuric acid as the catalyst. The mixture is heated in a microwave reactor for 40…
Outline why the estimated rate calculated from the preliminary experiment is not the initial rate of the reaction.
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.
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.
A student determines the concentration of a solution of hydrochloric acid by titration. The same titration is repeated five times, and the titres are scattered both above and below the mean, because the student finds it difficult to judge the exact point at…
The end point was reached after 3.0 ± 0.1 cm3 of titrant had been run in. (i) Calculate the percentage uncertainty in this titre. (ii) Suggest one change to the procedure that would lower the percentage uncertainty of a single titration, apart from…
The result is roughly 30 times higher than the iron content of spinach given in reference tables (as a percentage by mass). Suggest one reason, apart from human error, for so large a difference.
The enthalpy change of combustion of ethanol was investigated in a school laboratory. A spirit burner containing ethanol was used to heat water in a metal can. A total of 0.0250 mol of ethanol was burned. The following data were recorded. (i) Calculate the…
A student determines the formula of hydrated copper(II) sulfate, CuSO4 ⋅ x H2O, by heating a weighed sample until its mass is constant. Which observation would explain a systematic error in the value of x? A. The crucible was always weighed while it was…
Ultraviolet (UV) light is being investigated as a way of killing micro-organisms in juice without heating it, so that less vitamin C is lost. The absorption spectrum of a dilute aqueous solution of sorbic acid, a preservative that is added to some bottled…
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.…
UV-C irradiation is an alternative to heat treatment that causes less loss of nutrients. The absorption spectrum of a solution of vitamin C is shown. (i) Deduce the type of electromagnetic radiation absorbed by vitamin C. Use section 5 of the data booklet.…
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…
Benzocaine, a local anaesthetic, is the ethyl ester of 4-aminobenzoic acid. The crude product of its synthesis is purified by recrystallization. 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. Discuss two ways in which the melting point of a crystallized sample of benzocaine can show that it still contains X.
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…
A student heated 3.492 g of calcium turnings in a crucible with a lid and obtained 4.490 g of solid product. If the product is assumed to be calcium oxide only, the percentage yield is 92 %. (i) Evaluate whether the formation of calcium nitride, rather than…
A 0.460 g piece of sodium was placed in 250.0 cm3 of water. (i) Calculate the molar concentration of the sodium hydroxide solution formed. Assume that the volume of the solution is 250.0 cm3. (ii) Calculate the volume of hydrogen gas…
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