Chemistry 0620/52 February/March 2025: question paper and mark scheme

Question

You are going to investigate the temperature change when aqueous copper(II) sulfate reacts separately with two different metals, zinc and iron. Read all of the instructions carefully before starting the experiments. Instructions You are going to do two experiments. (a) Experiment 1 • Use the 50 cm3 measuring cylinder to pour 30 cm3 of aqueous copper(II) sulfate into the 100 cm3 beaker. • Use the thermometer to measure the temperature of the contents of the beaker. • Record this temperature in Table 1.1 at time = 0 s. • Add 3 g of zinc powder to the beaker. At the same time start the stop-watch. • Using the thermometer, continually stir the mixture in the beaker. • Measure the temperature of the mixture every 30 seconds for 210 seconds. • Record the temperatures in Table 1.1. • Complete Table 1.1 by calculating the temperature changes from the temperature at 0 s. • Empty and rinse the beaker with distilled water. Table 1.1 time in s 0 30 60 90 120 150 180 210 temperature in °C temperature change 0.0 since time = 0 s in °C Experiment 2 • Repeat Experiment 1, using 3 g of iron powder instead of 3 g of zinc powder. • Record your results in Table 1.2, and complete Table 1.2 by calculating the temperature changes from the temperature at 0 s. Table 1.2 time in s 0 30 60 90 120 150 180 210 temperature in °C temperature change 0.0 since time = 0 s in °C [5] (b) Complete a suitable scale on the y-axis, and plot your results for Experiment 1 and Experiment 2 on Fig. 1.1. The point at (0,0) has been plotted for you. Draw two curves of best fit. Both curves must start at (0,0). Label both curves. temperature change since time = 0 s in °C 0 0 50 100 150 200 250 time in s Fig. 1.1 [5] (c) Extrapolate the curve for Experiment 1 on your graph in Fig. 1.1 to deduce the temperature change since time = 0 s in Experiment 1 after 240 seconds. Show clearly on Fig. 1.1 how you worked out your answer. temperature change = …… [3] (d) State which experiment, Experiment 1 or Experiment 2, is the more exothermic. Explain your answer. more exothermic experiment …… explanation …… [1] (e) Predict the temperature of the solution in Experiment 1 after 3 hours. temperature after 3 hours = …… °C [1] (f) Explain why using a copper container instead of the beaker would not be an improvement in this investigation. …… [1] (g) Describe two changes to the apparatus that will improve the results of this investigation. For each change, explain why it will improve the results. change 1 …… explanation 1 …… change 2 …… explanation 2 …… [4] [Total: 20] Question 2 starts on the next page.

Question

You are provided with two substances: solution A and solid B. Do the following tests on solution A and solid B. Record all of your observations at each stage. Tests on solution A Divide solution A into four approximately equal portions in one test-tube and three boiling tubes. (a) To the first portion of solution A in a boiling tube, add about 3 cm depth of aqueous sodium carbonate. Record your observations. …… [1] (b) To the second portion of solution A in a boiling tube, add aqueous ammonia dropwise until it is in excess. Record your observations. …… [2] (c) To the third portion of solution A in a boiling tube, add aqueous sodium hydroxide dropwise until it is in excess. Record your observations. …… [2] (d) To the fourth portion of solution A in the test-tube, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Leave the mixture to stand for a few minutes. Record your observations. …… [1] (e) Identify solution A. …… [2] Tests on solid B (f) Carry out a flame test on solid B. Record your observations. …… [1] Transfer the remaining solid B to a boiling tube. Add about 5 cm depth of distilled water to the boiling tube. Place a stopper in the top of the boiling tube, and shake the boiling tube to dissolve solid B. The solution formed is solution B. Divide solution B into three approximately equal portions in three test-tubes. (g) To the first portion of solution B, add a few drops of acidified aqueous potassium manganate(VII). Record your observations. …… [1] (h) To the second portion of solution B, add about 1 cm depth of aqueous sodium hydroxide. Record your observations. …… [1] (i) To the third portion of solution B, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. Record your observations. …… [1] (j) Identify solid B. …… [2] [Total: 14]

Question

Metal spoons can be electroplated with silver. Describe how a metal spoon can be electroplated with silver. Include in your answer how you could determine the mass of the silver electroplated onto the metal spoon. You are provided with solid silver nitrate, a metal spoon, a piece of solid silver, distilled water and common laboratory apparatus. You must include a diagram in your answer. …… [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