In an acidic solution, why is the OH- concentration lower than it is in pure water?
Because (H^+)(OH^-) = Kw which means
if H^+ goes up, OH^- must go down. If H^+ goes down, OH^- most go up. The product will always be 1E-14.
In an acidic solution, the OH- concentration is lower than it is in pure water due to the presence of excess H+ ions. Here's a step-by-step explanation:
1. In pure water, a small percentage of water molecules dissociate into H+ ions (protons) and OH- ions. This dissociation occurs because water molecules can transfer protons between each other through a process called autoionization.
2. In an acidic solution, there is an excess of H+ ions. These H+ ions come from the dissociation of acid molecules in water. Acidic substances donate protons, increasing the concentration of H+ ions in the solution.
3. As H+ ions increase, they tend to react with the small amount of OH- ions present in water, forming more water molecules. The reaction is as follows: H+ + OH- -> H2O.
4. This reaction reduces the concentration of OH- ions in the solution, leading to a lower OH- concentration compared to pure water.
5. The pH of an acidic solution is below 7 because it indicates a higher concentration of H+ ions relative to OH- ions.
Overall, in an acidic solution, the excess of H+ ions leads to the formation of water molecules by reacting with OH- ions, resulting in a lower concentration of OH- ions compared to pure water.
In an acidic solution, the OH- concentration is lower than it is in pure water due to the presence of excess H+ ions. To understand why this happens, we need to consider the concept of equilibrium in water.
Water molecules can undergo a self-ionization reaction, where a water molecule donates a proton (H+) to another water molecule, forming a hydronium ion (H3O+) and a hydroxide ion (OH-):
H2O + H2O ⇌ H3O+ + OH-
In pure water, this self-ionization occurs to a very small extent, and we have a dynamic equilibrium where the concentration of H3O+ ions is equal to the concentration of OH- ions. Therefore, the concentration of each is approximately 1 x 10^-7 mol/L at room temperature.
However, in an acidic solution, additional H+ ions are introduced. These H+ ions can react with the OH- ions in the water through an acid-base reaction, forming more water molecules:
H+ + OH- ⇌ H2O
As a result, the concentration of OH- ions decreases because they are consumed in the neutralization reaction with H+. The excess H+ ions in the solution shift the equilibrium of the self-ionization reaction towards the left, reducing the concentration of OH- ions.
In other words, in an acidic solution, the concentration of H+ ions increases while the concentration of OH- ions decreases compared to pure water. This creates a situation where the OH- concentration is lower than it is in pure water.