Chemistry 0620/53 May/June 2023: question paper and mark scheme

Question

You are going to investigate the temperature change when solid citric acid reacts with solid sodium carbonate. Read all of the instructions carefully before starting the experiments. Instructions You are going to do six experiments. (a) Experiment 1 ● Place 5.0 g of solid sodium carbonate in a 100 cm3 beaker. ● Use a thermometer to stir the solid sodium carbonate for 30 seconds. Measure the temperature of the solid sodium carbonate and record the temperature in Table 1.1. ● Keep the sodium carbonate in the beaker for Experiment 2. Experiment 2 ● Add 1.0 g of solid citric acid to the sodium carbonate in the beaker from Experiment 1. ● Use the thermometer to stir the mixture for 30 seconds. Measure the temperature of the mixture and record the temperature in Table 1.1. ● Rinse the beaker and thermometer with water. Experiment 3 ● Place 5.0 g of solid sodium carbonate in the 100 cm3 beaker. ● Add 2.0 g of solid citric acid to the sodium carbonate in the beaker. ● Use the thermometer to stir the mixture for 30 seconds. Measure the temperature of the mixture and record the temperature in Table 1.1. ● Rinse the beaker and thermometer with water. Experiment 4 ● Repeat Experiment 3, using 4.0 g of solid citric acid instead of 2.0 g. Experiment 5 ● Repeat Experiment 4, using 5.0 g of solid citric acid instead of 4.0 g. Experiment 6 ● Repeat Experiment 5, using 6.0 g of solid citric acid instead of 5.0 g. Complete Table 1.1. Table 1.1 mass of solid mass of solid temperature after experiment sodium carbonate / g citric acid / g 30 seconds / °C 1 5.0 0.0 2 5.0 1.0 3 4 5 6 [5] (b) Complete a suitable scale on the y-axis and plot your results from Experiments 1 to 6 on Fig. 1.1. Draw a line of best fit through your points. temperature / C mass of 0 citric acid 0 1 2 3 4 5 6 /g Fig. 1.1 [4] (c) State whether the reaction between solid sodium carbonate and solid citric acid is exothermic or endothermic. Explain your answer. . …… . …… [1] (d) Deduce which experiment had the greatest temperature change compared to the temperature in Experiment 1. . …… [1] (e) From your graph, deduce the temperature, after stirring for 30 seconds, that is obtained when 3.5 g of solid citric acid is added to 5.0 g of solid sodium carbonate. Show clearly on the grid how you worked out your answer. temperature = …… °C [2] (f) Suggest why the solid sodium carbonate and solid citric acid are stirred before the temperature is measured. . …… . …… [2] (g) Explain why using a polystyrene cup in place of the glass beaker would increase the accuracy of the results. . …… . …… [2] [Total: 17] Question 2 starts on the next page.

Question

You are provided with solid H. Do the following tests on solid H, recording all of your observations at each stage. Tests on solid H (a) Describe the appearance of solid H. . …… [1] (b) Carry out a flame test on solid H. Record your observations. . …… [1] Divide the remaining solid H into two approximately equal portions in two boiling tubes. (c) Gently heat the first portion of solid H. Record your observations. . …… . …… . …… [3] Add about 10 cm3 of distilled water to the boiling tube containing the second portion of solid H. Place a stopper in the boiling tube and shake the tube for one minute to dissolve solid H and form solution H. If any undissolved solid H remains, pour solution H into a clean boiling tube, leaving the undissolved solid behind. Divide solution H into five approximately equal portions in five test-tubes. (d) To the first portion of solution H, add aqueous ammonia dropwise and then in excess. Record your observations. dropwise …… in excess . …… [2] (e) To the second portion of solution H, add aqueous sodium hydroxide dropwise and then in excess. Record your observations. dropwise …… in excess . …… [2] (f) (i) To the third portion of solution H, add a few drops of acidified aqueous potassium manganate(VII). Record your observations. . …… . …… [1] (ii) State what conclusion can be made from the result of (f)(i). . …… [1] (g) To the fourth portion of solution H, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. Record your observations. . …… . …… [1] (h) To the fifth portion of solution H, add about 1 cm depth of aqueous sodium carbonate. Record your observations. . …… . …… [2] (i) Identify the three ions contained in solid H. . …… . …… . …… [3] [Total: 17]

Question

Oxalic acid is a white solid which is soluble in both water and ethanol to form colourless solutions. Plan an experiment to determine if oxalic acid is more soluble in water or in ethanol, at room temperature. Your answer should include how your results tell you if oxalic acid is more soluble in water or in ethanol, at room temperature. You are provided with oxalic acid, water, ethanol and common laboratory apparatus. . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… [6] Notes for use in qualitative analysis Tests for anions anion test test result carbonate, CO32– add dilute acid, then test for carbon effervescence, carbon dioxide dioxide gas produced chloride, Cl – acidify with dilute nitric acid, then white ppt. [in solution] add aqueous silver nitrate bromide, Br – acidify with dilute nitric acid, then cream ppt. [in solution] add aqueous silver nitrate iodide, I– acidify with dilute nitric acid, then yellow ppt. [in solution] add aqueous silver nitrate nitrate, NO3– add aqueous sodium hydroxide, ammonia produced [in solution] then aluminium foil; warm carefully sulfate, SO42– acidify with dilute nitric acid, then white ppt. [in solution] add aqueous barium nitrate sulfite, SO32– add a small volume of acidified the acidified aqueous potassium aqueous potassium manganate(VII) manganate(VII) changes colour from purple to colourless Tests for aqueous cations cation effect of aqueous sodium hydroxide effect of aqueous ammonia aluminium, Al 3+ white ppt., soluble in excess, giving white ppt., insoluble in excess a colourless solution ammonium, NH4+ ammonia produced on warming – calcium, Ca2+ white ppt., insoluble in excess no ppt. or very slight white ppt. chromium(III), Cr3+ green ppt., soluble in excess green ppt., insoluble in excess copper(II), Cu2+ light blue ppt., insoluble in excess light blue ppt., soluble in excess, giving a dark blue solution iron(II), Fe2+ green ppt., insoluble in excess, green ppt., insoluble in excess, ppt. turns brown near surface on ppt. turns brown near surface on standing standing iron(III), Fe3+ red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc, Zn2+ white ppt., soluble in excess, giving white ppt., soluble in excess, giving a colourless solution a colourless solution Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 turns limewater milky chlorine, Cl 2 bleaches damp litmus paper hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium manganate(VII) from purple to colourless Flame tests for metal ions metal ion flame colour lithium, Li+ red sodium, Na+ yellow potassium, K+ lilac calcium, Ca2+ orange-red barium, Ba2+ light green copper(II), Cu2+ blue-green