A white salt-like compound – what is it? - simulation of laboratory exercises Jens Josephsen Science Department (Institut for Natur, Systemer og Modeller) Roskilde University Denmark IYC Nordic Chemistry Teachers Conference1

Roles of experimental and practical work: to get experience with phenomena to practice academic processes to practice skills (White 1996) IYC Nordic Chemistry Teachers Conference2

to get experience with inorganic compounds laboratory investigations written problems IYC Nordic Chemistry Teachers Conference3

Possible elements of an ”unknown” inorganic compound Typically a simple salt (solid or in solution) Li +, Na +, K +, H (in HX, H 2 O, OH - ) B (in borates), O (in oxyanions and H 2 O) C +4 (as H x CO 3 (2-x)- ) N+5, +3, and -3 (as NO 3 -, NO 2 -, NH 4 + ) P+5 (as H x PO 4 (3-x)- ) S+6, +4, +2, and -2 (as H x SO 4 (2-x)-, H x SO 3 (2-x)-, S 2 O 3 2-, S 2- ) Cl +5, +3, +1, and -1 (as ClO x - ) Br, I +7, +5, +3, +1, and -1 (as BrO x -, IO x - ) 20 hours lab-investigation, students working in pairs IYC Nordic Chemistry Teachers Conference4

Standard laboratory procedures Laboratory manuals for Qualitative analysis (semi micro or micro) Quantitative analysis (mainly volumetric) IYC Nordic Chemistry Teachers Conference5

to get experience with inorganic compounds laboratory investigations written problems IYC Nordic Chemistry Teachers Conference6

Written problems example: (formulated mainly at the macroscopic level, following lab-procedures) A white crystalline compound A is soluble in water. The conductivity is proportional to concentration. Flame colour is violet. Air passed through an acid solution of A, and then directed through a solution of barium hydroxide gives a white precipitate B. B is isolated and treated with aqueous potassium triiodide until a brown colour appears and the white residue C is insoluble in hydrochloric acid (4M). The component giving rise to the violet flame colour is quantified: Its concentration is found as 18mM in a solution of 43.7 mg A in 25 ml of water mg of A is dissolved in 10 ml of sulphuric acid (.125M) and the solution boiled while air is passed through. After cooling the solution is titrated with 16.6 ml sodium hydroxide (.100M) while added phenolphthalein turns red. What is the composition of the white salt A? (K 2 SO 3 ∙2H 2 O) IYC Nordic Chemistry Teachers Conference7

to get experience with inorganic compounds laboratory investigations written problems computer simulation IYC Nordic Chemistry Teachers Conference8

(eller../KCO2) IYC Nordic Chemistry Teachers Conference9

What did we learn ? Interactive self-instructive IT-resources may function as a valuable supplement if properly co- ordinated with other teaching and learning activities A tailored simulation programme may support teaching and scaffold student learning - it leaves capacity in the short time memory for thinking. Co-working between pairs of students support learning IYC Nordic Chemistry Teachers Conference10

Simulation of laboratory exercises -extends laboratory time Jens Josephsen Science Department (NSM) Roskilde University Denmark IYC Nordic Chemistry Teachers Conference11 Thank you for being here Please comment on: in your opinion does it fit with upper sec. school A-level? do your students know the chemistry of simple salts like NH 4 NO 3 (acid-base, redox, solubility)

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What did we learn ? Interactive self-instructive IT-resources may function as a valuable supplement if properly co- ordinated with other teaching and learning activities. A tailored simulation programme may support teaching and scaffold student learning - it leaves capacity in the short time memory for thinking. Co-working between pairs of students support learning IYC Nordic Chemistry Teachers Conference27

Written problems example: ( formulated mainly at the macroscopic level) 960 mg of the reducing component (A) in ”Cowboy-matches” was burned off in an atmosphere of pure oxygen (1 atm) in a closed glass container, equipped with a little water. The formation of a white compound (B) was observed. When shaking the container and then opening it, air was obviously sucked in. The aqueous solution was strongly acidic. The white compound B was dissolved in the solution, which was made up to ml (solution C). To a drop of solution C was added aqueous barium chloride (0.1 M), and a white precipitate was formed. To a hot, acidic solution of ammonium molybdate was added a drop of solution C. A yellow precipitate was formed. No other components was identified Potentiometric titration of 4.00 of solution C with 1.00 M sodium hydroxide revealed a jump in pH (3-6) at 1.76 ml and another jump (8- 11) at 2.46 ml. ( numbers not given in the text, but taken from the original titration curve shown in the text ) Find the formula and name of the reductor A.(Found:P 4 S 3 ) IYC Nordic Chemistry Teachers Conference28