Q: Which equation is used to calculate the initial rate of the reaction from absorbance data, as described in the experiment?

$$\text{Rate} = \dfrac{\Delta A}{\Delta t}$$

Question 1

Which of the following best describes the primary objective of the experiment involving potassium iodide (KI) and iron(III) chloride (FeCl$$_3$$)?

Accepted Answer

To determine the effect of reactant concentrations on the reaction rate and deduce the rate law

Question 2

In the experiment, why is it important to fill the cuvette with distilled water and wipe it with a lint-free tissue before measuring absorbance?

Accepted Answer

To remove any impurities or residues that could interfere with the absorbance measurement

Question 3

Given the following data for Trial 1: 10.0 mL of 0.020 M FeCl$$_3$$ and 10.0 mL of 0.020 M KI are mixed, and the total volume is brought to 20.0 mL. What is the final concentration of FeCl$$_3 in $$the reaction mixture?

Accepted Answer

$$0.010\ \mathrm{M}$$

Question 4

Why is it necessary to record the absorbance of the reaction mixture at regular time intervals after mixing KI and FeCl$$_3$$?

Accepted Answer

To monitor the progress of the reaction and calculate the initial rate

Question 5

If the initial rate of the reaction doubles when the concentration of KI is doubled (with FeCl$$_3$$ constant), what is the order of the reaction with respect to KI?

Accepted Answer

First order

Question 6

A student accidentally introduces air bubbles into the cuvette before measuring absorbance. What is the most likely effect on the absorbance reading?

Accepted Answer

The absorbance reading will be artificially low due to scattering of light by the bubbles

Question 7

Which equation is used to calculate the initial rate of the reaction from absorbance data, as described in the experiment?

Accepted Answer

$$	ext{Rate} = \dfrac{\Delta A}{\Delta t}$$

Question 8

Suppose the absorbance vs. time graph for a trial is nonlinear and curves downward. What does this indicate about the reaction?

Accepted Answer

The reaction rate is decreasing as the reactants are consumed

Question 9

If the initial rate of the reaction is found to be independent of the concentration of FeCl$$_3$$, what is the order of the reaction with respect to FeCl$$_3$$?

Accepted Answer

Zero order

Question 10

During the experiment, why is it important to always position the cuvette so that light passes through the clear sides?

Accepted Answer

To ensure accurate and consistent absorbance measurements

Question 11

A student mixes 10.0 mL of 0.020 M FeCl$$_3$$ with 5.0 mL of 0.020 M KI and 5.0 mL of water. What is the concentration of KI in the final 20.0 mL mixture?

Accepted Answer

$$0.005\ \mathrm{M}$$

Question 12

Which of the following best explains why the initial rate is determined using the first few seconds of data after mixing the reactants?

Accepted Answer

The reactant concentrations are highest and have not changed significantly

Question 13

If the rate law for the reaction is $$	ext{Rate} = k[\mathrm{KI}]^1[\mathrm{FeCl}_3]^0$$, what will happen to the rate if the concentration of FeCl$$_3 is $$doubled while KI is kept constant?

Accepted Answer

The rate will remain unchanged

Question 14

A student forgets to calibrate the spectrometer before starting the experiment. What is the most likely consequence?

Accepted Answer

The absorbance readings may be inaccurate, affecting the calculated reaction rates

Question 15

Which of the following is a valid reason for using a time-based data collection mode with a rate of 0.5 samples/second in this experiment?

Accepted Answer

To ensure enough data points are collected to accurately determine the initial rate

Question 16

If the absorbance of the first data point is 0.200 and it takes 10 seconds to reach this value, what is the initial rate using Method 2 ($$	ext{Rate} = \dfrac{	ext{absorbance}}{	ext{time}}$$)?

Accepted Answer

$$0.020\ \mathrm{s}^{-1}$$

Question 17

In a real-world scenario, why might understanding the rate law of a reaction like that between KI and FeCl$$_3 be $$important in an industrial setting?

Accepted Answer

It allows for optimization of reactant concentrations to maximize product formation and efficiency

Kinetics of the Reaction Between Potassium Iodide and Iron(III) Chloride: Experimental Procedure and Data Analysis

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