Units, uncertainties and graphs

(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…

(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…

The student's results are shown below. Each time was measured to ± 0.1 s. Concentration of $\ce{Na2S2O3}$ / $\mathrm{mol\,dm^{-3}}$ Time, trial 1 / s Time, trial 2 / s Time, trial 3 / s Time, trial 4 / s Time, trial 5 / s Average time / s 0.2000 ± 0.08 % 17.2…

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. Trial 1 Trial 2 Trial 3 Trial 4 Final burette reading / $\mathrm{cm^3}$ (± 0.05…

For the AAS method, a series of standards of known concentration was prepared by diluting a stock solution of $\ce{Cu^2+}$ 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 $\ce{NO2}$ prepared was checked by titration. The gas was first absorbed in water: $\ce{2NO2(g) + H2O(l) -> HNO3(aq) + HNO2(aq)}$ The resulting solution was made up to 200.0 $\mathrm{cm^3}$ in a volumetric flask, and 20.0 $\mathrm{cm^3}$ portions…

The student recorded the following masses. Sample Mass / g (± 0.01 g) Percentage by mass Mixture before separation 6.35 not applicable Iron after separation 2.58 Calcium carbonate after separation 1.71 Potassium chloride after separation 2.31 36.4 % Calculate…

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 $\mathrm{mol\,dm^{-3}}$ solution of nickel(II) sulfate.

Predict the difference, if any, between the absorbance of the 0.400 $\mathrm{mol\,dm^{-3}}$ 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 ($M_r$ of $\ce{H2O}$ = 18.02). Student Mass of $\ce{CuSO4 * XH2O}$ / g Mass of $\ce{CuSO4}$ / g Loss in mass / g Amount of $\ce{CuSO4}$ / mol Amount of…

The student pipetted 25.00 $\mathrm{cm^3}$ of the potassium hydroxide solution into a conical flask and titrated it with nitric acid, $\ce{HNO3(aq)}$, of concentration 0.1250 $\mathrm{mol\,dm^{-3}}$. The burette readings before and after the titration are…

Using the concentration determined in 1c and the intended concentration of 0.1500 $\mathrm{mol\,dm^{-3}}$, 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. $\ce{C6H12(g) <=> C6H6(g) + 3H2(g)}$ (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 $\ce{Sn^4+}/\ce{Sn^2+}$ half-cell is not fixed: it depends on the concentrations of the two tin ions, as given by the equation: $E = 0.15 + \dfrac{RT}{2F}\ln\dfrac{[\ce{Sn^4+}]}{[\ce{Sn^2+}]}$ 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. Source Temperature / °C Solubility of chlorine A 5 1.18 g per 100…

Hypochlorous acid is a weak acid. In water it is in equilibrium with its conjugate base, the hypochlorite ion, $\ce{OCl-}$, 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 $\mathrm{cm^3}$ Initial burette reading = 1.15 ± 0.05 $\mathrm{cm^3}$ 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 $\mathrm{cm^3\,s^{-1}}$.

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'.