Aim: To see how changing the concentration of Hydrochloric Acid affects the rate of reaction. Prediction: In this experiment I predict that the more diluted the acid is, the longer it takes for it to react. For example, If 2 molar HCL added to X molar Na2S2O3 took 40sec to react, 1 molar HCL added to X molar Na2S2O3 will take 80sec to react. This is my prediction of the results table (not necessary the times, but the pattern of the times and rate) HCL(cm3) H20(cm3) Na2S2O3(cm3).

Time (sec) Rate (sec) (1/X) (2mol/dm3) 25(from bottle A) (1mol/dm3) 25(from bottle B) 0(0. 5mol/dm3) 12. 5(from bottle B)  (0. 25mol/dm3) 6. 25(from bottle B)  (0. 125mol/dm3) 3. 125(from bottle B) .

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I believe this will happen because each time the acid becomes more diluted, the amount of acid particles is halved. Therefore if there are half of the acid particles to react with, the time must be doubled because it will take twice as long for the Sodium Thiosulphate particles to collide with the Hydrochloric acid particles.

Also the rate of reaction is halved each time, there for it will take double the time to react. Although the particles may hit each other, they need to have hit each other hard enough to reach activation energy. It is when they reach activation energy is when they react with each other. The rate of the reaction is when more successful collisions happen per second. The reason why the rate of reaction is faster when the solution is more concentrated is that the ions are closer together in a concentrated solution. The closer together they are the more frequent do the ions collide. Method and Equipment:

Equipment –  Beakers – To put both of the reactants in/diluted Acid  Measuring cylinders – To measure out the right measurements for the dilutions and Sodium Thiosulphate.  Black cross – To place underneath the beaker that has both of the reactants in.  Distilled water – Used for diluting the HCL and washing out the equipment.  Bottle A = 2mol/dm3 Hydrochloric Acid Bottle B = 1mol/dm3 Hydrochloric Acid Method: 1. Set up equipment, put everything needed for Hydrochloric acid on one side and mark it A, and everything needed for the Sodium Thiosulphate on another side of the table marked B.

This is so there is no contamination of the two liquids making the test unfair. 2. Make Acid dilutions. To make less than (1mol/dm) use the bottle of (1mol/dm) Hydrochloric Acid, for the (2mol/dm) there is a designated bottle. (Make enough for the experiment to be repeated 3 times) (Xmol/dm3) HCL(cm3) H20(cm3) 2(from bottle A) 100 0 1(from bottle B) 100 0 0. 5 (from bottle B)(from bottle B) 2. After making all of the dilutions, wash equipment with distilled water; place the black cross underneath a clean beaker. 4.

Add both liquids (following the measurement table below) to the beaker and time how long it takes until the cross cannot be seen. Make dilutions for, this will allow for results to be even more reliable so we can check in between the acid dilutions as I original predicted. (Xmol/dm3). Repeat each dilution three times to get an average. Fair Test:  Na2S2O3 25cm3 each time.

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