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At room temperature and pressure (r.t.p.), \(10\text{ cm}^3\) of a gaseous hydrocarbon \(C_xH_y\) was exploded with \(100\text{ cm}^3\) of oxygen (an excess). After cooling to r.t.p., the total volume of gas remaining was \(85\text{ cm}^3\). On shaking this gas mixture with aqueous sodium hydroxide, the volume of gas decreased to \(45\text{ cm}^3\).

What is the molecular formula of the hydrocarbon?

A \(1.00\text{ g}\) sample of a Group 2 metal \(M\) reacts completely with excess dilute hydrochloric acid.

\(M(s) + 2HCl(aq) \rightarrow MCl_2(aq) + H_2(g)\)

The reaction produces \(600\text{ cm}^3\) of hydrogen gas, measured at room temperature and pressure (r.t.p.).

What is the identity of metal \(M\)? [Molar volume of gas at r.t.p. is \(24.0\text{ dm}^3\text{ mol}^{-1}\)]

An oxide of a Period 3 element, \(X\), is a white solid with a high melting point. It is insoluble in water and does not react with dilute hydrochloric acid, but it reacts with hot, concentrated aqueous sodium hydroxide.

What is the element \(X\)?

Which sequence of Period 3 ions is written in order of decreasing ionic radius?

An aqueous solution of cobalt(II) sulfate is pink due to the presence of \([Co(H_2O)_6]^{2+}\) ions. When excess concentrated hydrochloric acid is added, the solution turns deep blue.

Which statement correctly explains this observation?

Which of the following transition metal complexes can exist as a pair of optical isomers (enantiomers)?

[where 'en' represents the bidentate ligand ethane-1,2-diamine]

The standard enthalpy changes of combustion, \(\Delta H^\ominus_c\), for carbon, hydrogen, and propanoic acid are given below:

- \(\Delta H^\ominus_c [C(\text{graphite})] = -394\text{ kJ mol}^{-1}\)
- \(\Delta H^\ominus_c [H_2(g)] = -286\text{ kJ mol}^{-1}\)
- \(\Delta H^\ominus_c [C_2H_5CO_2H(l)] = -1527\text{ kJ mol}^{-1}\)

What is the standard enthalpy change of formation, \(\Delta H^\ominus_f\), of propanoic acid?

Nitrogen dioxide, \(NO_2\), is a brown gas that exists in dynamic equilibrium with colorless dinitrogen tetroxide, \(N_2O_4\).

\(2NO_2(g) \rightleftharpoons N_2O_4(g) \quad \Delta H = -57\text{ kJ mol}^{-1}\)

A mixture of these two gases is at equilibrium in a sealed gas syringe at room temperature. The plunger of the syringe is suddenly pushed in, reducing the volume of the gas mixture, and the plunger is held in this position.

What describes the immediate color change and the subsequent color change of the gas mixture?

How many total ions are present in \(25.0\text{ cm}^3\) of a \(0.150\text{ mol dm}^{-3}\) solution of aluminium sulfate, \(\text{Al}_2(\text{SO}_4)_3\)?

A solid mixture of anhydrous sodium carbonate (\(\text{Na}_2\text{CO}_3\), \(M_r = 106.0\)) and sodium hydrogencarbonate (\(\text{NaHCO}_3\), \(M_r = 84.0\)) has a mass of \(5.00\text{ g}\). When heated strongly, the sodium hydrogencarbonate completely decomposes to form sodium carbonate, water, and carbon dioxide: \(2\text{NaHCO}_3(\text{s}) \rightarrow \text{Na}_2\text{CO}_3(\text{s}) + \text{H}_2\text{O}(\text{g}) + \text{CO}_2(\text{g})\). The sodium carbonate does not decompose. After heating, the remaining dry solid has a mass of \(4.07\text{ g}\). What is the percentage by mass of sodium hydrogencarbonate in the original mixture?

Which statement about the reactions of Period 3 elements with water is correct?

