Concluding and evaluating

(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). Ion Concentration / $\mathrm{g\,dm^{-3}}$, 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 ($\pm 0.05\ \mathrm{m}$) 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…

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. Metal Specific heat capacity / $\mathrm{J\,g^{-1}\,K^{-1}}$ 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.

Student B pipetted 30.00 $\mathrm{cm^3}$ of the potassium hydroxide solution into a 150 $\mathrm{cm^3}$ glass beaker and added the nitric acid from a burette in portions of 4.00 $\mathrm{cm^3}$, recording the steady temperature after each addition. Volume of…

The iron(II) concentration is found by titrating against a standard solution of potassium manganate(VII), $\ce{KMnO4}$. At intervals of a few days, a 20.00 $\mathrm{cm^3}$ sample is withdrawn from each flask and made up to 250.0 $\mathrm{cm^3}$ 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 $\ce{C19H40}$ is $-12\,660\ \mathrm{kJ\,mol^{-1}}$. (i) Calculate the maximum energy released when 1.50 g of $\ce{C19H40}$ is burned completely. (ii) Determine the maximum temperature increase when $400.0\ \mathrm{cm^3}$ of water…