No questions found
Sulfides are compounds that contain sulfur but not oxygen.
(a) Carbon disulfide, CS$_2$, is a volatile liquid at room temperature and pressure.
(i) State the meaning of volatile.
......................................................................................................................... [1]
(ii) Draw a 'dot-and-cross' diagram of the CS$_2$ molecule.
(iii) Suggest the bond angle in a molecule of CS$_2$.
......................................................................................................................... [1]
(iv) CS$_2$ is a liquid under room conditions, while CO$_2$ is a gas.
Explain what causes the difference in the physical properties between CS$_2$ and CO$_2$.
..........................................................................................................................
..........................................................................................................................
.......................................................................................................................... [2]
(b) The enthalpy change of combustion of CS$_2$(l) is represented by the following equation.
CS$_2$(l) + 3O$_2$(g) $\xrightarrow[]{\Delta H_c}$ CO$_2$(g) + 2SO$_2$(g)
(i) Define enthalpy change of combustion.
.........................................................................................................................
.........................................................................................................................
......................................................................................................................... [2]
(ii) The table shows the enthalpy changes of formation of CS$_2$(l), CO$_2$(g) and SO$_2$(g).
$$\begin{array}{|c|c|} \hline \text{compound} & \text{enthalpy change of formation, } \Delta H_f/ \text{kJ mol}^{-1} \\ \hline \text{CS}_2(l) & +89.7 \\ \text{CO}_2(g) & -394 \\ \text{SO}_2(g) & -297 \\ \hline \end{array}$$
Use the data in the table to calculate the enthalpy change of combustion, $\Delta H_c^\circ$, of CS$_2$(l), in kJ mol$^{-1}$.
Show your working.
..........................................................................................................................
$\Delta H_c$ of CS$_2$(l) = .......................... kJ mol$^{-1}$ [2]
(c) Hydrogen sulfide gas, H$_2$S(g), is slightly soluble in water. It acts as a weak acid in aqueous solution.
(i) State the meaning of weak acid.
.........................................................................................................................
......................................................................................................................... [1]
(ii) Give the formula of the conjugate base of H$_2$S.
......................................................................................................................... [1]
(iii) H$_2$S(aq) reacts slowly with oxygen dissolved in water. The reaction is represented by the following equation.
$$ \text{H}_2\text{S(aq)} + \frac{1}{2}\text{O}_2\text{(aq)} \rightarrow \text{H}_2\text{O(l)} + \text{S(s)} $$
Explain, with reference to oxidation numbers, why this reaction is a redox reaction.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
.......................................................................................................................... [2]
(d) The compound As$_2$S$_3$ is a common mineral.
When As$_2$S$_3$ is heated strongly in air, it forms a mixture of products, as shown.
$$2\text{As}_2\text{S}_3\text{(s)} + 9\text{O}_2\text{(g)} \rightarrow \text{As}_4\text{O}_6\text{(s)} + 6\text{SO}_2\text{(g)}$$
(i) A sample containing 0.198 g As$_2$S$_3$ is placed in 0.100 dm$^3$ of pure oxygen, an excess, in a reaction chamber connected to a gas syringe at room temperature.
The reactants are heated until no further change is observed. The products are then allowed to cool to room temperature.
Calculate the volume, in dm$^3$, of gas present at the end of the experiment.
The molar volume of gas is 24.0 dm$^3$ mol$^{-1}$ under these conditions. Assume that the pressure is constant throughout the experiment.
Show your working.
..........................................................................................................................
volume of gas remaining = .......................... dm$^3$ [4]
(ii) State the environmental consequences of releasing SO$_2$(g) into the atmosphere.
......................................................................................................................... [1]
(iii) SO$_2$(g) can be removed from the air by reacting it with NaOH(aq).
Construct an equation for the reaction of SO$_2$(g) with NaOH(aq). Include state symbols.
.......................................................................................................................... [2]
547
574
544
The reaction scheme shows some reactions of calcium.
(a) (i) Reaction 1 produces Ca(NO$_3$)$_2$ and one other product. Identify the other product. [1]
(ii) Construct an equation for the thermal decomposition of Ca(NO$_3$)$_2$(s). [1]
(iii) State the trend in the thermal stability of the Group 2 nitrates down the group. [1]
(iv) In reaction 3, excess CO$_2$ is bubbled through water containing CaCO$_3$. A solution of Ca(HCO$_3$)$_2$(aq) forms. Construct an equation for reaction 3. [1]
(b) Describe how Ca(OH)$_2$ is used in agriculture. [1]
(c) In reaction 4, calcium carbide, CaC$_2$, is formed from CaO. CaC$_2$ contains the C$_2^{2-}$ anion. Each carbon in C$_2^{2-}$ is sp hybridised.
(i) Describe how sp hybridised orbitals are formed. [1]
(ii) Sketch a diagram to show how two sp hybrid orbitals can form a sigma ($\sigma$) bond. [2]
(d) The flowchart shows some reactions of CaC$_2$.
