Chemistry 0620/51 May/June 2023: question paper and mark scheme

Question

You are going to investigate the reaction between aqueous ammonia and two different aqueous solutions of copper(II) sulfate labelled A and B. Solutions A and B have different concentrations. Read all of the instructions carefully before starting the experiments. Instructions You are going to do two experiments. (a) Experiment 1 ● Fill a burette with solution A. Run some of solution A out of the burette so that the level of solution A is on the burette scale. ● Record the initial burette reading in Table 1.1. ● Use the measuring cylinder to pour 25 cm3 of the aqueous ammonia into the conical flask. ● Stand the conical flask on a white tile. ● Slowly add solution A from the burette to the conical flask, while swirling the flask, until the mixture in the conical flask just starts to become cloudy. ● Record the final burette reading in Table 1.1. Experiment 2 ● Empty the conical flask and rinse it with distilled water. ● Empty the burette and rinse it with distilled water. ● Rinse the burette with solution B. ● Repeat Experiment 1 using solution B instead of solution A. ● omplete Table 1.1. C Table 1.1 Experiment 1 Experiment 2 using solution A using solution B final burette reading / cm3 initial burette reading / cm3 volume of aqueous copper(II) sulfate added / cm3 [4] (b) Explain why a white tile is used during the titration. . …… . …… [1] (c) In Experiment 2 the burette and the conical flask are both rinsed with water. The burette is then rinsed with solution B. (i) State why both the burette and the conical flask are rinsed with water. . …… [1] (ii) Explain why the burette is then rinsed with solution B. . …… . …… [1] (iii) Describe how the result of Experiment 2 would be different if the conical flask is rinsed with aqueous ammonia after rinsing with water. Explain your answer. . …… . …… [2] (d) (i) Deduce which solution of copper(II) sulfate, A or B, is more concentrated. Explain your answer. . …… . …… [1] (ii) Deduce how many times more concentrated this solution of copper(II) sulfate is than the other solution of copper(II) sulfate. . …… [1] (e) Describe how the reliability of the results obtained can be checked. . …… . …… [1] (f) Deduce the volume of solution A required when Experiment 1 is carried out with 10 cm3 of aqueous ammonia. . …… [2] (g) In Experiments 1 and 2, the volume of aqueous ammonia is measured using a measuring cylinder. Give an advantage and a disadvantage of using a volumetric pipette instead of a measuring cylinder to measure the volume of aqueous ammonia. advantage . …… disadvantage …… [2] [Total: 16]

Question

You are provided with solid E. Do the following tests on solid E, recording all of your observations at each stage. Tests on solid E Divide solid E into two approximately equal portions in two boiling tubes. (a) Gently heat the first portion of solid E. Record your observations. . …… . …… [2] (b) State what conclusion can be made about solid E from the observations in (a). . …… . …… [1] Add about 15 cm3 of distilled water to the boiling tube containing the second portion of solid E. Place a stopper in the boiling tube and shake the tube to dissolve solid E and form solution E. Divide solution E into seven approximately equal portions in one boiling tube and six test-tubes. (c) To the first portion of solution E in the boiling tube, add aqueous sodium hydroxide dropwise and then in excess. Keep the product for use in (d). Record your observations. dropwise …… in excess . …… [2] (d) Transfer about 2 cm depth of the product from (c) into a clean boiling tube. Warm the mixture gently. Test and identify the gas produced. . …… . …… identity of gas …… [2] (e) To the second portion of solution E, add about 1 cm depth of aqueous sodium thiosulfate. Leave the mixture to stand for about three minutes. Record your observations. . …… . …… [2] (f) To the third portion of solution E, 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 E, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. . …… . …… [1] (h) To the fifth portion of solution E, add about 2 cm depth of aqueous sodium carbonate. Record your observations. . …… . …… [1] (i) To the sixth portion of solution E, add about 1 cm depth of aqueous potassium iodide followed by about 1 cm depth of starch solution. Record your observations. . …… . …… [2] (j) To the seventh portion of solution E add a few drops of acidified aqueous potassium manganate(VII). Record your observations. . …… . …… [1] (k) Identify the three ions in solid E. . …… . …… [3] [Total: 18]

Question

Solid cobalt(II) oxide is a base which is insoluble in water. It reacts very slowly with cold dilute sulfuric acid to form a solution of cobalt(II) sulfate. Describe how to make pure, dry crystals of hydrated cobalt(II) sulfate. You are provided with cobalt(II) oxide, dilute sulfuric acid 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