Sodium Thiosulfate Reaction

eLearning 2009 Publication none 91860 Rate of Reaction of Sodium Thiosulfate and Hydrochloric Acid Rate Laws Introduction The purpose of this demonstration is to check up on the effect of sodium thiosulfate c erstntration on the rate of reception of sodium thiosulfate with hydrochloric acid. The answer, which turns solid sulfur, go out be followed by measuring the time needed for the chemical reaction mixture to become opaque. The results will be analyzed graphically to determine the order of reaction the mathematical relationship between the reactant dumbness and the rate.Concepts Kinetics fiat of reaction Rate law Concentration Materials Hydrochloric acid solution, HCl, 2 M, 25 mL Sodium thiosulfate solution, Na2S2O3, 0. 15 M, 150 mL Distilled or deionized water Beakers, 100-mL, 5 Graduated cylinders, 50- or 100-mL, 2 Graduated cylinders, 10-mL, 5 Overhead projector or light box Permanent marker Stirring rods Stopwatch or horologe Safety Precautions Hydrochloric acid solution is corrosive to eyeball and skin. It is moderately toxic by ingestion and inhalation. Sodium thiosulfate solution is a body tissue irritant.The reaction of sodium thiosulfate and hydrochloric acid generates sulfur dioxide gas, which is a skin and eye irritant. Perform this demonstration in a well-ventilated science laboratory only. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles, temperature-resistant gloves, and chemical-resistant apron. Please review current Material Safety Data Sheets for additional safety, handling, and disposal information. Procedure 1. Label five 100-mL beakers 15 and clean the bottom of each beaker. 2. Draw a large X across the bottom on the outside of each beaker.Place the beakers on an viewgraph projector stage or a light box so that students can view the X. 3. Using separate graduated cylinders for the solution and water, measure and add the unavoidable amounts of 0. 15 M sodium thiosulfate and distilled water to each beaker. Be as precise as possible. Beaker 0. 15 M Na2S2O3 Distilled Water 1 50. 0 mL 0 mL 2 40. 0 mL 10. 0 mL 3 30. 0 mL 20. 0 mL 4 20. 0 mL 30. 0 mL 5 10. 0 mL 40. 0 mL 4. Have students calculate the final denseness of sodium thiosulfate in each beaker 15. 91860 011509 Flinn ScientificTeaching Chemistry eLearning Video Series 5.Record the following information in a data table Beaker, volume of Na2S2O3 solution, volume of distilled water, concentration of Na2S2O3, reaction time (sec), and 1/reaction time (reaction rate). See the Sample Data and Results table in the Discussion section. 6. Measure 5. 0 mL of 2 M hydrochloric acid into each of five 10-mL graduated cylinders. 7. Starting with beaker 1, c arfully add the HCl all in one pour to the sodium thiosulfate solution. Stir the solution once with a stirring rod and immediately start timing. 8. Stop timing when the black X is no longer visible. Record the reaction time in seconds in the data table. . Repeat steps 7 and 8 w ith beakers 25. 10. Calculate 1/reaction time for each trial. Plot concentration vs. time and concentration vs. 1/time on separate graphs. judicature Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and precise procedures governing the disposal of laboratory waste. Collect the leftover reaction mixtures and filter to separate the solid sulfur product. The sulfur may be disposed of in a landfill according to Flinn Suggested Disposal Method 26a. The filtrate may be neutralized and disposed of down the drain with excess water according toFlinn Suggested Disposal Method 26b. Tips This activity may be performed as a chemical demonstration with classroom participation or as a student activity. The contents of the beakers project well on an overhead projector and the time to the disappearance of the black X is easily seen and measured. The reaction may be downsized for a student lab activity. Carry out individual trials in separate wells in a 6-well reaction plate or in small medicine cups. If students will be doing the experiment in the lab, it is a good idea for them to start with beaker 5, because it takes the longest time. The activity may also be performed as a accommodative class exercise with different groups investigating different variables, including the effect of HCl concentration and the effect of temperature. The reaction rate is zero-order with respect to