True/ False: The pH of a soln that is 0.20 M CH3COOH and 0.20 M CH3COONa should be higher than the pH of a 0.20 M CH3COOH soln
Would it be true since CH3COOH and CH3COONa are both weak acids, and if you mix them together, it becomes more diluted, and hence should have a higher pH than just simply CH3COOH?
I didn't work it out. I think it is true, too, but not for the reasons you gave. The acid by itself has a certain pH. The mixture consists of a weak acid (acetic acid) and its salt(the sodium acetate which by the way is a base); therefore, this is a buffered solution. Most, if not all, buffered solutions have a higher pH than the pure acid. I worked it out very quick estimates. The pH of the buffer is 4.74 and the pH of the acid alone is about 2.7.
To determine if the statement is true or false, we need to consider the properties of the substances involved and their respective pH values.
CH3COOH is a weak acid, and when dissolved in water, it partially dissociates to release H+ ions. CH3COONa is the sodium salt of the weak acid CH3COOH, and when dissolved in water, it dissociates into Na+ and CH3COO- ions.
When adding CH3COONa to a solution of CH3COOH, the CH3COO- ions from the salt react with the H+ ions produced by the acid, forming undissociated CH3COOH molecules. This reaction is referred to as a buffer system.
The pH of a solution depends on the concentration of H+ ions. In a buffer system, the pH is determined by the equilibrium between the weak acid and its conjugate base. Specifically, the pH is determined by the ratio of acid and base concentrations.
Given that the concentration of CH3COOH is the same in both solutions (0.20 M), the presence of CH3COONa does not change the concentration of the weak acid. Therefore, the pH of the solution containing CH3COOH and CH3COONa will be the same as the pH of the solution containing only CH3COOH.
In conclusion, the statement is false. The pH of the solution containing 0.20 M CH3COOH and 0.20 M CH3COONa will not be higher than the pH of the solution containing 0.20 M CH3COOH alone.
False. The pH of a solution containing 0.20 M CH3COOH and 0.20 M CH3COONa should be lower than the pH of a 0.20 M CH3COOH solution.
When CH3COOH (acetic acid) is dissolved in water, it donates a proton (H+) to water molecules, resulting in the formation of hydronium ions (H3O+). The equilibrium between CH3COOH and its conjugate base CH3COO- is shifted towards the undissociated CH3COOH in water.
When CH3COONa (sodium acetate) is dissolved in water, it completely dissociates into CH3COO- and Na+ ions. The presence of sodium acetate increases the concentration of the acetate ions (CH3COO-) in the solution.
The acetate ion (CH3COO-) is the conjugate base of CH3COOH and can react with water to form additional OH- ions via the hydrolysis reaction CH3COO- + H2O ⇌ CH3COOH + OH-.
This increase in OH- concentration due to the hydrolysis of acetate ions causes the pH to rise, making the solution more basic than a solution of pure CH3COOH. Therefore, the pH of a solution containing both CH3COOH and CH3COONa is higher than the pH of a solution of pure CH3COOH.