Experimental Contexts

Do a flame test on solution W. Describe the method you use.

method _____

observations _____

conclusion _____

To $1\text{ cm}$ depth of W in a test-tube, add $1\text{ cm}$ depth of aqueous chlorine. Keep this mixture for use in (b)(ii).

observations _____

conclusion _____

Add $1\text{ cm}$ depth of starch solution to the contents of the solution from (b)(i).

observations _____

Test W for the presence of sulfate ions. Describe how you do the test and record your observations.

test _____

observations _____

To $1\text{ cm}$ depth of W in a test-tube, add $1\text{ cm}$ depth of dilute nitric acid and $1\text{ cm}$ depth of aqueous silver nitrate.

observations _____

conclusion _____

To $1\text{ cm}$ depth of W in a test-tube, add $1\text{ cm}$ depth of aqueous iron(III) nitrate.

observations _____

Put $1\text{ cm}$ depth of X into a boiling tube.

Add aqueous sodium hydroxide until no further change is seen.

Keep the mixture for use in (f)(ii).

observation _____

conclusion about solution X _____

Put a $1\text{ cm}$ depth of the mixture from (f)(i) into a clean boiling tube.

Add a small piece of aluminium foil to the mixture and warm gently.

Test any gas evolved.

observations _____

conclusion about solution X _____

To $1\text{ cm}$ depth of $\mathbf{R}$ in a test-tube, add a few drops of dilute nitric acid.

Add $1\text{ cm}$ depth of aqueous barium nitrate.

observations ______
conclusions ______

To $1\text{ cm}$ depth of $\mathbf{R}$ in a test-tube, add a few drops of dilute nitric acid.

Add $1\text{ cm}$ depth of aqueous silver nitrate.

observations ______
conclusions ______

Describe one other observation.

______

Suggest why it is important to add dilute nitric acid in (b).

______

Place the end of the wooden splint which has been in $\mathbf{R}$ into the flame of a Bunsen burner with the air hole open. Record the first flame colour seen.

first flame colour seen ______
conclusions ______

Explain why it is difficult to make a definite conclusion from the flame colour in (d)(i).

______

To $1\text{ cm}$ depth of $\mathbf{R}$ in a boiling tube, add aqueous sodium hydroxide drop by drop until a change is seen.

Then add excess aqueous sodium hydroxide.

Keep the mixture for use in (f).

observations ______
conclusions ______

Gently warm the mixture from (e).

observations ______
conclusions ______

Solution $\mathbf{R}$ is made from a mixture of two different ionic compounds.

Suggest the names of these two compounds.

______

You are going to investigate the temperature change when a solid, $\text{X}$, is dissolved in water.

Read all the instructions below carefully before starting the experiment.

Instructions
You are going to do one experiment.

• Use a measuring cylinder to add $25\text{ cm}^3$ of distilled water to a $100\text{ cm}^3$ beaker.
• Use a thermometer to measure the initial temperature of the water in the beaker.
• Record this temperature to the nearest $0.5^\circ\text{C}$ in Table 1.1 at time $0\text{ s}$.
• Add all the sample of solid $\text{X}$ to the beaker and start the stopwatch.
  Do not stop the stopwatch until the whole experiment is complete.
• Carefully stir the mixture.
• Measure the temperature after approximately $30\text{ s}$ and again after approximately $60\text{ s}$.
• Record the times, to the nearest second, and the temperatures, to the nearest $0.5^\circ\text{C}$, in Table 1.1.
• Continue stirring the mixture.
• Measure the temperature at approximately $60\text{ s}$ intervals for a total of $300\text{ s}$.
• Record the times, to the nearest second, and the temperatures, to the nearest $0.5^\circ\text{C}$, in Table 1.1.

Table 1.1

Describe the appearance of the mixture in the beaker at the end of the experiment.

______

Calculate the maximum temperature change in the experiment.

maximum temperature change = ______ $^\circ\text{C}$

Describe the trends shown in your results.

______

Suggest the temperature of the mixture if it is left for 60 minutes.

Explain your answer

temperature after 60 minutes = ______ $^\circ\text{C}$

explanation ______

Describe the energy change when $\text{X}$ dissolves in water.

Explain how the results in Table 1.1 support your answer.

description ______

explanation ______

Name a piece of equipment to measure the volume of water more precisely.

______

Explain how to obtain a more precise temperature measurement.

______

The maximum temperature change calculated is less than the true value for this experiment.

Suggest a reason for this, other than the precision of measurements.

Describe an improvement to the method which reduces this error.

reason ______

improvement ______

Experiment 1

• Use a volumetric pipette to add $25.0\text{ cm}^3$ of Y to a conical flask.
• Add five drops of methyl orange indicator to the conical flask.
• Place the conical flask on a white tile.
• Record the initial burette reading in Table 1.1.
• Add X from the burette while swirling the flask, adding drop by drop near the end-point, until the solution just changes colour.
• Record the final burette reading in Table 1.1.

Experiments 2, 3 and 4

• Empty the conical flask and rinse it with distilled water.
• Refill the burette if necessary.
• Repeat Experiment 1.

Calculate the volume used in each experiment and record your values in Table 1.1.

Table 1.1

Tick ($\checkmark$) the two best titration results in Table 1.1.

Explain your choice.

______

Use the ticked ($\checkmark$) titration results in Table 1.1 to calculate the average volume of X needed to neutralise $25.0\text{ cm}^3$ of Y.

volume = ______ $\text{cm}^3$

Use your answer from (c) to calculate the number of moles of $\text{HCl}$ in the average volume of X needed to neutralise $25.0\text{ cm}^3$ of Y.

number of moles = ______

The equation for the reaction between hydrochloric acid and sodium carbonate is shown.

$$2\text{HCl} + \text{Na}_2\text{CO}_3 \rightarrow 2\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2$$

Use your answer from (d) to calculate the concentration of sodium carbonate in Y.

Give your answer to three significant figures.

concentration = ______ $\text{mol / dm}^3$

Use your answer to (e) to calculate the mass of $\text{Na}_2\text{CO}_3$ in $150\text{ cm}^3$ of Y.

[$A_r$: $\text{C}$, 12; $\text{O}$, 16; $\text{Na}$, 23]

mass = ______ $\text{g}$

State why the conical flask is swirled while X is added from the burette.

______

State why X is added drop by drop from the burette near the end-point.

______