Synoptic Data Handling & Graphical Skills (DP IB Chemistry: SL)

Aluminium will react with copper(II) sulfate solution according to the following equation:

2Al (s) + 3CuSO₄ (aq) "  3Cu (s) + Al₂(SO₄)₃ (aq)

The reaction is quite slow at room temperature, but when chloride ions in the form of hydrochloric acid are added, the rate increases significantly. The chloride ions catalyse the reaction.

An experiment was carried out to determine the yield of the reaction. A student made a solution of aqueous copper(II) sulfate by dissolving 2.00 g of copper(II) sulfate pentahydrate, CuSO₄.5H₂O (M_r  249.72 g mol^-1) in 10.0 mL of distilled water in a small beaker.

To this solution she added 0.25 g of aluminium foil followed by 2.0 mL of 6.0 mol dm^-3 hydrochloric acid.

After the reaction was complete, she collected, dried, and weighed the copper that was produced.

She recorded the measurements in Table 1 below.

Table 1

Use the data to show that the copper sulfate is the limiting reagent in the experiment and calculate the mass of aluminium in excess.

Calculate the actual yield and the percentage yield of copper in the experiment.

Determine the percentage uncertainty in the mass of copper produced, and the overall percentage error for the experiment.

Discuss the impact on the percentage yield of copper from the following systematic errors:

A student carried out a metal displacement reaction between zinc powder and copper(II) sulfate solution. The equation for the reaction is

Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)

3.78 g of zinc powder was added to 50.0 cm³ of 0.250 moldm^-3 copper(II) sulfate solution.

Determine the limiting reagent showing your working.

The reaction between the zinc and copper sulfate was carried out in a polystyrene cup and the temperature change was measured using a temperature probe. The maximum temperature rise the student recorded was 8.5 ^oC. 

Using section 1 and 2 of the data booklet, calculate the enthalpy change, ∆H, for the reaction, in kJ.

Assume that all the heat evolved was absorbed by the solution, and that the density and specific heat capacity of the copper(II) sulfate solution are the same as pure water.

State two further assumptions made in the calculation of ∆H.

Using Figure 1, sketch a graph of the concentration of zinc sulfate, ZnSO₄ (aq), versus time and show how the graph may be used to find the initial rate of reaction.

                                                                  Figure 1

The concentration of coloured metal ions in a solution can be determined by spectroscopic methods, such as colorimetry. A colorimeter is used to measure relative absorbance of a number of standard solutions and a calibration graph is drawn.

Table 1 shows the concentration of nickel(II) ions and the relative absorbance of light at 635 nm wavelength.

Table 1

Using Figure 1, draw a labelled a graph of concentration against relative absorbance and draw a line of best fit through the points.

Figure 1

Identify the dependent and independent variables and use the graph in part (a) to determine the concentration of a solution of Ni(II) ions whose relative absorbance is 0.560. Show how you arrive at your answer.

Use your graph from part (a) to answer the following questions.

Determine the value of in the formula: .
 

The relationship between concentration and absorbance is only linear at low concentrations. Suggest a possible reason for this.

The Winkler method is a chemical technique used to measure the concentration of dissolved oxygen in water samples. The method involves treating the samples to convert the dissolved oxygen into iodine which is then titrated against standard sodium thiosulfate solution as shown below:

Step 1:             2Mn²⁺ (aq) + O₂ (aq) + 4OH⁻ (aq) → 2MnO₂ (s) + 2H₂O (l)

Step 2:             MnO₂ (s) + 2I⁻ (aq) + 4H⁺ (aq) → Mn²⁺ (aq) + I₂ (aq) + 2H₂O (l)

Step 3:             2S₂O₃²⁻ (aq) + I₂ (aq) → 2I⁻ (aq) + S₄O₆²⁻ (aq)

A student wanted to check if the water in a fish tank was sufficiently oxygenated and analysed two 500 cm³ samples, five days apart.