Two Period 3 elements, \(\text{A}\) and \(\text{B}\), react with chlorine to form chlorides \(\text{X}\) and \(\text{Y}\) respectively. Chloride \(\text{X}\) dissolves in water to form a solution with a pH of approximately 7. Chloride \(\text{Y}\) reacts violently with water to form a strongly acidic solution with pH less than 2, while releasing white fumes. Which pair could represent elements \(\text{A}\) and \(\text{B}\)?

The addition of concentrated hydrochloric acid to an aqueous solution containing \([\text{Co(H}_2\text{O)}_6]^{2+}\) ions results in a color change from pink to blue. Which statement correctly explains this observation?

Which statement correctly explains why many transition metal complex ions are coloured?

The standard enthalpy changes of formation, \(\Delta H_f^\theta\), of gaseous butane (\(\text{C}_4\text{H}_{10}\)), carbon dioxide (\(\text{CO}_2\)), and liquid water (\(\text{H}_2\text{O}\)) are given in the table below: \(\text{C}_4\text{H}_{10}(\text{g})\) is \(-126\text{ kJ mol}^{-1}\); \(\text{CO}_2(\text{g})\) is \(-394\text{ kJ mol}^{-1}\); \(\text{H}_2\text{O}(\text{l})\) is \(-286\text{ kJ mol}^{-1}\). What is the standard enthalpy change of combustion of gaseous butane, \(\Delta H_c^\theta[\text{C}_4\text{H}_{10}(\text{g})]\)?

A mixture of \(1.00\text{ mol}\) of \(\text{X}_2(\text{g})\) and \(1.00\text{ mol}\) of \(\text{Y}_2(\text{g})\) is placed in a sealed vessel of volume \(V\text{ dm}^3\) and allowed to reach equilibrium at temperature \(T\). \(\text{X}_2(\text{g}) + \text{Y}_2(\text{g}) \rightleftharpoons 2\text{XY}(\text{g})\). At equilibrium, the concentration of \(\text{XY}(\text{g})\) is \(1.50\text{ mol dm}^{-3}\) and the equilibrium constant \(K_c\) for the reaction is \(9.00\). What is the volume, \(V\), of the vessel?

10\text{ cm}^3 of a gaseous hydrocarbon \(C_xH_y\) is reacted with excess oxygen (100\text{ cm}^3). After complete combustion and cooling to room temperature and pressure, the remaining gas volume is 80\text{ cm}^3. When this remaining gas is passed through aqueous sodium hydroxide, the volume decreases to 40\text{ cm}^3.

What is the molecular formula of the hydrocarbon?

An equimolar mixture of two Period 3 oxides is added to a large excess of water. The resulting mixture is stirred thoroughly and then filtered to remove any insoluble material. The pH of the filtrate is measured at 25 \(^{\circ}\text{C}\) and found to be approximately 2.

Which pair of oxides could have been used?

Which statement best explains why aqueous transition metal complexes, such as \([Cu(H_2O)_6]^{2+}\), are coloured?

A cobalt complex has the formula \([Co(NH_3)_4Cl_2]^+\).

Which row correctly describes the coordination number of cobalt, its oxidation state, and the total number of stereoisomers possible for this complex?

The standard enthalpies of combustion, \(\Delta H_c^{\ominus}\), for carbon, hydrogen, and propanoic acid, \(C_2H_5COOH(l)\), are given below:

- \(\Delta H_c^{\ominus}[\text{C}(s)] = -394\text{ kJ mol}^{-1}\)
- \(\Delta H_c^{\ominus}[\text{H}_2(g)] = -286\text{ kJ mol}^{-1}\)
- \(\Delta H_c^{\ominus}[C_2H_5COOH(l)] = -1527\text{ kJ mol}^{-1}\)

What is the standard enthalpy change of formation, \(\Delta H_f^{\ominus}\), of propanoic acid in \(\text{kJ mol}^{-1}\)?