(i) Reaction 5 can be used to prepare NH$_3$.
CaCN$_2$ + 3H$_2$O $\rightarrow$ CaCO$_3$ + 2NH$_3$
Calculate the minimum mass, in tonnes, of calcium cyanamide, CaCN$_2$, that is required to produce 1.50 $\times$ 10$^6$ tonnes of NH$_3$.
Show your working.
1 tonne = 1.00 $\times$ 10$^6$ g
minimum mass of CaCN$_2$ = ...................... tonnes [2]
(ii) Draw the structure of the organic products formed in the following reactions.
CH$_3$CH$_2$Br $\xrightarrow{\text{dissolved in ethanol}}$ NaCN $\rightarrow$ [Structure]
H$_2$SO$_4$(aq) $\xrightarrow{\text{heat under reflux}}$ [Structure]
(3) $\rightarrow$ [Structure]
[Total: 13]
504
590
548
Phosphorus is a reactive Period 3 element.
(a) Phosphorus has several allotropes. Details of two allotropes are given.
[Table_1]
(i) White phosphorus and red phosphorus both have covalent bonding.
Suggest the types of structure shown by white phosphorus ($P_4$) and red phosphorus ($P$).
Explain why red phosphorus ($P$) has a higher melting point than white phosphorus ($P_4$).
structure of $P_4$ ..................................................
structure of $P$ ......................................................
explanation .........................................................
.................................................................
[3]
(ii) Red phosphorus ($P$) forms when white phosphorus ($P_4$) is exposed to sunlight.
$\frac{1}{4}P_4(s) \rightarrow P(s)$ $\Delta H = -17.6\text{kJ mol}^{-1}$
Use this information to draw a reaction pathway diagram to show the formation of red phosphorus ($P$) from white phosphorus ($P_4$).
[1]
(b) Some reactions of $P_4(s)$ are shown in the reaction scheme.
(i) State the oxidation number of phosphorus in $P_4O_{10}$.
.........................................................
[1]
(ii) Deduce the identity of $Q$ and hence construct chemical equations for reactions 1 and 2.
reaction 1 $PCl_5 + .......H_2O \rightarrow ................................................$
reaction 2 $P_4O_{10} + .......H_2O \rightarrow ................................................$
[2]
(c) Triphenylphosphine is used in a type of reaction known as a Wittig reaction.
(i) Give the empirical formula of triphenylphosphine.
.........................................................
[1]
In a Wittig reaction, an aldehyde reacts with a halogenoalkane to form an alkene. The conversion is shown in the following unbalanced equation.
Compound $H$ can be made from propanal, $C_2H_5CHO$. Stage 3 in the reaction scheme is a Wittig reaction.
(ii) State the types of reaction that occur in stages 1 and 2.
stage 1 .........................................................
stage 2 .........................................................
[2]
(iii) Draw the structures of $G$ and $H$ in the boxes provided.
[2]
(d) Identify the organic products formed when compound $J$, shown below, is heated with hot concentrated acidified manganate(VII) ions.
[2]
506
536
595
(a) (i) Reaction 1 is an oxidation reaction.
Give the reagent(s) and conditions required for reaction 1.
reagent(s) ............................................................................................................................
conditions ............................................................................................................................
............................................................................................................................ [2]
(ii) Construct an equation to represent reaction 1.
Use [O] to represent an oxygen atom from the oxidising agent in this reaction.
............................................................................................................................ [1]
(iii) Suggest the type of reaction that occurs in reaction 2.
............................................................................................................................ [1]
(iv) $H_2SO_4$ acts as a homogeneous catalyst in reaction 3.
Explain why $H_2SO_4$ is described as homogeneous.
............................................................................................................................
............................................................................................................................ [1]
(b) Reaction 2 needs to take place in the absence of water to prevent formation of compound C.
If C is present in the reaction mixture of reaction 3, a different compound, compound D, will also form. Compound D has two identical functional groups.
The infrared spectrum of D shows strong absorptions at 1100 $\text{cm}^{-1}$ and 1720 $\text{cm}^{-1}$, but no absorption due to O–H bonds.
Use the Data Booklet to identify the functional group present in D.
Explain your answer as fully as you can.
............................................................................................................................
............................................................................................................................
............................................................................................................................ [3]
(c) Some other reactions of C are shown.
(i) Draw the structure of E.
............................................................................................................................ [1]
(ii) Suggest why $NaBH_4$ is not a suitable reagent to make F, $(CH_2OH)_2$, from C.
Explain your answer.
............................................................................................................................
............................................................................................................................ [1]
(iii) Construct an equation for the reaction of $(CH_2OH)_2$ with $SOCl_2$ to form G, $(CH_2Cl)_2$.
............................................................................................................................ [1]
(d) Explain why C is very soluble in water.
............................................................................................................................
............................................................................................................................ [1]
558
518
576
