Planning

the independent variable,

the dependent variable.

a balanced equation for the reaction between aqueous calcium hydroxide and hydrochloric acid,

a list of apparatus with volumes where appropriate,

a suitable indicator with relevant colours,

a detailed method for the dilution of the hydrochloric acid such that when a titration is carried out the two reacting volumes are approximately equal at the end-point. The relevant calculations and reasoning must be shown in full.

a detailed method for carrying out sufficient titrations to allow an accurate end-point to be obtained,

State one hazard that must be considered when planning the experiment and describe a precaution that should be taken to keep risks from this hazard to a minimum. You should use the information in (c).

the independent variable,

the dependent variable.

You are to plan an experiment to determine as accurately as possible the concentration of a saturated aqueous solution of chlorine by titration. You are reminded that the approximate solubility of chlorine is $5\text{ g dm}^{-3}$ at $25^\circ\text{C}$.

The following information gives some of the hazards associated with chlorine, iodine and sodium thiosulfate.

Aqueous chlorine, $\text{Cl}_2$, displaces iodine, $\text{I}_2$, from aqueous potassium iodide.

Therefore if a solution of chlorine is mixed with an excess of aqueous potassium iodide, iodine is displaced in a $1 : 1$ molar ratio with chlorine.

The concentration of chlorine in the original solution can therefore be calculated from the concentration of the displaced iodine.

You are provided with the following materials:

• saturated aqueous chlorine,
• solid sodium thiosulfate $\text{Na}_2\text{S}_2\text{O}_3\cdot5\text{H}_2\text{O}$,
• concentrated aqueous potassium iodide. This will be used in excess.

Give a step-by-step description of how you would carry out the experiment by including:

(i) a list of apparatus with volumes where appropriate,
(ii) a suitable indicator with relevant colours,
(iii) a calculation of the approximate concentration of saturated aqueous chlorine in $\text{mol dm}^{-3}$ at $25^\circ\text{C}$,
$[A_r: \text{Cl}, 35.5]$
(iv) a detailed description of the method for preparing a solution of aqueous sodium thiosulfate that can be used in the titration. In a titration, it is usual for the two reacting volumes to be approximately equal at the end-point. Calculate the mass of sodium thiosulfate, $\text{Na}_2\text{S}_2\text{O}_3\cdot5\text{H}_2\text{O}$, which will produce a solution suitable for use in this titration. The relevant calculations and reasoning must be shown in full,
$[A_r: \text{H}, 1.0; \text{O}, 16.0; \text{Na}, 23.0; \text{S}, 32.1]$
(v) a detailed method for carrying out sufficient titrations to allow an accurate end-point to be obtained,
(vi) an outline calculation to show how the results are to be used to determine the accurate concentration of the aqueous chlorine.

State one hazard that must be considered when planning the experiment and describe a precaution that should be taken to keep risks from this hazard to a minimum. You should use the information in (c).

Draw a diagram of the apparatus and experimental set up you would use in the experiment. Your apparatus should use only standard items found in a school or college laboratory and should show clearly

(i) how the copper(II) carbonate will be heated,

(ii) how the volume of the gas evolved will be collected and its volume measured.

Label each piece of apparatus used, indicating its size or capacity.

stating how you would ensure that the decomposition is complete.

State one hazard that must be considered when planning the experiment and describe a precaution that should be taken to keep risks to a minimum.

If the rate of reaction was only controlled by the polarity of the carbon-halogen bond, the order of reactivity (most reactive to least reactive) would be

........................................................................................................................................... .

Explain the variation in the polarity of the carbon-halogen bonds.

If the rate of reaction was only controlled by the bond strength of the carbon-halogen bond, the order of reactivity (most reactive to least reactive) would be

........................................................................................................................................... .

Explain the variation in the bond strength of the carbon-halogen bonds.

Identify the independent variable and the dependent variable in this experiment.

independent variable ..........................................................................................................

dependent variable .............................................................................................................

The amount of each halogenoalkane liquid to use is most practically measured by its volume. Usually equal volumes of the three halogenoalkanes are used.