The following reversible reaction is allowed to reach equilibrium in a sealed container of fixed volume:

\(2NO_2(g) \rightleftharpoons N_2O_4(g) \quad \Delta H = -57\text{ kJ mol}^{-1}\)

The temperature of the container is increased.

Which statement correctly describes the effect of this change on the position of equilibrium and the value of the equilibrium constant, \(K_c\)?

What is the total number of ions present in 25.0\text{ cm}^3 of 0.120\text{ mol dm}^{-3} aqueous aluminium sulfate, \(Al_2(SO_4)_3\)?

[Avogadro constant, \(L = 6.02 \times 10^{23}\text{ mol}^{-1}\)]

Two test-tubes containing water have a small amount of a Period 3 chloride added to them.

- Test-tube 1: Chloride \(X\) dissolves to form a solution with pH \(\approx 7\).
- Test-tube 2: Chloride \(Y\) reacts rapidly with water, releasing misty white fumes and forming a solution with pH \(\approx 2\).

Which row correctly identifies Chloride \(X\) and Chloride \(Y\)?

A \(20.0\text{ cm}^3\) sample of a gaseous hydrocarbon, \(\text{C}_x\text{H}_y\), is exploded with an excess of oxygen (\(150.0\text{ cm}^3\)). After cooling to room temperature and pressure, the total volume of gas remaining is \(110.0\text{ cm}^3\). When this remaining gas is shaken with aqueous sodium hydroxide, the volume of gas decreases to \(50.0\text{ cm}^3\).

What is the molecular formula of the hydrocarbon?

An excess of water is added to a solid mixture containing equal moles of silicon(IV) chloride, \(\text{SiCl}_4\), and phosphorus(V) chloride, \(\text{PCl}_5\).

Which statement about the resulting mixture is correct?

The standard enthalpy changes of combustion of carbon (graphite), hydrogen gas, and propan-1-ol are given below:

- \(\Delta H^\ominus_c \text{ [C(graphite)]} = -393.5\text{ kJ mol}^{-1}\)
- \(\Delta H^\ominus_c \text{ [H}_2\text{(g)]} = -285.8\text{ kJ mol}^{-1}\)
- \(\Delta H^\ominus_c \text{ [CH}_3\text{CH}_2\text{CH}_2\text{OH(l)]} = -2021.0\text{ kJ mol}^{-1}\)

What is the standard enthalpy change of formation, \(\Delta H^\ominus_f\), of propan-1-ol?

A mixture of \(1.00\text{ mol}\) of \(\text{X}_2\text{(g)}\) and \(3.00\text{ mol}\) of \(\text{Y}_2\text{(g)}\) is placed in a closed container of volume \(2.00\text{ dm}^3\) and allowed to reach equilibrium at a constant temperature.

\(\text{X}_2\text{(g)} + 3\text{Y}_2\text{(g)} \rightleftharpoons 2\text{XY}_3\text{(g)}\)

At equilibrium, it is found that \(0.60\text{ mol}\) of \(\text{XY}_3\text{(g)}\) has been formed.

What is the value of the equilibrium constant, \(K_c\), at this temperature?

A sample of hydrated copper(II) sulfate is dissolved in water to form a blue solution. An excess of concentrated hydrochloric acid is added dropwise to this solution, resulting in a yellow-green solution.

Which of the following describes the changes in coordination number, geometry, and oxidation state of the copper species during this reaction?

An element \(X\) in Period 3 forms an oxide \(X_2\text{O}_3\) that reacts with both aqueous sodium hydroxide and dilute hydrochloric acid. Another element \(Y\) in Period 3 forms an oxide \(Y\text{O}_2\) that reacts with aqueous sodium hydroxide but not with dilute hydrochloric acid.

Which statement about \(X\) and \(Y\) is correct?

