Handle units, significant figures and uncertainties: propagate absolute and percentage uncertainties, distinguish random from systematic error, draw and read graphs including lines of best fit, gradients and intercepts.
Tę umiejętność sprawdza 68 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) Describe the general trend in the rate…
(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,…
Suggest how the total quantity of light emitted in each run could be obtained from the graph.
Explain how the rate at which the light intensity was falling after 15 minutes in the 44.8 °C run could be determined from the graph.
In Method 1 the flask containing 25.0 cm3 of the aqueous acid was put on the balance, which was then set to zero; 0.400 g of MgCO3 was added and the reading was noted every 20 seconds until the reaction had stopped. Each point is the mean of…
Calculate the change in temperature for trial 5 and its uncertainty. Give the temperature change to a suitable number of decimal places and the uncertainty to a suitable number of significant figures.
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.
Determine the mean specific energy of ethanol from the five trials, explaining your method. If you did not obtain an answer to (c), use 8000 J g−1 for trial 5; this is not the correct value.
Calculate the percentage error in the mean specific energy of ethanol. Literature value of the specific energy of ethanol = 29.7 kJ g−1
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…
Suggest why diluting the standard solution was necessary.
(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…
Ka was also calculated for Trials 2 and 3, and the experimental error was found for each, as shown in the table. Determine the experimental error for Trial 1, using a literature value of Ka = 1.35 × 10−5 for propanoic acid. If…
Comment on how the uncertainty of the pH probe affects the accuracy of the Ka values obtained.
The student's results are shown below. Each time was measured to ± 0.1 s. Rather than diluting the stock solution, the student prepared every solution separately, weighing the required mass of the solid on a balance reading to ± 0.01 g and making each one up…
The average times were plotted against concentration. Draw a curve of best fit through the points on the graph.
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…
For the AAS method, a series of standards of known concentration was prepared by diluting a stock solution of Cu2+ ions. The instrument was zeroed with deionized water and the absorbance of each standard was recorded. (i) Draw the line of best fit for…
The amount of NO2 prepared was checked by titration. The gas was first absorbed in water: 2 NO2(g) + H2O(l) → HNO3(aq) + HNO2(aq) The resulting solution was made up to 200.0 cm3 in a volumetric flask, and 20.0 cm3 portions…
The student recorded the following masses. Calculate the percentage by mass of iron and of calcium carbonate in the mixture.
Draw a line of best fit on the graph, extrapolating it beyond the range of the data.
State, in mathematical terms, how the absorbance of these solutions depends on their concentration.
Deduce the equation that relates absorbance to concentration for these solutions, including the numerical value of the constant.
Estimate the absorbance of a 0.400 mol dm−3 solution of nickel(II) sulfate.
Predict the difference, if any, between the absorbance of the 0.400 mol dm−3 solution read from the extrapolated line and the value calculated from the equation in 3d.
Each student used a different mass of the hydrated salt. The results of the whole class are shown below (Mr of H2O = 18.02). (i) Determine the two missing values in the table. The class results were plotted on the graph below. (ii) Draw a line of…
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…
Using the concentration determined in 1c and the intended concentration of 0.1500 mol dm−3, calculate the percentage error in the concentration of the potassium hydroxide solution. If you have no value from 1c, take the concentration to be…
Titanium is not included in the graph. Use sections 9 and 10 of the data booklet to find its atomic radius and first ionization energy, and annotate the graph with a cross (X) at the position of the data point for titanium.
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.
(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…
The forward reaction is first order with respect to cyclohexane. C6H12(g) ⇌ C6H6(g) + 3 H2(g) (i) Sketch a graph showing how the rate varies with the concentration of cyclohexane. (ii) Deduce the reaction's rate equation, and state the units of the…
The electrode potential, E, of the Sn4+/Sn2+ half-cell is not fixed: it depends on the concentrations of the two tin ions, as given by the equation: Determine the electrode…
A student writing a report on chlorine as a disinfectant collects, from several websites and reference books, values for how much chlorine dissolves in pure water at various temperatures. (i) Identify one difficulty in comparing the solubility values from…
Hypochlorous acid is a weak acid. In water it is in equilibrium with its conjugate base, the hypochlorite ion, OCl−, which kills microorganisms far less effectively than the acid molecule does. The graph shows what percentage of the dissolved chlorine…
The following burette readings are recorded in one of the titrations. Final burette reading = 26.15 ± 0.05 cm3 Initial burette reading = 1.15 ± 0.05 cm3 Calculate the percentage uncertainty in the titre volume.
By drawing a suitable line on the graph, determine the rate at which carbon dioxide is released at the start of Experiment 1. Give your answer in cm3 s−1.
