Analysis, Conclusions and Evaluation

Using your answers to (iv) and (v), calculate the value of $y$ to one decimal place.

Apart from altering the balance or the masses of FA 5 used, state one improvement you could make to the experimental procedure to improve its accuracy.

Which experiment should be more accurate, Experiment 1 or Experiment 2?
Explain your answer.

Suggest the formulae of the two salts that could have been mixed to make FA 5.

........................................ and ........................................

FA 6 and FA 7 are different organic liquids. Their possible identities are listed below.

• 2-methylpropan-2-ol
• propanal
• propanone

Half fill the $250\text{ cm}^3$ beaker with water and heat to about $50^\circ\text{C}$. You will use this as a hot water bath.

Turn off the Bunsen burner.

Carry out the following tests and record your observations.

Suggest the identity of FA 6 and FA 7 with an explanation.

FA 6 ...........................................................................................................................................

FA 7 ...........................................................................................................................................

Calculate the enthalpy change, in $\text{kJ mol}^{-1}$, for the reaction below.

Use your answer to (a)(iii) to calculate the enthalpy change, in $\text{kJ mol}^{-1}$, for the reaction below.

Use your values for the enthalpy changes calculated in (a)(iv) and (b)(iii) to calculate the enthalpy change for the reaction below.

Show clearly how you obtained your answer by drawing a Hess’ Law energy cycle.

(If you were unable to calculate the enthalpy changes, assume that the value of the enthalpy change in (a)(iv) is $-58.7\text{ kJ mol}^{-1}$ and the value in (b)(iii) is $-140.3\text{ kJ mol}^{-1}$. Note: these are not the correct values.)

Calculate the maximum percentage error in the temperature rise in (b)(i).

The magnesium oxide, FA 5, was weighed with a balance measuring to one decimal place.
A student suggested that the accuracy of the experiment in (b)(i) would be improved by weighing FA 5 using a balance measuring to two decimal places.
State and explain whether or not the student is correct.

In Question 1 you used FA 2. This solution was prepared from hydrated ammonium iron(II) sulfate, $(\text{NH}_4)_2\text{Fe}(\text{SO}_4)_2\cdot6\text{H}_2\text{O}$.

To a $1\text{ cm}$ depth of FA 2 in a test-tube, add a small spatula measure of sodium carbonate. Record your observations.

Solutions containing $\text{Fe}^{2+}$ ions can quickly be oxidised in air if they are prepared by dissolving the solid in distilled water.
Use your observations to suggest what other substance was added to solid $(\text{NH}_4)_2\text{Fe}(\text{SO}_4)_2\cdot6\text{H}_2\text{O}$ to prepare FA 2.

Suggest possible identities for the ions present in FA 6.

cations ................................................................................................................................

anions .................................................................................................................................

Describe a further test that would allow you to determine exactly which anions are present. Explain your choice. Do not do this test.

What element is present in both FB 7 and FB 8?

Suggest which cation is present in both FB 9 and FB 10.

What change in the oxidation state of magnesium is occurring during reaction (c)(iii)?

Oxidation state change from ................................... to ...................................

In which part of the Periodic Table are the elements identified as being present in FB 7, FB 8, FB 9 and FB 10?

Identify the ions present in FA 6.

cations: $\text{Fe}^{2+}$ and ......................................... anion: .................................................

FA 7, FA 8 and FA 9 are aqueous solutions. Each contains one cation and one anion.
FA 3 is dilute sulfuric acid, $\text{H}_2\text{SO}_4$.

Mix pairs of solutions so that you can complete the table below.
For each test, use $1\text{ cm}$ depths of each solution in clean test-tubes.
Record your observations in the table.

From your observations, complete the following statements.

The anion in FA 7 is ...................................................

The cation in FA 8 is ..................................................

The anion in FA 9 is ...................................................

FB 5, FB 6, FB 7 and FB 8 are aqueous solutions each of which contains a single cation and a single anion. Some of the ions present are listed below.

By observing the reactions that occur when pairs of the solutions are mixed together, you will be able to identify which solution contains which of these ions.

Use $1\text{ cm}$ depth of each solution in a test-tube and record your observations in the following table.

From your observations, deduce which solution contains each of the following ions.

Which anion is present in FB 9?

Calculation

Show your working and express your answers to three significant figures.

Using the mean temperature rise above, calculate the mean heat energy produced in the reaction.
(You may assume that $4.3\text{ J}$ are required to raise the temperature of $1.0\text{ cm}^3$ of any solution by $1.0\text{ }^\circ\text{C}$.)

heat energy produced = ........................ ............ (value, unit)

Calculate the enthalpy change, $\Delta H_2$, in $\text{kJ mol}^{-1}$, for the following reaction.

You should assume that the magnesium in your reaction is in excess.

Calculation

Show your working and express your answers to three significant figures.

Calculate the heat energy produced in the reaction.
(You may assume that $4.3\text{ J}$ are required to raise the temperature of $1.0\text{ cm}^3$ of any solution by $1.0\text{ }^\circ\text{C}$.)

heat energy produced = ........................ ............ (value, unit)

Calculate the enthalpy change, $\Delta H_3$, in $\text{kJ mol}^{-1}$, for the following reaction.

You should assume that the magnesium oxide in your reaction is in excess.

The enthalpy change for the following reaction is $-286\text{ kJ mol}^{-1}$.

Use the Hess’ Law cycle given below to calculate $\Delta H_1$, the enthalpy change for the reaction of magnesium with oxygen.

Suggest one improvement to the method by which heat losses from your apparatus could have been reduced.

Identify the metal present in FB 5, FB 6 and FB 7.

FB 5 contains ................................................

FB 6 contains ................................................

FB 7 contains ................................................

Leave the test-tube and contents to cool completely.

To the cooled test-tube add a $1\text{ cm}$ depth of aqueous sodium hydroxide. Observe the appearance of the contents of the test-tube.

appearance .........................................................................................................................

Carry out your tests on FB 6 until you have identified the anion. Record your observations and deductions in your table.

anion in FB 6 = ..............................