The reaction between gaseous nitrogen and gaseous hydrogen to form gaseous hydrazine, \(\text{N}_2\text{H}_4\text{(g)}\), is represented by the equation below:

\(\text{N}_2\text{(g)} + 2\text{H}_2\text{(g)} \rightarrow \text{N}_2\text{H}_4\text{(g)} \quad \Delta H = +95\text{ kJ mol}^{-1}\)

Some average bond energies are given in the table:
- \(\text{N}\equiv\text{N} = 945\text{ kJ mol}^{-1}\)
- \(\text{H}-\text{H} = 436\text{ kJ mol}^{-1}\)
- \(\text{N}-\text{H} = 391\text{ kJ mol}^{-1}\)

What is the average bond energy of the \(\text{N}-\text{N}\) single bond in hydrazine?

An element \(Z\) has three naturally occurring isotopes. The mass spectrum of \(Z\) shows the following peaks:
- \(^{24}Z\) relative abundance \(79.0\%\)
- \(^{25}Z\) relative abundance \(10.0\%\)
- \(^{26}Z\) relative abundance \(11.0\%\)

A sample of \(Z\) reacts with an excess of dilute hydrochloric acid to produce a salt \(Z\text{Cl}_2\) and hydrogen gas.

What is the mass of \(Z\text{Cl}_2\) produced when \(0.120\text{ mol}\) of \(Z\) reacts completely with hydrochloric acid? [\(A_r(\text{Cl}) = 35.5\)]

A sample of 1.38 g of an anhydrous metal carbonate, \(X_2\text{CO}_3\), was dissolved in excess dilute hydrochloric acid.

\(X_2\text{CO}_3(\text{s}) + 2\text{HCl}(\text{aq}) \rightarrow 2\text{XCl}(\text{aq}) + \text{H}_2\text{O}(\text{l}) + \text{CO}_2(\text{g})\)

The volume of carbon dioxide gas collected at room temperature and pressure (r.t.p.) was 240 \(\text{cm}^3\).

What is the identity of the metal \(X\)?

[Take the molar volume of a gas at r.t.p. as 24.0 \(\text{dm}^3\text{ mol}^{-1}\).]

How many total ions are present in a solution prepared by dissolving 9.52 g of anhydrous magnesium chloride, \(\text{MgCl}_2\), in water to make a total volume of 500 \(\text{cm}^3\)?

[Take the Avogadro constant, \(L = 6.02 \times 10^{23}\text{ mol}^{-1}\); relative atomic masses, \(A_r\): \(\text{Mg} = 24.3\), \(\text{Cl} = 35.5\)]

Two Period 3 elements, \(Y\) and \(Z\), each form a chloride that reacts with or dissolves in water.

- The chloride of \(Y\) reacts vigorously with water to form a strongly acidic solution (\(\text{pH} \approx 2\)) and white fumes.
- The chloride of \(Z\) dissolves in water to form a neutral solution (\(\text{pH} \approx 7\)).

Which elements are represented by \(Y\) and \(Z\)?

An element \(X\) in Period 3 is burned in oxygen to form an oxide \(Y\).

Oxide \(Y\) is a white solid that reacts with both dilute hydrochloric acid and aqueous sodium hydroxide.

What is the identity of element \(X\)?

Which transition metal species has the electronic configuration \([\text{Ar}] 3\text{d}^5\)?

Which statement correctly explains the origin of colour in transition metal complexes such as \([\text{Cu}(\text{H}_2\text{O})_6]^{2+}\)?

Consider the following standard enthalpy changes:

1) \(\text{C}(\text{s}) + \text{O}_2(\text{g}) \rightarrow \text{CO}_2(\text{g})\) \(\Delta H^\ominus = -393.5\text{ kJ mol}^{-1}\)
2) \(\text{H}_2(\text{g}) + \frac{1}{2}\text{O}_2(\text{g}) \rightarrow \text{H}_2\text{O}(\text{l})\) \(\Delta H^\ominus = -285.8\text{ kJ mol}^{-1}\)
3) \(\text{CH}_3\text{COOH}(\text{l}) + 2\text{O}_2(\text{g}) \rightarrow 2\text{CO}_2(\text{g}) + 2\text{H}_2\text{O}(\text{l})\) \(\Delta H^\ominus = -874.2\text{ kJ mol}^{-1}\)

What is the standard enthalpy change of formation of ethanoic acid, \(\text{CH}_3\text{COOH}(\text{l})\)?

