1. Explain how different experimental errors can affect the reported value of Keq.

1. Explain how different experimental errors can affect the reported value of Keq. Clearly state why the reported value of Keq would be bigger or smaller than the actual value. Examples may include:

a) You thought the spectrometer was set to read trasmittance/absorbance at a wavelength of 447 nm, but it was actually set at 520 nm.

b) You thought you measured the transmittance/absorbance in a cuvetter with a 1-cm pathlength, but it was actually 1.5 cm.

2. Would your Keq results have been affected if you had chosen to use 5.00 mL of KSCN and altered the volume of Fe(NO3)3 solutions used?

Solutions

Expert Solution

Measurement of an equilibrium constant involves appropriate standards and titration to be done perfectly. This maybe achieved when the following conditions are met, while the errors can result in the as mentioned variation in values of K_eq -

a. Higher/Lower setting of the wavelength of spectrophotometer - When this occurs, either some of the ions show absorbance/transmittance depending on the setting. For instance, 470-477 nm is the best to determine [FeSCN]⁺², and in case any other setting is used, this affects the molar absorptivity (a) in the Beer's Law equation. Now, a rise in the value of a shall show higher absorbance and vice-versa. If more is the absorbance, higher is K_eq.

b. Path Length - Path length (b) is one of the factors that affects the Beer's Law equation. It is directly proportional to the absorbance, and in case b is higher, absorbance is higher and in turn K_eq is also higher.

A combination of factors in values of a and b, involving the changes in the wavelength can alter the observations dramatically.

c. Nitric Acid amount - Nitric acid prevents the precipitation reaction of Fe⁺³ with water, forming Ferric hydroxide. In case, less amount is used, then Fe⁺³ shall be precipitated and less amount of Ferric ions shall be available for the reaction, thereby making the observed K_eq lower than anticipated. This shall not be affecting the main titration reaction, since it does not involve H⁺ or NO₃^- which are a part of the dissociation of nitric acid.

d. Number of Data points - The linearization of the curve from which the slope states the K_eq, shall depend on the number of data points for less error, statistically less r².

2. No, if the change in the volume is done proportionately, nothing should be affected. It is because the molarity, i.e. concentration of the species involved in the reaction remains same.

queen_honey_blossom answered 1 year ago

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