The following results in Table 1 were obtained when the resulting iodine was titrated against 0.0120 moldm^-3 Na₂S₂O₃ (aq).

Table 1

Oxygen analysis in fish tank water on day 0

Determine the number of moles of oxygen in the 500 cm³ sample and hence the concentration in ppm.

It is generally considered that dissolved oxygen levels of at least 4-5 ppm are sufficient for most aquatic life. The day 5 sample contained 5.03 × 10⁻⁵ moles of oxygen.

Discuss whether the student should be concerned about the oxygen levels in the fish tank over the 5-day period.

Suggest a modification to the procedure which would make the result more reliable.

A student investigated the rate of decomposition of hydrogen peroxide, H₂O₂, at a temperature of 45 ^o The decomposition reaction occurs in the presence of a catalyst, MnO₂.

The results she obtained are shown in Table 1 below.

Table 1

Plot a graph on the axes below in Figure 1 and from it determine the rate of reaction after 60 s.

Figure 1

On the same graph sketch the shape obtained if the student had carried out the same reaction at 60 ^oC. Explain the shape of the graph at 60 ^oC.

The decomposition of hydrogen peroxide can be investigated by measuring the volume of oxygen given off using the apparatus shown in Figure 2.

Figure 2

Two students decide to measure the rate of decomposition for H₂O₂ using the change in mass as oxygen escapes from the reaction container.

One student says that they should use a three decimal place rather than two decimal place balance because it will make their results more accurate. The second student disagrees and says it will make their results more precise, but not more accurate.

Which student is correct?

A student prepared some phenyl benzoate by reacting phenol with benzoyl chloride in alkaline conditions. The equation for the reaction is:

The table shows the data recorded by the student:

State the names of two functional groups found in the product

Determine the following quantities from the data in part a):

[2]

[2]

[1]

State the number of significant figures associated with the mass of phenyl benzoate obtained and calculate the percentage uncertainty associated with this mass.

Another student repeated the experiment and obtained an experimental yield of 145%. 

The teacher checked the student's calculations and found no errors.
Suggest an explanation for this result.

A student titrated hydrochloric acid solution against 50.0 cm³ of 0.950 mol dm^-3 sodium hydroxide solution to determine is concentration.

After each addition of acid the temperature was measured to the nearest 0.5 ^oC and recorded and plotted on a graph:

What should the labels be on each axis?

Use the graph to:

[1]

Use the values obtained in part b) to determine the temperature change and percentage uncertainty in the calculated value.

Determine the concentration of the acid used in the experiment.

A student investigated the diffusion of ammonia and hydrogen chloride gases in a 1.00 m glass tube. She placed cotton wool plugs containing concentrated ammonia and hydrochloric acid at either end of the tube and sealed the ends with stoppers. 

Where the two gases meet a white smoke ring of ammonium chloride, NH₄Cl, appears. The student recorded the time taken for the white smoke to appear and the distance travelled by each gas.

The rate of diffusion of a gas is proportional to the square root of the mass of its particles.

Calculate the mean rate of diffusion of ammonia and hydrogen chloride, expressing your answer to an appropriate number of significant figures.

The rate of diffusion of a gas is proportional to the square root of its mass.

When two gases, A and B, are compared the relative rates of diffusion are: 

Determine the relative rate of diffusion of the ammonia and hydrogen chloride from their molar masses and from part a).

Comment on your result.

Determine the percentage error in the experiment.

The student cleans and dries the glass tube between each run of the experiment. If the glass tube is not completely dry, state what type of error can occur and what its impact on the results would be.

The graph below shows measurements of pressure and volume for a sample of air at constant temperature.

Draw a best fit line through the points.

Deduce the relationship between pressure and volume in the sample of air.

Given the average molar mass of air is 28.97 g mol^-1, find the number of moles of air used in the experiment using the values at point X.

Determine the percentage uncertainty in the measure data at point, X.