\(2\text{C}(\text{s}) + 2\text{H}_2(\text{g}) + \text{O}_2(\text{g}) \rightarrow \text{CH}_3\text{COOH}(\text{l})\)

The reaction below is in dynamic equilibrium in a closed container at a constant temperature:

\(2\text{SO}_2(\text{g}) + \text{O}_2(\text{g}) \rightleftharpoons 2\text{SO}_3(\text{g})\) \(\Delta H = -197\text{ kJ mol}^{-1}\)

The volume of the container is suddenly halved while keeping the temperature constant.

Which statement about the system immediately after this change is correct?

This question is about determining the empirical and molecular formulas of an organic compound and investigating its reactions.

(a) Define the terms:
(i) relative molecular mass, \(M_r\) [1]
(ii) empirical formula [1]
(iii) State the difference between an empirical formula and a molecular formula. [1]

(b) An organic compound \(X\) contains only carbon, hydrogen, and chlorine. Complete combustion of a 1.485 g sample of \(X\) in excess oxygen produced 1.320 g of carbon dioxide, \(CO_2\), and 0.540 g of water, \(H_2O\).
Calculate the empirical formula of \(X\). Show your working. [4]

(c) A 0.297 g sample of \(X\) was vaporised in a gas syringe at 373 K and a pressure of \(1.01 \times 10^5\text{ Pa}\). The volume of the vaporised gas was measured as \(92.1\text{ cm}^3\).
(i) Use the ideal gas equation, \(pV = nRT\), to calculate the relative molecular mass, \(M_r\), of \(X\). [3]
(ii) Deduce the molecular formula of \(X\). [1]

(d) Compound \(X\) is identified as 1,2-dichloroethane.
(i) Write a balanced chemical equation for the hydrolysis of 1,2-dichloroethane with excess aqueous sodium hydroxide to form ethane-1,2-diol, \(CH_2(OH)CH_2(OH)\). [1]
(ii) In an experiment, 4.95 g of 1,2-dichloroethane is heated with excess aqueous sodium hydroxide. The reaction has a percentage yield of 75.0%. Calculate the mass of ethane-1,2-diol produced. (\(M_r\) of ethane-1,2-diol = 62.0). [3]

This question concerns the chemical periodicity of the elements in Period 3 of the Periodic Table.

(a) Sodium and sulfur both react with oxygen when heated.
(i) Describe the observations made during each reaction, and write a balanced equation for each reaction. [4]
(ii) State the type of bonding and structure shown by sodium oxide and sulfur dioxide. [2]

(b) The melting points of silicon dioxide, \(SiO_2\), and phosphorus(V) oxide, \(P_4O_{10}\), are shown below:
- Melting point of \(SiO_2\) = 1883 K
- Melting point of \(P_4O_{10}\) = 573 K
Explain this difference in melting points in terms of structure and bonding. [4]

(c) Phosphorus(V) chloride, \(PCl_5\), is added to water.
(i) Describe what is observed and write a balanced chemical equation for the reaction. [3]
(ii) Predict the approximate pH of the resulting solution and explain your prediction. [2]

This question is about chemical energetics, calorimetry, and Hess's Law.

