3. R1 Determine the effect of conc on rate of rxn_ Answer

10 Name: ___________________________( ) Class: _______ Date: __________ Rate of Reaction Skills: MMO: Manipulation, measurement, and observation PDO: Presentation of data and observations ACE: Analysis, conclusions and evaluation P: Planning Experiment R1: Concentration and Speed of Reaction (Modified from 5074/03/O/N/15) Aim: To investigate the effect of concentration on the speed of reaction Apparatus and chemicals 250 cm3 conical flask Burette 25 cm3 measuring cylinder Distilled water 10 cm3 measuring cylinder P: Aqueous solution of ammonium peroxodisulfate, (NH4)2S2O8 Stop watch Q: Aqueous solution containing iodide ions, I-, and another substance White tile Background When P and Q are mixed together, they react to produce iodine. S2O82- + 2I- → 2SO42- + I2 The addition of starch allows the iodine to be detected as the solution turns blue-black. Procedure 1. Put Q into a burette and use it to measure 10 cm 3 of Q into a conical flask. To Q in the flask, add 2 cm3 of starch solution using a 10 cm3 measuring cylinder. Place the flask and its contents on a white tile. 2. Measure 25 cm3 of P as accurately as possible, using a 25 cm3 measuring cylinder. Pour this volume of P rapidly into the mixture of Q and starch solution in the flask. Start the stopwatch immediately and swirl the contents of the flask, then leave the mixture to stand. When the mixture first turns blue -black, stop the stopwatch. Record the time to the nearest second in column E of the table. 3. Empty the conical flask and rinse it thoroughly with water. 4. Repeat the procedure described in step s 1 to 3 but in step 2 use the different volumes of P and water given in columns C and D of the table. For example in experiment 2, measure 20 cm3 of P as accurately as possible, using a measuring cylinder and then add water to P until the total volume of liquid in the measuring cylinder is 25 cm3. A B C D E Experiment no. Volume of Q / cm3 Volume of P / cm3 Volume of water / cm3 Time taken for blue-black colour to appear / s 1 10 25 0 17 2 10 20 5 23 3 10 15 10 35 4 10 10 15 56 5 10 5 20 115

11 (a) Plot a graph of time taken for the blue-black colour to appear (column E) against volume of P (column C) on the grid below. Draw a line of best fit.

12 (a) Compare the concentration of ammonium peroxodisulfate in experiment 2 and its concentration in experiment 4. The concentration of ammonium peroxodisulfate in experiment 2 is doubled / twice the concentration in experiment 4. (b) Explain, in terms of collisions between reacting particles, why the time taken for the blue-black colour to appear increases as the volume of P decreases. As the volume of P decreases, the concentration of P decreases. The number of particles per unit volume of solution decreases. As such, the particles collide less frequently, and the frequency of effective collision