Calculate [H3O+] in each aqueous solution at 25 C, and classify each solution as acidic or basic. a. [OH-] = 1.1 * 10-9 M b. [OH-] = 2.9 * 10-2 M c. [OH-] = 6.9 * 10-12 M

Water can undergo a special kind of ionization known as autoionization or self-ionization. This process is where a water molecule (H2O) donates a proton to another water molecule, leading to the formation of hydronium (H3O+) and hydroxide (OH−) ions. At 25°C, the equilibrium constant (Kw) for the autoionization of water is always 1.0 * 10^-14. This Kw value is derived from the product of the concentrations of these two ions, mathematically expressed as Kw = [H3O+] [OH-]. Understanding this fundamental concept is crucial when working with acid-base reactions and pH calculations. Because this establishes a direct relationship between H3O+ and OH− concentrations, knowing one allows us to calculate the other.

The pH scale is a measure of the acidity or basicity of an aqueous solution. It is defined as the negative logarithm (base 10) of the hydronium ion concentration. The formula to calculate pH is pH = -log[H3O+]. In a neutral solution at 25°C, the [H3O+] concentration is 1.0 * 10^-7 M, making the pH equal to 7. If the pH is below 7, the solution is acidic; if it is above 7, it is basic. When calculating the pH from a given hydroxide ion concentration (OH−), as seen in our exercises, one must first find the H3O+ concentration using the autoionization constant of water then apply the pH formula. The importance of mastering pH calculation is pivotal, as it helps to quantify the level of acidity or basicity, which can be an essential factor in chemical reactions, biological systems, and environmental science.

Acid-base classification is determined by comparing the hydronium and hydroxide ion concentrations in a solution. A solution is acidic if the concentration of hydronium ions (H3O+) is greater than that of hydroxide ions (OH−), basic if the opposite is true, and neutral if their concentrations are equal, typically at 1.0 * 10^-7 M. In the context of the exercises, after calculating H3O+, we compared it to the neutral H3O+ concentration to classify the solution's acid-base nature. This classification helps in identifying the properties of the solution, which in turn informs its potential reactivity, biological compatibility, and suitability for various industrial applications.