kinetics of phenolphthalein based on these lab results how would I find the rate

Question

kinetics of phenolphthalein

based on these lab results how would I find the rate constant for k

+NaOH +NaOH OH -H,0 COONa tri sodium salt (coloriess) phenolphthalein (colorless) di sodium salt (red) A simplified (and less intimidatingl) version of the equation is: PN OH (hydroxide) (phenolphthalein (sodium complex) The rate law for this reaction is inthe form: rate= k[PNPI0HP, where k is the rate constant for the reaction, m is the order with respect to phenolphthalein (PN), and n is the order with respect to the hydroxide ion. Since the hydroxide ion concentration is much larger than the concentration of phenolphthalein, [OH] will not change appreciably during this experiment. Thus, you will find the order with respect to phenolphthalein (m), but not the order with respect to hydroxide (n). As the reaction proceeds, a red reactant will be slowly changing to a colorless product. Using the light source of a colorimeter, you will monitor the absorbance over a period of time. We will assume that absorbance is proportional to the concentration of phenolphthalein (Beer's law). Absorbance will be used in place of concentration in plotting the following three graphs: . Absorbance vs. time: A linear plot indicates a zero order reaction (k=-slope). oe@k «a

Explanation / Answer

Kinetics of phenolphthalein

From the above data,

we see that we get straight line plot in case of ln[Abs] vs time plot

This is typical for a first-order reaction kinetics

Therefore the reaction follows a first-order rate law.

The slope of the straight line gives us the reaction rate constant -k

So,

slope = -k

or rate constant = -(slope)

Here the rate constant would be,

k = -(-2.21622 + 1.95998)/10 = 0.025624 (unit of 1/time)

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