Question

All of the following are TRUE for activities and activity coefficients, except: A) activity for a chemical species is the product of concentration and activity coefficient. B) the activity coefficient corrects for non-ideal behavior due to ionic strength. C) as ionic strength increases, the value of the activity coefficient increases. D) for ions, the activity coefficient approaches unity as the ionic strength approaches 0. E) the activity coefficient for neutral molecules is approximately unity.

Answer 1

The incorrect statement is that the activity coefficient increases as ionic strength increases. In fact, it decreases and approaches unity as ionic strength approaches zero.

Step-by-step explanation:

The statement among the given options that is NOT TRUE regarding activities and activity coefficients is C) as ionic strength increases, the value of the activity coefficient increases. The correct relationship is that as ionic strength increases, the activity coefficient generally decreases, approaching unity as the ionic strength approaches zero. This is because the activity coefficient accounts for the non-ideal behavior in solutions, particularly due to electrostatic interactions between ions which are more prominent at higher ionic strengths.

The activity of a chemical species is indeed the product of concentration and activity coefficient, which corrects for deviations from ideal behavior. The activity coefficient is closer to one for dilute solutions, indicating less deviation from ideal behavior. For neutral molecules, the activity coefficient is typically taken as approximately unity.

Answer 2

C) as ionic strength increases, the value of the activity coefficient increases.

Step-by-step explanation:

The effective concentration of ions available for reactions is known as the activity of the ion.

The activity coefficient important in chemistry because it accounts for the deviation of a solution from ideal behaviour.

The activity of a chemical species is defines as the product of concentration and activity coefficient.

Following the Debye–Hückel limiting law; log γ = −0.509z2I1/2. The ionic strength of a solution tends to increase as the activity coefficient (γ) of the ion decreases.