Explain why this is not ideal and what change should be made to obtain a more reliable comparison between the halogenoalkanes.

Answer the following questions about the experiment.

• Having measured the quantity of halogenoalkanes, what must be ensured about the amount of sodium hydroxide used?

............................................................................................................................................

• How would the reaction tubes be heated and the experiment be started?

............................................................................................................................................

• What reagent could be added which would ensure that after 2 minutes the reaction was stopped?

............................................................................................................................................

• After the reaction has been stopped and aqueous silver nitrate added, the amount of precipitate formed could be determined by measuring its height. Why is it necessary to leave the tubes for some time before making this measurement?

The use of halogenoalkanes is hazardous and both gloves and eye protection are necessary. State one other essential precaution which should be taken when carrying out the experiments.

Write an equation for the thermal decomposition of magnesium nitrate(V).

Calculate the mass of magnesium oxide and volumes of nitrogen(IV) oxide and oxygen produced under room conditions when 1 mole of magnesium nitrate(V) is heated.

$[A_r: \text{O}, 16.0; \text{Mg}, 24.3]$

You should assume that one mole of any gas occupies $24.0\text{ dm}^3$ under room conditions.

Draw and label a diagram of the apparatus and experimental set-up you would use. The set-up needs to be capable of absorbing the nitrogen(IV) oxide and collecting the oxygen separately and in sequence.

State the volume of the gas collector to be used to collect oxygen in (i). Calculate a mass of magnesium nitrate(V) to be heated that would produce a stated volume of oxygen appropriate for the collector.

$[A_r: \text{N}, 14.0; \text{O}, 16.0; \text{Mg}, 24.3]$

You should assume that one mole of any gas occupies $24.0\text{ dm}^3$ under room conditions.

List the measurements you would make when carrying out the experiment.

How could you make sure that the magnesium nitrate(V) had completely decomposed in the experiment?

To make sure that the volume of gas measured is accurate, what should you do before taking the measurement?

What precautions would you take to make sure that the experiment could be performed safely?

Predict how $\Delta H_r$ may change as $E^\ominus_{\text{cell}}$ increases. Give a reason for your prediction.

The first part of the investigation is to determine the enthalpy change, $\Delta H_r$, for the reaction of the same number of moles of three powdered metals with $0.500\text{ mol dm}^{-3}$ copper(II) sulfate.

When determining the $\Delta H_r$ for the reaction of the metals listed above with aqueous copper(II) sulfate,

the independent variable is,

the dependent variable is.

Draw a fully labelled diagram to show how the apparatus should be set up to allow you to determine the increase in temperature of aqueous copper(II) sulfate.

You should use apparatus normally found in a school or college laboratory.

State the measurements you would make in your experiment.

Other than eye protection, state one precaution you would take to make sure that the experiment proceeds safely.

For the reaction with magnesium, calculate the mass of magnesium, in g, you would use so that it is in a small excess. You must show your working.

[$A_r$: Mg, 24.3]

Explain why the metal used should be in powdered form rather than in strips.

The aqueous copper(II) sulfate and metal mixture should be stirred continuously. Explain why.

The second part of the investigation involves determining the cell potential, $E^\ominus_{\text{cell}}$, for the three electrochemical cells.

Draw a diagram of the apparatus you would use to measure the $E^\ominus_{\text{cell}}$ for the magnesium/copper cell. Your labels should include the names of the metals and the names and concentrations of the solutions you would use.

Explain why the enthalpy change determination and cell potential determination should be carried out at the same temperature as each other.

Draw the apparatus you could use to measure the volume of hydrogen produced, using standard laboratory equipment.

Label the chemicals in your diagram and show how the reactants can be kept apart until the reaction is started.

Beginning with a large piece of lithium being removed from the oil, state how you would prepare a small piece of lithium for use in this experiment.

By only observing the gas collecting apparatus, state how you would know the reaction had stopped.

Other than eye protection, state two precautions you would take to make sure that the experiment proceeds safely.