HCl. Empty the beakers and clean them thoroughly utilise paper towels to remove the sulfur. If the colloidal sulfur is allowed to sit in the beakers for an extended time, it will be much more difficult to remove the deposits from the glass. To achieve wagerer mixing of the reactants, add the hydrochloric acid using a 10-mL luer-lock plastic syringe (without needle).Squirt the acid using a fair amount of force. When lower concentrations of sodium thiosulfate are used, the rate law does not appear to be as simple as predicted in this experiment. At lower concentrations, the reaction appears to be closer to 3/2-order in sodium thiosulfate and 1/2-order in hydrochloric acid. The reaction time is more difficult to measure at lower concentrations because the onset of turbidity is more gradual. both the overall chemical equation and the mechanism for the decomposition of sodium thiosulfate are more complex than suggested by Equation 1.The reaction is acid-catalyzed, which means that the acid concentration must have some bearing on the rate in terms of producing an equilibrium concentration of HS2O3 ions, The HS2O3 ion is a reactive intermediate, reacting further with additional S2O32 ions to produce polymeric ions containing multiple S atoms. When the chain of S atoms in a polymeric ion becomes long enough, it closes in on itself to form a ring of master(a) sulfur (S8). S2O32 + H+ HS2O3 HSSO3 + nS2O32 HS(S)nSO3 + nSO32 HSSnSO3 H+ + SSnSO3 SS7SO3 S8 + SO32 2 2009 Flinn Scientific, Inc. altogether Rights Reserve d. 91860 Discussion Sodium thiosulfate reacts with hydrochloric acid to form sulfur and sulfur dioxide (Equation 1). Na2S2O3(aq) + 2HCl(aq) S(s) + SO2(g) + 2NaCl(aq) Equation 1 The kinetics of the reaction can be analyzed by graphing the concentration of Na2S2O3 as a function of both reaction time and 1/time. A plot of concentration versus time gives a curved line, which levels off as it approaches the x-axisthe reaction slows down as the reactant concentration decreases. The rate of a reaction is inversely proportional to reaction time.A plot of concentration of versus 1/time gives a straight line. The rate is directly proportional to concentration, and the reaction appears to be first order with respect to sodium thiosulfate concentration. Sample Data and Results Beaker 1 2 3 4 5 Volume of Na2S2O3 (mL) 50 40 30 20 10 Volume of H2O (mL) 0 10 20 30 40 Na2S2O3, M 0. 15 0. 12 0. 090 0. 060 0. 030 Reaction time (sec) 22. 5 27. 3 35. 1 60. 0 159. 1 Reaction rate (1/time, sec1) . 0444 . 0367 . 0285 . 0167 . 00629 180 clx 140 120 100 80 60 40 20 0 0. 00 Effect of concentration on reaction time 0. 05 0. 10 0. 15 0. 20 Na 2 S2 O3 Concentration, M 0. 07 0. 6 0. 05 0. 04 0. 03 0. 02 0. 01 0 0. 00 Effect of concentration on reaction rate 0. 05 Na 2 S2 O3 Concentration, M 0. 10 0. 15 0. 20 3 2009 Flinn Scientific, Inc. All Rights Reserved. 91860 Connecting to the National Standards This laboratory activity relates to the following National Science Education Standards (1996) Unifying Concepts and Processes Grades K12 Evidence, models, and write up Constancy, change, and measurement Content Standards Grades 912 Content Standard A Science as Inquiry Content Standard B Physical Science, organize and properties of matter, chemical reactions, motions and forcesFlinn ScientificTeaching Chemistry eLearning Video Series A video of the Rate of Reaction of Sodium Thiosulfate and Hydrochloric Acid activity, presented by Annis Hapkiewicz, is available in Rate Laws, part of the Fli nn ScientificTeaching Chemistry eLearning Video Series. Materials for Rate of Reaction of Sodium Thiosulfate and Hydrochloric Acid are available from Flinn Scientific, Inc. Materials required to perform this activity are available in the Reaction Order and Rate LawsStudent Laboratory Kit available from Flinn Scientific.Materials may also be purchased separately. Catalog No. Description AP4864 H0034 S0114 AP1572 GP1010 GP2005 GP2015 Reaction Order and Rate LawsStudent Laboratory Kit Hydrochloric Acid, 3 M, 500 mL Sodium Thiosulfate Pentahydrate, Reagent, 500 g Timer, Stopwatch, Flinn Beaker, Borosilicate Glass, 100 mL Graduated Cylinder, Borosilicate Glass, 10-mL Graduated Cylinder, Borosilicate Glass, 50-mL Consult your Flinn Scientific Catalog/Reference Manual for current prices. 4 2009 Flinn Scientific, Inc. All Rights Reserved. 91860