(a) A student determines the enthalpy change of neutralisation, \(\Delta H_{neut}\), of hydrochloric acid with aqueous sodium hydroxide.
\(50.0\text{ cm}^3\) of \(1.00\text{ mol dm}^{-3}\ HCl(aq)\) is mixed with \(50.0\text{ cm}^3\) of \(1.05\text{ mol dm}^{-3}\ NaOH(aq)\) in a polystyrene cup. Both solutions are initially at 21.5 °C. The maximum temperature reached is 28.2 °C.
Assume the density of the solution is \(1.00\text{ g cm}^{-3}\) and its specific heat capacity is \(4.18\text{ J g}^{-1}\text{ K}^{-1}\).
(i) Calculate the heat energy, \(q\), in Joules, released during this reaction. [2]
(ii) Show that \(HCl\) is the limiting reagent and state the number of moles of water formed. [2]
(iii) Calculate the enthalpy change of neutralisation, \(\Delta H_{neut}\), in \(\text{kJ mol}^{-1}\), for this reaction. Include a sign. [2]

(b) Explain why the experimental value of \(\Delta H_{neut}\) obtained is less exothermic than the standard literature value of \(-57.1\text{ kJ mol}^{-1}\), and suggest a practical improvement to the setup. [2]

(c) Standard enthalpy changes of combustion, \(\Delta H_c^\ominus\), are given below:
- \(\Delta H_c^\ominus [C(s)] = -393.5\text{ kJ mol}^{-1}\)
- \(\Delta H_c^\ominus [H_2(g)] = -285.8\text{ kJ mol}^{-1}\)
- \(\Delta H_c^\ominus [C_2H_5COOH(l)] = -1527.0\text{ kJ mol}^{-1}\)

(i) Write the chemical equation, with state symbols, for the standard enthalpy change of formation of liquid propanoic acid, \(C_2H_5COOH\). [2]
(ii) Draw a labeled Hess’s Law cycle connecting the formation of propanoic acid with its combustion products. [2]
(iii) Calculate the standard enthalpy change of formation, \(\Delta H_f^\ominus\), of liquid propanoic acid in \(\text{kJ mol}^{-1}\). [3]

This question is about chemical equilibria and the determination of equilibrium constants.

Ethanoic acid reacts with ethanol in a reversible reaction to form ethyl ethanoate and water. The equation for this reaction is:
\[CH_3COOH(l) + C_2H_5OH(l) \rightleftharpoons CH_3COOC_2H_5(l) + H_2O(l)\]

(a) Write the expression for the equilibrium constant, \(K_c\), for this reaction. State why the volumes of the mixture cancel in the expression for \(K_c\). [2]

(b) In an experiment, 1.00 mol of ethanoic acid and 1.50 mol of ethanol are mixed in a sealed container and allowed to reach equilibrium at a constant temperature, \(T\).
At equilibrium, it is found that 0.80 mol of ethyl ethanoate has been formed.
Calculate the value of \(K_c\) at temperature \(T\). Show your working. [4]

(c) A different equilibrium mixture is prepared at the same temperature, \(T\), containing 2.00 mol of ethanoic acid, 1.00 mol of ethanol, and 0.50 mol of water. Let \(x\) represent the equilibrium amount, in moles, of ethyl ethanoate.
Write an expression using your calculated value of \(K_c\) from (b) to show how \(x\) could be calculated. (You do not need to solve the equation). [3]

(d) Use Le Chatelier's principle to predict and explain the effect on the position of equilibrium and the value of \(K_c\) when:
(i) More ethanol is added to the mixture. [3]
(ii) The temperature is increased, given that the forward reaction is exothermic. [3]

### Practical Task 1: Enthalpy Change of Neutralisation

In this experiment, you are to determine the enthalpy change of neutralisation, \(\Delta H_{\text{neut}}\), when a weak monobasic acid, \(\text{HA}\), is neutralised by aqueous sodium hydroxide, \(\text{NaOH}\).

$$\text{HA(aq)} + \text{NaOH(aq)} \rightarrow \text{NaA(aq)} + \text{H}_2\text{O(l)}$$

**Method**

1. A student transferred \(25.0\text{ cm}^3\) of \(1.60\text{ mol dm}^{-3}\) aqueous sodium hydroxide, \(\text{NaOH}\), into a polystyrene cup.
2. The student measured the initial temperature of the \(\text{NaOH}\) solution.
3. A second student transferred \(25.0\text{ cm}^3\) of \(1.60\text{ mol dm}^{-3}\) weak acid, \(\text{HA}\), into a beaker and measured its temperature, which was identical to that of the \(\text{NaOH}\).
4. The student then added the acid quickly to the polystyrene cup, stirred the mixture continuously, and recorded the maximum temperature reached.