What would be the capacity (volume) of the gas collecting apparatus you would use for the volume of hydrogen produced in (iv)?

State how you would accurately measure the total volume of distilled water in step 1.

State how you would know that the reaction between lithium and distilled water was complete.

State how you would transfer $25.0\text{ cm}^3$ of the solution of lithium hydroxide into a clean conical flask in step 3.

State how you would ensure that your titration result was reliable.

Draw the apparatus you could use to measure the volume of hydrogen produced, using standard laboratory equipment.

Label the chemicals in your diagram and show how the reactants can be kept apart until the reaction is started.

Beginning with a large piece of lithium being removed from the oil, state how you would prepare a small piece of lithium for use in this experiment.

By only observing the gas collecting apparatus, state how you would know the reaction had stopped.

Other than eye protection, state two precautions you would take to make sure that the experiment proceeds safely.

What would be the capacity (volume) of the gas collecting apparatus you would use for the volume of hydrogen produced in (iv)?

State how you would accurately measure the total volume of distilled water in step 1.

State how you would know that the reaction between lithium and distilled water was complete.

State how you would transfer 25.0 cm$^3$ of the solution of lithium hydroxide into a clean conical flask in step 3.

State how you would ensure that your titration result was reliable.

Write an equation for the thermal decomposition of magnesium nitrate(V).

Draw and label a diagram of the apparatus and experimental set-up you would use. The set-up needs to be capable of absorbing the nitrogen(IV) oxide and collecting the oxygen separately and in sequence.

State the volume of the gas collector to be used to collect oxygen in (i). Calculate a mass of magnesium nitrate(V) to be heated that would produce a stated volume of oxygen appropriate for the collector.

[$A_r$: N, 14.0; O, 16.0; Mg, 24.3]

You should assume that one mole of any gas occupies $24.0\text{ dm}^3$ under room conditions.

List the measurements you would make when carrying out the experiment.

How could you make sure that the magnesium nitrate(V) had completely decomposed in the experiment?

To make sure that the volume of gas measured is accurate, what should you do before taking the measurement?

What precautions would you take to make sure that the experiment could be performed safely?

the independent variable,

the dependent variable.

You are to plan an experiment to determine as accurately as possible how the temperature change varies when different solutions are made, each with different concentrations of ammonium nitrate. You are reminded that the approximate solubility of ammonium nitrate is $2.5\text{ mol}/100\text{ g}$ at $25\text{ }^\circ\text{C}$.

The following information gives some of the hazards associated with ammonium nitrate.

Ammonium nitrate $\text{NH}_4\text{NO}_3$. Contact with combustible material may cause fire. Explosive when mixed with combustible material.
Do not allow the salt to become contaminated with organic matter and do not grind it.
Solutions should be diluted to less than $0.5\text{ mol dm}^{-3}$ for disposal.

You should use only standard apparatus found in a school or college laboratory. Draw a diagram of the apparatus and experimental set up you would use showing clearly the following:

(i) the apparatus used, such as the reaction vessel, and how the thermometer will be positioned in order to measure the temperature of the solution as accurately as possible,
(ii) how the apparatus will be insulated.

Label each piece of apparatus used, indicating its size or capacity and both the temperature range and the precision of the thermometer.

Using the apparatus shown in (c) design an experiment to test your prediction in (a)(ii) of how the temperature change of the solution varies with solutions of different concentration.

In addition to the apparatus normally found in a laboratory you are provided with the following materials;

• a supply of solid ammonium nitrate,
• distilled (deionised) water.

Give a step-by-step description of how you would carry out the experiment to include;

(i) the number of experiments you would do,
(ii) the temperature measurements you would take,
(iii) the volume of water you would use,
(iv) a calculation to show the maximum mass of ammonium nitrate you could use for your volume of water in (iii) and a range of masses for the other experiments.

[$A_r$: H, 1.0; N, 14.0; O, 16.0]

State one hazard that must be considered when planning the experiment and describe a precaution that should be taken to keep risks from this hazard to a minimum. You may use the information in (c) if you wish.