Chemistry 9701/23 May/June 2021: question paper and mark scheme

Question

The elements in Group 17 are known as the halogens. (a) Between the molecules of Group 17 elements van der Waals’ forces exist. (i) State the trend in the relative strength of van der Waals’ forces down Group 17. . …… [1] (ii) State the physical state of each of the halogens under room conditions. chlorine …… bromine . …… iodine …… [1] (b) A solution of aqueous bromide ions, Br –(aq), is added to separate samples of Cl 2(aq) and I2(aq). Describe what is observed in each reaction. Explain your answer in terms of the relative reactivity of these elements as oxidising agents. observation on addition to Cl 2(aq) …… . …… observation on addition to I2(aq) …… . …… explanation …… . …… . …… [3] (c) Bleach is made by reacting Cl 2 with cold NaOH(aq). Write an equation for the reaction of Cl 2 with cold NaOH. . …… [1] (d) When Cl O–(aq) is added to water, it behaves as a Brønsted-Lowry base. (i) Define the term Brønsted-Lowry base. . …… [1] (ii) Write an ionic equation for the reaction between Cl O– and H2O. . …… [1] (e) The concentration of NaCl O in bleach S is x g dm–3. NaCl O reacts with H2O2(aq) as shown. H2O2(aq) + NaCl O(aq) → H2O(l) + NaCl (aq) + O2(g) A 5.00 cm3 sample of S completely reacts with H2O2(aq). The volume of O2(g) produced is 24.0 cm3 under room conditions. Assume that only the NaCl O in S reacts with H2O2(aq). Calculate x. Show your working. x = …… g dm–3 [3] (f) Sodium chlorate(I), NaCl O, oxidises dilute hydrochloric acid to form three products. The products which contain chlorine have chlorine species with oxidation number –1 or 0. No other species changes its oxidation number during the reaction. Use this information to complete the ionic equation. ……Cl O– + ……HCl → …… + …… + …… [2] [Total: 13]

Question

Methanol, CH3OH, is soluble in water because it forms hydrogen bonds with water molecules. (a) Draw a fully labelled diagram to show how a hydrogen bond forms between a water molecule and a methanol molecule. [3] (b) Methanol has a melting point of –97.6 °C and a boiling point of 64.7 °C. A sample of pure liquid methanol is added to a flask and then sealed. The sealed flask is left for several days at constant temperature. The vapour pressure is then measured as 17 kPa. (i) Describe what is meant by the term vapour pressure of methanol. . …… . …… . …… [2] (ii) Explain why some of the liquid becomes a vapour. . …… . …… . …… [1] (iii) Suggest and explain why the vapour pressure of water at room temperature is lower than the vapour pressure of methanol at room temperature. Refer to the correct intermolecular forces in your answer. . …… . …… . …… [2] (c) Methanol is made by reacting carbon monoxide with hydrogen. CO(g) + 2H2(g) CH3OH(g) Carbon monoxide and hydrogen react at 1.0 × 107 Pa and 200 °C. Eventually the reaction mixture reaches dynamic equilibrium. The table shows the amounts of each species present in the mixture. CO(g) H2(g) CH3OH(g) initial amount / mol 1.0 2.0 0 equilibrium amount / mol 0.030 0.060 0.97 (i) Explain what is meant by dynamic equilibrium. . …… . …… . …… [2] (ii) Calculate the partial pressure of methanol vapour at equilibrium under these conditions. Show your working. …… Pa [2] (iii) Write an expression for the equilibrium constant, Kp, for this reaction. State the units in your answer. Kp = units = …… [2] [Total: 14]

Question

Separate samples of R, S, T and U are added to cold water. The identity of each sample is unknown. However, each sample is known to be pure and can only be one of Ba(OH)2, NaCl, P4O10 or SiCl 4. (a) (i) Use the observations in the table to identify each sample as one of Ba(OH)2, NaCl, P4O10 and SiCl 4. Write your answers in the table. state at room observations on addition identity of sample temperature of sample to water alkaline, colourless solution is produced, R solid some white solid remains white solid disappears, S solid solution is neutral misty fumes produced, T liquid white solid is made in vigorous reaction acidic, colourless solution produced in U solid vigorous reaction [4] (ii) Identify the formula of the white solid made when sample T reacts with water. . …… [1] (iii) Name the solution formed when sample U reacts with water. . …… [1] (b) Magnesium oxide and aluminium oxide have properties typical of ceramic materials. (i) Name one physical property typical of ceramic materials. . …… [1] (ii) Give the formula of another Period 3 oxide which behaves as a ceramic material. . …… [1] (c) Tungsten oxide, WxOy, is used to give colour to ceramic materials. A sample of WxOy contains 79.29% tungsten by mass. Calculate the empirical formula of WxOy. Show your working. empirical formula = …… [3] [Total: 11]

Question

(a) 1,3-dichloropropan-2-ol can be made by reacting M. M 1,3-dichloropropan-2-ol Cl Cl O HO Cl Cl (i) Give the systematic name of M. . …… [1] (ii) Name the functional group present in M that changes during this reaction. . …… [1] (iii) State a suitable reagent for this reaction. . …… [1] (b) Separate samples of 1,3-dichloropropan-2-ol and 3-chloropropane-1,2-diol are heated with excess acidified Cr2O72– until there is no further reaction. In each reaction, a different organic product, Q or R, is made. 1,3-dichloropropan-2-ol 3-chloropropane-1,2-diol Cl Cl Q R HO HO Cl OH Q and R are tested separately with 2,4-dinitrophenylhydrazine solution, 2,4-DNPH, and sodium carbonate solution, Na2CO3(aq). Complete the table to give any relevant observations. If no reaction occurs, write ‘no visible change’. reagent observation with Q observation with R 2,4-DNPH Na2CO3(aq) [4] (c) Citric acid can be made from M in a four-step reaction. M Cl Cl Cl O N O step 1 step 2 OH HO HO Cl Cl Cl step 3 citric acid O O HO OH N O O step 4 OH OH OH HO N Complete the table for each step of the reaction sequence to identify: ● the reagents and conditions required ● the type of reaction. step reagent and conditions type of reaction 1 2 dilute sulfuric acid 3 4 dilute sulfuric acid [5] [Total: 12]

Question

Compound X contains the same functional groups as citric acid. citric acid O O HO OH O OH OH The table describes some of the similarities and differences between citric acid and compound X. citric acid X chiral centre no yes reaction with Na fizzing fizzing reaction with H+ / Cr2O72– remains orange orange to green (a) Complete the equation to show the reaction of excess sodium with citric acid. Show the skeletal structure of the product. O O HO OH O + ……Na OH OH [3] (b) (i) Use the information in the table to deduce the skeletal formula of X, C3H6O3. Draw the skeletal formula of X in the box. Label the chiral centre of compound X with an asterisk (*). [2] (ii) Explain why compound X reacts with acidified Cr2O72– but citric acid does not. . …… . …… . …… [2] (c) Compound X is one of a pair of stereoisomers. Stereoisomerism occurs when a molecule has at least one of two key features. State the two key features that give rise to stereoisomerism. 1 . …… . …… 2 . …… . …… [2] (d) A structural isomer of compound X does not fizz when added to sodium. Explain what is meant by structural isomer. . …… . …… [1] [Total: 10]