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Analysis of Two Brands of Commercial Bleaches

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PLK TANG YUK TIEN COLLEGE ADVANVED LEVEL CHEMISTRY (TAS) EXPERIMENT 3 Analysis of Two Brands of Commercial Bleaches Objective To determine the concentration of sodium chlorate(I) (NaClO) in two commercial bleaches and compare the two bleaches on both concentration and price. Procedures 1. 10.0 cm3 of the bleach "KAO" was pipetted into a clean 250 cm3 volumetric flask. It was made up to the mark using deionized water. 2. 25.0 cm3 of the diluted solution was pipetted into a conical flask. 3. 10 cm3 of 1 M potassium iodide solution and 10 cm3 of dilute sulphuric acid was added into the conical flask also. 4. The mixture in the conical flask was titrated against the 0.0992 M sodium thiosulphate solution. 5. Three drops of freshly prepared starch indicator are added into the conical flask when the reaction mixture turned pale yellow . 6. The mixture was titrated to the end-point. 7. At the end point, the solution turned from dark blue to colourless. 8. Steps (1) to (7) were repeated with another bleach "LION" Results Concentration of standard sodium thiosulphate solution : 0.0992M Brand 1 Trade Name : KAO Bleach Price : $7.33per dm3 ($11/1500mL) ...read more.


of mole of S2O32- )/2 =0.00069936mol ?no. of mole of OCl- in10 cm3 solution = no. of mole of I2 x10 =0.00069936x10 =0.0069936mol ?Mass of OCl- contained in 10 cm3 solution=0.0069936x(16+35.45) =0.35982072g ?Concentration of OCl- (active ingredient available) =0.35982072/(10/1000)=35.98gdm-3 1b)For KAO Bleach, Cost per one gram of OCl- = 11 /[29.474676x(1500/1000)] =$0.277/g For LION Bleach, Cost per one gram of OCl- = 10 /[35.982072x(1500/1000)] =$0.185/g 2. Based on the calculated results, decide which of the two brands of bleach is a better buy. When compring the costs per one gram of OCl- of KAO(0.277/g) and LION($0.185/g), as we can pay a lower price ($0.185)to buy the same weight of active ingredient (OCl- ) in LION bleach, LION bleach is a better buy. 3. Explain why potassium iodide and sulphuric acid must be in excess. ClO-(aq) + 2I-(aq) + 2H+(aq) � I2(aq) + H2O(l) + Cl-(aq) From the equation above, iodide ions and hydrogen ions react with Hypochlorite ions to form iodine ,water and chloride ions.To determine the actual number of mole of ClO- ,all ClO- ions sholud react to give iodine. ...read more.


When sodium hypochlorite is heated or evaporated, sodium chlorate and sodium chloride will be formed. Chemical equation: 3 NaOCl(aq) � NaClO3 (aq)+ 2 NaCl(aq) 5. The starch indicator should not be added too early. Why? Starch is often used in chemistry as an indicator for redox titrations where iodine is present as starch forms a very dark blue-black complex with iodine. Moreover,the indicator is not affected by the presence of iodide (I-). In order for the the starch solution to change colour, both starch and iodide must be present. Starch forms an unstable complex which is blue coloured in low concentrations of iodine. However, this complex is in high concentrations of iodine . If starch solution is added too early, the conical flask still contains high concentration of iodine.As a result, highly stable complex is formed,the starch indicator then cannot be decolourised and the complex will spoil the reaction medium. Consequently, the titration cannot continue. Therefore the iodine must be diluted first with the titrant ,sodium thiosulphate to ensure no higly stable complex is formed.After that the starch can be added. The End ?? ?? ?? ?? F.6 Chemistry TAS/Experiment 3/P.1(3) 1 ...read more.

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Response to the question

The response to the question is done to a very high level. With the combination of accuracy and scientific detail the experiment is flawless in calculations. The improvements would be to add an evaluation of where the experiment could have ...

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Response to the question

The response to the question is done to a very high level. With the combination of accuracy and scientific detail the experiment is flawless in calculations. The improvements would be to add an evaluation of where the experiment could have been improved and what errors may have occurred to show an understanding of how the experiment went.

Level of analysis

The candidate should include in their introduction why they are examining sodium chlorate(I) in their experiment, such as what significance this has to the action of the bleach. The procedure is recorded very clearly and would be easy to follow. The questions are answered to a very high level of detail and the calculations are all correct. Decimal places lack consistency in places.

Quality of writing

Grammar, spelling and punctuation to an high standard. Good, clear format.

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