The article "Evaluating Vent Manifold Inerting Requirements: Flash Point Modeling for Organic Acid-Water Mixtures" (R. Garland and M. Malcolm, Process Safety Progress, 2002:254-260) presents a model to predict the flash point (in —¦F) of a mixture of water, acetic acid, propionic acid, and butyric acid from the concentrations (in weight %) of the three acids. The results are as follows. The variable "Butyric Acid ˆ— Acetic Acid" is the interaction between butyric acid concentration and acetic acid concentration.

a. Predict the flash point for a mixture that is 30% acetic acid, 35% propionic acid, and 30% butyric acid. (Note: In the model, 30% is represented by 30, not by 0.30.)
b. Someone asks by how much the predicted flash point will change if the concentration of acetic acid is increased by 10% while the other concentrations are kept constant. Is it possible to answer this question? If so, answer it. If not, explain why not.
c. Someone asks by how much the predicted flash point will change if the concentration of propionic acid is increased by 10% while the other concentrations are kept constant. Is it possible to answer this question? If so, answer it. If not, explain why not.

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Predictor Constant Acetic Acid Propionic Acid Butyric Acid Butyric Acid Acetic Acid Coef 267.53 -1.5926 1.3897 1.0934 -0.002658 SE Coef 11.306 0.1295 0.1260 0.1164 0.001145 23.66 12.30 -11.03 -9.39 2.32 0.000 0.000 0.000 0.000 0.034