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.
(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). Ion Concentration / , based on Source 1…
(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: Depth water sample was obtained from / m () Electric current recorded by the…
(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…
(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…
A second student repeated the experiment with the same five solutions and the same apparatus and obtained the following times. Concentration of / Reaction time / s (± 0.1 s) 0.2000 ± 0.08 % 20.1 0.1000 ± 0.2 % 37.5 0.0500…
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…
If the reaction with 0.80 went to completion, the theoretical mass of released would be 1.76 g. (i) Use the graph to determine the mass, in g, of actually released in this reaction. (ii)…
(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…
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. Metal Specific heat capacity / Tin 0.228 Zinc 0.388 Titanium 0.523 Magnesium 1.02
Deduce, from the results obtained, two sources of systematic error in this procedure.
(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 of the potassium hydroxide solution into a 150 glass beaker and added the nitric acid from a burette in portions of 4.00 , recording the steady temperature after each addition. Volume of…
(i) To check the value of found in (d)(viii), a student set up an experiment: 0.500 mol each of propan-1-ol and ethanoic acid were mixed with a small amount of concentrated sulfuric acid at 25 °C, and the mixture's volume was kept constant throughout.…
The student measures the hydrogensulfite concentration by titrating samples against a standard iodine solution, with starch as the indicator. Every three days, 25.00 of cordial is withdrawn from each flask, diluted to 250.0 with…
The student's results are plotted below. (i) Calculate the average rate at which the hydrogensulfite concentration in the 24 h flask decreased over the 12 days. Include units in your answer. (ii) Before starting, the student wrote this hypothesis: "The longer…
The enthalpy of combustion of is . (i) Calculate the maximum amount of energy that the complete combustion of 1.75 g of pentadecane can release. (ii) The energy from burning the 1.75 g sample is used to heat…