**Results**
- Initial temperature of both solutions = \(21.4\text{ }^\circ\text{C}\)
- Maximum temperature reached = \(31.2\text{ }^\circ\text{C}\)

---

### Questions

**(a)** Calculate the temperature rise, \(\Delta T\), of the mixture.

$$\Delta T = \text{................... }^\circ\text{C}$$

[1]

**(b)** Calculate the heat energy, \(q\), released in the reaction in joules.
*(Assume that the density of the reaction mixture is \(1.00\text{ g cm}^{-3}\) and that its specific heat capacity is \(4.18\text{ J g}^{-1}\text{ K}^{-1}\).)*

$$q = \text{................... J}$$

[2]

**(c)** Calculate the number of moles of water formed during this neutralisation reaction.

$$\text{moles of H}_2\text{O} = \text{................... mol}$$

[2]

**(d)** Use your answers to **(b)** and **(c)** to calculate the enthalpy change of neutralisation, \(\Delta H_{\text{neut}}\), in \(\text{kJ mol}^{-1}\).
Include the appropriate sign and give your answer to **three** significant figures.

$$\Delta H_{\text{neut}} = \text{................... kJ mol}^{-1}$$

[3]

**(e)** In an improved experiment, a student records the temperature at \(1\)-minute intervals for both the solutions and the mixture, and uses a cooling curve extrapolation.
Explain why this extrapolation method provides a more accurate value for the temperature change than simply recording the maximum temperature.

[2]

**(f)** Sketch the graph of temperature against time that would be obtained for this experiment.
- Clearly label the axes.
- Assume the solutions are mixed at \(t = 3\text{ min}\).
- Show how the extrapolation is performed to find the theoretical maximum temperature rise, \(\Delta T_{\text{theory}}\).

[3]

**(g)** Another student carried out the exact same experiment but used a simple glass beaker instead of a polystyrene cup.
State and explain how the temperature rise and the magnitude of the calculated \(\Delta H_{\text{neut}}\) would compare to those obtained using a polystyrene cup.

[2]

An experiment was carried out to determine the enthalpy change of hydration of anhydrous magnesium sulfate, \(\Delta H_{\text{hyd}}\), which cannot be measured directly.

$$\text{MgSO}_4\text{(s)} + 7\text{H}_2\text{O(l)} \rightarrow \text{MgSO}_4 \cdot 7\text{H}_2\text{O(s)} \quad \Delta H_{\text{hyd}}$$

Two experiments were conducted using a simple polystyrene cup calorimeter.
[Assume the specific heat capacity of the solution is \(4.18 \text{ J g}^{-1} \text{ K}^{-1}\) and the density of the solution is \(1.00 \text{ g cm}^{-3}\).]

**Experiment 1: Enthalpy change of solution of anhydrous magnesium sulfate, \(\Delta H_1\)**
* Mass of weighing bottle + \(\text{MgSO}_4\text{(s)}\) = \(14.85 \text{ g}\)
* Mass of empty weighing bottle = \(9.15 \text{ g}\)
* Volume of distilled water in the plastic cup = \(50.0 \text{ cm}^3\)
* Initial temperature of water = \(21.5 \ ^\circ\text{C}\)
* Maximum temperature reached = \(39.0 \ ^\circ\text{C}\)

