This experiment was performed to determine the rate constant k, for hydrolysis of tertiary butyl chloride to tertiary butanol. The solvent system for this reaction is 45% isopropyl alcohol and 55% water. The rate of hydrolysis oft-butyl chloride is measured by the decrease in the concentration of this reagent with time. The rate of decomposition of t-butyl chloride must be equal to the rate of formation of hydrochloric acid.

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The rate of hydrochloric acid formation was measured by titrating the acid produced with a base, NaOH. Introduction The field of chemical kinetics studies the speed of chemical reactions and the reasons that affect the speed of a reaction. The speed of a chemical reaction is usually called the reaction rate. The reaction rate Is deflned as the change In concentration of a reactant’s or a product’s concentration per unit time. It is defined so that you will gain the same rate no matter which species in a chemical reaction Is chosen.

For this experiment, the rate of hydrochloric acid formation was measured by titrating the acid produced with a base. The order of reaction, as carried out by this method is first order. This reaction is first order because of the large excess of water present In the reaction mixture. The concentration of water does not change to any considerable extent during the reacuon and does not appear In the rate law. This experiment was an intermediate event and such a reaction is most often called hydrolysis and Is represented by the equation: C4H9Cl H20 C] C4HIOO HCI.

Experimental A burette was rinsed with 0. 25M sodium hydroxide. The burette was drained and refilled with the sodium hydroxide solution. 100mL of Isopropyl alcohol/water solvent was placed in a 100 mL volumetric flask. This solution was put into a 250 mL flask in a constant temperature water bath and the temperature of the bath and the contents of the flask were allowed to equilibrate. A thermometer was used to measure the solution temperature in the flask and recorded. The lab Instructor added exactly 1. 0 mL of

Page 2 Determination of the Rate Constant Essay

the t-butyl chloride to the flask. The reaction began on this addition and the hydrochloric acid began to produce. This was time “zero” and the stopwatch was started. The contents of the flask were swirled to facilitate the mlxlng and 2 mL of the 0. 25 M sodium hydroxide was added expeditiously. The exact mount of sodium hydroxide solution added to the flask was recorded and the solution turned pink. The pink color produced when sodium hydroxide was added, eventually faded due to the production of hydrochloric acid.

The time that had elapsed from the zero time of the t-butyl chloride addition to the color fade was recorded as well as the temperature. 2 mL of sodium hydroxide was added In 1 OF3 Increments ana tne tlmes ana temperature Tor tne color cnanges was recoroea Tor approximately 10 additions. At the end of the titrations the contents of the flask were kept and a stopper was placed on the flask and placed in the locker to titrate the xcess HCI produced at the next lab. The initial concentration oft-butyl chloride was calculated after the reaction had gone to completion.

The number of moles oft-butyl chloride present in the solution before the reaction is the total number of moles oft- butyl chloride added. This quantity is equal to the total moles of HCI produced after the reaction had gone to completion. The total moles of HCI were measured by titrating with sodium hydroxide and the initial moles of t-butyl chloride were determined. Results and Discussion The calculations for this experiment are shown in the following table and from this ata two graphs were made. Graph 1 shows [RCl]t versus time, t, in seconds.

Graph 2 shows ln[RCl]t versus time, t, in seconds. The first graph indicates the typical exponential decay curve and half-life is defined as the length of time it takes for the reactant to drop to half its initial concentration. The second graph is linear and the slope of the graph is -k and that value is -0. 0003 and R= 0. 999. Conclusion From the data and graphs, we can conclude that the total moles of HCI produced from the reaction of t-butyl chloride were calculated and were very close to the initial moles oft-butyl chloride added.

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