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Chemistry Concerntration Analysis

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Chemistry Concentration Investigation Aim This investigation was conducted to see how changing the acid concentration affects the reaction rate between Potassium Iodide and Potassium Peroxydisulphate using a clock reaction. 2KI(aq) + K2S2O8(aq) � l2(aq) + 2K2SO4 (Reaction 1) (CLOCK PROCESS= l2(aq)+2Na2S2O3(aq) � Na2S2O6(aq) + 2NaI(aq)) Background When Potassium Iodide and Potassium Peroxydisulphate, the mixture turns to a blue/black colour. There are two main methods for carrying out this experiment, one is the Clock Process, in which white card is placed under the reaction and the clock is stopped manually when the white card is no longer visible. This method is extremely straight forward, but may not be very accurate, as the clock is stopped manually when the card cannot be seen. There may be some inaccuracy in judging when the card is no longer visible, as we are simply using the naked eye. Also, human's reactions are limited to around a tenth of a second; therefore, the stopping of the stopwatch may not be precise. The other method would be to use a Colorimeter which electronically detects and records the change of colour in the reaction. ...read more.


I was originally going to use Test Tubes, but I found Boiling Tubes more suitable due to their larger width, which enabled me to see the reaction more clearly, and therefore determine when the white card was out of view. Stopwatch To time how long the reaction takes at the specified concentration. The stopwatch is being used to give an accurate measurement of time, the only limitation is how fast a human is able to stop the clock. Potassium Iodide Solution Potassium Peroxydisulphate Solution Sodium Thiosulphate Solution Starch Solution 2.5cm� Graduated Plastic Pipettes To measure out each chemical. The pipettes are extremely accurate in measuring out liquids, therefore, they should give a precise measurement. White Card To place underneath each Boiling Tube to determine when each reaction has fully completed. Test Tube To contain the Potassium Peroxydisulphate before adding it to the Boiling Tube The Test Tube should be clean and new, it should be in perfect condition to prevent leakages. The Test Tube will effectively contain the chemical. Variables Same The same card - otherwise there may be a slight variation in colour which could lead to a misjudgement of when the reaction is complete Stopclock - There may be a slight difference in time if ...read more.


* Place the White Card with a black cross on it directly under the Boiling Tube * Add the Potassium Peroxydisulphate from the Test Tube to the Boiling Tube, and immediately start the stopwatch. * Mix the liquid with 4 even stirs, use 4 even stirs for each concentration to ensure each test is completely fair. * Observe the colour change of the liquid, look at the White Card through the liquid, from above. Immediately stop the stopwatch when the White Card is out of visibility due to the colour change of the liquid. * Record the result in a table as shown below- * Conduct the exact same test twice more, and record the results in the allocated space in the Results Table. Make sure that all environmental conditions (temperature etc.), hygiene conditions and stirs are kept the same. * The proceed to make the 2nd concentration by adding 1cm� of water to the Boiling Tube with the other chemicals. * Repeat the experiment on the 2nd concentration and record all results on the Results Table * Then create the 3rd concentration by adding 2cm� of water to the Boiling Tube and so on, until you have tested 5 concentrations, up to 4cm� of water. Each should have been tested 3 times, so in all, 15 tests have been conducted. ...read more.

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