**Experiment 2: Enthalpy change of solution of hydrated magnesium sulfate, \(\Delta H_2\)**
* Mass of weighing bottle + \(\text{MgSO}_4 \cdot 7\text{H}_2\text{O(s)}\) = \(21.95 \text{ g}\)
* Mass of empty weighing bottle = \(10.25 \text{ g}\)
* Volume of distilled water in the plastic cup = \(50.0 \text{ cm}^3\)
* Initial temperature of water = \(22.0 \ ^\circ\text{C}\)
* Minimum temperature reached = \(18.5 \ ^\circ\text{C}\)

**(a)** Calculate the heat energy released, \(q_1\), in Joules, during Experiment 1.

**(b)** Calculate the enthalpy change of solution of anhydrous magnesium sulfate, \(\Delta H_1\), in \(\text{kJ mol}^{-1}\). Show your working and give your answer to 3 significant figures.
\([A_{\text{r}}: \text{Mg} = 24.3, \text{S} = 32.1, \text{O} = 16.0, \text{H} = 1.0]\)

**(c)** Calculate the enthalpy change of solution of hydrated magnesium sulfate, \(\Delta H_2\), in \(\text{kJ mol}^{-1}\). Show your working and give your answer to 3 significant figures.

**(d)** Construct an energy cycle using Hess's Law to connect the three enthalpy changes, and calculate the enthalpy change of hydration, \(\Delta H_{\text{hyd}}\), of anhydrous magnesium sulfate in \(\text{kJ mol}^{-1}\).

**(e)**
(i) Calculate the percentage uncertainty in the temperature change, \(\Delta T\), for Experiment 1, if the thermometer used has an uncertainty of \(\pm 0.5 \ ^\circ\text{C}\) for each individual reading. Show your working.
(ii) Suggest one improvement to the experimental setup to reduce heat loss, other than adding a lid.

### Qualitative Analysis

In this task, you will identify the cations and anions present in three aqueous solutions: **FA 5**, **FA 6**, and **FA 7**.
Each solution contains **one** cation and **one** anion from the standard list of ions in the Qualitative Analysis Notes.

**(a)** Carry out the following tests and record all your observations in a single, clearly structured table.

* **Test 1:** Add aqueous sodium hydroxide, \(\text{NaOH}\), dropwise until in excess to separate 1 cm depths of **FA 5**, **FA 6**, and **FA 7** in test-tubes.
* **Test 2:** Add aqueous ammonia, \(\text{NH}_3\), dropwise until in excess to separate 1 cm depths of **FA 5**, **FA 6**, and **FA 7** in test-tubes.
* **Test 3:** Add a few drops of aqueous silver nitrate, \(\text{AgNO}_3\), to separate 1 cm depths of **FA 5**, **FA 6**, and **FA 7** in test-tubes. To any precipitate formed, add aqueous ammonia until in excess.
* **Test 4:** Mix a 1 cm depth of **FA 6** with a 1 cm depth of **FA 7** in a test-tube. To the resulting mixture, add dilute nitric acid, \(\text{HNO}_3\).

[8 marks]

**(b)** Use your observations from **(a)** to identify the ions present in **FA 5**, **FA 6**, and **FA 7**. State the evidence for each ion.

* Cation in **FA 5**:
* Anion in **FA 5**:
* Cation in **FA 6**:
* Anion in **FA 6**:
* Cation in **FA 7**:
* Anion in **FA 7**:

Support each of your identifications with a brief summary of the evidence from your observations.

[5 marks]

**(c)** (i) A student suggests that the cation in **FA 7** could be zinc, \(\text{Zn}^{2+}\), rather than aluminium, \(\text{Al}^{3+}\). Explain how your observations in **(a)** show that **FA 7** contains \(\text{Al}^{3+}\) and not \(\text{Zn}^{2+}\).

(ii) Suggest a chemical test, other than mixing **FA 6** and **FA 7**, that can be used to confirm that the anion in **FA 7** is sulfate, \(\text{SO}_4^{2-}\). State the reagent(s) you would use and the expected observation.

[2 marks]