Chemistry 0620/52 October/November 2022: question paper and mark scheme

Question

You are going to investigate the temperature change when two different aqueous solutions of sodium hydroxide, solution G and solution H, react with dilute hydrochloric acid. Read all of the instructions carefully before starting the experiments. Instructions You are going to do two experiments. (a) Experiment 1 ● Rinse a burette with distilled water and then with the dilute hydrochloric acid for Question 1. ● Fill the burette to the 0.00 cm3 mark with the dilute hydrochloric acid. ● Use a 50 cm3 measuring cylinder to pour 20 cm3 of solution G into a beaker. ● Use a thermometer to measure the initial temperature of solution G. Record the initial temperature in the table. ● Add 5 cm3 of dilute hydrochloric acid from the burette into the beaker. ● Stir the mixture in the beaker using the thermometer and measure the temperature of the mixture. Record the temperature in the table. ● Add another 5 cm3 of dilute hydrochloric acid from the burette into the beaker. ● Stir the mixture in the beaker using the thermometer and measure the temperature of the mixture. Record the temperature in the table. ● Continue to add 5 cm3 portions of dilute hydrochloric acid and record the temperature of the mixture in the table until you have added a total of 35 cm3 of dilute hydrochloric acid. Experiment 2 ● Repeat Experiment 1 using solution H instead of solution G. Complete the table. Experiment 1 using solution G Experiment 2 using solution H total volume of dilute temperature temperature temperature temperature hydrochloric acid change since change since / °C /°C added / cm3 start / °C start / °C 0 5 10 15 20 25 30 35 [6] (b) Complete a suitable scale on the y-axis and plot your results from Experiments 1 and 2 on the grid. Draw two smooth line graphs. Both curves must start at (0,0). Clearly label your lines. temperature change / C 0 0 5 10 15 20 25 30 35 total volume of dilute hydrochloric acid added / cm3 [5] (c) From your graph, deduce the temperature change obtained when a total volume of 13 cm3 of dilute hydrochloric acid is added in Experiment 1. Show clearly on the grid how you worked out your answer. temperature change = …… °C [2] (d) Explain why the temperature change decreases towards the end of each experiment. …… [1] (e) Explain what conclusion about the concentrations of solution G and solution H can be made from the results of Experiments 1 and 2. …… [2] (f) Explain how the results obtained would be different if a polystyrene cup is used instead of the beaker. …… [2] (g) Give an advantage and a disadvantage of using a burette rather than a measuring cylinder to add the dilute hydrochloric acid to solution G and solution H. advantage . …… disadvantage …… [2] [Total: 20]

Question

You are provided with solid I and solid J. Do the following tests on the substances, recording all of your observations at each stage. tests on solid I (a) To the boiling tube containing solid I add 15 cm3 of the dilute hydrochloric acid for Question 2. Test any gas produced. Keep the mixture in the boiling tube for (b). Record your observations. …… [3] (b) Carry out a flame test on the mixture formed in the boiling tube from (a). Record your observations. …… [1] (c) Identify solid I. …… [2] tests on solid J Add about 10 cm3 of distilled water to the boiling tube containing solid J. Replace the stopper and shake the boiling tube to dissolve solid J and form solution J. Divide solution J into four approximately equal portions in four test-tubes. (d) To the first portion of solution J add aqueous sodium hydroxide dropwise and then in excess. Record your observations. …… [2] (e) To the second portion of solution J add aqueous ammonia dropwise and then in excess. Record your observations. …… [2] (f) To the third portion of solution J add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. Record your observations. …… [1] (g) To the fourth portion of solution J add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. …… [1] (h) Identify solid J. …… [2] [Total: 14]

Question

Hydrogels are powders that absorb water to form hydrated solids. Hydrogels and the hydrated solids formed are insoluble in water. Plan an investigation to find which hydrogel, hydrogel A or hydrogel B, is able to absorb the greater mass of water. You are provided with samples of hydrogel A, hydrogel B, water and common laboratory apparatus. …… [6] Notes for use in qualitative analysis Tests for anions anion test test result carbonate (CO32–) add dilute acid effervescence, carbon dioxide produced chloride (Cl –) acidify with dilute nitric acid, then add white ppt. [in solution] aqueous silver nitrate bromide (Br –) acidify with dilute nitric acid, then add cream ppt. [in solution] aqueous silver nitrate iodide (I–) acidify with dilute nitric acid, then add yellow ppt. [in solution] aqueous silver nitrate nitrate (NO3–) add aqueous sodium hydroxide, then ammonia produced [in solution] aluminium foil; warm carefully sulfate (SO42–) acidify, then add aqueous white ppt. [in solution] barium nitrate sulfite (SO32–) add dilute hydrochloric acid, warm sulfur dioxide produced gently and test for the presence of will turn acidified aqueous sulfur dioxide potassium manganate(VII) 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 a white ppt., insoluble in excess 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 grey-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 iron(III) (Fe3+) red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc (Zn2+) white ppt., soluble in excess, giving a white ppt., soluble in excess, giving a colourless solution colourless solution Tests for gases Flame tests for metal ions gas test and test result metal ion flame colour ammonia (NH3) turns damp red litmus paper blue lithium (Li+) red carbon dioxide (CO2) turns limewater milky sodium (Na+) yellow chlorine (Cl 2) bleaches damp litmus paper potassium (K+) lilac hydrogen (H2) ‘pops’ with a lighted splint copper(II) (Cu2+) blue-green oxygen (O2) relights a glowing splint sulfur dioxide (SO2) turns acidified aqueous potassium manganate(VII) from purple to colourless