9701_w23_qp_22 - revisedeck

1

The elements silicon, phosphorus and sulfur are in Period 3 of the Periodic Table. Describe the variation in atomic radius from silicon to sulfur. The melting point of silicon is 1410 °C. The melting point of sulfur is 113 °C. Explain this difference. Table 1.1 shows some properties of the elements Si to S. The first ionisation energy of P is not shown. Table 1.1 property Si P S total number of electrons in s subshells total number of electrons in p subshells first ionisation energy / kJ mol–1 formula of most common chloride SiCl 4 PCl 5 SCl 2 Complete Table 1.1 to show the total number of s and p electrons in an atom of Si, P and S. Construct an equation to represent the first ionisation energy of Si. Three possible values for the first ionisation energy of P are given. 619 kJ mol–1 893 kJ mol–1 1060 kJ mol–1 Circle the correct value. Explain your choice, including a comparison of your chosen value to those of Si and S. SiCl 4 and PCl 5 each react with water, forming misty fumes. Identify the chemical responsible for the misty fumes. Predict the shape of the SCl 2 molecule.

1. Atomic structure → 1.4. Ionisation energy

9. The Periodic Table: chemical periodicity → 9.2. Periodicity of chemical properties of the elements in Period 3

Open

2

NO and NO2 react at 25 °C to give N2O3 as shown in the equation. NO+ NO2N2O3ΔH = –7.2 kJ mol–1 The reaction is reversible and reaches equilibrium in a closed system. shows how the rate of the forward reaction changes with time. Initially, the rate of the reverse reaction is zero. Complete to sketch how the rate of the reverse reaction changes with time. rate of reaction time State how the position of equilibrium changes, if at all, when the reaction takes place at 100 °C. Explain your answer. Assume the pressure remains constant. Table 2.1 shows the composition of an equilibrium mixture of NO, NO2and N2O3at 101 kPa. Table 2.1 gas number of moles at equilibrium / mol NO 0.605 NO2 0.605 N2O3 0.390 Calculate Kp , the equilibrium constant with respect to partial pressures. Deduce the units of Kp. Kp = units Identify one natural process and one man-made process that cause the formation of atmospheric NO and NO2. natural process man-made process NO2 is a brown gas that can be used to form nitric acid. NO2 is a free radical. Define free radical. NO2 has a catalytic role in the oxidation of atmospheric sulfur dioxide. Write equations to show the catalytic role of NO2 in this oxidation. State one environmental consequence of the oxidation of atmospheric sulfur dioxide. A student titrates nitric acid with a base to form a solution containing aqueous magnesium nitrate. Identify a base that the student could use. The student evaporates the water to obtain magnesium nitrate solid. When this solid is heated it decomposes. Write an equation for the decomposition of magnesium nitrate. State how the thermal stability of Group 2 nitrates changes down the group.

12. Nitrogen and sulfur → 12.1. Nitrogen and sulfur

7. Equilibria → 7.1. Chemical equilibria: reversible reactions, dynamic equilibrium

Open

3

Phosphoric(acid, H3PO4, is used in both inorganic and organic reactions. H3PO4 is made in a two-step process from phosphorus. step 1 Phosphorus reacts with an excess of oxygen to form a white solid. step 2 The white solid then reacts with water to form H3PO4. Write an equation for each step. step 1 step 2 H3PO4 is a weak Brønsted–Lowry acid. Define weak Brønsted–Lowry acid. H3PO4 is also formed in the process shown in reaction 1. reaction 1 4H3PO3 3H3PO4 + PH3 Table 3.1 shows some relevant thermodynamic data. Table 3.1 compound enthalpy change of formation, ΔHf / kJ mol–1 H3PO3 –972 H3PO4 –1281 PH3 +9 Define enthalpy change of formation. Use the data in Table 3.1 to calculate the enthalpy change, ΔH r , of reaction 1. ΔH r = kJ mol–1 Explain why reaction 1 is a disproportionation reaction. Explain your reasoning with reference to relevant oxidation numbers. shows a reaction scheme that involves H3PO4 in several reactions. reaction 2 reaction 3 oxidation A and H3PO4 KBr and H3PO4 CH3COOH B OH O O O and H3PO4 Identify A, which reacts with propene in the presence of H3PO4 in reaction 2. Draw the structure of B. Name the type of reaction that occurs in reaction 3. Reaction 3 is monitored using infrared spectroscopy. It is not possible to use the O—H absorption frequency to monitor the reaction. Use Table 3.2 to identify a suitable bond whose absorption frequency can be used to monitor the progress of reaction 3. State the change you would see in the infrared spectrum during reaction 3. bond change in infrared spectrum Table 3.2 bond functional groups containing the bond characteristic infrared absorption range (in wavenumbers) / cm–1 C–O hydroxy, ester 1040–1300 C=C aromatic compound, alkene 1500–1680 C=O amide carbonyl, carboxyl ester 1640–1690 1670–1740 1710–1750 C–H alkane 2850–2950 H3PO4 also reacts with alcohols to form organophosphates. Organophosphates are compounds similar to esters. They have the general structure shown in . O O O P R = alkyl group R R R O Complete the equation to suggest the products of the reaction of H3PO4 with methanol, CH3OH. H3PO4 + 3CH3OH Compound T is a simple organophosphate. The mass spectrum of T shows a molecular ion peak at m / e = 182. This peak has a relative intensity of 12.7. The relative intensity of the M +1 peak is 0.84. Deduce the number of carbon atoms in T. Hence suggest the molecular formula of T. Assume that phosphorus and oxygen exist as single isotopes. Show your working. number of carbon atoms in T = molecular formula of T =

5. Chemical energetics → 5.1. Enthalpy change, \(\Delta H\)

11. Group 17 → 11.4. The reactions of chlorine

Open

4

Lactic acid, CH3CH(OH)COOH, and pyruvic acid, CH3COCOOH, both contain two functional groups. lactic acid pyruvic acid H O O H C C O H H3C O O H3C O C C H Explain why lactic acid exists as optical isomers. Give the systematic name of lactic acid. Lactic acid forms hydrogen bonds with water. Complete to show the formation of a hydrogen bond between one molecule of lactic acid and one molecule of water. Label the hydrogen bond. Show any relevant dipoles and lone pairs of electrons. H O O H C C O H H3C Two possible syntheses of pyruvic acid are shown in and . Each synthesis has a total of three steps. propene Br2 pyruvic acid CH3COCOOH [O] Br Br first step second step third step ethanal pyruvic acid CH3COCOOH lactic acid CH3CH(OH)COOH [O] O first step second step third step Complete the diagram in to show the mechanism for the reaction of propene with Br2. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate. Br Br Br Br Write an equation for the oxidation of lactic acid to pyruvic acid, the third step of . Use [O] to represent one atom of oxygen from an oxidising agent. CH3CH(OH)COOH + Complete Table 4.1 to give details of the reagents and conditions used in each of the two syntheses shown in and . Table 4.1 synthesis from propene (shown in ) synthesis from ethanal (shown in ) reagents and conditions used first step Br2 second step third step

14. Hydrocarbons → 14.1. Alkanes

7. Equilibria → 7.2. Brønsted–Lowry theory of acids and bases

Open