Estimate how long after the start of the experiment the piston would first move if a total mass of 750 g were loaded on it.
Use the volumes collected at 120 s in Experiment 1 and Experiment 3 to calculate by what percentage the final volume of carbon dioxide falls for each 100 g added to the piston.
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'.
(i) Calculate, in J, the thermal energy gained by the water. Use sections 1 and 2 of the data booklet. (ii) Determine the percentage uncertainty of the energy value from (i). (iii) Suggest one way to reduce the effect of random uncertainty on the final result.
(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…
The uncertainty in each mass reading is ±0.04 g. (i) Calculate the percentage uncertainty in the total mass loss. (ii) Using your answer to (i), calculate the absolute uncertainty in the number of moles of water per mole of MgSO4, that is the…
A 25.0 cm3 sample of ethanol weighed 19.725 g at 20 °C. What is the density of ethanol in g cm−3? A. 0.79 B. 0.789 C. 0.7890 D. 0.78900
Young mussels were placed in a contaminated harbour. Samples were taken at regular intervals and the tin content of the soft tissue was determined. (i) The tin content follows a linear trend during the first six weeks. Deduce the equation for this part of the…
The concentration of tin in a sample of mussel tissue is 0.0064 ± 0.0002 mg Sn g−1. (i) Calculate the mass of tin, in mg, in 2.416 g of the sample. (ii) Calculate the percentage uncertainty of the concentration.
A conductivity probe is used to follow the concentration of sodium chloride in dilute aqueous solutions. A solution of concentration 0.015 mol dm−3 gives a conductivity of 1.8 mS cm−1. On the axes, draw a graph of conductivity…
The concentration of copper(II) ions in wastewater from a plating works was determined by colorimetry. Excess ammonia solution was added to each solution so that all the copper(II) ions formed the deep blue complex ion [Cu(NH3)4]2+, and the absorbance…
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…
State the class of error that always shifts the results of an experiment in the same direction.
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 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 prepared standard solutions of copper(II) sulfate and measured the absorbance of each with a colorimeter. The graph shows the calibration line. A sample of copper(II) sulfate solution of unknown concentration has an absorbance of 0.600. State its…
A student determined the enthalpy of combustion of a fuel as −680 kJ mol−1. The literature value is −850 kJ mol−1. What is the percentage error of the experimental result? A. 20 % B. 25 % C. 80 % D. 125 %
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…
Heat treatment at 90 °C is used to destroy spoilage micro-organisms in pineapple juice. The concentration of vitamin C was measured over 56 days in untreated juice and in heat-treated juice from the same batch. (i) Identify the dependent variable in this…
The concentration of vitamin C and the pH of five fruit juices were measured. Use the data to deduce whether pH and the concentration of vitamin C are correlated, giving a reason.
(i) Identify the dependent variable plotted on the graph. (ii) Calculate the decrease in the concentration of vitamin C, in μg cm−3, caused by the heat treatment. (iii) Calculate the average rate of decrease of the vitamin C concentration in…
The concentration of vitamin C and the pH of juice from five different fruits were measured. Deduce, with a reason, whether the data show a correlation between the concentration of vitamin C and pH.
Approximate enthalpy changes of reactions can be found from bond enthalpies. (i) Determine the enthalpy change, ΔH⊖, of this reaction, in kJ mol−1, using section 12 of the data booklet. (ii) Each bond enthalpy is uncertain by 0.1…
Bond enthalpies give an estimate of the enthalpy change of a reaction. Assume that all species are gases. (i) Use bond enthalpies from section 12 of the data booklet to determine the standard enthalpy change, ΔH⊖, of the forward reaction. (ii)…
The concentration of protein in an extract can be found by mixing it with a dye that binds to protein and measuring the absorbance at 595 nm. The calibration line for standard protein solutions is shown. Its equation is y = 0.2903x + 0.0090, where y is the…
The concentration of protein in egg white was determined by a dye-binding method. The absorbance at 595 nm of protein solutions of known concentration was used to draw a calibration line, with the equation shown. Calculate, using the linear equation, the…
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.…
In an experiment, calcium turnings were heated strongly in a crucible with a lid. The following data were recorded: (i) Calculate the amount of calcium, in mol, that was used. (ii) Determine the percentage uncertainty in the final mass of product. (iii) Assume…
The rate constant, k, of a reaction was measured at several temperatures, and ln k was plotted against , where T is the temperature in kelvin. Two points on the line of best fit are marked on the graph.…
A student investigates the dissolution of ammonium chloride in water as the basis of an instant cold pack, in which solid ammonium chloride is kept apart from water by a thin membrane. The enthalpy change when one mole of solid ammonium chloride dissolves in…
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